arXiv subjects

T. Gautier

Publications and source records attributed to T. Gautier.

6 recordsLinked to original sources

arXiv2025

Deimos photometric properties: analysis of 20 years of observations (2004-2024) by the Mars Express HRSC camera

The goal of this study is to analyze the photometric properties of Deimos using Mars Express (MEX) observations, to improve the photometric properties and provide new insights into the texture and composition of the surface of Deimos, in preparation for the MMX mission. We analyzed the data obtained by the HRSC and the SRC cameras onboard MEX. The HRSC data, obtained through the use of four filters (blue, green, red, IR), provides 390 to 800 m/px resolution, while the SRC data reach 85 to 300 m/px and cover a wide phase angle range (0.06-138{\deg}). We performed the disk-integrated and disk-resolved photometric analysis using the Hapke model. The Deimos surface is dark and predominantly backscattering, with a single-scattering albedo (SSA) value (6.8%-7.5%) comparable to Phobos. The Deimos phase curve shows a strong opposition effect due to shadow-hiding, with negligible coherent backscattering. The amplitude and the half-width of the shadow-hiding opposition surge were found to be 2.14 +/- 0.14 and 0.065 +/- 0.004, respectively. We found a high porosity of 86% at the top-layer surface, consistent with complex-shaped grains or fractal aggregates, suggesting a thick dust layer. We did not observe significant variations of the opposition surge across the surface. A blue unit on Deimos, located on streamers of the equatorial ridge, shows reflectance increases up to 58%, and a spectral slope decrease of 50% in comparison with the average surface. This blue unit may be due to a different texture of the surface between the two units, with finer grain and/or higher porosity. Deimos photometric properties, including SSA, opposition surge, and phase integral, are very similar to Phobos. The presence of a blue unit on Deimos reinforces the idea that the Martian moons have a common origin, making the capture of two different bodies with such similar properties unlikely.

astro-ph.EP↗

arXiv2024

Phobos photometric properties from Mars Express HRSC observations

This study aims to analyze Phobos' photometric properties using Mars Express mission observations to support the Martian Moons eXploration mission. We analyzed resolved images of Phobos acquired between 2004 and 2022 by the HRSC and the SRC cameras on board the Mars Express spacecraft. We performed photometric analysis using the Hapke model for both integrated and disk-resolved data. The Phobos phase function has a strong opposition effect due to shadow hiding, with an amplitude and a half-width of the opposition surge of 2.28$\pm$0.03 and 0.0573$\pm$0.0001, respectively. Overall, the surface of Phobos is dark, with a geometric albedo of 6.8 % in the green filter and backscattering. We also found a surface porosity of 87\%, indicating the presence of a thick dust mantle or of fractal aggregates on the top surface. The SSA maps revealed high reflectance variability, with the blue unit area in the northeast Stickney rim being up to 65\% brighter than average, while the Stickney floor is among the darkest regions, with reflectance 10 to 20% lower than average. Photometric modeling of the regions of interest selected in the red and blue units indicates that red unit terrains have a stronger opposition effect and a smaller SSA value than the blue ones, but they have similar porosity and backscattering properties. The HRSC data provide a unique investigation of the Phobos phase function and opposition surge, which is valuable information for the MMX observational planning. The Phobos opposition surge, surface porosity, phase integral, and spectral slope are very similar to the values observed for the comet 67P and for Jupiter family comets in general. Based on these similarities, we formulate a hypothesis that the Mars satellites might be the results of a binary or bilobated comet captured by Mars.

