arXiv subjects

David Nesvorný

Publications and source records attributed to David Nesvorný.

At least 55 records · Page 3Linked to original sources

arXiv2020

A pair of Jovian Trojans at the L4 Lagrange point

Asteroid pairs, two objects that are not gravitationally bound to one another, but share a common origin, have been discovered in the Main belt and Hungaria populations. Such pairs are of major interest, as the study of their evolution under a variety of dynamical influences can indicate the time since the pair was created. To date, no asteroid pairs have been found in the Jovian Trojans, despite the presence of several binaries and collisional families in the population. The search for pairs in the Jovian Trojan population is of particular interest, given the importance of the Trojans as tracers of planetary migration during the Solar system's youth. Here we report a discovery of the first pair, (258656) 2002~ES$_{76}$ and 2013~CC$_{41}$, in the Jovian Trojans. The two objects are approximately the same size and are located very close to the L4 Lagrange point. Using numerical integrations, we find that the pair is at least $360$~Myr old, though its age could be as high as several Gyrs. The existence of the (258656) 2002~ES$_{76}$--2013~CC$_{41}$ pair implies there could be many such pairs scattered through the Trojan population. Our preferred formation mechanism for the newly discovered pair is through the dissociation of an ancient binary system, triggered by a sub-catastrophic impact, but we can not rule out rotation fission of a single object driven by YORP torques. A by-product of our work is an up-to-date catalog of Jovian Trojan proper elements, which we have made available for further studies.

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arXiv2020

Modeling the chronologies and size distributions of Ceres and Vesta craters

We infer the crater chronologies of Ceres and Vesta from a self-consistent dynamical model of asteroid impactors. The model accounts for planetary migration/instability early in the solar system history and tracks asteroid orbits over 4.56 Gy. It is calibrated on the current population of the asteroid belt. The model provides the number of asteroid impacts on different worlds at any time throughout the solar system history. We combine the results with an impactor-crater scaling relationship to determine the crater distribution of Ceres and Vesta and compare these theoretical predictions with observations. We find that: (i) The Ceres and Vesta chronologies are similar, whereas they significantly differ from the lunar chronology. Therefore, using the lunar chronology for main belt asteroids, as often done in previous publications, is incorrect. (ii) The model results match the number and size distribution of large (diameter $>90$ km) craters observed on Vesta, but overestimate the number of large craters on Ceres. This implies that large crater erasure is required for Ceres. (iii) In a model where planetary migration/instability happens early, the probability to form the Rheasilvia basin on Vesta during the last 1 Gy is 10\%, a factor of $\sim1.5$ higher than for the late instability case and $\sim2.5$ times higher than found in previous studies. Thus, while the formation of the Rheasilvia at $\sim1$ Gy ago (Ga) would be somewhat unusual, it cannot be ruled out at more than $\simeq1.5σ$. In broader context, our work provides a self-consistent framework for modeling asteroid crater records.

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arXiv2019

A resonant pair of warm giant planets revealed by TESS

We present the discovery of a pair of transiting giant planets, TOI-216b and c, using four sectors of TESS photometry. TOI-216 is a $0.87 M_{\odot}$ dwarf orbited by two transiters with radii of $8.2 R_{\oplus}$ and $11.3 R_{\oplus}$, and periods of $17.01$d and $34.57$d, respectively. Anti-correlated TTVs are clearly evident indicating that the transiters orbit the same star and interact via a near 2:1 mean motion resonance. By fitting the TTVs with a dynamical model, we infer masses of $26_{-11}^{+24} M_{\oplus}$ and $190_{-80}^{+220} M_{\oplus}$, establishing that the objects are planetary in nature and have likely sub-Kronian and Kronian densities. TOI-216 lies close to the southern ecliptic pole and thus will be observed by TESS throughout the first year, providing an opportunity for continuous dynamical monitoring and considerable refinement of the dynamical masses presented here. TOI-216 closely resembles Kepler-9 in architecture, and we hypothesize that in such systems these Saturn-analogs failed to fully open a gap and thus migrated far deeper into the system before becoming trapped into resonance, which would imply that future detections of new analogs may also have sub-Jupiter masses.

