arXiv subjects

Jean-Marc Petit

Publications and source records attributed to Jean-Marc Petit.

45 records · Page 3Linked to original sources

arXiv2014

Carbon-rich planet formation in a solar composition disk

The C--to--O ratio is a crucial determinant of the chemical properties of planets. The recent observation of WASP 12b, a giant planet with a C/O value larger than that estimated for its host star, poses a conundrum for understanding the origin of this elemental ratio in any given planetary system. In this paper, we propose a mechanism for enhancing the value of C/O in the disk through the transport and distribution of volatiles. We construct a model that computes the abundances of major C and O bearing volatiles under the influence of gas drag, sublimation, vapor diffusion, condensation and coagulation in a multi--iceline 1+1D protoplanetary disk. We find a gradual depletion in water and carbon monoxide vapors inside the water's iceline with carbon monoxide depleting slower than water. This effect increases the gaseous C/O and decreases the C/H ratio in this region to values similar to those found in WASP 12b's day side atmosphere. Giant planets whose envelopes were accreted inside the water's iceline should then display C/O values larger than those of their parent stars, making them members of the class of so-called ``carbon-rich planets''.

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arXiv2013

A Uranian Trojan and the frequency of temporary giant-planet co-orbitals

Trojan objects share a planet's orbit, never straying far from the triangular Lagrangian points, 60 degrees ahead of (L4) or behind (L5) the planet. We report the detection of a Uranian Trojan; in our numerical integrations, 2011 QF99 oscillates around the Uranian L4 Lagrange point for >70 kyr and remains co-orbital for ~1 Myr before becoming a Centaur. We constructed a Centaur model, supplied from the transneptunian region, to estimate temporary co-orbital capture frequency and duration (to factor of two accuracy), finding that at any time 0.4% and 2.8% of the population will be Uranian and Neptunian co-orbitals, respectively. The co-orbital fraction (~2.4%) among Centaurs in the IAU Minor Planet Centre database is thus as expected under transneptunian supply.

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arXiv2013

2011 HM102: Discovery of a High-Inclination L5 Neptune Trojan in the Search for a post-Pluto New Horizons Target

We present the discovery of a long-term stable L5 (trailing) Neptune Trojan in data acquired to search for candidate Trans-Neptunian objects for the New Horizons spacecraft to fly by during an extended post-Pluto mission. This Neptune Trojan, 2011 HM102, has the highest inclination (29.4 degrees) of any known member of this population. It is intrinsically brighter than any single L5 Jupiter Trojan at H~8.18. We have determined its gri colors (a first for any L5 Neptune Trojan), which we find to be similar to the moderately red colors of the L4 Neptune Trojans, suggesting similar surface properties for members of both Trojan clouds. We also present colors derived from archival data for two L4 Neptune Trojans (2006 RJ103 and 2007 VL305), better refining the overall color distribution of the population. In this document we describe the discovery circumstances, our physical characterization of 2011 HM102, and this object's implications for the Neptune Trojan population overall. Finally, we discuss the prospects for detecting 2011 HM102 from the New Horizons spacecraft during their close approach in mid- to late-2013.

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arXiv2012

The dual origin of the nitrogen deficiency in comets: selective volatile trapping in the nebula and postaccretion radiogenic heating

We propose a scenario that explains the apparent nitrogen deficiency in comets in a way consistent with the fact that the surfaces of Pluto and Triton are dominated by nitrogen-rich ice. We use a statistical thermodynamic model to investigate the composition of the successive multiple guest clathrates that may have formed during the cooling of the primordial nebula from the most abundant volatiles present in the gas phase. These clathrates agglomerated with the other ices (pure condensates or stoichiometric hydrates) and formed the building blocks of comets. We report that molecular nitrogen is a poor clathrate former, when we consider a plausible gas phase composition of the primordial nebula. This implies that its trapping into cometesimals requires a low disk temperature ($\sim$20 K) in order to allow the formation of its pure condensate. We find that it is possible to explain the lack of molecular nitrogen in comets as a consequence of their postformation internal heating engendered by the decay of short-lived radiogenic nuclides. This scenario is found consistent with the presence of nitrogen-rich ice covers on Pluto and Triton. Our model predicts that comets should present xenon-to-water and krypton-to-water ratios close to solar xenon-to-oxygen and krypton-to-oxygen ratios, respectively. In contrast, the argon-to-water ratio is predicted to be depleted by a factor of $\sim$300 in comets compared to solar argon-to-oxygen, as a consequence of poor trapping efficiency and radiogenic heating.

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arXiv2011

Characterization of Seven Ultra-Wide Trans-Neptunian Binaries

The low-inclination component of the Classical Kuiper Belt is host to a population of extremely widely-separated binaries. These systems are similar to other Trans-Neptunian binaries (TNBs) in that the primary and secondary components of each system are of roughly equal size. We have performed an astrometric monitoring campaign of a sample of seven wide-separation, long-period TNBs and present the first-ever well-characterized mutual orbits for each system. The sample contains the most eccentric (2006 CH69, e=0.9) and the most widely-separated, weakly bound (2001 QW322, a/Rh~0.22) binary minor planets known, and also contains the system with lowest-measured mass of any TNB (2000 CF105, M~1.85E17 kg). Four systems orbit in a prograde sense, and three in a retrograde sense. They have a different mutual inclination distribution compared to all other TNBs, preferring low mutual-inclination orbits. These systems have geometric r-band albedos in the range of 0.09-0.3, consistent with radiometric albedo estimates for larger solitary low-inclination Classical Kuiper Belt objects, and we limit the plausible distribution of albedos in this region of the Kuiper Belt. We find that gravitational collapse binary formation models produce a similar orbital distribution to that currently observed, which along with a confluence of other factors supports formation of the cold Classical Kuiper Belt in situ through relatively rapid gravitational collapse rather than slow hierarchical accretion. We show that these binary systems are sensitive to disruption via collisions, and their existence suggests that the size distribution of TNOs at small sizes remains relatively shallow.

