Born as ice-rich planetesimals, cometary nuclei were gravitationally scattered onto their current orbits in the Kuiper Belt and the Oort Cloud during the giant planets' dynamical instability in the early stages of our Solar System's history. Here, we model the thermal evolution of planetesimals during and after the giant planet instability. We couple an adapted thermal evolution model to orbital trajectories provided by \textitN-body simulations to account for the planetesimals' orbital evolution, a parameter so far neglected by previous thermal evolution studies. Our simulations demonstrate intense thermal processing in all planetesimal populations, concerning mainly the hyper-volatile ice content. Unlike previous predictions, we show that hyper-volatile survival was possible in a significant number of planetesimals of the Kuiper Belt and the Oort Cloud. Planetesimals ejected into the interstellar space proved to be the most processed, while planetesimals ending in the Oort Cloud were the least processed population. We show that processing differences between populations are a direct consequence of their orbital evolution patterns, and that they provide a natural explanation for the observed variability in the abundance ratios of CO on cometary populations and on the recent observations of long-distance CO-driven activity on inbound Long-period Comets.
We perform simulations here that include the gravitational effects of the primordial planetesimal belt consisting of ~10^5 massive bodies. In our simulations, Neptune unlocks from resonance with the other giant planets and begins to migrate outward due to interactions with planetesimals before a planetary orbital instability is triggered, and afterward, residual Neptunian migration completes the formation of the modern Kuiper belt. Our present work exhibits a number of notable differences from prior work. First, Neptune's planetary resonance unlocking requires the Neptunian 3:2 mean motion resonance to sweep much of the primordial disk interior to 30 au prior to the giant planet instability. The pre-instability population of planetesimals is consequently lower in semimajor axis, eccentricity, and inclination, and this effect persists after the instability. Second, direct scattering between Pluto-mass bodies and other small bodies removes material from Neptunian resonances more efficiently than resonant dropout resulting from small changes in Neptune's semimajor axis during scattering between Pluto-mass bodies and Neptune. Thus, the primordial population of Pluto-mass bodies may be as few as ~200 objects. Finally, our simulation end states display a wide variety of orbital distributions, and clear relationships between final bulk Kuiper belt properties and Neptune's migration or initial planetesimal properties largely elude us. In particular, we find that the rapid, stochastic planetary orbital evolution occurring during the giant planet instability can significantly alter final Kuiper belt properties such as its inclination dispersion and the prominence of resonant populations. This complicates using modern Kuiper belt properties to confidently constrain early solar system events and conditions, including planetary orbital migration and the primordial Kuiper belt's characteristics.
Reconstructions of the paleoclimate indicate that ancient climatic fluctuations on Earth are often correlated with variations in its orbital elements. However, the chaos inherent in the solar system's orbital evolution prevents numerical simulations from confidently predicting Earth's past orbital evolution beyond 50-100 Myrs. Gravitational interactions among the Sun's planets and asteroids are believed to set this limiting time horizon, but most prior works approximate the solar system as an isolated system and neglect our surrounding Galaxy. Here we present simulations that include the Sun's nearby stellar population, and we find that close-passing field stars alter our entire planetary system's orbital evolution via their gravitational perturbations on the giant planets. This shortens the timespan over which Earth's orbital evolution can be definitively known by a further ~10%. In particular, in simulations that include an exceptionally close passage of the Sun-like star HD 7977 2.8 Myrs ago, new sequences of Earth's orbital evolution become possible in epochs before ~50 Myrs ago, which includes the Paleocene-Eocene Thermal Maximum. Thus, simulations predicting Earth's past orbital evolution before ~50 Myrs ago must consider the additional uncertainty from passing stars, which can open new regimes of past orbital evolution not seen in previous modeling efforts.
We present a statistical characterization of circumstellar disk orientations toward 12 protostellar multiple systems in the Perseus molecular cloud using the Atacama Large Millimeter/submillimeter Array at Band 6 (1.3 mm) with a resolution of 25 mas (8 au). This exquisite resolution enabled us to resolve the compact inner disk structures surrounding the components of each multiple system and to determine the projected 3-D orientation of the disks (position angle and inclination) to high precision. We performed a statistical analysis on the relative alignment of disk pairs to determine whether the disks are preferentially aligned or randomly distributed. We considered three subsamples of the observations selected by the companion separations, a <100 au, a >500 au, and a < 10,000 au. We found for the compact (< 100 au) subsample, the distribution of orientation angles is best described by an underlying distribution of preferentially aligned sources (within 30deg) but does not rule out distributions with 40% misaligned sources. The wide companion (>500 au) subsample appears to be consistent with a distribution of 40%-80% preferentially aligned sources. Similarly, the full sample of systems with companions (a< 10, 000 au) is most consistent with a fractional ratio of at most 80% preferentially aligned source and rules out purely randomly aligned distributions. Thus our results imply the compact sources (<100 au) and the wide companions (>500 au) are statistically different.
Given the inexorable increase in the Sun's luminosity, Earth will exit the habitable zone in ~1 Gyr. There is a negligible chance that Earth's orbit will change during that time through internal Solar System dynamics. However, there is a ~1% chance per Gyr that a star will pass within 100 au of the Sun. Here, we use N-body simulations to evaluate the possible evolutionary pathways of the planets under the perturbation from a close stellar passage. We find a ~92% chance that all eight planets will survive on orbits similar to their current ones if a star passes within 100 au of the Sun. Yet a passing star may disrupt the Solar System, by directly perturbing the planets' orbits or by triggering a dynamical instability. Mercury is the most fragile, with a destruction rate (usually via collision with the Sun) higher than that of the four giant planets combined. The most probable destructive pathways for Earth are to undergo a giant impact (with the Moon or Venus) or to collide with the Sun. Each planet may find itself on a very different orbit than its present-day one, in some cases with high eccentricities or inclinations. There is a small chance that Earth could end up on a more distant (colder) orbit, through re-shuffling of the system's orbital architecture, ejection into interstellar space (or into the Oort cloud), or capture by the passing star. We quantify plausible outcomes for the post-flyby Solar System.
Dynamical instabilities among giant planets are thought to be nearly ubiquitous, and culminate in the ejection of one or more planets into interstellar space. Here we perform N-body simulations of dynamical instabilities while accounting for torques from the galactic tidal field. We find that a fraction of planets that would otherwise have been ejected are instead trapped on very wide orbits analogous to those of Oort cloud comets. The fraction of ejected planets that are trapped ranges from 1-10%, depending on the initial planetary mass distribution. The local galactic density has a modest effect on the trapping efficiency and the orbital radii of trapped planets. The majority of Oort cloud planets survive for Gyr timescales. Taking into account the demographics of exoplanets, we estimate that one in every 200-3000 stars could host an Oort cloud planet. This value is likely an overestimate, as we do not account for instabilities that take place at early enough times to be affected by their host stars' birth cluster, or planet stripping from passing stars. If the Solar System's dynamical instability happened after birth cluster dissolution, there is a ~7% chance that an ice giant was captured in the Sun's Oort cloud.
The chemical compositions of Earth's core and mantle provide insight into the processes that led to their formation. N-body simulations, on the other hand, generally do not contain chemical information, and seek to only reproduce the masses and orbits of the terrestrial planets. These simulations can be grouped into four potentially viable scenarios of Solar System formation (Classical, Annulus, Grand Tack, and Early Instability) for which we compile a total of 433 N-body simulations. We relate the outputs of these simulations to the chemistry of Earth's core and mantle using a melt-scaling law combined with a multi-stage model of core formation. We find the compositions of Earth analogs to be largely governed by the fraction of equilibrating embryo cores and the initial embryo masses in N-body simulations. Simulation type may be important when considering magma ocean lifetimes, where Grand Tack simulations have the largest amounts of material accreted after the last giant impact. However, we cannot rule out any accretion scenarios or initial embryo masses due to the sensitivity of Earth's mantle composition to different parameters and the stochastic nature of N-body simulations. Comparing the last embryo impacts experienced by Earth analogs to specific Moon-forming scenarios, we find the characteristics of the Moon-forming impact are dependent on the initial conditions in N-body simulations where larger initial embryo masses promote larger and slower Moon-forming impactors. Mars-sized initial embryos are most consistent with the canonical hit-and-run scenario onto a solid mantle. Our results suggest that constraining the fraction of equilibrating impactor core and the initial embryo masses in N-body simulations could be significant for understanding both Earth's accretion history and characteristics of the Moon-forming impact.
The inner solar system's modern orbital architecture provides inferences into the epoch of terrestrial planet formation; a ~100 Myr time period of planet growth via collisions with planetesimals and other proto-planets. While classic numerical simulations of this scenario adequately reproduced the correct number of terrestrial worlds, their semi-major axes and approximate formation timescales, they struggled to replicate the Earth-Mars and Venus-Mercury mass ratios. In a series of past independent investigations, we demonstrated that Mars' mass is possibly the result of Jupiter and Saturn's early orbital evolution, while Mercury's diminutive size might be the consequence of a primordial mass deficit in the region. Here, we combine these ideas in a single modeled scenario designed to simultaneously reproduce the formation of all four terrestrial planets and the modern orbits of the giant planets in broad strokes. By evaluating our Mercury analogs' core mass fractions, masses, and orbital offsets from Venus, we favor a scenario where Mercury forms through a series of violent erosive collisions between a number of ~Mercury-mass embryos in the inner part of the terrestrial disk. We also compare cases where the gas giants begin the simulation locked in a compact 3:2 resonant configuration to a more relaxed 2:1 orientation and find the former to be more successful. In 2:1 cases, the entire Mercury-forming region is often depleted due to strong sweeping secular resonances that also tend to overly excite the orbits of Earth and Venus as they grow. While our model is quite successful at replicating Mercury's massive core and dynamically isolated orbit, the planets' low mass remains extremely challenging to match. Finally, we discuss the merits and drawbacks of alternative evolutionary scenarios and initial disk conditions.
Within the dynamically cold low inclination portion of the Classical Kuiper Belt, there exists a population of weakly bound binary systems with a number of unusual properties; most notable of which is their extremely wide orbital separations; beyond 7% of their Hill radii. The stability and evolution of these Ultra-Wide Trans-Neptunian Binaries (TNBs) have, in the past, been studied extensively under the assumption that the primary evolving mechanisms are interactions between the binary components and impacting Trans-Neptunian Objects (TNOs). Here, we instead study their evolution as driven by the gravitational perturbations of close passing but non-impacting TNOs. By simulating these passages, we show that the aggregate effects of encounters over billions of years have a significant effect on Kuiper Belt binary evolution. Such processes can lead to tight binaries widening significantly over time, approaching and sometimes surpassing the separation of the widest known TNBs. We also find that the eccentricity and inclination distributions of observed Ultra-Wide TNBs can be sampled from such widened binaries. While we are unable to produce enough wide binaries to explain their abundance, the orbital properties of ones we do produce are consistent with known wide binaries.