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arXiv2019

Origin and evolution of long-period comets

We develop an evolutionary model of the long-period comet (LPC) population, starting from their birthplace in a massive trans-Neptunian disk that was dispersed by migrating giant planets. Most comets that remain bound to the Solar system are stored in the Oort cloud. Galactic tides and passing stars make some of these bodies evolve into observable comets in the inner Solar system. Our approach models each step in a full-fledged numerical framework. Subsequent analysis consists of applying plausible fading models and computing the original orbits to compare with observations. Our results match the observed semimajor axis distribution of LPCs when Whipple's power-law fading scheme with an exponent $κ= 0.6^{+0.1}_{-0.2}$ is adopted. The cumulative perihelion ($q$) distribution is fit well by a linear increase plus a weak quadratic term. Beyond $q = 15$~au, however, the population increases steeply and the isotropy of LPC orbital planes breaks. We find tentative evidence from the perihelion distribution of LPCs that the returning comets are depleted in supervolatiles and become active due to water ice sublimation for $q\leq 3$ au. Using an independent calibration of the population of the initial disk, our predicted LPC flux is smaller than observations suggest by a factor of $\simeq 2$. Current data only characterize comets from the outer Oort cloud (semimajor axes $\gtrsim 10^4$~au). A true boost in understanding the Oort cloud's structure should result from future surveys when they detect LPCs with perihelia beyond $15$~au. Our results provide observational predictions of what can be expected from these new data.

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arXiv2018

Dynamics of multiple protoplanets embedded in gas/pebble disks and its dependence on $Σ$ and $ν$ parameters

Protoplanets of Super-Earth sizes may get trapped in convergence zones for planetary migration and form gas giants there. These growing planets undergo accretion heating, which triggers a hot-trail effect that can reverse migration directions, increase eccentricities and prevent resonant captures (Chrenko et al. 2017). We study populations of embryos accreting pebbles using Fargo-Thorin 2D hydrocode. We find that embryos in a disk with high surface density ($Σ_0 = 990\,{\rm g}\,{\rm cm}^{-2}$) undergo `unsuccessful' two-body encounters which do not lead to a merger. Only when a 3rd protoplanet arrives to the convergence zone, three-body encounters lead to mergers. For a low-viscosity disk ($ν= 5\times10^{13}\,{\rm cm}^2\,{\rm s}^{-1}$) a massive coorbital is a possible outcome, for which a pebble isolation develops and the coorbital is stabilised. For more massive protoplanets ($5\,M_\oplus$), the convergence radius is located further out, in the ice-giant zone. After a series of encounters, there is an evolution driven by a dynamical torque of a tadpole region, which is systematically repeated several times, until the coorbital configuration is disrupted and planets merge. This may be a pathway how to solve the problem that coorbitals often form in simulations but they are not observed in nature. In contrast, the joint evolution of 120 low-mass protoplanets ($0.1\,M_\oplus$) reveals completely different dynamics. The evolution is no longer smooth, but rather a random walk. This is because the spiral arms, developed in the gas disk due to Lindblad resonances, overlap with each other and affect not only a single protoplanet but several in the surroundings. Our hydrodynamical simulations may have important implications for N-body simulations of planetary migration that use simplified torque prescriptions and are thus unable to capture protoplanet dynamics in its full glory.