astro-ph.EP↗

arXiv2022

Moonraker -- Enceladus Multiple Flyby Mission

Enceladus, an icy moon of Saturn, possesses an internal water ocean and jets expelling ocean material into space. Cassini investigations indicated that the subsurface ocean could be a habitable environment having a complex interaction with the rocky core. Further investigation of the composition of the plume formed by the jets is necessary to fully understand the ocean, its potential habitability, and what it tells us about Enceladus' origin. Moonraker has been proposed as an ESA M-class mission designed to orbit Saturn and perform multiple flybys of Enceladus, focusing on traversals of the plume. The proposed Moonraker mission consists of an ESA-provided platform, with strong heritage from JUICE and Mars Sample Return, and carrying a suite of instruments dedicated to plume and surface analysis. The nominal Moonraker mission has a duration of 13.5 years. It includes a 23-flyby segment with 189 days allocated for the science phase, and can be expanded with additional segments if resources allow. The mission concept consists in investigating: i) the habitability conditions of present-day Enceladus and its internal ocean, ii) the mechanisms at play for the communication between the internal ocean and the surface of the South Polar Terrain, and iii) the formation conditions of the moon. Moonraker, thanks to state-of-the-art instruments representing a significant improvement over Cassini's payload, would quantify the abundance of key species in the plume, isotopic ratios, and physical parameters of the plume and the surface. Such a mission would pave the way for a possible future landed mission.

astro-ph.EP↗

arXiv2020

Compositional Measurements of Saturn's Upper Atmosphere and Rings from Cassini INMS

The Cassini spacecraft's last orbits directly sampled Saturn's thermosphere and revealed a much more chemically complex environment than previously believed. Observations from the Ion and Neutral Mass Spectrometer (INMS) aboard Cassini provided compositional measurements of this region and found an influx of material raining into Saturn's upper atmosphere from the rings. We present here an in-depth analysis of the CH$_4$, H$_2$O, and NH$_3$ signal from INMS and provide further evidence of external material entering Saturn's atmosphere from the rings. We use a new mass spectral deconvolution algorithm to determine the amount of each species observed in the spectrum and use these values to determine the influx and mass deposition rate for these species.

astro-ph.EP↗

arXiv2011

NEOWISE Observations of Near-Earth Objects: Preliminary Results

With the NEOWISE portion of the \emph{Wide-field Infrared Survey Explorer} (WISE) project, we have carried out a highly uniform survey of the near-Earth object (NEO) population at thermal infrared wavelengths ranging from 3 to 22 $μ$m, allowing us to refine estimates of their numbers, sizes, and albedos. The NEOWISE survey detected NEOs the same way whether they were previously known or not, subject to the availability of ground-based follow-up observations, resulting in the discovery of more than 130 new NEOs. The survey's uniformity in sensitivity, observing cadence, and image quality have permitted extrapolation of the 428 near-Earth asteroids (NEAs) detected by NEOWISE during the fully cryogenic portion of the WISE mission to the larger population. We find that there are 981$\pm$19 NEAs larger than 1 km and 20,500$\pm$3000 NEAs larger than 100 m. We show that the Spaceguard goal of detecting 90% of all 1 km NEAs has been met, and that the cumulative size distribution is best represented by a broken power law with a slope of 1.32$\pm$0.14 below 1.5 km. This power law slope produces $\sim13,200\pm$1,900 NEAs with $D>$140 m. Although previous studies predict another break in the cumulative size distribution below $D\sim$50-100 m, resulting in an increase in the number of NEOs in this size range and smaller, we did not detect enough objects to comment on this increase. The overall number for the NEA population between 100-1000 m are lower than previous estimates. The numbers of near-Earth comets will be the subject of future work.

astro-ph.EP↗

arXiv2010

Polychronous Interpretation of Synoptic, a Domain Specific Modeling Language for Embedded Flight-Software

The SPaCIFY project, which aims at bringing advances in MDE to the satellite flight software industry, advocates a top-down approach built on a domain-specific modeling language named Synoptic. In line with previous approaches to real-time modeling such as Statecharts and Simulink, Synoptic features hierarchical decomposition of application and control modules in synchronous block diagrams and state machines. Its semantics is described in the polychronous model of computation, which is that of the synchronous language Signal.

cs.PL↗