L. Ferellec | Searcharxiv

arXiv2026

High nitrogen and carbon isotopic ratios in the interstellar comet 3I/ATLAS

Interstellar objects provide a unique opportunity to further our understanding of the planetary formation process by studying in detail material formed around another star. Their ices contain precious clues about the environment and conditions prevailing in their home system. As fractionation processes can be sensitive to the temperature and radiation environment, isotopic ratios are powerful tracers of the origin and evolution of different species. While isotopic ratios have been measured in solar system comets, previously detected interstellar objects have been too faint to measure isotopic ratios. Here we report the measurement of two ratios in 3I/ATLAS from observations of the CN molecule: $^{12}$C/$^{13}$C and $^{14}$N/$^{15}$N. We report $^{12}$C/$^{13}$C=$147^{+87}_{-40}$ and $^{14}$N/$^{15}$N=$343^{+454}_{-124}$. The $^{14}$N/$^{15}$N is higher than the value of $\sim$~150 usually measured for solar system comets, close to the values measured in the interstellar medium, pre-stellar phases or the outside of protoplanetary discs. The $^{12}$C/$^{13}$C is marginally higher than the values usually measured for solar system comets and in the interstellar medium. These measurements could indicate an origin of 3I in the outer disc around an older low-metallicity star.

astro-ph.EP↗

arXiv2019

Surface composition and properties of Ganymede: Updates from ground-based observations with the near-infrared imaging spectrometer SINFONI/VLT/ESO

Ganymede's surface exhibits great geological diversity, with old dark terrains, expressed through the surface composition, which is known to be dominated by two constituents: H2O-ice and an unidentified darkening agent. In this paper, new investigations of the composition of Ganymede's surface at global scale are presented. The analyses are derived from the linear spectral modeling of a high spectral resolution dataset, acquired with the near-infrared ground-based integral field spectrometer SINFONI of the VLT. We find that the Oren-Nayar (1994) model, generalizing the Lambert's law for rough surfaces, produces excellent photometric corrections. Modeling confirms that Ganymede's surface composition is dominated by H2O-ice, mostly crystalline, as well as a darkening agent, but it also highlights the necessity of secondary species to better fit the measurements: sulfuric acid hydrate and salts. A latitudinal gradient and a hemispherical dichotomy are the strongest spatial patterns observed for the darkening agent, the H2O-ice, and the sulfuric acid: the darkening agent is the major compound at the equator and mid-latitudes, especially on the trailing hemisphere, while the H2O-ice and the sulfuric acid are mostly located at high latitudes and on the leading hemisphere. This anti-correlation is likely a consequence of the bombardment of the constituents in the Jovian magnetosphere which are more intense at higher latitudes. Furthermore, the modeling confirms that polar caps are enriched in small, fresh, H2O-ice grains while equatorial regions are composed of larger grains. Finally, the spatial distribution of the salts is neither related to the Jovian magnetospheric bombardment nor the craters. These species are mostly detected on bright grooved terrains surrounding darker areas. Endogenous processes, such as freezing of upwelling fluids in the ice shell, may explain this distribution.

astro-ph.EP↗