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arXiv2018

Binary planet formation by gas-assisted encounters of planetary embryos

We present radiation hydrodynamic simulations in which binary planets form by close encounters in a system of several super-Earth embryos. The embryos are embedded in a protoplanetary disk consisting of gas and pebbles and evolve in a region where the disk structure supports convergent migration due to Type I torques. As the embryos accrete pebbles, they become heated and thus affected by the thermal torque (Benítez-Llambay et al. 2015) and the hot-trail effect (Chrenko et al. 2017) which excites orbital eccentricities. Motivated by findings of Eklund & Masset (2017), we assume the hot-trail effect operates also vertically and reduces the efficiency of inclination damping. Non-zero inclinations allow the embryos to become closely packed and also vertically stirred within the convergence zone. Subsequently, close encounters of two embryos assisted by the disk gravity can form transient binary planets which quickly dissolve. Binary planets with a longer lifetime $\sim$$10^{4}$ yr form in 3-body interactions of a transient pair with one of the remaining embryos. The separation of binary components generally decreases in subsequent encounters and due to pebble accretion until the binary merges, forming a giant planet core. We provide an order-of-magnitude estimate of the expected occurrence rate of binary planets, yielding one binary planet per $\simeq$$2$--$5\times10^{4}$ planetary systems. Therefore, although rare, the binary planets may exist in exoplanetary systems and they should be systematically searched for.

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arXiv2018

Secular Resonance Between Iapetus and the Giant Planets

Using numerical integrations, we find that the orbital eccentricity of Saturn's moon Iapetus undergoes prominent multi-Myr oscillations. We identify the responsible resonant argument to be $\varpi-\varpi_{g5}+Ω-Ω_{eq}$, with the terms being the longitudes of pericenter of Iapetus and planetary secular mode $g_5$, Iapetus's longitude of the node and Saturn's equinox. We find that this argument currently (on a $10^7$~yr timescale) appears to librate with a very large amplitude. On longer timescales, the behavior of this resonant angle is strongly dependent on the resonant interaction between Saturn's spin axis and the planetary mode $f_8$, with long-term secular resonance being possible if Saturn's equinox is librating relative to the node of the $f_8$ eigenmode. We present analytical estimates of the dependence of the resonant argument on the orbital elements of Iapetus. We find that this Iapetus-$g_5$ secular resonance could have been established only after the passage of Iapetus through the 5:1 mean-motion resonance with Titan, possibly in the last Gyr. Using numerical simulations, we show that the capture into the secular resonance appears to be a low-probability event. While the Iapetus-$g_5$ secular resonance can potentially help us put new constraints on the past dynamics of the Saturnian system, uncertainties in both the spin axis dynamics of Saturn and the tidal evolution rate of Titan make it impossible to make any firm conclusions about the resonance's longevity and origin.

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arXiv2018

Cladistical analysis of the Jovian and Saturnian satellite systems

Jupiter and Saturn each have complex systems of satellites and rings. These satellites can be classified into dynamical groups, implying similar formation scenarios. Recently, a larger number of additional irregular satellites have been discovered around both gas giants that have yet to be classified. The aim of this paper is to examine the relationships between the satellites and rings of the gas giants, using an analytical technique called cladistics. Cladistics is traditionally used to examine relationships between living organisms, the `tree of life'. In this work, we perform the first cladistical study of objects in a planetary science context. Our method uses the orbital, physical and compositional characteristics of satellites to classify the objects in the Jovian and Saturnian systems. We find that the major relationships between the satellites in the two systems, such as families, as presented in previous studies, are broadly preserved. In addition, based on our analysis of the Jovian system, we identify a new retrograde irregular family, the Iocaste family, and suggest that the Phoebe family of the Saturnian system can be further divided into two subfamilies. We also propose that the Saturnian irregular families be renamed, to be consistent with the convention used in Jovian families. Using cladistics, we are also able to assign the new unclassified irregular satellites into families. Taken together, the results of this study demonstrate the potential use of the cladistical technique in the investigation of relationships between orbital bodies.

