Engineering topics

Guilbert-Lepoutre, Aurelie

Publications and source records attributed to Guilbert-Lepoutre, Aurelie.

7 records

NASA NTRS2016

OSSOS. IV. Discovery of a Dwarf Planet Candidate in the 9:2 Resonance with Neptune

We report the discovery and orbit of a new dwarf planet candidate, 2015 RR245, by the Outer Solar System Origins Survey (OSSOS). The orbit of 2015 RR245 is eccentric (e 0.586), with a semimajor axis near 82 au, yielding a perihelion distance of 34 au. 2015 RR245 has g - r 0.59 +/- 0.11 and absolute magnitude Hr 3.6 +/- 0.1; for an assumed albedo of pV 12, the object has a diameter of approximately 670 km. Based on astrometric measurements from OSSOS and Pan-STARRS1, we find that 2015 RR245 is securely trapped on ten-megayear timescales in the 9:2 mean-motion resonance with Neptune. It is the first trans-Neptunian object (TNO) identied in this resonance. On hundred-megayear timescales, particles in 2015 RR245-like orbits depart and sometimes return to the resonance, indicating that 2015 RR245 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 modeling of the transient sticking population.

Bannister, Michele T.↗

NASA NTRS2016

The Outer Solar System Origins Survey: Design and First-Quarter Discoveries - I.

We report the discovery, tracking, and detection circumstances for 85 trans-Neptunian objects (TNOs) from the first 42 square degrees of the Outer Solar System Origins Survey. This ongoing r-band solar system survey uses the 0.9 square degree field of view MegaPrime camera on the 3.6 meter Canada-France-Hawaii Telescope. Our orbital elements for these TNOs are precise to a fractional semimajor axis uncertainty of less than 0.1 percent. We achieve this precision in just two oppositions, as compared to the normal three to five 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. 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.

Bannister, Michele T.↗

DOE OSTI2012

SURVIVAL OF AMORPHOUS WATER ICE ON CENTAURS

Centaurs are believed to be Kuiper Belt objects in transition between Jupiter and Neptune before possibly becoming Jupiter family comets. Some indirect observational evidence is consistent with the presence of amorphous water ice in Centaurs. Some of them also display a cometary activity, probably triggered by the crystallization of the amorphous water ice, as suggested by Jewitt and this work. Indeed, we investigate the survival of amorphous water ice against crystallization, using a fully three-dimensional thermal evolution model. Simulations are performed for varying heliocentric distances and obliquities. They suggest that crystallization can be triggered as far as 16 AU, though amorphous ice can survive beyond 10 AU. The phase transition is an efficient source of outgassing up to 10-12 AU, which is broadly consistent with the observations of the active Centaurs. The most extreme case is 167P/CINEOS, which barely crystallizes in our simulations. However, amorphous ice can be preserved inside Centaurs in many heliocentric distance-obliquity combinations, below a {approx}5-10 m crystallized crust. We also find that outgassing due to crystallization cannot be sustained for a time longer than 10{sup 4}-10{sup 4} years, leading to the hypothesis that active Centaurs might have recently suffered from orbital changes. This could be supported by both observations (although limited) and dynamical studies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

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 that is 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 ({approx}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 to be 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 {approx}300 in comets compared to solar argon-to-oxygen, as a consequence of poor trapping efficiency and radiogenic heating.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2012

THE SOURCES OF HCN AND CH{sub 3}OH AND THE ROTATIONAL TEMPERATURE IN COMET 103P/HARTLEY 2 FROM TIME-RESOLVED MILLIMETER SPECTROSCOPY

One of the least understood properties of comets is the compositional structure of their nuclei, which can either be homogeneous or heterogeneous. The nucleus structure can be conveniently studied at millimeter wavelengths, using velocity-resolved spectral time series of the emission lines, obtained simultaneously for multiple molecules as the body rotates. Using this technique, we investigated the sources of CH{sub 3}OH and HCN in comet 103P/Hartley 2, the target of NASA's EPOXI mission, which had an exceptionally favorable apparition in late 2010. Our monitoring with the IRAM 30 m telescope shows short-term variability of the spectral lines caused by nucleus rotation. The varying production rates generate changes in brightness by a factor of four for HCN and by a factor of two for CH{sub 3}OH, and they are remarkably well correlated in time. With the addition of the velocity information from the line profiles, we identify the main sources of outgassing: two jets, oppositely directed in a radial sense, and icy grains, injected into the coma primarily through one of the jets. The mixing ratio of CH{sub 3}OH and HCN is dramatically different in the two jets, which evidently shows large-scale chemical heterogeneity of the nucleus. We propose a network of identities linking the two jets with morphological features reported elsewhere and postulate that the chemical heterogeneity may result from thermal evolution. The model-dependent average production rates are 3.5 Multiplication-Sign 10{sup 26} molecules s{sup -1} for CH{sub 3}OH and 1.25 Multiplication-Sign 10{sup 25} molecules s{sup -1} for HCN, and their ratio of 28 is rather high but not abnormal. The rotational temperature from CH{sub 3}OH varied strongly, presumably due to nucleus rotation, with the average value being 47 K.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

LIMITS TO ICE ON ASTEROIDS (24) THEMIS AND (65) CYBELE

We present optical spectra of (24) Themis and (65) Cybele, two large main-belt asteroids on which exposed water ice has recently been reported. No emission lines, expected from resonance fluorescence in gas sublimated from the ice, were detected. Derived limits to the production rates of water are {approx}<400 kg s{sup -1} (5{sigma}) for each object, assuming a cometary H{sub 2}O/CN ratio. We rule out models in which a large fraction of the surface is occupied by high-albedo ('fresh') water ice because the measured albedos of Themis and Cybele are low ({approx}0.05-0.07). We also rule out models in which a large fraction of the surface is occupied by low-albedo ('dirty') water ice because dirty ice would be warm and would sublimate strongly enough for gaseous products to have been detected. If ice exists on these bodies it must be relatively clean (albedo {approx}>0.3) and confined to a fraction of the Earth-facing surface {approx}<10%. By analogy with impacted asteroid (596) Scheila, we propose an impact excavation scenario, in which 10 m scale projectiles have exposed buried ice. If the ice is even more reflective (albedo {approx}>0.6), then the timescale for sublimation of an optically thick layer can rival the {approx}10{sup 3} yr interval between impacts with bodies this size. In this sense, exposure by impact may be a quasi steady-state feature of ice-containing asteroids at 3 AU.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2011

THERMAL SHADOWS AND COMPOSITIONAL STRUCTURE IN COMET NUCLEI

We use a fully three-dimensional thermal evolution model to examine the effects of a non-uniform surface albedo on the subsurface thermal structure of comets. Surface albedo markings cast 'thermal shadows' with strong lateral thermal gradients. Corresponding compositional gradients can be strong, especially if the crystallization of amorphous water ice is triggered in the hottest regions. We show that the spatial extent of the structure depends mainly on the obliquity, thermal conductivity, and heliocentric distance. In some circumstances, subsurface structure caused by the thermal shadows of surface features can be maintained for more than 10 Myr, the median transport time from the Kuiper Belt to the inner solar system. Non-uniform compositional structure can be an evolutionary product and does not necessarily imply that comets consist of building blocks accumulated in different regions of the protoplanetary disk.

79 ASTRONOMY AND ASTROPHYSICS↗