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arXiv2011

The Canada-France Ecliptic Plane Survey - Full Data Release: The orbital structure of the Kuiper belt

We report the orbital distribution of the trans-neptunian objects (TNOs) discovered during the Canada-France Ecliptic Plane Survey, whose discovery phase ran from early 2003 until early 2007. The follow-up observations started just after the first discoveries and extended until late 2009. We obtained characterized observations of 321 sq.deg. of sky to depths in the range g ~ 23.5--24.4 AB mag. We provide a database of 169 TNOs with high-precision dynamical classification and known discovery efficiency. Using this database, we find that the classical belt is a complex region with sub-structures that go beyond the usual splitting of inner (interior to 3:2 mean-motion resonance [MMR]), outer (exterior to 2:1 MMR), and main (in between). The main classical belt (a=40--47 AU) needs to be modeled with at least three components: the `hot' component with a wide inclination distribution and two `cold' components (stirred and kernel) with much narrower inclination distributions. The hot component must have a significantly shallower absolute magnitude (Hg) distribution than the other two components. With 95% confidence, there are 8000+1800-1600 objects in the main belt with Hg <= 8.0, of which 50% are from the hot component, 40% from the stirred component and 10% from the kernel; the hot component's fraction drops rapidly with increasing Hg. Because of this, the apparent population fractions depend on the depth and ecliptic latitude of a trans-neptunian survey. The stirred and kernel components are limited to only a portion of the main belt, while we find that the hot component is consistent with a smooth extension throughout the inner, main and outer regions of the classical belt; the inner and outer belts are consistent with containing only hot-component objects. The Hg <= 8.0 TNO population estimates are 400 for the inner belt and 10,000 for the outer belt within a factor of two.

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arXiv2011

On the formation location of Uranus and Neptune as constrained by dynamical and chemical models of comets

The D/H enrichment observed in Saturn's satellite Enceladus is remarkably similar to the values observed in the nearly-isotropic comets. Given the predicted strong variation of D/H with heliocentric distance in the solar nebula, this observation links the primordial source region of the nearly-isotropic comets with the formation location of Enceladus. That is, comets from the nearly-isotropic class were most likely fed into their current reservoir, the Oort cloud, from a source region near the formation location of Enceladus. Dynamical simulations of the formation of the Oort cloud indicate that Uranus and Neptune are, primarily, responsible for the delivery of material into the Oort cloud. In addition, Enceladus formed from material that condensed from the solar nebula near the location at which Saturn captured its gas envelope, most likely at or near Saturn's current location in the solar system. The coupling of these lines of evidence appears to require that Uranus and Neptune were, during the epoch of the formation of the Oort cloud, much closer to the current location of Saturn than they are currently. Such a configuration is consistent with the Nice model of the evolution of the outer solar system. Further measurements of the D/H enrichment in comets, particularly in ecliptic comets, will provide an excellent discriminator among various models of the formation of the outer solar system.

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arXiv2010

Impact regimes and post-formation sequestration processes: implications for the origin of heavy noble gases in terrestrial planets

The difference between the measured atmospheric abundances of neon, argon, krypton and xenon for Venus, the Earth and Mars is striking. Because these abundances drop by at least two orders of magnitude as one moves outward from Venus to Mars, the study of the origin of this discrepancy is a key issue that must be explained if we are to fully understand the different delivery mechanisms of the volatiles accreted by the terrestrial planets. In this work, we aim to investigate whether it is possible to quantitatively explain the variation of the heavy noble gas abundances measured on Venus, the Earth and Mars, assuming that cometary bombardment was the main delivery mechanism of these noble gases to the terrestrial planets. To do so, we use recent dynamical simulations that allow the study of the impact fluxes of comets upon the terrestrial planets during the course of their formation and evolution. Assuming that the mass of noble gases delivered by comets is proportional to rate at which they collide with the terrestrial planets, we show that the krypton and xenon abundances in Venus and the Earth can be explained in a manner consistent with the hypothesis of cometary bombardment. In order to explain the krypton and xenon abundance differences between the Earth and Mars, we need to invoke the presence of large amounts of CO2-dominated clathrates in the Martian soil that would have efficiently sequestered these noble gases.

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arXiv2003

KBO binaries: are they really primordial ?

Given the large orbital separation and high satellite-to-primary mass ratio of all known Kuiper Belt Object (KBO) binaries, it is important to reassess their stability as bound pairs with respect to several disruptive mechanisms. Besides the classical shattering and dispersing of the secondary due to a high-velocity impact, we considered the possibility that the secondary is kicked off its orbit by a direct collision of a small impactor, or that it is gravitationally perturbed due to the close approach of a somewhat larger TNO. Depending on the values for the size/mass/separation of the binaries that we used, 2 or 3 of the 8 pairs can be dispersed in a timescale shorter than the age of the solar system in the current rarefied environment. A contemporary formation scenario could explain why we still observe these binaries, but no convincing mechanism has been proposed to date. The primordial formation scenarios, which seem to be the only viable ones, must be revised to increase the formation efficiency in order to account for this high dispersal rate. Objects like the large-separatioKBO binary n2001 QW$_{322}$ must have been initially an order of magnitude more numerous. If the KBO binaries are indeed primordial, then we show that the mass depletion of the Kuiper belt cannot result from collisional grinding, but must rather be due to dynamical ejection.

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