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arXiv2017

Detection of the Yarkovsky effect for C-type asteroids in the Veritas family

The age of a young asteroid family can be determined by tracking the orbits of family members backward in time and showing that they converge at some time in the past. Here we consider the Veritas family. We find that the membership of the Veritas family increased enormously since the last detailed analysis of the family. Using backward integration, we confirm the convergence of nodal longitudes $Ω$, and, for the first time, also obtain a simultaneous convergence of pericenter longitudes $\varpi$. The Veritas family is found to be $8.23^{+0.37}_{-0.31}$~Myr old. To obtain a tight convergence of $Ω$ and $\varpi$, as expected from low ejection speeds of fragments, the Yarkovsky effect needs to be included in the modeling of the past orbital histories of Veritas family members. Using this method, we compute the Yarkovsky semi-major axis drift rates, ${\rm d}a/{\rm d}t$, for 274 member asteroids. The distribution of ${\rm d}a/{\rm d}t$ values is consistent with a population of C-type objects with low densities and low thermal conductivities. The accuracy of individual ${\rm d}a/{\rm d}t$ measurements is limited by the effect of close encounters of member asteroids to (1) Ceres and other massive asteroids, which cannot be evaluated with confidence.

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arXiv2017

Planetary Chaos and the (In)stability of Hungaria Asteroids

The Hungaria asteroid group is located interior to the main asteroid belt, with semimajor axes between 1.8 and 2 AU, low eccentricities and inclinations of 16-35 degrees. Recently, it has been proposed that Hungaria asteroids are a secularly declining population that may be related to the Late Heavy Bombardment (LHB) impactors (Ćuk et al. 2012, Bottke et al. 2012). While Ćuk et al. (2012) and Bottke et al. (2012) have reproduced a Hungaria-like population that declined exponentially, the real Hungarias were never confirmed to be unstable to the same degree. Here we find that the stability of Hungarias is strongly dependent on the evolution of the eccentricity of Mars, which is chaotic and unpredictable on Gyr timescales. We find that the high Martian eccentricity chiefly affects Hungarias through close approaches with Mars, rather than planetary secular modes. However, current minimum perihelia of Hungarias (over Myr timescales) are not diagnostic of their long-term stability due to a number of secular and mean motion resonances affecting the Hungaria region (Milani et al. 2010). We conclude that planetary chaos makes it impossible to determine the effective lifetimes of observed Hungarias. Furthermore, long-term changes of Martian eccentricity could lead to variable Hungaria loss over time. We speculate that some of the most stable Hungarias may have been placed in their present orbit when the eccentricity of Mars was significantly higher than today.

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arXiv2017

Masses of Kepler-46b, c from Transit Timing Variations

We use 16 quarters of the \textit{Kepler} mission data to analyze the transit timing variations (TTVs) of the extrasolar planet Kepler-46b (KOI-872). Our dynamical fits confirm that the TTVs of this planet (period $P=33.648^{+0.004}_{-0.005}$ days) are produced by a non-transiting planet Kepler-46c ($P=57.325^{+0.116}_{-0.098}$ days). The Bayesian inference tool \texttt{MultiNest} is used to infer the dynamical parameters of Kepler-46b and Kepler-46c. We find that the two planets have nearly coplanar and circular orbits, with eccentricities $\simeq 0.03$ somewhat higher than previously estimated. The masses of the two planets are found to be $M_{b}=0.885^{+0.374}_{-0.343}$ and $M_{c}=0.362^{+0.016}_{-0.016}$ Jupiter masses, with $M_{b}$ being determined here from TTVs for the first time. Due to the precession of its orbital plane, Kepler-46c should start transiting its host star in a few decades from now.

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arXiv2017

Scattering V-type asteroids during the giant planets instability: A step for Jupiter, a leap for basalt

V-type asteroids are a taxonomic class whose surface is associated to a basaltic composition. The only known source of V-type asteroids in the Main Asteroid Belt is (4) Vesta, that is located in the inner part of the belt. However, many V-type asteroids cannot be dynamically linked to Vesta., in particular, those asteroids located in the middle and outer parts of the Belt. Previous works have failed to find mechanisms to transport V-type asteroids from the inner to the middle and outer belt. In this work we propose a dynamical mechanism that could have acted on primordial asteroid families. We consider a model of the giant planets migration known as the jumping Jupiter model with five planets. Our study is focused on the period of 10 Myr that encompasses the instability phase of the giant planets. We show that, for different hypothetical Vesta-like paleo-families in the inner belt, the perturbations caused by the ice giant that is scattered into the asteroid belt before being ejected from the solar system, are able to scatter V-type asteroids to the middle and outer belt. Based on the orbital distribution of V-type candidates identified from the Sloan Digital Sky Survey and the VISTA Survey colours, we show that this mechanism is efficient enough provided that the hypothetical paleo-family originated from a 100 to 500 km crater excavated on the surface of (4) Vesta. This mechanism is able to explain the currently observed V-type asteroids in the middle and outer belt, with the exception of (1459) Magnya.

