Distant trans-Neptunian Objects Research Articles

Study of Migration of Giant Planets and Formation of Populations of Distant Trans-Neptunian Objects in the Nice Model

Study of Migration of Giant Planets and Formation of Populations of Distant Trans-Neptunian Objects in the Nice Model

Radial distribution of distant trans-Neptunian objects points to Sun’s formation in a stellar cluster

The Scattered Disk Objects (SDOs) are a population of trans-Neptunian bodies with semimajor axes 50<a≲1000 au and perihelion distances q≳30 au. The detached SDOs with orbits beyond the reach of Neptune (roughly q>35 au) are of special interest here as an important constraint on the early evolution of the outer Solar System. The semimajor axis profile of detached SDOs at 50–500 au, as characterized from the Dark Energy Survey (DES), is radially extended, but previous dynamical models of Neptune’s early migration produce a relatively compact profile. This problem is most likely related to Sun’s birth environment in a stellar cluster. We perform new dynamical simulations that account for cluster effects and show that the orbital distribution of SDOs can be explained if a particularly close stellar encounter occurred early on (e.g., M dwarf with the mass ≃0.2M⊙ approaching the Sun at ≃200 au). For such an encounter to happen with a reasonably high probability the Sun must have formed in a stellar cluster with ηT≳104 Myr pc−3, where η is the stellar number density and T is the Sun’s residence time in the cluster.

A dynamical survey of the trans-Neptunian region − II. On the nature of chaotic diffusion

ABSTRACT On long enough time-scales, chaotic diffusion has the potential to significantly alter the appearance of a dynamical system. The Solar system is no exception: diffusive processes take part in the transportation of small bodies and provide dynamical pathways even for the distant trans-Neptunian objects to reach the inner Solar system. In this letter, we carry out a thorough investigation of the nature of chaotic diffusion. We analyse the temporal evolution of the mean squared displacement of 10 000 ensembles of test particles and quantify in each case the diffusion exponent (enabling the classification between normal, sub-, and superdiffusion), the generalized diffusion coefficient, and a characteristic diffusion time-scale, too. This latter quantity is compared with an entropy-based time-scale, and the two approaches are studied in light of direct computations as well. Our results are given in the context of two-dimensional maps, thereby facilitating the understanding of the relationship between the typical phase space structures and the properties of chaotic diffusion.

The Possibility of Mirror Planet as Planet Nine in the Solar System

A series of dynamical anomalies in the orbits of distant trans-Neptunian objects points to a new celestial body (usually named Planet Nine) in the solar system. In this draft, we point out that a mirror planet captured from the outer solar system or formed in the solar system is also a possible candidate. The introduction of the mirror matter model is due to an unbroken parity symmetry and is a potential explanation for dark matter. This mirror planet has null or fainter electromagnetic counterparts with a smaller optical radius and might be explored through gravitational effects.

A Low-inclination Neutral Trans-Neptunian Object in an Extreme Orbit

We present photometric observations and numerical simulations of 2016 SD106, a low-inclination (i = 4.°8) extreme trans-Neptunian Object with a large semimajor axis (a = 350 au) and perihelion (q = 42.6 au). This object possesses a peculiar neutral color of g − r = 0.45 ± 0.05 and g − i = 0.72 ± 0.06, in comparison with other distant trans-Neptunian objects, all of which have moderate-red to ultra-red colors. A numerical integration based on orbital fitting on astrometric data covering eight years of arc confirms that 2016 SD106 is a metastable object without significant scattering evolution. Each of the clones survived at the end of the 1 Gyr simulation. However, very few neutral objects with inclinations <5° have been found in the outer solar system, even in the main Kuiper Belt. Furthermore, most mechanisms that lift perihelion distances are expected to produce a very low number of extreme objects with inclinations <5°. We thus explored the possibility that a hypothetical distant planet could increase the production of such objects. Our simulations show that no 2016 SD106–like orbits can be produced from three Kuiper Belt populations tested (i.e., plutinos, twotinos, and the Haumea Family) without the presence of a hypothetical planet, while a few similar orbits can be obtained with it; however, the presence of the additional planet produces a wide range of large semimajor-axis/large perihelion objects, in apparent contradiction with the observed scarcity of objects in those regions of phase space. Future studies may determine if there is a connection between the existence of a perihelion gap and a particular orbital configuration of a hypothetical distant planet.