The majority of binary star systems that host exoplanets will spend the first portion of their lives within a star-forming cluster that may drive dynamical evolution of the binary-planet system. We perform numerical simulations of S-type planets, with masses and orbital architecture analogous to the solar system's 4 gas giants, orbiting within the influence of a 0.5 solar-mass binary companion. The binary-planet system is integrated simultaneously with an embedded stellar cluster environment. ~10% of our planetary systems are destabilized when perturbations from our cluster environment drive the binary periastron toward the planets. This destabilization occurs despite all of our systems being initialized with binary orbits that would allow stable planets in the absence of the cluster. The planet-planet scattering triggered in our systems typically results in the loss of lower mass planets and the excitement of the eccentricities of surviving higher mass planets. Many of our planetary systems that go unstable also lose their binary companions prior to cluster dispersal and can therefore masquerade as hosts of eccentric exoplanets that have spent their entire histories as isolated stars. The cluster-driven binary orbital evolution in our simulations can also generate planetary systems with misaligned spin-orbit angles. This is typically done as the planetary system precesses as a rigid disk under the influence of an inclined binary, and those systems with the highest spin-orbit angles should often retain their binary companion and possess multiple surviving planets.
The Oort cloud and the scattered disk are the two primary reservoirs for long-period and short-period comets, respectively. In this review, we assess the known observational constraints on these reservoirs' properties and their formation. In addition, we discuss how the early orbital evolution of the giant planets generated the modern scattered disk from the early, massive planetesimal disk and how $\sim$5\% of this material was captured into the Oort cloud. We review how the Sun's birth environment and dynamical history within the Milky Way alters the formation and modern structure of the Oort cloud. Finally, we assess how the coming decade's anticipated observing campaigns may provide new insights into the formation and properties of the Oort cloud and scattered disk.
The discovery probability of long-period comets (LPCs) passing near the Sun is highest during their first passage and then declines, or fades, during subsequent return passages. Comet fading is largely attributed to devolatilization and fragmentation via thermal processing within 2-3 au of the Sun (1 au being the Earth-Sun distance). Here our numerical simulations show that comet observing campaigns miss vast numbers of LPCs making returning passages through the Saturn region (near 10 au) because these comets fade during prior, even more distant passages exterior to Saturn and thus elude detection. Consequently, comet properties significantly evolve at solar distances much larger than previously considered, and this offers new insights into the physical and dynamical properties of LPCs, both near and far from Earth.
A distant, massive planet in the outer solar system has recently been proposed to explain some observed features of extreme trans-Neptunian objects (TNOs). Here we use N-body simulations of the formation of the Kuiper belt and Oort cloud as well as a survey simulator to compare models of the solar system with and without a 9th planet to one another as well as to observations. The main mechanism for TNOs to be deposited into the distant ($a$ > au), detached ($q$ > au) region of the Kuiper Belt in the 8-planet model is Kozai-Lidov oscillation of objects in mean motion resonances (MMR) with Neptune. This effect does not deposit low-inclination ($i \lesssim$ 20\deg) objects into this region. However, we find that the 9th planet generates a group of distant, detached TNOs at low inclinations that are not present in the 8-planet model. This disparity between the 8-planet and the 9-planet models could provide a strong constraint on a possible planet 9 with further detections of TNOs in the distant, detached region of the Kuiper Belt.
The formation of the solar system's giant planets predated the ultimate epoch of massive impacts that concluded the process of terrestrial planet formation. Following their formation, the giant planets' orbits evolved through an episode of dynamical instability. Several qualities of the solar system have recently been interpreted as evidence of this event transpiring within the first ~100 Myr after the Sun's birth; around the same time as the final assembly of the inner planets. In a series of recent papers we argued that such an early instability could resolve several problems revealed in classic numerical studies of terrestrial planet formation; namely the small masses of Mars and the asteroid belt. In this paper, we revisit the early instability scenario with a large suite of simulations specifically designed to understand the degree to which Earth and Mars' formation are sensitive to the specific evolution of Jupiter and Saturn's orbits. By deriving our initial terrestrial disks directly from recent high-resolution simulations of planetesimal accretion, our results largely confirm our previous findings regarding the instability's efficiency of truncating the terrestrial disk outside of the Earth-forming region in simulations that best replicate the outer solar system. Moreover, our work validates the primordial 2:1 Jupiter-Saturn resonance within the early instability framework as a viable evolutionary path for the solar system. While our simulations elucidate the fragility of the terrestrial system during the epoch of giant planet migration, many realizations yield outstanding solar system analogs when scrutinized against a number of observational constraints. Finally, we highlight the inability of models to form adequate Mercury-analogs and the low eccentricities of Earth and Venus as the most significant outstanding problems for future numerical studies to resolve.
In a recent paper we proposed that the giant planets' primordial orbits may have been eccentric (~0.05), and used a suite of dynamical simulations to show outcomes of the giant planet instability that are consistent with their present-day orbits. In this follow-up investigation, we present more comprehensive simulations incorporating superior particle resolution, longer integration times, and eliminating our prior means of artificially forcing instabilities to occur at specified times by shifting a planets' position in its orbit. While we find that the residual phase of planetary migration only minimally alters the the planets' ultimate eccentricities, our work uncovers several intriguing outcomes in realizations where Jupiter and Saturn are born with extremely large eccentricities (~0.10 and ~0.25, respectively). In successful simulations, the planets' orbits damp through interactions with the planetesimal disk prior to the instability, thus loosely replicating the initial conditions considered in our previous work. Our results therefore suggest an even wider range of plausible evolutionary pathways are capable of replicating Jupiter and Saturn's modern orbital architecture.
The non-resonant Kuiper belt objects (KBOs) between the 3:2 and 2:1 Neptunian mean motion resonances can be largely divided between a cold classical belt (CCB) and a hot classical belt (HCB). A notable difference between these two subpopulations is the prevalence of widely spaced, equal-mass binaries in the CCB and a much smaller but non-zero number in the HCB. The primary reason for this difference in binary rate remains unclear. Here using N-body simulations we examine whether close encounters with the giant planets during an early outer solar system instability may have disrupted primordial Kuiper Belt binaries that existed within the primordial Kuiper belt before they attained HCB orbits. We find that such encounters are very effective at disrupting binaries down to separations of ~1% of their Hill radius (as measured in the modern Kuiper belt), potentially explaining the paucity of widely spaced, equal mass binaries in the modern HCB. Moreover, we find that the widest binaries observed in the modern HCB are quite unlikely to survive planetary encounters, but these same planetary encounters can widen a small subset of tighter binaries to give rise to the small population of very wide binaries seen in today's HCB.
The orbital architecture of the Solar System is thought to have been sculpted by a dynamical instability among the giant planets. During the instability a primordial outer disk of planetesimals was destabilized and ended up on planet-crossing orbits. Most planetesimals were ejected into interstellar space but a fraction were trapped on stable orbits in the Kuiper belt and Oort cloud. We use a suite of N-body simulations to map out the diversity of planetesimals' dynamical pathways. We focus on two processes: tidal disruption from very close encounters with a giant planet, and loss of surface volatiles from repeated passages close to the Sun. We show that the rate of tidal disruption is more than a factor of two higher for ejected planetesimals than for surviving objects in the Kuiper belt or Oort cloud. Ejected planetesimals are preferentially disrupted by Jupiter and surviving ones by Neptune. Given that the gas giants contracted significantly as they cooled but the ice giants did not, taking into account the thermal evolution of the giant planets decreases the disruption rate of ejected planetesimals. The frequency of volatile loss and extinction is far higher for ejected planetesimals than for surviving ones and is not affected by the giant planets' contraction. Even if all interstellar objects were ejected from Solar System-like systems, our analysis suggests that their physical properties should be more diverse than those of Solar System small bodies as a result of their divergent dynamical histories. This is consistent with the characteristics of the two currently-known interstellar objects.
An episode of dynamical instability is thought to have sculpted the orbital structure of the outer solar system. When modeling this instability, a key constraint comes from Jupiter's fifth eccentric mode (quantified by its amplitude M55), which is an important driver of the solar system's secular evolution. Starting from commonly-assumed near-circular orbits, the present-day giant planets' architecture lies at the limit of numerically generated systems, and M55 is rarely excited to its true value. Here we perform a dynamical analysis of a large batch of artificially triggered instabilities, and test a variety of configurations for the giant planets' primordial orbits. In addition to more standard setups, and motivated by the results of modern hydrodynamical simulations of the giant planets' evolution within the primordial gaseous disk, we consider the possibility that Jupiter and Saturn emerged from the nebular gas locked in 2:1 resonance with non-zero eccentricities. We show that, in such a scenario, the modern Jupiter-Saturn system represents a typical simulation outcome, and M55 is commonly matched. Furthermore, we show that Uranus and Neptune's final orbits are determined by a combination of the mass in the primordial Kuiper belt and that of an ejected ice giant.
The longitudes of perihelia and orbital poles of the solar system's dozen or so most remote detected objects are clustered in a manner inconsistent with that of a random sample of uniformly distributed orbits. While small number statistics and observational biases may explain these features, the statistical significance of the clustering has led to the recent development of the "Planet Nine hypothesis." In the proposed scenario, orbits in the distant solar system are shepherded via secular perturbations from an undetected massive planet on an eccentric orbit. However, the precession of perihelia and nodes in the outer Kuiper Belt and inner Oort Cloud are also affected by the the giant planets, passing stars, and the galactic tide. We perform a large suite of numerical simulations designed to study the orbital alignment of Extreme Trans-Neptunian Objects (ETNOs) and Inner Oort Cloud Objects (IOCOs). In our various integrations that include Planet Nine, we consistently find that >60% of ETNOs and IOCOs that are detectable after 4 Gyr are also anti-aligned in perihelia with the distant massive perturber. However, when we randomly select 17 objects from this sample of remaining orbits, there is significant scatter in the degree of longitude of perihelion and orbital pole clustering that might be observed. Furthermore, we argue that, in the absence of Planet Nine, 17 randomly drawn orbits should still exhibit some clustering even if the underlying distribution is uniform. Thus, we find that still more ETNO and IOCO detections are required to confidently infer the presence of Planet Nine.
The solar system's terrestrial planets are thought to have accreted over millions of years out of a sea of smaller embryos and planetesimals. Because it is impossible to know the surface density profile for solids and size frequency distribution in the primordial solar nebula, distinguishing between the various proposed evolutionary schemes has been historically difficult. Nearly all previous simulations of terrestrial planet formation assume that Moon to Mars massed embryos formed throughout the inner solar system during the primordial gas-disk phase. However, validating this assumption through models of embryo accretion is computationally challenging because of the large number of bodies required. Here, we reevaluate this problem with GPU-accelerated, direct N-body simulations of embryo growth starting from r~100 km planetesimals. We find that embryos emerging from the primordial gas phase at a given radial distance already have masses similar to the largest objects at the same semi-major axis in the modern solar system. Thus, Earth and Venus attain ~50% of their modern mass, Mars-massed embryos form in the Mars region, and Ceres-massed objects are prevalent throughout asteroid belt. Consistent with other recent work, our new initial conditions for terrestrial accretion models produce markedly improved solar system analogs when evolved through the giant impact phase of planet formation. However, we still conclude that an additional dynamical mechanism such as giant planet migration is required to prevent Earth-massed Mars analogs from growing.