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arXiv2016

Hektor - an exceptional D-type family among Jovian Trojans

In this work, we analyze Jovian Trojans in the space of suitable resonant elements and we identify clusters of possible collisional origin by two independent methods: the hierarchical clustering and a so-called "randombox". Compared to our previous work (Brož and Rozehnal 2011), we study a twice larger sample. Apart from Eurybates, Ennomos and $1996\,\rm RJ$ families, we have found three more clusters --- namely families around asteroids (20961)~Arkesilaos, (624)~Hektor in the $L_4$ libration zone and (247341)~$2001\,\rm UV_{209}$ in $L_5$. The families fulfill our stringent criteria, i.e. a high statistical significance, an albedo homogeneity and a steeper size-frequency distribution than that of background. In order to understand their nature, we simulate their long term collisional evolution with the Boulder code (Morbidelli et al. 2009) and dynamical evolution using a modified SWIFT integrator (Levison and Duncan, 1994). Within the framework of our evolutionary model, we were able to constrain the the age of the Hektor family to be either 1 to 4 Gyr or, less likely, 0.1 to 2.5 Gyr, depending on initial impact geometry. Since (624) Hektor itself seems to be a bilobed--shape body with a satellite (Marchis et al. 2014), i.e. an exceptional object, we address its association with the D--type family and we demonstrate that the moon and family could be created during a single impact event. We simulated the cratering event using a Smoothed Particle Hydrodynamics (SPH, Benz and Asphaug, 1994). This is also the first case of a family associated with a D--type parent body.

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arXiv2016

Detection of the YORP Effect for Small Asteroids in the Karin Cluster

The Karin cluster is a young asteroid family thought to have formed only $\simeq 5.75$~My ago. The young age can be demonstrated by numerically integrating the orbits of Karin cluster members backward in time and showing the convergence of the perihelion and nodal longitudes (as well as other orbital elements). Previous work has pointed out that the convergence is not ideal if the backward integration only accounts for the gravitational perturbations from the Solar System planets. It improves when the thermal radiation force known as the Yarkovsky effect it is accounted for. This argument can be used to estimate the spin obliquities of the Karin cluster members. Here we take advantage of the fast growing membership of the Karin cluster and show that the obliquity distribution of diameter $D\simeq 1-2$ km Karin asteroids is bimodal, as expected if the YORP effect acted to move obliquities toward the extreme values ($0^\circ$ or $180^\circ$). The measured magnitude of the effect is consistent with the standard YORP model. The surface thermal conductivity is inferred to be $0.07$-0.2 W m$^{-1}$ K$^{-1}$ (thermal inertia $\simeq 300-500$ J m$^{-2}$ K$^{-1}$s$^{-1/2}$). We find that the strength of the YORP effect is roughly $\simeq 0.7$ of the nominal strength obtained for a collection of random Gaussian spheroids. These results are consistent with a surface composed of rough, rocky regolith. The obliquity values predicted here for 480 members of the Karin cluster can be validated by the light-curve inversion method.