Dynamical evolution of a self-gravitating planetesimal disk in the distant trans-Neptunian region

Aims. We study the dynamical evolution of a system consisting of the giant planets and a massive planetesimal disk over the age of the Solar System. The main question addressed in this study is whether distant trans-Neptunian objects could have come about as a result of the combined action of planetary perturbations and the self-gravity of the disk. Methods. We carried out a series of full N-body numerical simulations of gravitational interactions between the giant planets and a massive outer disk of planetesimals. Results. Our simulations show that the collective gravity of the giant planets and massive planetesimals produces distant trans-Neptunian objects across a wide range of the initial disk mass. The majority of objects that survive up through the age of the Solar System have perihelion distances of q &gt; 40 au. In this region, there is a tendency toward a slow decrease in eccentricities and an increase in perihelion distances for objects with semimajor axes a &gt; 150 au. Secular resonances between distant planetesimals play a major role in increasing their perihelion distances. This explains the origin of Sedna-type objects. In our integrations for the age of the Solar System, we registered times with both high and low clustering of longitudes of perihelion and arguments of perihelion for objects with q &gt; 40 au, a &gt; 150 au. The resulting distribution of inclinations in our model and the observed distribution of inclinations for distant trans-Neptunian objects have similar average values of around 20°. Conclusions. Distant trans-Neptunian objects are a natural consequence in the models that include migrating giant planets and a self-gravitating planetesimal disk.

The Stability Boundary of the Distant Scattered Disk

Abstract The distant scattered disk is a vast population of trans-Neptunian minor bodies that orbit the Sun on highly elongated, long-period orbits. The orbital stability of scattered-disk objects (SDOs) is primarily controlled by a single parameter—their perihelion distance. While the existence of a perihelion boundary that separates chaotic and regular motion of long-period orbits is well established through numerical experiments, its theoretical basis as well as its semimajor axis dependence remain poorly understood. In this work, we outline an analytical model for the dynamics of distant trans-Neptunian objects and show that the orbital architecture of the scattered disk is shaped by an infinite chain of exterior 2:j resonances with Neptune. The widths of these resonances increase as the perihelion distance approaches Neptune’s semimajor axis, and their overlap drives chaotic motion. Within the context of this theoretical picture, we derive an analytic criterion for instability of long-period orbits, and demonstrate that rapid dynamical chaos ensues when the perihelion drops below a critical value, given by q crit = a N ln ( ( 24 2 / 5 ) ( m N / M ⊙ ) a / a N 5 / 2 ) 1 / 2 . This expression constitutes an analytic boundary between the “detached” and actively “scattering” subpopulations of distant trans-Neptunian minor bodies. Additionally, we find that within the stochastic layer, the Lyapunov time of SDOs approaches the orbital period, and show that the semimajor axis diffusion coefficient is approximated by  a ∼ ( 8 / ( 5 π ) ) ( m N / M ⊙ )  M ⊙ a N exp ​ − q / a N 2 / 2 . We confirm our results with direct N-body simulations and highlight the connections between scattered-disk dynamics and the Chirikov Standard Map. Implications of our results for the long-term evolution of minor bodies in the distant solar system are discussed.

Features of the Dynamical Evolution of a Massive Disk of Trans-Neptunian Objects

—The dynamical features of a massive disk of distant trans-Neptunian objects are considered in the model of the formation of small bodies in the Hill region of a giant gas-dust clump that arose as a result of gravitational instability and fragmentation of the protoplanetary disk. The dynamical evolution of the orbits of small bodies under the action of gravitational perturbations from the outer planets and self-gravity of the disk has been studied for a time interval of the order of a billion years. It is shown that the secular effects of the gravitational influence of a massive disk of small bodies lead to an increase in the eccentricities of the orbits of individual objects. The result of this dynamical behavior is the creation of a flux of small bodies coming close to the orbit of Neptune. The change in the number of objects surviving in the observable region of distant trans-Neptunian objects (the region of orbits with perihelion distances of 40 < q < 80 AU and semimajor axes 150 < a < 1000 AU), over time depends on the initial mass of the disk. For disks with masses exceeding several Earth masses, there is a tendency to a decrease in the number of distant trans-Neptunian objects surviving in the observable region after evolution for a time interval of the order of the age of the Solar System, with an increase in the initial mass. On the other hand, for most objects, orbital eccentricities decrease under the influence of the self-gravity of the disk. Therefore, the main part of the disk is preserved in the region of heliocentric distances exceeding 100 AU.