The asteroid belt is characterized by an extreme low total mass of material on dynamically excited orbits. The Nice Model explains many peculiar qualities of the solar system, including the belt's excited state, by invoking an orbital instability between the outer planets. However, previous studies of the Nice Model's effect on the belt's structure struggle to reproduce the innermost asteroids' orbital inclination distribution. Here, we show how the final phase of giant planet migration sculpts the asteroid belt, in particular its inclination distribution. As interactions with leftover planetesimals cause Saturn to move away from Jupiter, its rate of orbital precession slows as the two planets' mutual interactions weaken. When the planets approach their modern separation, where Jupiter completes just short of five orbits for every two of Saturn's, Jupiter's eccentric forcing on Saturn strengthens. We use numerical simulations to show that the absence of asteroids with orbits that precess between 24-28 arcsec/yr is related to the inclination problem. As Saturn's precession speeds back up, high inclination asteroids are excited on to planet crossing orbits and removed from the inner main belt. Through this process, the asteroid belt's orbital structure is reshaped, leading to markedly improved simulation outcomes.
Most known trans-Neptunian objects (TNOs) gravitationally scattering off the giant planets have orbital inclinations consistent with an origin from the classical Kuiper belt, but a small fraction of these "scattering TNOs" have inclinations that are far too large (i > 45 deg) for this origin. These scattering outliers have previously been proposed to be interlopers from the Oort cloud or evidence of an undiscovered planet. Here we test these hypotheses using N-body simulations and the 69 centaurs and scattering TNOs detected in the Outer Solar Systems Origins Survey and its predecessors. We confirm that observed scattering objects cannot solely originate from the classical Kuiper belt, and we show that both the Oort cloud and a distant planet generate observable highly inclined scatterers. Although the number of highly inclined scatterers from the Oort Cloud is ~3 times less than observed, Oort cloud enrichment from the Sun's galactic migration or birth cluster could resolve this. Meanwhile, a distant, low-eccentricity 5 Earth-mass planet replicates the observed fraction of highly inclined scatterers, but the overall inclination distribution is more excited than observed. Furthermore, the distant planet generates a longitudinal asymmetry among detached TNOs that is less extreme than often presumed, and its direction reverses across the perihelion range spanned by known TNOs. More complete models that explore the dynamical origins of the planet are necessary to further study these features. With observational biases well-characterized, our work shows that the orbital distribution of detected scattering bodies is a powerful constraint on the unobserved distant solar system.
Of the solar system's four terrestrial planets, the origin of Mercury is perhaps the most mysterious. Modern numerical simulations designed to model the dynamics of terrestrial planet formation systematically fail to replicate Mercury; which possesses just 5% the mass of Earth and the highest orbital eccentricity and inclination among the planets. However, Mercury's large iron-rich core and low volatile inventory stand out among the inner planets, and seem to imply a violent collisional origin. Because most algorithms used for simulating terrestrial accretion do not consider the effects of collisional fragmentation, it has been difficult to test these collisional hypotheses within the larger context of planet formation. Here, we analyze a large suite of terrestrial accretion models that account for the fragmentation of colliding bodies. We find that planets with core mass fractions boosted as a result of repeated hit-and-run collisions are produced in 90% of our simulations. While many of these planets are similar to Mercury in mass, they rarely lie on Mercury-like orbits. Furthermore, we perform an additional batch of simulations designed to specifically test the single giant impact origin scenario. We find less than a 1% probability of simultaneously replicating the Mercury-Venus dynamical spacing and the terrestrial system's degree of orbital excitation after such an event. While dynamical models have made great strides in understanding Mars' low mass, their inability to form accurate Mercury analogs remains a glaring problem.
Modern studies of the early solar system routinely invoke the possibility of an orbital instability among the giant planets triggered by gravitational interactions between the planets and a massive exterior disk of planetesimals. Previous works have suggested that this instability can be substantially delayed ($\sim$100s Myr) after the formation of the giant planets. Bodies in the disk are typically treated in a semi-active manner, wherein their gravitational force on the planets is included, but interactions between the planetesimals are ignored. We perform $N$-body numerical simulations using GENGA, which makes use of GPUs to allow for the inclusion of all gravitational interactions between bodies. Although our simulated Kuiper belt particles are more massive than the probable masses of real primordial Kuiper belt objects, our simulations indicate that the self-stirring of the primordial Kuiper belt is very important to the dynamics of the giant planet instability. We find that interactions between planetesimals dynamically heat the disk and typically prevent the outer solar system instability from being delayed by more than a few tens of million years after giant planet formation. Longer delays occur in a small fraction of systems that have at least 3.5 AU gaps between the planets and planetesimal disk. Our final planetary configurations match the solar system at a rate consistent with other previous works in most regards. Pre-instability heating of the disk typically yields final Jovian eccentricities comparable to the modern solar system value, which has been a difficult constraint to match in past works.
The solar system's dynamical state can be explained by an orbital instability among the giant planets. A recent model has proposed that the giant planet instability happened during terrestrial planet formation. This scenario has been shown to match the inner solar system by stunting Mars' growth and preventing planet formation in the asteroid belt. Here we present a large sample of new simulations of the "Early Instability" scenario. We use an N-body integration scheme that accounts for collisional fragmentation, and also perform a large set of control simulations that do not include an early giant planet instability. Since the total particle number decreases slower when collisional fragmentation is accounted for, the growing planets' orbits are damped more strongly via dynamical friction and encounters with small bodies that dissipate angular momentum (eg: hit-and-run impacts). Compared with simulations without collisional fragmentation, our fully evolved systems provide better matches to the solar system's terrestrial planets in terms of their compact mass distribution and dynamically cold orbits. Collisional processes also tend to lengthen the dynamical accretion timescales of Earth analogs, and shorten those of Mars analogs. This yields systems with relative growth timescales more consistent with those inferred from isotopic dating. Accounting for fragmentation is thus supremely important for any successful evolutionary model of the inner solar system.
Containing only a few percent the mass of the moon, the current asteroid belt is around three to four orders of magnitude smaller that its primordial mass inferred from disk models. Yet dynamical studies have shown that the asteroid belt could not have been depleted by more than about an order of magnitude over the past ~4 Gyr. The remainder of the mass loss must have taken place during an earlier phase of the solar system's evolution. An orbital instability in the outer solar system occurring during the process of terrestrial planet formation can reproduce the broad characteristics of the inner solar system. Here, we test the viability of this model within the constraints of the main belt's low present-day mass and orbital structure. While previous studies modeled asteroids as massless test particles because of limited computing power, our work uses GPU (Graphics Processing Unit) acceleration to model a fully self-gravitating asteroid belt. We find that depletion in the main belt is related to the giant planets' exact evolution within the orbital instability. Simulations that produce the closest matches to the giant planets' current orbits deplete the main belt by two to three orders of magnitude. These simulated asteroid belts are also good matches to the actual asteroid belt in terms of their radial mixing and broad orbital structure.
Inner Oort Cloud objects (IOCs) are Trans-Plutonian for their entire orbits. They are beyond the strong gravitational influences of the known planets yet close enough to the Sun that outside forces are minimal. Here we report the discovery of the third known IOC after Sedna and 2012 VP113, called 2015 TG387. 2015 TG387 has a perihelion of $65 \pm 1$ au and semi-major axis of $1170 \pm 70$ au. The longitude of perihelion angle, $\bar{\omega}$, for 2015 TG387 is between that of Sedna and 2012 VP113, and thus similar to the main group of clustered extreme trans-Neptunian objects (ETNOs), which may be shepherded into similar orbital angles by an unknown massive distant planet, called Planet X or Planet Nine. 2015 TG387's orbit is stable over the age of the solar system from the known planets and Galactic tide. When including outside stellar encounters over 4 Gyrs, 2015 TG387's orbit is usually stable, but its dynamical evolution depends on the stellar encounter scenarios used. Surprisingly, when including a massive Planet X beyond a few hundred au on an eccentric orbit that is anti-aligned in longitude of perihelion with most of the known ETNOs, we find 2015 TG387 is typically stable for Planet X orbits that render the other ETNOs stable as well. Notably, 2015 TG387's argument of perihelion is constrained and its longitude of perihelion librates about 180 degs from Planet X's longitude of perihelion, keeping 2015 TG387 anti-aligned with Planet X over the age of the solar system. We find a power law slope near 3 for the semi-major axis distribution of IOCs, meaning there are many more high than low semi-major axis IOCs. There are about 2 million IOCs larger than 40 km, giving a mass of $10^{22}$ kg. The IOCs inclination distribution is similar to the scattered disk, with an average inclination of 19 degs.
S. M. Lawler, R. E. Pike, N. Kaib, M. Alexandersen, M. T. Bannister, Y.-T. Chen, B. Gladman, S. Gwyn, J. J. Kavelaars, J.-M. Petit, K. Volk The migration of Neptune's resonances through the proto-Kuiper belt has been imprinted in the distribution of small bodies in the outer Solar System. Here we analyze five published Neptune migration models in detail, focusing on the high pericenter distance (high-q) trans-Neptunian Objects (TNOs) near Neptune's 5:2 and 3:1 mean-motion resonances, because they have large resonant populations, are outside the main classical belt, and are relatively isolated from other strong resonances. We compare the observationally biased output from these dynamical models with the detected TNOs from the Outer Solar System Origins Survey, via its Survey Simulator. All of the four new OSSOS detections of high-q non-resonant TNOs are on the Sunward side of the 5:2 and 3:1 resonances. We show that even after accounting for observation biases, this asymmetric distribution cannot be drawn from a uniform distribution of TNOs at 2sigma confidence. As shown by previous work, our analysis here tentatively confirms that the dynamical model that uses grainy slow Neptune migration provides the best match to the real high-q TNO orbital data. However, due to extreme observational biases, we have very few high-q TNO discoveries with which to statistically constrain the models. Thus, this analysis provides a framework for future comparison between the output from detailed, dynamically classified Neptune migration simulations and the TNO discoveries from future well-characterized surveys. We show that a deeper survey (to a limiting r-magnitude of 26.0) with a similar survey area to OSSOS could statistically distinguish between these five Neptune migration models.