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arXiv2016

Dynamical Evidence for a Late Formation of Saturn's Moons

We explore the past evolution of Saturn's moons using direct numerical integrations. We find that the past Tethys-Dione 3:2 orbital resonance predicted in standard models likely did not occur, implying that the system is less evolved than previously thought. On the other hand, the orbital inclinations of Tethys, Dione and Rhea suggest that the system did cross the Dione-Rhea 5:3 resonance, which is closely followed by a Tethys-Dione secular resonance. A clear implication is that either the moons are significantly younger than the planet, or that their tidal evolution must be extremely slow (Q > 80,000). As an extremely slow-evolving system is incompatible with intense tidal heating of Enceladus, we conclude that the moons interior to Titan are not primordial, and we present a plausible scenario for the system's recent formation. We propose that the mid-sized moons re-accreted from a disk about 100 Myr ago, during which time Titan acquired its significant orbital eccentricity. We speculate that this disk has formed through orbital instability and massive collisions involving the previous generation of Saturn's mid-sized moons. We identify the solar evection resonance perturbing a pair of mid-sized moons as the most likely trigger of such an instability. This scenario implies that most craters on the moons interior to Titan must have been formed by planetocentric impactors.

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arXiv2016

Jumping Jupiter can explain Mercury's orbit

The orbit of Mercury has large values of eccentricity and inclination that cannot be easily explained if this planet formed on a circular and coplanar orbit. Here, we study the evolution of Mercury's orbit during the instability related to the migration of the giant planets in the framework of the jumping Jupiter model. We found that some instability models are able to produce the correct values of Mercury's eccentricity and inclination, provided that relativistic effects are included in the precession of Mercury's perihelion. The orbital excitation is driven by the fast change of the normal oscillation modes of the system corresponding to the perihelion precession of Jupiter (for the eccentricity), and the nodal regression of Uranus (for the inclination).

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arXiv2016

Characterizing the original ejection velocity field of the Koronis family

An asteroid family forms as a result of a collision between an impactor and a parent body. The fragments with ejection speeds higher than the escape velocity from the parent body can escape its gravitational pull. The cloud of escaping debris can be identified by the proximity of orbits in proper element, or frequency, domains. Obtaining estimates of the original ejection speed can provide valuable constraints on the physical processes occurring during collision, and used to calibrate impact simulations. Unfortunately, proper elements of asteroids families are modified by gravitational and non-gravitational effects, such as resonant dynamics, encounters with massive bodies, and the Yarkovsky effect, such that information on the original ejection speeds is often lost, especially for older, more evolved families. It has been recently suggested that the distribution in proper inclination of the Koronis family may have not been significantly perturbed by local dynamics, and that information on the component of the ejection velocity that is perpendicular to the orbital plane ($v_W$), may still be available, at least in part. In this work we estimate the magnitude of the original ejection velocity speeds of Koronis members using the observed distribution in proper eccentricity and inclination, and accounting for the spread caused by dynamical effects. Our results show that i) the spread in the original ejection speeds is, to within a 15% error, inversely proportional to the fragment size, and ii) the minimum ejection velocity is of the order of 50 m/s, with larger values possible depending on the orbital configuration at the break-up.

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arXiv2016

Constraints on the original ejection velocity fields of asteroid families

Asteroid families form as a result of large-scale collisions among main belt asteroids. The orbital distribution of fragments after a family-forming impact could inform us about their ejection velocities. Unfortunately, however, orbits dynamically evolve by a number of effects, including the Yarkovsky drift, chaotic diffusion, and gravitational encounters with massive asteroids, such that it is difficult to infer the ejection velocities eons after each family's formation. Here we analyze the inclination distribution of asteroid families, because proper inclination can remain constant over long time intervals, and could help us to understand the distribution of the component of the ejection velocity that is perpendicular to the orbital plane ($v_{W}$). From modeling the initial breakup, we find that the distribution of $v_{W}$ of the fragments, which manage to escape the parent body's gravity, should be more peaked than a Gaussian distribution (i.e., be leptokurtic) even if the initial distribution was Gaussian. We surveyed known asteroid families for signs of a peaked distribution of $v_{W}$ using a statistical measure of the distribution peakedness or flatness known as kurtosis. We identified eight families whose $v_{W}$ distribution is significantly leptokurtic. These cases (e.g. the Koronis family) are located in dynamically quiet regions of the main belt, where, presumably, the initial distribution of $v_{W}$ was not modified by subsequent orbital evolution. We suggest that, in these cases, the inclination distribution can be used to obtain interesting information about the original ejection velocity field.

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