Orbital features of distant trans-Neptunian objects induced by giant gaseous clumps

Context.The discovery of distant trans-Neptunian objects has led to heated discussions about the structure of the outer Solar System.Aims.We study the dynamical evolution of small bodies from the Hill regions of migrating giant gaseous clumps that form in the outer solar nebula via gravitational fragmentation. We attempt to determine whether the observed features of the orbital distribution of distant trans-Neptunian objects could be caused by this process.Methods.We consider a simple model that includes the Sun, two point-like giant clumps with masses of ∼10 Jupiter masses, and a set of massless objects initially located in the Hill regions of these clumps. We carry out numerical simulations of the motions of small bodies under gravitational perturbations from two giant clumps that move in elliptical orbits and approach each other. The orbital distribution of these small bodies is compared with the observed distribution of distant trans-Neptunian objects.Results.In addition to the known grouping in longitudes of perihelion, we note new features for observed distant trans-Neptunian objects. The observed orbital distribution points to the existence of two groups of distant trans-Neptunian objects with different dynamical characteristics. We show that the main features of the orbital distribution of distant trans-Neptunian objects can be explained by their origin in the Hill regions of migrating giant gaseous clumps. Small bodies are ejected from the Hill regions when the giant clumps move in high-eccentricity orbits and have a close encounter with each other.Conclusions.The resulting orbital distribution of small bodies in our model and the observed distribution of distant trans-Neptunian objects have similar features.

Migration of Giant Gaseous Clumps and Structure of the Outer Solar System

New data on the distribution of distant trans-Neptunian objects and on the properties of comets indicate the importance of dynamical processes in the outer part of the protoplanetary disk in the formation of the observed structure of the Solar system. In this paper, we examined the possible action of giant gaseous clumps, resulting from gravitational instability and fragmentation of circumstellar disks, on the orbital distribution of the population of small bodies in the outer Solar system. Basically, we studied those features of migration and gravitational interaction of giant clumps that were found previously by Vorobyov and Elbakyan (2018). Our modeling showed that the main features of the distribution of small bodies resulting from the gravitational influence of giant clumps are consistent with the observed orbital distribution of distant trans-Neptunian objects. The studied dynamical process associated with a single giant clump is very short-time event (no more than several tens of thousands of years). The main factor affecting the orbital distribution of small bodies is close encounters with giant clumps. A significant part of small bodies (comets) is very quickly transferred to distant orbits with large eccentricities, which allows them to avoid mutual collisions.

Chaos in the inert Oort cloud

Context. Distant trans-Neptunian objects are subject to planetary perturbations and galactic tides. The former decrease with the distance, while the latter increase. In the intermediate regime where they have the same order of magnitude (the “inert Oort cloud”), both are weak, resulting in very long evolution timescales. To date, three observed objects can be considered to belong to this category. Aims. We aim to provide a clear understanding of where this transition occurs, and to characterise the long-term dynamics of small bodies in the intermediate regime: relevant resonances, chaotic zones (if any), and timescales at play. Methods. The different regimes are explored analytically and numerically. We also monitored the behaviour of swarms of particles during 4.5 Gyrs in order to identify which of the dynamical features are discernible in a realistic amount of time. Results. There exists a tilted equilibrium plane (Laplace plane) about which orbits precess. The dynamics is integrable in the low and high semi-major axis regimes, but mostly chaotic in between. From about 800 to 1100 astronomical units (au), the chaos covers almost all the eccentricity range. The diffusion timescales are large, but not to the point of being indiscernible in a 4.5 Gyrs duration: the perihelion distance can actually vary from tens to hundreds of au. Orbital variations are damped near the ecliptic (where previous studies focussed), but favoured in specific ranges of inclination corresponding to well-defined resonances. Moreover, starting from uniform distributions, the orbital angles cluster after 4.5 Gyrs for semi-major axes larger than 500 au, because of a very slow differential precession. Conclusions. Even if it is characterised by very long timescales, the inert Oort cloud mostly features chaotic regions; it is therefore much less inert than it appears. Orbits can be considered inert over 4.5 Gyrs only in small portions of the space of orbital elements, which include (90377) Sedna and 2012VP113. Effects of the galactic tides are discernible down to semi-major axes of about 500 au. We advocate including the galactic tides in simulations of distant trans-Neptunian objects, especially when studying the formation of detached bodies or the clustering of orbital elements.