Michele T. Bannister, Brett J. Gladman, J.J. Kavelaars, Jean-Marc Petit, Kathryn Volk, Ying-Tung Chen, Mike Alexandersen, Stephen D. J. Gwyn, Megan E. Schwamb, Edward Ashton, Susan D. Benecchi, Nahuel Cabral, Rebekah I. Dawson, Audrey Delsanti, Wesley C. Fraser, Mikael Granvik, Sarah Greenstreet, Aurélie Guilbert-Lepoutre, Wing-Huen Ip, Marian Jakubik, et al (16) The Outer Solar System Origins Survey (OSSOS), a wide-field imaging program in 2013-2017 with the Canada-France-Hawaii Telescope, surveyed 155 deg$^{2}$ of sky to depths of $m_r = 24.1$-25.2. We present 838 outer Solar System discoveries that are entirely free of ephemeris bias. This increases the inventory of trans-Neptunian objects (TNOs) with accurately known orbits by nearly 50%. Each minor planet has 20-60 Gaia/Pan-STARRS-calibrated astrometric measurements made over 2-5 oppositions, which allows accurate classification of their orbits within the trans-Neptunian dynamical populations. The populations orbiting in mean-motion resonance with Neptune are key to understanding Neptune's early migration. Our 313 resonant TNOs, including 132 plutinos, triple the available characterized sample and include new occupancy of distant resonances out to semi-major axis $a \sim 130$ au. OSSOS doubles the known population of the non-resonant Kuiper belt, providing 436 TNOs in this region, all with exceptionally high-quality orbits of $a$ uncertainty $\sigma_{a} \leq 0.1\%$; they show the belt exists from $a \gtrsim 37$ au, with a lower perihelion bound of $35$ au. We confirm the presence of a concentrated low-inclination $a\simeq 44$ au "kernel" population and a dynamically cold population extending beyond the 2:1 resonance. We finely quantify the survey's observational biases. Our survey simulator provides a straightforward way to impose these biases on models of the trans-Neptunian orbit distributions, allowing statistical comparison to the discoveries. The OSSOS TNOs, unprecedented in their orbital precision for the size of the sample, are ideal for testing concepts of the history of giant planet migration in the Solar System.
Many dynamical aspects of the solar system can be explained by the outer planets experiencing a period of orbital instability sometimes called the Nice Model. Though often correlated with a perceived delayed spike in the lunar cratering record known as the Late Heavy Bombardment (LHB), recent work suggests that this event may have occurred much earlier; perhaps during the epoch of terrestrial planet formation. While current simulations of terrestrial accretion can reproduce many observed qualities of the solar system, replicating the small mass of Mars requires modification to standard planet formation models. Here we use 800 dynamical simulations to show that an early instability in the outer solar system strongly influences terrestrial planet formation and regularly yields properly sized Mars analogs. Our most successful outcomes occur when the terrestrial planets evolve an additional 1-10 million years (Myr) following the dispersal of the gas disk, before the onset of the giant planet instability. In these simulations, accretion has begun in the Mars region before the instability, but the dynamical perturbation induced by the giant planets' scattering removes large embryos from Mars' vicinity. Large embryos are either ejected or scattered inward toward Earth and Venus (in some cases to deliver water), and Mars is left behind as a stranded embryo. An early giant planet instability can thus replicate both the inner and outer solar system in a single model.
S. M. Lawler, C. Shankman, JJ. Kavelaars, M. Alexandersen, M. T. Bannister, Y.-T. Chen, B. Gladman, W. C. Fraser, S. Gwyn, N. Kaib, J.-M. Petit, K. Volk The scattering trans-Neptunian Objects (TNOs) can be measured to smaller sizes than any other distant small-body population. We use the largest sample yet obtained, 68 discoveries, primarily by the Outer Solar System Origins Survey (OSSOS), to constrain the slope of its luminosity distribution, with sensitivity to much fainter absolute $H$ magnitudes than previous work. Using the analysis technique in Shankman et al. (2016), we confirm that a single slope for the $H$-distribution is not an accurate representation of the scattering TNOs and Centaurs, and that a break in the distribution is required, in support of previous conclusions. A bright-end slope of $\alpha_b=0.9$ transitioning to a faint-end slope $\alpha_f$ of 0.4-0.5 with a differential number contrast $c$ from 1 (a knee) to 10 (a divot) provides an acceptable match to our data. We find that break magnitudes $H_b$ of 7.7 and 8.3, values both previously suggested for dynamically hot Kuiper belt populations, are equally non-rejectable for a range of $\alpha_f$ and $c$ in our statistical analysis. Our preferred divot $H$-distribution transitions to $\alpha_f=0.5$ with a divot of contrast $c=3$ at $H_b=8.3$, while our preferred knee $H$-distribution transitions to $\alpha_f=0.4$ at $H_b=7.7$. The intrinsic population of scattering TNOs required to match the OSSOS detections is $3\times10^6$ for $H_r<12$, and $9\times10^4$ for $H_r<8.66$ ($D\gtrsim100$~km), with Centaurs having an intrinsic population two orders of magnitude smaller.
The stability limit for circumbinary planets (CBPs) is not well defined and can depend on initial parameters defining either the planetary orbit or the inner binary orbit. We expand on the work of Holman & Wiegert (1999, AJ 117, 621) to develop numerical tools for quick, easy, and accurate determination of the stability limit. The results of our simulations, as well as our numerical tools, are available to the community through $\texttt{Zenodo}$ and $\texttt{GitHub}$, respectively. We employ a grid interpolation method based on $\sim$150 million full N-body simulations of initially circular, coplanar systems and compare to the 9 known Kepler CBP systems. Using a formalism from planet packing studies, we find that 55% of the Kepler CBP systems allow for an additional equal-mass planet to potentially exist on an interior orbit relative to the observed planet. Therefore, we do $\textit{not}$ find strong evidence for a pile-up in the Kepler CBP systems and more detections are needed to adequately characterize the formation mechanisms for the CBP population. Observations from the Transiting Exoplanet Survey Satellite are expected to substantially increase the number of detections using the unique geometry of CBP systems, where multiple transits can occur during a single conjunction.
We extend our study of the extent of the regions within the $\alpha$ Centauri AB star system where small planets are able to orbit for billion-year timescales (Quarles & Lissauer 2016, AJ 151, 111) to investigate the effects of minimizing the forced eccentricity of initial trajectories. We find that initially prograde, circumstellar orbits require a piecewise quadratic function to accurately approximate forced eccentricity as a function of semimajor axis, but retrograde orbits can be modeled using a linear function. Circumbinary orbits in the $\alpha$ Centauri AB system are less affected by the forced eccentricity. Planets on circumstellar orbits that begin with eccentricity vectors near their forced values are generally stable, up to $\sim$$10^9$ yr, out to a larger semimajor axis than are planets beginning on circular orbits. The amount by which the region of stability expands is much larger for retrograde orbits than it is for prograde orbits. The location of the stability boundary for two planet systems on prograde, circular orbits is much more sensitive to the initial eccentricity state than it is for analogous single planet systems.
The galactic environment has been suspected to influence planetary habitability in many ways. Very metal-poor regions of the Galaxy, or those largely devoid of atoms more massive than H and He, are thought to be unable to form habitable planets. Moreover, if such planets do form, the young system is subjected to close stellar passages while it resides in its stellar birth cluster. Various potential hazards remain after clusters disperse. For instance, central galactic regions may present risks to habitability via nearby supernovae, gamma ray bursts (GRBs), and frequent comet showers. In addition, planets residing within very wide binary star systems are affected by the Galaxy, as local gravitational perturbations from the Galaxy can increase the binary's eccentricity until it destabilizes the planets it hosts. Here we review the most recent work on the main galactic influences over planetary habitability. Although there must be some metallicity limit below which rocky planets cannot form, recent exoplanet surveys show that they form around stars with a very large range of metallicities. Once formed, the probability of star clusters destabilizing planetary systems only becomes high for rare, extremely long-lived clusters. Regarding threats to habitability from supernovae, GRBs, and comet showers, many recent studies suggest that their hazards are more limited than originally thought. Finally, denser regions of the Galaxy enhance the threat that very wide binary companions pose to planetary habitability, but the probability that a very wide binary star disrupts habitability will always be substantially below 100% for any environment. While some Milky Way regions must be more hospitable to habitable planets than others, it is difficult to state that habitable planets are confined to any well-defined region of the Galaxy or that any other particular region of the Galaxy is uninhabitable.
Fomalhaut A is among the most well-studied nearby stars and has been discovered to possess a putative planetary object as well as a remarkable eccentric dust belt. This eccentric dust belt has often been interpreted as the dynamical signature of one or more planets that elude direct detection. However, the system also contains two other stellar companions residing ~100,000 AU from Fomalhaut A. We have designed a new symplectic integration algorithm to model the evolution of Fomalhaut A's planetary dust belt in concert with the dynamical evolution of its stellar companions to determine if these companions are likely to have generated the dust belt's morphology. Using our numerical simulations, we find that close encounters between Fomalhaut A and B are expected, with a ~25% probability that the two stars have passed within at least 400 AU of each other at some point. Although the outcomes of such encounter histories are extremely varied, these close encounters nearly always excite the eccentricity of Fomalhaut A's dust belt and occasionally yield morphologies very similar to the observed belt. With these results, we argue that close encounters with Fomalhaut A's stellar companions should be considered a plausible mechanism to explain its eccentric belt, especially in the absence of detected planets capable of sculpting the belt's morphology. More broadly, we can also conclude from this work that very wide binary stars may often generate asymmetries in the stellar debris disks they host.
Comets are icy objects that orbitally evolve from the trans-Neptunian region (the Kuiper belt and beyond) into the inner Solar System, where they are heated by solar radiation and become active due to sublimation of water ice. Here we perform end-to-end simulations in which cometary reservoirs are formed in the early Solar System and evolved over 4.5 Gyr. The gravitational effects of Planet 9 (P9), hypothesized to circle the Sun on a wide orbit, are included in some of our simulations. Different models are considered for comets to be active, including a simple assumption that comets remain active for Np(q) perihelion passages with perihelion distance q<2.5 au. The orbital distribution and number of active comets produced in our model is compared to observations. The orbital distribution of ecliptic comets (ECs) is well reproduced in models with Np(2.5)=500 and without P9. With P9, the inclination distribution of model ECs is wider than the observed one. We find that the known Halley-type comets (HTCs) have a nearly isotropic inclination distribution (with only a slight preference for prograde orbits). In our model, the HTCs appear to be an extension of the population of returning Oort-cloud comets (OCCs) to shorter orbital periods. The inclination distribution of model HTCs becomes broader with increasing Np, but the existing observational data are not good enough to constrain Np from orbital fits. Np(2.5)>1000 is required to obtain a steady-state population of large active HTCs that is consistent with observations. To fit the ratio of the returning-to-new OCCs, by contrast, our model implies that Np(2.5)<10, possibly because the detected long-period comets are smaller and much easier to disrupt than observed HTCs.
Cory Shankman, JJ Kavelaars, Michele Bannister, Brett Gladman, Samantha Lawler, Ying-Tung Chen, Marian Jakubik, Nathan Kaib, Mike Alexandersen, Stephen Gwyn, Jean-Marc Petit, Kathryn Volk The accumulating, but small, set of large semi-major axis trans-Neptunian objects (TNOs) shows an apparent clustering in the orientations of their orbits. This clustering must either be representative of the intrinsic distribution of these TNOs, or else arise as a result of observation biases and/or statistically expected variations for such a small set of detected objects. The clustered TNOs were detected across different and independent surveys, which has led to claims that the detections are therefore free of observational bias. This apparent clustering has led to the so-called "Planet 9" hypothesis that a super-Earth currently resides in the distant solar system and causes this clustering. The Outer Solar System Origins Survey (OSSOS) is a large program that ran on the Canada-France-Hawaii Telescope from 2013--2017, discovering more than 800 new TNOs. One of the primary design goals of OSSOS was the careful determination of observational biases that would manifest within the detected sample. We demonstrate the striking and non-intuitive biases that exist for the detection of TNOs with large semi-major axes. The eight large semi-major axis OSSOS detections are an independent dataset, of comparable size to the conglomerate samples used in previous studies. We conclude that the orbital distribution of the OSSOS sample is consistent with being detected from a uniform underlying angular distribution.
