Sublimation of Ices Containing Organics and/or Minerals and Implications for Icy Bodies Surface Structure and Spectral Properties

International audienceThe surfaces of many objects in the Solar System comprise substantial quantities of water ice either in pure form or mixed with minerals and/or organic molecules. Sublimation is a process responsible for shaping and changing the reflectance properties of these objects.We present laboratory data on the evolution of the structure and the visible and near-infrared spectral reflectance of icy surfaces made of mixtures of water ice and non-volatile components (complex organic matter and silicates), as they undergo sublimation of the water ice under low temperature and pressure conditions (Poch et al., under review). We prepared icy surfaces which are potential analogues of ices found on comets, icy satellites or trans-neptunian objects (TNOs). The experiments were carried out in the SCITEAS simulation setup recently built as part of the Laboratory for Outflow Studies of Sublimating Materials (LOSSy) at the University of Bern (Pommerol et al., 2015a).As the water ice sublimated, we observed in situ the formation of a sublimation lag deposit, or sublimation mantle, made of the non-volatiles at the top of the samples. The texture (porosity, internal cohesiveness etc.), the activity (outbursts and ejection of mantle fragments) and the spectro-photometric properties of this mantle are found to differ strongly depending on the chemical nature of the non-volatiles, the size of their particles, the way they are mixed with the volatile component and the dust/ice mass ratio. The results also indicate how the band depths of the sub-surface water ice evolve during the build-up of the sublimation mantle.These data provide useful references for interpreting remote-sensing observations of Rosetta (see Pommerol et al., 2015b), and also New Horizons

Evolution of ice/dust mixtures upon sublimation of ice, implications for comets and larger icy objects

International audienceThe surfaces of many objects in the Solar System comprise substantial quantities of water ice either in pure form or mixed with minerals and/or organic molecules. Sublimation is a process responsible for shaping and changing the reflectance properties of these objects.This peculiar process is not known enough and requires experimental studies

Hydrogen peroxide and conductivity measurements at 7 ice core drilling sites in northern Greenland

This is accumulation data is derived from the Light weight In Situ Analysis (LISA) box at the EastGRIP ice coring site in Greenland in summer 2019, H2O2 is analysed by means of continuous flow analysis, but no standards were analysed for aclinartion and is thus represented as light counts in abritary units as described in Kaufmann et al., 2008; Röthlisberger et al., 2000. Conductivity is the electrical melt water conductivity as detected using a 3082 with micro flow cell 829 from Amber Science similarly to Bigler et al. 2011

Snow pits density, accumulation, peroxide and conductivity by A portable Lightweight In Situ Analysis (LISA) box at several sites in Northern Greenland

One and two metre snow pit accumulation, density, peroxide and conductivity on a depth and age scale from summer 2019 obtained at 7 ice core drilling sites; NEEM, B16, B19, B22 as well as 3 sites in the vicinity of EastGRIP representing the years 2014 to summer 2019. The data was analysed by means of continuous flow using the Light weight In Situ Analysis (LISA) box (Kjær et al, 2021)

Comet 67P/CG Nucleus Composition and Comparison to Other Comets

International audienceWe review our current knowledge of comet 67P/Churyumov-Gerasimenko nucleus composition as inferred from measurements made by remote sensing and in-situ instruments aboard Rosetta orbiter and Philae lander. Spectropho-tometric properties (albedos, color indexes and Hapke parameters) of 67P/CG derived by Rosetta are discussed in the context of other comets previously explored by space missions. Composed of an assemblage made of ices, organic materials and minerals, cometary nuclei exhibit very dark and red surfaces which can be described by means of spectrophotometric quantities and reproduced with laboratory measurements. The presence of surface water and carbon dioxide ices was found by Rosetta to occur at localized sites where the the activity driven by solar input, gaseous condensation or exposure of G. Filacchione 2 G. Filacchione et al. pristine inner layers can maintain these species on the surface. Apart from these specific areas, 67P/CG's surface appears remarkably uniform in composition with a predominance of organic materials and minerals. The organic compounds contain abundant hydroxyl group and a refractory macromolecular material bearing aliphatic and aromatic hydrocarbons. The mineral components are compatible with a mixture of silicates and fine-grained opaques, including Fe-sulfides, like troilite and pyrrhotite, and ammoniated salts. In the vicinity of the perihelion several active phenomena, including the erosion of surface layers, the localized activity in cliffs, fractures and pits, the collapse of overhangs and walls, the transfer and redeposition of dust, cause the evolution of the different regions of the nucleus by inducing color, composition and texture changes

Accumulation of snow as determined by the summer hydrogen peroxide peak measured using the LISA box for several sites in northern Greenland

This is accumulation data is derived from the Light weight In Situ Analysis (LISA) box at the EastGRIP ice coring site in Greenland in summer 2019, by means of H2O2 summer peak identification and mean densities from 1 meter snow tubes