arXiv subjects

B. Seignovert

Publications and source records attributed to B. Seignovert.

2 recordsLinked to original sources

arXiv2026

Near-perihelion activity and composition of 3I/ATLAS from JUICE/MAJIS observations

We present visible-to-infrared (0.5-5.56 microns) observations of the interstellar comet 3I/ATLAS obtained with the Moons and Jupiter Imaging Spectrometer (MAJIS) aboard the Jupiter Icy Moons Explorer (JUICE) spacecraft between 2025 November 2 and 25, shortly after perihelion. The fluorescence emission from H2O at 2.7 microns and CO2 at 4.3 microns is detected at heliocentric distances of 1.36-1.68 au. A weak dust-scattered continuum is identified from which we determine the spectral slope, with values ranging from ~15% per 100 nm in the 0.65-0.9 microns region to 1-3% per 100 nm from 0.9 to 2.6 microns. Spatially resolved measurements show that the radial distributions of H2O and CO2 species are consistent with release in the near-nucleus environment. We derive H2O production rates that decreased from 8 x 1028 s-1 to 4 x 1028 s-1 over the period November 2-25, while the CO2/H2O ratio remained nearly constant at ~10%. The heliocentric evolution of the CO2 production rate indicates activity controlled by solar heating. Combined with published CO measurements and the low gas expansion velocities, our analyses support a scenario in which CO2 plays a major role in driving the activity of 3I/ATLAS near perihelion. In addition, broad emission features are identified in the 3.2-3.6 microns region that cannot be explained by the fluorescence of common cometary CH-bearing volatiles. Their spectral characteristics are consistent with aliphatic C-H functional groups and provide tentative evidence for the release of complex organic material from dust grains in the coma.

astro-ph.EP↗

arXiv2025

Investigating the extent of bladed terrain on Pluto via photometric surface roughness

NASA's New Horizons spacecraft discovered fields of sub-parallel sets of steep ridges situated in the high-altitude, low-latitude regions in Pluto's encounter hemisphere called 'bladed terrain'. Thought to be formed due to sublimational erosion of methane ice, bladed terrain represents an active response of Pluto's landscape to current and past climates. The observation of a strong methane signature within the low latitudes of Pluto's non-encounter hemisphere points to the possibility that this terrain type is also present there. To test this hypothesis, in the absence of high resolution images of Pluto's non-encounter hemisphere, we employ photometric analysis of the methane rich regions. We specifically focus on determining the macroscopic surface roughness in selected images, whose photometric-effect can be apparent even in low-resolution images. We employ the `crater-roughness' photometric model of Buratti & Veverka (1985), which assumes that the surface is covered with parabolic depressions defined by a depth-to-radius ratio parameter $q$ (higher $q$ values correspond to rougher surfaces). Despite the high uncertainty in the retrieved roughness values from our analysis, we can safely conclude that the hypothesized bladed terrain region on the non-encounter hemisphere of Pluto is very rough ($q = 0.47_{-0.11}^{+0.10}$, 2$\sigma$), with the median roughness more than twice that of other broad regions of Pluto studied in this work, including the encounter-hemisphere bladed terrain region ($q = 0.21_{-0.18}^{+0.08}$, 2$\sigma$).

astro-ph.EP↗