The Case for a Large-scale Occultation Network

Abstract We discuss the feasibility of and present initial designs and approximate cost estimates for a large (N ∼ 2000) network of small photometric telescopes that is purpose-built to monitor V ≲ 15 Gaia mission program stars for occultations by minor solar system bodies. The implementation of this network would permit measurement of the solar system’s tidal gravity field to high precision, thereby revealing the existence of distant trans-Neptunian objects such as the proposed “Planet Nine.” As a detailed example of the network capabilities, we investigate how occultations by Jovian Trojans can be monitored to track the accumulation of gravitational perturbations, thereby constraining the presence of undetected massive solar system bodies. We also show that the tidal influence of Planet Nine can be discerned from that of smaller, nearer objects in the Kuiper Belt. Moreover, ephemerides for all small solar system bodies observed in occultation could be significantly improved using this network, thereby improving spacecraft navigation and refining solar system modeling. Finally, occultation monitoring would generate direct measurements of size distributions for asteroid populations, permitting a better understanding of their origins.

Dynamical Analysis of Three Distant Trans-Neptunian Objects with Similar Orbits

Abstract This paper reports the discovery and orbital characterization of two extreme trans-Neptunian objects (ETNOs), 2016 QV89 and 2016 QU89, which have orbits that appear similar to that of a previously known object, 2013 UH15. All three ETNOs have semimajor axes a ≈ 172 au and eccentricities e ≈ 0.77. The angular elements (i, ω, Ω) vary by 6°, 15°, and 49°, respectively, between the three objects. The two new objects add to the small number of TNOs currently known to have semimajor axes between 150 and 250 au, and they serve as an interesting dynamical laboratory to study the outer realm of our solar system. Using a large ensemble of numerical integrations, we find that the orbits are expected to reside in close proximity in the (a, e) phase plane for roughly 100 Myr before diffusing to more separated values. We find that an explanation for the orbital configuration of the bodies as a collision product is disfavored. We then explore other scenarios that could influence their orbits. With aphelion distances over 300 au, the orbits of these ETNOs extend far beyond the classical Kuiper Belt and an order of magnitude beyond Neptune. As a result, their orbital dynamics can be affected by the proposed new solar system member, referred to as Planet Nine in this work. With perihelion distances of 35–40 au, these orbits are also influenced by resonant interactions with Neptune. A full assessment of any possible new solar system planets must thus take into account this emerging class of TNOs.

The Influence of Planet Nine on the Orbits of Distant TNOs: The Case for a Low-perihelion Planet

Abstract The hypothesis of an additional planet in the outer solar system has gained new support as a result of the confinement noted in the angular orbital elements of distant trans-Neptunian objects. Orbital parameters proposed for the external perturber suggest semimajor axes between 500 and 1000 au, perihelion distances between 200 and 400 au for masses between 10 and 20 M ⊕. In this paper, we study the possibility that lower perihelion distances for the additional planet can lead to angular confinements as observed in the population of objects with semimajor axes greater than 250 au and perihelion distances higher than 40 au. We performed numerical integrations of a set of particles subjected to the influence of the Sun, the known giant planets, and the putative perturber during the age of the solar system and compared our outputs with the observed population through a statistical analysis. Our investigations showed that lower perihelion distances from the outer planet usually lead to more substantial confinements than higher ones, while retaining the Classical Kuiper Belt as well as the ratio of the number of detached with perihelion distances higher than 42 au to scattering objects in the range of semimajor axes from 100 to 200 au.

Chaotic Dynamics of Trans-Neptunian Objects Perturbed by Planet Nine

Abstract Observations of clustering among the orbits of the most distant trans-Neptunian objects (TNOs) has inspired interest in the possibility of an undiscovered ninth planet lurking in the outskirts of the solar system. Numerical simulations by a number of authors have demonstrated that, with appropriate choices of planet mass and orbit, such a planet can maintain clustering in the orbital elements of the population of distant TNOs, similar to the observed sample. However, many aspects of the rich underlying dynamical processes induced by such a distant eccentric perturber have not been fully explored. We report the results of our investigation of the dynamics of coplanar test-particles that interact with a massive body on an circular orbit (Neptune) and a massive body on a more distant, highly eccentric orbit (the putative Planet Nine). We find that a detailed examination of our idealized simulations affords tremendous insight into the rich test-particle dynamics that are possible. In particular, we find that chaos and resonance overlap plays an important role in particles’ dynamical evolution. We develop a simple mapping model that allows us to understand, in detail, the web of overlapped mean-motion resonances explored by chaotically evolving particles. We also demonstrate that gravitational interactions with Neptune can have profound effects on the orbital evolution of particles. Our results serve as a starting point for a better understanding of the dynamical behavior observed in more complicated simulations that can be used to constrain the mass and orbit of Planet Nine.

