Jean Marc Christille | Searcharxiv

arXiv2026

Kilometre-scale Jovian moon characterized for a potential JUICE flyby

Jupiter's irregular satellites are thought to be relics of early Solar System planetesimals. However, their small sizes, large distances from Earth and close angular proximity to Jupiter make them difficult to characterize remotely. Here we report multi-instrument observations of kilometre-sized Kallichore, the only irregular moon of Jupiter amenable to a close flyby by ESA's Jupiter Icy Moons Explorer (JUICE), whose astrometric and physical properties were still poorly constrained. We used Hubble photometry and astrometry, followed by a ground-based, multi-site stellar occultation campaign and astrometric and photometric observations with the 10.4-m Gran Telescopio Canarias. We reduced Kallichore's orbital uncertainty by up to approximately 80% and determined its shape: an elongated object with a minimum semi-axis ratio of a/b = 1.53 +/- 0.10, an area-equivalent diameter of 3.8 (+2.3/-0.3) km and a dark surface with a geometric albedo of 3.7% (+0.7/-2.2). No close companions were detected. These new constraints provide a viable pathway towards a JUICE flyby once the spacecraft arrives in the Jupiter system in 2031.

astro-ph.EP↗

arXiv2016

SIOUX project: a simultaneous multiband camera for exoplanet atmospheres studies

The exoplanet revolution is well underway. The last decade has seen order-of-magnitude increases in the number of known planets beyond the Solar system. Detailed characterization of exoplanetary atmospheres provide the best means for distinguishing the makeup of their outer layers, and the only hope for understanding the interplay between initial composition chemistry, temperature-pressure atmospheric profiles, dynamics and circulation. While pioneering work on the observational side has produced the first important detections of atmospheric molecules for the class of transiting exoplanets, important limitations are still present due to the lack of sys- tematic, repeated measurements with optimized instrumentation at both visible (VIS) and near-infrared (NIR) wavelengths. It is thus of fundamental importance to explore quantitatively possible avenues for improvements. In this paper we report initial results of a feasibility study for the prototype of a versatile multi-band imaging system for very high-precision differential photometry that exploits the choice of specifically selected narrow-band filters and novel ideas for the execution of simultaneous VIS and NIR measurements. Starting from the fundamental system requirements driven by the science case at hand, we describe a set of three opto-mechanical solutions for the instrument prototype: 1) a radial distribution of the optical flux using dichroic filters for the wavelength separation and narrow-band filters or liquid crystal filters for the observations; 2) a tree distribution of the optical flux (implying 2 separate foci), with the same technique used for the beam separation and filtering; 3) an exotic solution consisting of the study of a complete optical system (i.e. a brand new telescope) that exploits the chromatic errors of a reflecting surface for directing the different wavelengths at different foci.

astro-ph.IM↗