Michele T. Bannister, Cory Shankman, Kathryn Volk, Ying-Tung Chen, Nathan Kaib, Brett J. Gladman, Marian Jakubik, J. J. Kavelaars, Wesley C. Fraser, Megan E. Schwamb, Jean-Marc Petit, Shiang-Yu Wang, Stephen D. J. Gwyn, Mike Alexandersen, Rosemary E. Pike We report the discovery of the minor planet 2013 SY$_{99}$, on an exceptionally distant, highly eccentric orbit. With a perihelion of 50.0 au, 2013 SY$_{99}$'s orbit has a semi-major axis of $730 \pm 40$ au, the largest known for a high-perihelion trans-Neptunian object (TNO), well beyond those of (90377) Sedna and 2012 VP$_{113}$. Yet, with an aphelion of $1420 \pm 90$ au, 2013 SY$_{99}$'s orbit is interior to the region influenced by Galactic tides. Such TNOs are not thought to be produced in the current known planetary architecture of the Solar System, and they have informed the recent debate on the existence of a distant giant planet. Photometry from the Canada-France-Hawaii Telescope, Gemini North and Subaru indicate 2013 SY$_{99}$ is $\sim 250$ km in diameter and moderately red in colour, similar to other dynamically excited TNOs. Our dynamical simulations show that Neptune's weak influence during 2013 SY$_{99}$'s perihelia encounters drives diffusion in its semi-major axis of hundreds of astronomical units over 4 Gyr. The overall symmetry of random walks in semi-major axis allow diffusion to populate 2013 SY$_{99}$'s orbital parameter space from the 1000-2000 au inner fringe of the Oort cloud. Diffusion affects other known TNOs on orbits with perihelia of 45 to 49 au and semi-major axes beyond 250 au, providing a formation mechanism that implies an extended population, gently cycling into and returning from the inner fringe of the Oort cloud.
The formation of the solar system's terrestrial planets has been numerically modeled in various works, and many other studies have been devoted to characterizing our modern planets' chaotic dynamical state. However, it is still not known whether our planet's fragile chaotic state is an expected outcome of terrestrial planet accretion. We use a suite of numerical simulations to present a detailed analysis and characterization of the dynamical chaos in 145 different systems produced via terrestrial planet formation in Kaib and Cowan (2015). These systems were created in the presence of a fully formed Jupiter and Saturn, using a variety of different initial conditions. They are not meant to provide a detailed replication of the actual present solar system, but rather serve as a sample of similar systems for comparison and analysis. We find that dynamical chaos is prevalent in roughly half of the systems we form. We show that this chaos disappears in the majority of such systems when Jupiter is removed, implying that the largest source of chaos is perturbations from Jupiter. Chaos is most prevalent in systems that form 4 or 5 terrestrial planets. Additionally, an eccentric Jupiter and Saturn is shown to enhance the prevalence of chaos in systems. Furthermore, systems in our sample with a center of mass highly concentrated between 0.8 -1.2 AU generally prove to be less chaotic than systems with more exotic mass distributions. Through the process of evolving systems to the current epoch, we show that late instabilities are quite common in our systems. Of greatest interest, many of the sources of chaos observed in our own solar system (such as the secularly driven chaos between Mercury and Jupiter) are shown to be common outcomes of terrestrial planetary formation.
Rory Barnes, Russell Deitrick, Rodrigo Luger, Peter E. Driscoll, Thomas R. Quinn, David P. Fleming, Benjamin Guyer, Diego V. McDonald, Victoria S. Meadows, Giada Arney, David Crisp, Shawn D. Domagal-Goldman, Daniel Foreman-Mackey, Nathan A. Kaib, Andrew Lincowski, Jacob Lustig-Yaeger, Eddie Schwieterman We analyze the evolution of the potentially habitable planet Proxima Centauri b to identify environmental factors that affect its long-term habitability. We consider physical processes acting on size scales ranging from the galactic to the stellar system to the planet's core. We find that there is a significant probability that Proxima Centauri has had encounters with its companion stars, Alpha Centauri A and B, that are close enough to destabilize an extended planetary system. If the system has an additional planet, as suggested by the discovery data, then it may perturb planet b's eccentricity and inclination, possibly driving those parameters to non-zero values, even in the presence of strong tidal damping. We also model the internal evolution of the planet, evaluating the roles of different radiogenic abundances and tidal heating and find that magnetic field generation is likely for billions of years. We find that if planet b formed in situ, then it experienced 169 +/- 13 million years in a runaway greenhouse as the star contracted during its formation. This early phase could remove up to 5 times as much water as in the modern Earth's oceans, possibly producing a large abiotic oxygen atmosphere. On the other hand, if Proxima Centauri b formed with a substantial hydrogen atmosphere (0.01 - 1% of the planet's mass), then this envelope could have shielded the water long enough for it to be retained before being blown off itself. After modeling this wide range of processes we conclude that water retention during the host star's pre-main sequence phase is the biggest obstacle for Proxima b's habitability. These results are all obtained with a new software package called VPLANET.
Michele T. Bannister, Mike Alexandersen, Susan D. Benecchi, Ying-Tung Chen, Audrey Delsanti, Wesley C. Fraser, Brett J. Gladman, Mikael Granvik, Will M. Grundy, Aurelie Guilbert-Lepoutre, Stephen D. J. Gwyn, Wing-Huen Ip, Marian Jakubik, R. Lynne Jones, Nathan Kaib, J. J. Kavelaars, Pedro Lacerda, Samantha Lawler, Matthew J. Lehner, Hsing Wen Lin, et al (15) We report the discovery and orbit of a new dwarf planet candidate, 2015 RR$_{245}$, by the Outer Solar System Origins Survey (OSSOS). 2015 RR$_{245}$'s orbit is eccentric ($e=0.586$), with a semi-major axis near 82 au, yielding a perihelion distance of 34 au. 2015 RR$_{245}$ has $g-r = 0.59 \pm 0.11$ and absolute magnitude $H_{r} = 3.6 \pm 0.1$; for an assumed albedo of $p_V = 12$% the object has a diameter of $\sim670$ km. Based on astrometric measurements from OSSOS and Pan-STARRS1, we find that 2015 RR$_{245}$ is securely trapped on ten-Myr timescales in the 9:2 mean-motion resonance with Neptune. It is the first TNO identified in this resonance. On hundred-Myr timescales, particles in 2015 RR$_{245}$-like orbits depart and sometimes return to the resonance, indicating that 2015 RR$_{245}$ likely forms part of the long-lived metastable population of distant TNOs that drift between resonance sticking and actively scattering via gravitational encounters with Neptune. The discovery of a 9:2 TNO stresses the role of resonances in the long-term evolution of objects in the scattering disk, and reinforces the view that distant resonances are heavily populated in the current Solar System. This object further motivates detailed modelling of the transient sticking population.
Recently, Sheppard et al. (2016) presented the discovery of seven new trans-Neptunian objects with moderate eccentricities, perihelia beyond 40 AU, and semimajor axes beyond 50 AU. Like the few previously known objects on similar orbits, these objects' semimajor axes are just beyond the Kuiper belt edge and clustered around Neptunian mean motion resonances (MMRs). These objects likely obtained their observed orbits while trapped within MMRs, when the Kozai-Lidov mechanism raised their perihelia and weakened Neptune's dynamical influence. Using numerical simulations that model the production of this population, we find that high-perihelion objects near Neptunian MMRs can constrain the nature and timescale of Neptune's past orbital migration. In particular, the population near the 3:1 MMR (near 62 AU) is especially useful due to its large population and short dynamical evolution timescale. If Neptune finishes migrating within ~100 Myrs or less, we predict over 90% of high-perihelion objects near the 3:1 MMR will have semimajor axes within 1 AU of each other, very near the modern resonance's center. On the other hand, if Neptune's migration takes ~300 Myrs, we expect ~50% of this population to reside in dynamically fossilized orbits over ~1 AU closer to the Sun than the modern resonance. We highlight 2015 KH162 as a likely member of this fossilized 3:1 population. Under any plausible migration scenario, nearly all high-perihelion objects in resonances beyond the 4:1 MMR (near 76 AU) reach their orbits well after Neptune stops migrating and comprise a recently generated, dynamically active population.
The orbital element distribution of trans-Neptunian objects (TNOs) with large pericenters has been suggested to be influenced by the presence of an undetected, large planet at >200 AU from the Sun. To find additional observables caused by this scenario, we here present the first detailed emplacement simulation in the presence of a massive ninth planet on the distant Kuiper Belt. We perform 4 Gyr N-body simulations with the currently known Solar System planetary architecture, plus a 10 Earth mass planet with similar orbital parameters to those suggested by Trujillo & Sheppard (2014) or Batygin & Brown (2016), and 10^5 test particles in an initial planetesimal disk. We find that including a distant superearth-mass planet produces a substantially different orbital distribution for the scattering and detached TNOs, raising the pericenters and inclinations of moderate semimajor axis (50<a<500 AU) objects. We test whether this signature is detectable via a simulator with the observational characteristics of four precisely characterized TNO surveys. We find that the qualitatively very distinct Solar System models that include a ninth planet are essentially observationally indistinguishable from an outer Solar System produced solely by the four giant planets. We also find that the mass of the Kuiper Belt's current scattering and detached populations is required to be 3-10 times larger in the presence of an additional planet. We do not find any evidence for clustering of orbital angles in our simulated TNO population. Wide-field, deep surveys targeting inclined high-pericenter objects will be required to distinguish between these different scenarios.
Cosmology experiments at mm-wavelengths can detect Planet Nine if it is the size of Neptune, has an effective temperature of 40 K, and is 700 AU from the Sun. It would appear as a ~30 mJy source at 1 mm with an annual parallax of ~5 arcmin. The challenge is to distinguish it from the approximately 4000 foreground asteroids brighter than 30 mJy. Fortunately, these asteroids are known to the Minor Planet Center and can be identified because they move across a resolution element in a matter of hours, orders of magnitude faster than Planet Nine. If Planet Nine is smaller, colder, and/or more distant than expected, then it could be as faint as 1 mJy at 1 mm. There are roughly $10^6$ asteroids this bright and many are unknown, making current cosmology experiments confusion limited for moving sources. Nonetheless, it may still be possible to find the proverbial needle in the haystack using a matched filter. This would require mm telescopes with high angular resolution and high sensitivity in order to alleviate confusion and to enable the identification of moving sources with relatively short time baselines. Regardless of its mm flux density, searching for Planet Nine would require frequent radio measurements for large swaths of the sky, including the ecliptic and Galactic plane. Even if Planet Nine had already been detected by other means, measuring its mm-flux would constrain its internal energy budget, and therefore help resolve the mystery of Uranus and Neptune, which have vastly different internal heat.