OBSERVATIONAL CONSTRAINTS ON PLANET NINE: ASTROMETRY OF PLUTO AND OTHER TRANS-NEPTUNIAN OBJECTS

ABSTRACT We use astrometry of Pluto and other trans-neptunian objects to constrain the sky location, distance, and mass of the possible additional planet (Planet Nine) hypothesized by Batygin &amp; Brown. We find that over broad regions of the sky, the inclusion of a massive, distant planet degrades the fits to the observations. However, in other regions, the fits are significantly improved by the addition of such a planet. Our best fits suggest a planet that is either more massive or closer than argued for by Batygin &amp; Brown based on the orbital distribution of distant trans-neptunian objects (or by Fienga et al. based on range measured to the Cassini spacecraft). The trend to favor larger and closer perturbing planets is driven by the residuals to the astrometry of Pluto, remeasured from photographic plates using modern stellar catalogs, which show a clear trend in decl. over the course of two decades, that drive a preference for large perturbations. Although this trend may be the result of systematic errors of unknown origin in the observations, a possible resolution is that the decl. trend may be due to perturbations from a body, in addition to Planet Nine, that is closer to Pluto but less massive than Planet Nine.

THE FATE OF SCATTERED PLANETS

As gas giant planets evolve, they may scatter other planets far from their original orbits to produce hot Jupiters or rogue planets that are not gravitationally bound to any star. Here, we consider planets cast out to large orbital distances on eccentric, bound orbits through a gaseous disk. With simple numerical models, we show that super-Earths can interact with the gas through dynamical friction to settle in the remote outer regions of a planetary system. Outcomes depend on planet mass, the initial scattered orbit, and the evolution of the time-dependent disk. Efficient orbital damping by dynamical friction requires planets at least as massive as the Earth. More massive, longer-lived disks damp eccentricities more efficiently than less massive, short-lived ones. Transition disks with an expanding inner cavity can circularize orbits at larger distances than disks that experience a global (homologous) decay in surface density. Thus, orbits of remote planets may reveal the evolutionary history of their primordial gas disks. A remote planet with an orbital distance ~100 AU from the Sun is plausible and might explain correlations in the orbital parameters of several distant trans-Neptunian objects.

A compositional interpretation of trans-neptunian objects taxonomies

Trans-neptunian objects (TNOs) are a population of small objects orbiting the Sun beyond Neptune. Because of their distance they are difficult to observe spectroscopically, but a large body of photometric observations is available and growing. TNOs are important tracers of the evolution of the outer Solar System and key when testing current dynamical evolution theories. Previous statistical studies of the colors of TNOs have yielded useful but limited results regarding the chemical history and evolution of these bodies.With the aim at obtaining compositional information on the small and distant TNOs we introduce a statistical cluster analysis (labelled albedo) based on colors and published albedos of TNOs. We compare it to a previous taxonomy, to illustrate the significance of including the albedo information when determining the composition of the objects. When the albedo contribution is removed from the data, the new taxonomy (now labelled classical) is in general agreement with the published ones, supporting the applicability of our approach. Making use of modeled reflectance spectra of a variety of plausible mixtures found on the surface of TNOs, we extract the average surface composition of each taxon, for both the classical and the albedo taxonomy, in a statistically consistent fashion.Differently from previous and classical, the albedo taxonomy establishes a direct link between the colors and albedos of the objects and their surface composition, allowing, for the first time, a quick assessment of the chemical history of TNOs. In fact, under closer examination the taxa show trends in composition that might be evolutionary in nature. If a simple ‘snow lines’ model is adopted, we can infer that albedo taxa relate the current objects’ locations to their original ones, prior to the migration of the outer planets. We regard the large population that characterizes the darkest classes spread at a variety of semi-major axis distances as one of the intriguing results of this work.

Resonant motion of trans-Neptunian objects in high-eccentricity orbits

A substantial fraction of the Edgeworth-Kuiper belt objects are presently known to move in resonance with Neptune (the principal commensurabilities are 1/2, 3/5, 2/3, and 3/4). We have found that many of the distant (with orbital semimajor axes a > 50 AU) trans-Neptunian objects (TNOs) also execute resonant motions. Our investigation is based on symplectic integrations of the equations of motion for all multiple-opposition TNOs with a > 50 AU with allowance made for the uncertainties in their initial orbits. Librations near such commensurabilities with Neptune as 4/9, 3/7, 5/12, 2/5, 3/8, 4/27, and others have been found. The largest number of distant TNOs move near the 2/5 resonance with Neptune: 12 objects librate with a probability higher than 0.75. The multiplicity of objects moving in 2/5 resonance and the longterm stability of their librations suggest that this group of resonant objects was formed at early formation stages of the Solar system. For most of the other resonant objects, the librations are temporary. We also show the importance of asymmetric resonances in the large changes in TNO perihelion distances.