Timothy J. Rodigas, Pamela Arriagada, Jackie Faherty, Guillem Anglada-Escude, Nathan Kaib, R. Paul Butler, Stephen Shectman, Alycia Weinberger, Jared R. Males, Katie M. Morzinski, Laird M. Close, Philip M. Hinz, Jeffrey D. Crane, Ian Thompson, Johanna Teske, Matias Diaz, Dante Minniti, Mercedes Lopez-Morales, Fred C. Adams, Alan P. Boss We present high-contrast Magellan adaptive optics (MagAO) images of HD 7449, a Sun-like star with one planet and a long-term radial velocity (RV) trend. We unambiguously detect the source of the long-term trend from 0.6-2.15 \microns ~at a separation of \about 0\fasec 54. We use the object's colors and spectral energy distribution to show that it is most likely an M4-M5 dwarf (mass \about 0.1-0.2 \msun) at the same distance as the primary and is therefore likely bound. We also present new RVs measured with the Magellan/MIKE and PFS spectrometers and compile these with archival data from CORALIE and HARPS. We use a new Markov chain Monte Carlo procedure to constrain both the mass ($> 0.17$ \msun ~at 99$\%$ confidence) and semimajor axis (\about 18 AU) of the M dwarf companion (HD 7449B). We also refine the parameters of the known massive planet (HD 7449Ab), finding that its minimum mass is $1.09^{+0.52}_{-0.19}$ \mj, its semimajor axis is $2.33^{+0.01}_{-0.02}$ AU, and its eccentricity is $0.8^{+0.08}_{-0.06}$. We use N-body simulations to constrain the eccentricity of HD 7449B to $\lesssim$ 0.5. The M dwarf may be inducing Kozai oscillations on the planet, explaining its high eccentricity. If this is the case and its orbit was initially circular, the mass of the planet would need to be $\lesssim$ 1.5 \mj. This demonstrates that strong constraints on known planets can be made using direct observations of otherwise undetectable long-period companions.
C. Shankman, J.J. Kavelaars, B. J. Gladman, M. Alexandersen, N. Kaib, J.-M. Petit, M. T. Bannister, Y.-T Chen, S. Gwyn, M. Jakubik, K. Volk We measure the absolute magnitude, $H$, distribution, $dN(H) \propto 10^{\alpha H}$ of the scattering Trans-Neptunian Objects (TNOs) as a proxy for their size-frequency distribution. We show that the H-distribution of the scattering TNOs is not consistent with a single-slope distribution, but must transition around $H_g \sim 9$ to either a knee with a shallow slope or to a divot, which is a differential drop followed by second exponential distribution. Our analysis is based on a sample of 22 scattering TNOs drawn from three different TNO surveys, the Canada-France Ecliptic Plane Survey (CFEPS, Petit et al. 2011), Alexandersen et al. (2014), and the Outer Solar System Origins Survey (OSSOS, Bannister et al. 2016), all of which provide well characterized detection thresholds, combined with a cosmogonic model for the formation of the scattering TNO population. Our measured absolute magnitude distribution result is independent of the choice of cosmogonic model. Based on our analysis, we estimate that number of scattering TNOs is (2.4-8.3)$\times 10^5$ for $H_r < 12$. A divot $H$-distribution is seen in a variety of formation scenarios and may explain several puzzles in Kuiper Belt science. We find that a divot $H$-distribution simultaneously explains the observed scattering TNO, Neptune Trojan, Plutino, and Centaur $H$-distributions while simultaneously predicting a large enough scattering TNO population to act as the sole supply of the Jupiter-Family Comets.
Michele T. Bannister, J. J. Kavelaars, Jean-Marc Petit, Brett J. Gladman, Stephen D. J. Gwyn, Ying-Tung Chen, Kathryn Volk, Mike Alexandersen, Susan Benecchi, Audrey Delsanti, Wesley Fraser, Mikael Granvik, Will M. Grundy, Aurelie Guilbert-Lepoutre, Daniel Hestroffer, Wing-Huen Ip, Marian Jakubik, Lynne Jones, Nathan Kaib, Catherine F. Kavelaars, et al (19) We report the discovery, tracking and detection circumstances for 85 trans-Neptunian objects (TNOs) from the first 42 deg$^{2}$ of the Outer Solar System Origins Survey (OSSOS). This ongoing $r$-band Solar System survey uses the 0.9 deg$^{2}$ field-of-view MegaPrime camera on the 3.6 m Canada-France-Hawaii Telescope. Our orbital elements for these TNOs are precise to a fractional semi-major axis uncertainty $<0.1\%$. We achieve this precision in just two oppositions, as compared to the normal 3-5 oppositions, via a dense observing cadence and innovative astrometric technique. These discoveries are free of ephemeris bias, a first for large trans-Neptunian surveys. We also provide the necessary information to enable models of TNO orbital distributions to be tested against our TNO sample. We confirm the existence of a cold "kernel" of objects within the main cold classical Kuiper belt, and infer the existence of an extension of the "stirred" cold classical Kuiper belt to at least several AU beyond the 2:1 mean motion resonance with Neptune. We find that the population model of Petit et al. (2011) remains a plausible representation of the Kuiper belt. The full survey, to be completed in 2017, will provide an exquisitely characterized sample of important resonant TNO populations, ideal for testing models of giant planet migration during the early history of the Solar System.
Many features of the outer solar system are replicated in numerical simulations if the giant planets undergo an orbital instability that ejects one or more ice giants. During this instability, Jupiter and Saturn's orbits diverge, crossing their 2:1 mean motion resonance (MMR), and this resonance-crossing can excite the terrestrial planet orbits. Using a large ensemble of simulations of this giant planet instability, we directly model the evolution of the terrestrial planet orbits during this process, paying special attention to systems that reproduce the basic features of the outer planets. In systems that retain four giant planets and finish with Jupiter and Saturn beyond their 2:1 MMR, we find at least an 85% probability that at least one terrestrial planet is lost. Moreover, systems that manage to retain all four terrestrial planets often finish with terrestrial planet eccentricities and inclinations larger than the observed ones. There is less than a ~5% chance that the terrestrial planet orbits will have a level of excitation comparable to the observed orbits. If we factor in the probability that the outer planetary orbits are well-replicated, we find a probability of 1% or less that the orbital architectures of the inner and outer planets are simultaneously reproduced in the same system. These small probabilities raise the prospect that the giant planet instability occurred before the terrestrial planets had formed. This scenario implies that the giant planet instability is not the source of the Late Heavy Bombardment and that terrestrial planet formation finished with the giant planets in their modern configuration.
Binaries are typically excluded from direct imaging exoplanet surveys. However, the recent findings of Kepler and radial velocity programs show that planets can and do form in binary systems. Here, we suggest that visual binaries offer unique advantages for direct imaging. We show that Binary Differential Imaging (BDI), whereby two stars are imaged simultaneously at the same wavelength within the isoplanatic patch at high Strehl ratio, offers improved point spread function (PSF) subtraction that can result in increased sensitivity to planets close to each star. We demonstrate this by observing a young visual binary separated by 4\asec ~with MagAO/Clio-2 at 3.9 \microns, where the Strehl ratio is high, the isoplanatic patch is large, and giant planets are bright. Comparing BDI to angular differential imaging (ADI), we find that BDI's 5$\sigma$ contrast is \about 0.5 mags better than ADI's within \about 1\asec ~for the particular binary we observed. Because planets typically reside close to their host stars, BDI is a promising technique for discovering exoplanets in stellar systems that are often ignored. BDI is also 2-4$\times$ more efficient than ADI and classical reference PSF subtraction, since planets can be detected around both the target and PSF reference simultaneously. We are currently exploiting this technique in a new MagAO survey for giant planets in 140 young nearby visual binaries. BDI on a space-based telescope would not be limited by isoplanatism effects and would therefore be an even more powerful tool for imaging and discovering planets.
Kaib & Cowan (2015) recently used terrestrial planet formation simulations to conclude that the moon-forming impactor (Theia) had only a ~5% or less chance of having the same oxygen isotope composition as Earth, while Mastrobuono-Battisti et al. (2015) used seemingly similar simulations and methods to arrive at a higher value of ~20% or more. Here we derive the results of both papers from a single set of simulations. Compared to Kaib & Cowan (2015), the analysis of Mastrobuono-Battisti et al. (2015) systematically yields more massive Theia analogs and imposes flatter isotopic gradients across the original protoplanetary disk. Both of these effects diminish isotopic differences between Earth and Theia analogs. While it is notoriously difficult to produce systems resembling our actual terrestrial planets, the analysis of Kaib & Cowan (2015) more often selects and analyzes Earth and Mars analogs at orbital locations near the real planets. Given this, we conclude that the greater isotopic differences between Earth and Theia found in Kaib & Cowan (2015) better reflect the predictions of terrestrial planet formation models. Finally, although simulation uncertainties and a terrestrial contribution to Moon formation enhance the fraction of Theia analogs consistent with the canonical giant impact hypothesis, this fraction still remains in the 5-8% range.
[Abridged] We present an extensive suite of terrestrial planet formation simulations that allows quantitative analysis of the stochastic late stages of planet formation. We quantify the feeding zone width, Delta a, as the mass-weighted standard deviation of the initial semi-major axes of the planetary embryos and planetesimals that make up the final planet. The size of a planet's feeding zone in our simulations does not correlate with its final mass or semi-major axis, suggesting there is no systematic trend between a planet's mass and its volatile inventory. Instead, we find that the feeding zone of any planet more massive than 0.1M_Earth is roughly proportional to the radial extent of the initial disk from which it formed: Delta a~0.25(a_max-a_min), where a_min and a_max are the inner and outer edge of the initial planetesimal disk. These wide stochastic feeding zones have significant consequences for the origin of the Moon, since the canonical scenario predicts the Moon should be primarily composed of material from Earth's last major impactor (Theia), yet its isotopic composition is indistinguishable from Earth. In particular, we find that the feeding zones of Theia analogs are significantly more stochastic than the planetary analogs. Depending on our assumed initial distribution of oxygen isotopes within the planetesimal disk, we find a ~5% or less probability that the Earth and Theia will form with an isotopic difference equal to or smaller than the Earth and Moon's. In fact we predict that every planetary mass body should be expected to have a unique isotopic signature. In addition, we find paucities of massive Theia analogs and high velocity moon-forming collisions, two recently proposed explanations for the Moon's isotopic composition. Our work suggests that there is still no scenario for the Moon's origin that explains its isotopic composition with a high probability event.
Mercedes Lopez-Morales, Amaury H. M. J. Triaud, Florian Rodler, Xavier Dumusque, Lars A. Buchhave, A. Harutyunyan, Sergio Hoyer, Roi Alonso, Michael Gillon, Nathan A. Kaib, David W. Latham, Christophe Lovis, Francesco Pepe, Didier Queloz, Sean N.Raymond, Damien Segransan, Ingo P. Waldmann, Stephane Udry We present Rossiter-McLaughlin observations of the transiting super-Earth 55 Cnc e collected during six transit events between January 2012 and November 2013 with HARPS and HARPS-N. We detect no radial-velocity signal above 35 cm/s (3-sigma) and confine the stellar v sin i to 0.2 +/- 0.5 km/s. The star appears to be a very slow rotator, producing a very low amplitude Rossiter-McLaughlin effect. Given such a low amplitude, the Rossiter-McLaughlin effect of 55 Cnc e is undetected in our data, and any spin-orbit angle of the system remains possible. We also performed Doppler tomography and reach a similar conclusion. Our results offer a glimpse of the capacity of future instrumentation to study low amplitude Rossiter-McLaughlin effects produced by super-Earths.
We present numerical simulations modeling the orbital evolution of very wide binaries, pairs of stars separated by over ~1000 AU. Due to perturbations from other passing stars and the Milky Way's tide, the orbits of very wide binary stars occasionally become extremely eccentric, which forces close encounters between the companion stars (Kaib et al. 2013). We show that this process causes a stellar collision between very wide binary companion stars once every 1000-7500 years on average in the Milky Way. One of the main uncertainties in this collision rate is the amount of energy dissipated by dynamic tides during close (but not collisional) periastron passages. This dissipation presents a dynamical barrier to stellar collisions and can instead transform very wide binaries into close or contact binaries. However, for any plausible tidal dissipation model, very wide binary stars are an unrealized, and potentially the dominant, source of stellar collisions in our Galaxy. Such collisions should occur throughout the thin disk of the Milky Way. Stellar collisions within very wide binaries should yield a small population of single, Li-depleted, rapidly rotating massive stars.
We study the influence of outer Solar System architecture on the structural evolution of the Oort Cloud (OC) and the flux of Earth-crossing comets. In particular, we seek to quantify the role of the giant planets as "planetary protectors". To do so, we have run simulations in each of four different planetary mass configurations to understand the significance of each of the giant planets. Because the outer planets modify the structure of the OC throughout its formation, we integrate each simulation over the full age of the Solar System. Over this time, we follow the evolution of cometary orbits from their starting point in the protoplanetary disk to their injection into the OC to their possible re-entry into the inner planetary region. We find that the overall structure of the OC, including the location of boundaries and the relative number of comets in the inner and outer parts, does not change significantly between configurations; however, as planetary mass decreases, the trapping efficiency (TE) of comets into the OC and the flux of comets into the observable region increases. We determine that those comets that evolve onto Earth-crossing orbits come primarily from the inner OC but show no preference for initial protoplanetary disk location. We also find that systems that have at least a Saturn-mass object are effective at deflecting possible Earth-crossing comets but the difference in flux between systems with and without such a planet is less than an order of magnitude. We conclude by discussing the individual roles of the planets and the implications of incorporating more realistic planetary accretion and migration scenarios into simulations, particularly on existing discrepancies between low TE and the mass of the protoplanetary disk and on determining the structural boundaries of the OC.
Nearly half of the exoplanets found within binary star systems reside in very wide binaries with average stellar separations beyond 1,000 AU (1 AU being the Earth-Sun distance), yet the influence of such distant binary companions on planetary evolution remains largely unstudied. Unlike their tighter counterparts, the stellar orbits of wide binaries continually change under the influence of the Galactic tide and impulses from other passing stars. Here we report numerical simulations demonstrating that the variable nature of wide binary star orbits dramatically reshapes the planetary systems they host, typically Gyrs after formation. Contrary to previous understanding, wide binary companions may often strongly perturb planetary systems, triggering planetary ejections and exciting orbital eccentricities of surviving planets. Indeed, observed exoplanet eccentricities offer evidence of this; giant exoplanet orbits within wide binaries are statistically more eccentric than those around isolated stars. Both eccentricity distributions are well-reproduced when we assume isolated stars and wide binaries host similar planetary systems whose outermost giant planets are scattered beyond ~10 AU from their parent stars via early internal instabilities. Consequently, our results suggest that although wide binaries eventually truncate their planetary systems, most isolated giant exoplanet systems harbor additional distant, still undetected planets.
Via joint analysis of a calibrated telescopic survey, which found scattering Kuiper Belt objects, and models of their expected orbital distribution, we measure the form of the scattering object's size distribution. Ruling out a single power-law at greater than 99% confidence, we constrain the form of the size distribution and find that, surprisingly, our analysis favours a very sudden decrease (a divot) in the number distribution as diameters decrease below 100 km, with the number of smaller objects then rising again as expected via collisional equilibrium. Extrapolating at this collisional equilibrium slope produced enough kilometer-scale scattering objects to supply the nearby Jupiter-Family comets. Our interpretation is that this divot feature is a preserved relic of the size distribution made by planetesimal formation, now "frozen in" to portions of the Kuiper Belt sharing a "hot" orbital inclination distribution, explaining several puzzles in Kuiper Belt science. Additionally, we show that to match today's scattering-object inclination distribution, the supply source that was scattered outward must have already been vertically heated to of order 10 degrees.
Megan E. Schwamb, Jerome A. Orosz, Joshua A. Carter, William F. Welsh, Debra A. Fischer, Guillermo Torres, Andrew W. Howard, Justin R. Crepp, William C. Keel, Chris J. Lintott, Nathan A. Kaib, Dirk Terrell, Robert Gagliano, Kian J. Jek, Michael Parrish, Arfon M. Smith, Stuart Lynn, Robert J. Simpson, Matthew J. Giguere, Kevin Schawinski We report the discovery and confirmation of a transiting circumbinary planet (PH1b) around KIC 4862625, an eclipsing binary in the Kepler field. The planet was discovered by volunteers searching the first six Quarters of publicly available Kepler data as part of the Planet Hunters citizen science project. Transits of the planet across the larger and brighter of the eclipsing stars are detectable by visual inspection every ~137 days, with seven transits identified in Quarters 1-11. The physical and orbital parameters of both the host stars and planet were obtained via a photometric-dynamical model, simultaneously fitting both the measured radial velocities and the Kepler light curve of KIC 4862625. The 6.18 +/- 0.17 Earth radii planet orbits outside the 20-day orbit of an eclipsing binary consisting of an F dwarf (1.734 +/- 0.044 Solar radii, 1.528 +/- 0.087 Solar masses) and M dwarf (0.378+/- 0.023 Solar radii, 0.408 +/- 0.024 Solar masses). For the planet, we find an upper mass limit of 169 Earth masses (0.531 Jupiter masses) at the 99.7% confidence level. With a radius and mass less than that of Jupiter, PH1b is well within the planetary regime. Outside the planet's orbit, at ~1000 AU,a previously unknown visual binary has been identified that is likely bound to the planetary system, making this the first known case of a quadruple star system with a transiting planet.
Although the 55 Cnc system contains multiple, closely packed planets that are presumably in a coplanar configuration, we use numerical simulations to demonstrate that they are likely to be highly inclined to their parent star's spin axis. Due to perturbations from its distant binary companion, this planetary system precesses like a rigid body about its parent star. Consequently, the parent star's spin axis and the planetary orbit normal likely diverged long ago. Because only the projected separation of the binary is known, we study this effect statistically, assuming an isotropic distribution for wide binary orbits. We find that the most likely projected spin-orbit angle is ~50 degrees, with a ~30% chance of a retrograde configuration. Transit observations of the innermost planet - 55 Cnc e - may be used to verify these findings via the Rossiter-McLaughlin effect. 55 Cancri may thus represent a new class of planetary systems with well-ordered, coplanar orbits that are inclined with respect to the stellar equator.
Recent numerical simulations have demonstrated that the Sun's dynamical history within the Milky Way may be much more complex than that suggested by its current low peculiar velocity. In particular, the Sun may have radially migrated through the galactic disk by up to 5-6 kpc. This has important ramifications for the structure of the Oort Cloud, as it means that the solar system may have experienced tidal and stellar perturbations that were significantly different from its current local galactic environment. To characterize the effects of solar migration within the Milky Way, we use direct numerical simulations to model the formation of an Oort Cloud around stars that end up on solar-type orbits in a galactic-scale simulation of a Milky Way-like disk formation. Surprisingly, our simulations indicate that Sedna's orbit may belong to the classical Oort Cloud. Contrary to previous understanding, we show that field star encounters play a pivotal role in setting the Oort Cloud's extreme inner edge, and due to their stochastic nature this inner edge sometimes extends to Sedna's orbit. The Sun's galactic migration heightens the chance of powerful stellar passages, and Sedna production occurs around ~20-30% of the solar-like stars we study. Considering the entire Oort Cloud, we find its median distance depends on the minimum galactocentric distance attained during the Sun's orbital history. The inner edge also shows a similar dependence but with increased scatter due to the effects of powerful stellar encounters. Both of these Oort Cloud parameters can vary by an order of magnitude and are usually overestimated by an Oort Cloud formation model that assumes a fixed galactic environment. In addition, the amount of material trapped in outer Oort Cloud orbits can be extremely low and may present difficulties for models of Oort Cloud formation and long-period comet production.
It has previously been shown that varying the numerical timestep during a symplectic orbital integration leads to a random walk in energy and angular momentum, destroying the phase space-conserving property of symplectic integrators. Here we show that when altering the timestep symplectic correctors can be used to reduce this error to a negligible level. Furthermore, these correctors can also be employed to avoid a large error introduction when changing the Hamiltonian's partitioning. We have constructed a numerical integrator using this technique that is nearly as accurate as widely used fixed-step routines. In addition, our algorithm is drastically faster for integrations of highly eccentricitic, large semimajor axis orbits, such as those found in the Oort Cloud.
We present numerical simulations to model the production of observable long-period comets (LPCs) from the Oort Cloud, a vast reservoir of icy bodies surrounding the Sun. We show that inner Oort Cloud objects can penetrate Jupiter's orbit via a largely unexplored dynamical pathway, and they are an important, if not the dominant, source of known LPCs. We use this LPC production to place observationally motivated constraints on the population and mass of the inner Oort Cloud, which are consistent with giant planet formation theory. These constraints indicate that only one comet shower producing late Eocene bombardment levels has likely occurred since the Cambrian Explosion, making these phenomena an improbable cause of additional extinction events.
CoRoT-7 b, a planet about 70% larger than the Earth orbiting a Sun-like star, is the first-discovered rocky exoplanet, and hence has been dubbed a "super-Earth". Some initial studies suggested that since the planet is so close to its host star, it receives enough insolation to partially melt its surface. However, these past studies failed to take into consideration the role that tides may play in this system. Even if the planet's eccentricity has always been zero, we show that tidal decay of semi-major axis could have been large enough that the planet formed on a wider orbit which received less insolation. Moreover, CoRoT-7 b could be tidally heated at a rate that dominates its geophysics and drives extreme volcanism. In this case, CoRoT-7 b is a "super-Io" that, like Jupiter's volcanic moon, is dominated by volcanism and rapid resurfacing. Such heating could occur with an eccentricity of just 10^-5. This small value could be driven by CoRoT-7 c if its own eccentricity is larger than ~10^-4. CoRoT-7 b may be the first of a class of planetary super-Ios likely to be revealed by the CoRoT and Kepler spacecraft.
LSST Science Collaborations, Paul A. Abell, Julius Allison, Scott F. Anderson, John R. Andrew, J. Roger P. Angel, Lee Armus, David Arnett, S. J. Asztalos, Tim S. Axelrod, Stephen Bailey, D. R. Ballantyne, Justin R. Bankert, Wayne A. Barkhouse, Jeffrey D. Barr, L. Felipe Barrientos, Aaron J. Barth, James G. Bartlett, Andrew C. Becker, Jacek Becla, et al (227) A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.
To date, no accretion model has succeeded in reproducing all observed constraints in the inner Solar System. These constraints include 1) the orbits, in particular the small eccentricities, and 2) the masses of the terrestrial planets -- Mars' relatively small mass in particular has not been adequately reproduced in previous simulations; 3) the formation timescales of Earth and Mars, as interpreted from Hf/W isotopes; 4) the bulk structure of the asteroid belt, in particular the lack of an imprint of planetary embryo-sized objects; and 5) Earth's relatively large water content, assuming that it was delivered in the form of water-rich primitive asteroidal material. Here we present results of 40 high-resolution (N=1000-2000) dynamical simulations of late-stage planetary accretion with the goal of reproducing these constraints, although neglecting the planet Mercury. We assume that Jupiter and Saturn are fully-formed at the start of each simulation, and test orbital configurations that are both consistent with and contrary to the "Nice model." We find that a configuration with Jupiter and Saturn on circular orbits forms low-eccentricity terrestrial planets and a water-rich Earth on the correct timescale, but Mars' mass is too large by a factor of 5-10 and embryos are often stranded in the asteroid belt. A configuration with Jupiter and Saturn in their current locations but with slightly higher initial eccentricities (e = 0.07-0.1) produces a small Mars, an embryo-free asteroid belt, and a reasonable Earth analog but rarely allows water delivery to Earth. None of the configurations we tested reproduced all the observed constraints. (abridged)
Nathan A. Kaib, Andrew C. Becker, R. Lynne Jones, Andrew W. Puckett, Dmitry Bizyaev, Benjamin Dilday, Joshua A. Frieman, Daniel J. Oravetz, Kaike Pan, Thomas Quinn, Donald P. Schneider, Shannon Watters We report the discovery of a minor planet (2006 SQ372) on an orbit with a perihelion of 24 AU and a semimajor axis of 796 AU. Dynamical simulations show that this is a transient orbit and is unstable on a timescale of 200 Myrs. Falling near the upper semimajor axis range of the scattered disk and the lower semimajor axis range of the Oort Cloud, previous membership in either class is possible. By modeling the production of similar orbits from the Oort Cloud as well as from the scattered disk, we find that the Oort Cloud produces 16 times as many objects on SQ372-like orbits as the scattered disk. Given this result, we believe this to be the most distant long-period comet ever discovered. Furthermore, our simulation results also indicate that 2000 OO67 has had a similar dynamical history. Unaffected by the "Jupiter-Saturn Barrier," these two objects are most likely long-period comets from the inner Oort Cloud.
A. C. Becker, K. Arraki, N. A. Kaib, W. M. Wood-Vasey, C. Aguilera, J. W. Blackman, S. Blondin, P. Challis, A. Clocchiatti, R. Covarrubias, G. Damke, T. M. Davis, A. V. Filippenko, R. J. Foley, A. Garg, P. M. Garnavich, M. Hicken, S. Jha, R. P. Kirshner, K. Krisciunas, et al (19) We report the discovery and orbit determination of 14 trans-Neptunian objects (TNOs) from the ESSENCE Supernova Survey difference imaging dataset. Two additional objects discovered in a similar search of the SDSS-II Supernova Survey database were recovered in this effort. ESSENCE repeatedly observed fields far from the Solar System ecliptic (-21 deg < beta < -5 deg), reaching limiting magnitudes per observation of I~23.1 and R~23.7. We examine several of the newly detected objects in detail, including 2003 UC_414 which orbits entirely between Uranus and Neptune and lies very close to a dynamical region that would make it stable for the lifetime of the Solar System. 2003 SS_422 and 2007 TA_418 have high eccentricities and large perihelia, making them candidate members of an outer class of trans-Neptunian objects. We also report a new member of the ''extended'' or ''detached'' scattered disk, 2004 VN_112, and verify the stability of its orbit using numerical simulations. This object would have been visible to ESSENCE for only ~2% of its orbit, suggesting a vast number of similar objects across the sky. We emphasize that off-ecliptic surveys are optimal for uncovering the diversity of such objects, which in turn will constrain the history of gravitational influences that shaped our early Solar System.
Kevin R. Covey, Zeljko Ivezic, David J. Schlegel, Douglas P. Finkbeiner, Nikhil Padmanabhan, Robert H. Lupton, Marcel A. Agueros, John J. Bochanski, Suzanne L. Hawley, Andrew A. West, Anil C. Seth, Amy E. Kimball, Stephanie M. Gogarten, Mark Claire, Daryl Haggard, Nathan A. Kaib, Donald P. Schneider, Branimir Sesar The Sloan Digital Sky Survey (SDSS) and Two Micron All Sky Survey (2MASS) are rich resources for studying stellar astrophysics and the structure and formation history of the Galaxy. As new surveys and instruments adopt similar filter sets, it is increasingly important to understand the properties of the ugrizJHKs stellar locus, both to inform studies of `normal' main sequence stars as well as for robust searches for point sources with unusual colors. Using a sample of ~600,000 point sources detected by SDSS and 2MASS, we tabulate the position and width of the ugrizJHKs stellar locus as a function of g-i color, and provide accurate polynomial fits. We map the Morgan-Keenan spectral type sequence to the median stellar locus by using synthetic photometry of spectral standards and by analyzing 3000 SDSS stellar spectra with a custom spectral typing pipeline. We develop an algorithm to calculate a point source's minimum separation from the stellar locus in a seven-dimensional color space, and use it to robustly identify objects with unusual colors, as well as spurious SDSS/2MASS matches. Analysis of a final catalog of 2117 color outliers identifies 370 white-dwarf/M dwarf (WDMD) pairs, 93 QSOs, and 90 M giant/carbon star candidates, and demonstrates that WDMD pairs and QSOs can be distinguished on the basis of their J-Ks and r-z colors. We also identify a group of objects with correlated offsets in the u-g vs. g-r and g-r vs. r-i color-color spaces, but subsequent follow-up is required to reveal the nature of these objects. Future applications of this algorithm to a matched SDSS-UKIDSS catalog may well identify additional classes of objects with unusual colors by probing new areas of color-magnitude space.
We study the influence of an open cluster environment on the formation and current structure of the Oort cloud. To do this, we have run 19 different simulations of the formation of the Oort Cloud for 4.5 Gyrs. In each simulation, the solar system spends its first 100 Myrs in a different open cluster environment before transitioning to its current field environment. We find that, compared to forming in the field environment, the inner Oort Cloud is preferentially loaded with comets while the Sun resides in the open cluster and that most of this material remains locked in the interior of the cloud for the next 4.4 Gyrs. In addition, the outer Oort Cloud trapping efficiencies we observe in our simulations are lower than previous formation models by about a factor of 2, possibly implying an even more massive early planetesimal disk. Furthermore, some of our simulations reproduce the orbits of observed extended scattered disk objects, which may serve as an observational constraint on the Sun's early environment. Depending on the particular open cluster environment, the properties of the inner Oort Cloud and extended scattered disk can vary widely. On the other hand, the outer portions of the Oort Cloud in each of our simulations are all similar.
Marcel A. Agueros, Zeljko Ivezic, Kevin R. Covey, Mirela Obric, Lei Hao, Lucianne M. Walkowicz, Andrew A. West, Daniel E. Vanden Berk, Robert H. Lupton, Gillian R. Knapp, James E. Gunn, Gordon T. Richards, John Bochanski, Jr., Alyson Brooks, Mark Claire, Daryl Haggard, Nathan Kaib, Amy Kimball, Stephanie M. Gogarten, et al (2) May 18 2005
astro-ph arXiv:astro-ph/0505334v1
We discuss the UV, optical, and IR properties of the SDSS sources detected by GALEX as part of its All-sky Imaging Survey Early Release Observations. Virtually all of the GALEX sources in the overlap region are detected by SDSS. GALEX sources represent ~2.5% of all SDSS sources within these fields and about half are optically unresolved. Most unresolved GALEX/SDSS sources are bright blue turn-off thick disk stars and are typically detected only in the GALEX near-UV band. The remaining unresolved sources include low-redshift quasars, white dwarfs, and white dwarf/M dwarf pairs, and these dominate the optically unresolved sources detected in both GALEX bands. Almost all the resolved SDSS sources detected by GALEX are fainter than the SDSS 'main' spectroscopic limit. These sources have colors consistent with those of blue (spiral) galaxies (u-r<2.2), and most are detected in both GALEX bands. Measurements of their UV colors allow much more accurate and robust estimates of star-formation history than are possible using only SDSS data. Indeed, galaxies with the most recent (<20 Myr) star formation can be robustly selected from the GALEX data by requiring that they be brighter in the far-UV than in the near-UV band. However, older starburst galaxies have UV colors similar to AGN, and thus cannot be selected unambiguously on the basis of GALEX fluxes alone. With the aid of 2MASS data, we construct and discuss median 10 band UV-optical-IR spectral energy distributions for turn-off stars, hot white dwarfs, low-redshift quasars, and spiral and elliptical galaxies. We point out the high degree of correlation between the UV color and the contribution of the UV flux to the UV-optical-IR flux of galaxies detected by GALEX.
Apr 12 2004
astro-ph arXiv:astro-ph/0404212v3
Recent results have shown that many of the known extrasolar planetary systems contain regions which are stable for both Earth-mass and Saturn-mass planets. Here we simulate the formation of terrestrial planets in four planetary systems -- 55 Cancri, HD 38529, HD 37124, and HD 74156 -- under the assumption that these systems of giant planets are complete and that their orbits are well-determined. Assuming the giant planets formed and migrated quickly, then terrestrial planets may form from a second generation of planetesimals. In each case, Moon- to Mars-sized planetary embryos are placed in between the giant planets and evolved for 100 Myr. We find that planets form relatively easily in 55 Cnc, with masses up to 0.6 Earth masses and in some cases substantial water contents and orbits in the habitable zone. HD 38529 is likely to support an asteroid belt but no terrestrial planets of significant mass. No terrestrial planets form in HD 37124 and HD 74156, although in some cases 1-2 lone embryos survive for 100 Myr. If migration occurred later, depleting the planetesimal disk, then massive terrestrial planets are unlikely to form in any of these systems.
Braneshop, and
the US National Science Foundation.
SciRate