¹E.Rondón,¹D.Lazzaro,¹J.Carvano,¹F.Monteiro,¹P.Arcoverde,¹M.Evangelista,¹J.Michimani,¹W.Mesquita,¹T.Rodrigues
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114723]
¹Observatório Nacional, Rua Gal. José Cristino 77, 20921-400, Rio de Janeiro, Brazil
Copyright Elsevier

The observation of objects of the Atiras population is a challenge due to the narrow time-window in which observations are possible and, even so, at very low altitudes. This is due to the orbit of these objects, internal to that of the Earth. In this work we present the results of a photometric observational campaign of Atiras aiming to determine their physical parameters using the rotational light curve, the solar phase curve and the photometric spectrum. The period and amplitude have been determined for the asteroids (163693) Atira, (413563) 2005 TG45 and 2017 YH. In the case of (163693) Atira, we have determined a plausible rotational period , where the composite light curve presents structure usually related to the presence of a companion, as it has been suggested by radar observations of this asteroid. For asteroids (163693) Atira, (413563) 2005 TG45, (481817) 2008 UL90 and 2018 JB3 it was possible to derive the absolute magnitude and the phase coefficient. The obtained values are similar to those observed for asteroids with intermediate to low albedo. Finally, for asteroid (163693) Atira we have obtained a featureless photometric spectrum which is compatible in the Carvano taxonomic scheme with the Xp, Dp or Cp classes. No appreciable surface variations were observed for this object.

¹Thomas M.McCollom,²Frieder Klein,¹Mitchell Ramba
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114754]
¹Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309, USA
²Woods Hole Oceanographic Institution, Wood Hole, MA 02543, USA
Copyright Elsevier

Serpentinization of olivine-rich ultramafic rocks is increasingly recognized to have been widespread in the solar system throughout its history. This process has gained particular attention among planetary scientists because it generates molecular hydrogen (H2) and methane (CH4), compounds that can supply metabolic energy to biological communities and contribute to greenhouse warming of planetary atmospheres. While serpentinization of olivine has been the subject of numerous experimental and theoretical studies over the years, this work has focused almost exclusively on the magnesium-rich olivine that is characteristic of the terrestrial mantle. In contrast, very few studies have examined serpentinization of the more iron-enriched olivine compositions that may be more common in other rocky planetary bodies in the solar system. Accordingly, a series of thermodynamic models were constructed to investigate secondary mineral formation and H2 generation during serpentinization of olivine as a function of Fe content and temperature. The results show that serpentinization of Fe-rich olivine is capable of generating substantially greater amounts of H2 per mole than is observed for serpentinization of Mg-rich olivine, by a factor of two to ten depending on temperature and olivine composition. For all olivine compositions, H2 is generated from ferric Fe incorporated into both magnetite and serpentine at higher temperatures; however, it is derived exclusively from precipitation of serpentine at lower temperatures as brucite replaces magnetite in the equilibrium secondary mineral assemblage. Serpentine and brucite formed during serpentinization are predicted to become increasingly enriched in Fe with greater Fe content of the original olivine, although the serpentine has proportionally lower Fe contents than the olivine while brucite has somewhat higher Fe contents. Between 10% and 40% of the Fe partitioned into serpentine occurs in the ferric state (FeIII), which accounts for a substantial fraction of H2 production for most conditions. In addition, the maximum temperature at which olivine undergoes serpentinization decreases with increasing Fe content of the olivine, so that Fe-enriched olivine can remain stable to lower temperatures when compared with more Mg-rich olivine compositions. Overall, the results indicate that serpentinization on other planetary bodies may have a substantially greater capacity to supply H2 to support biological communities and enhance atmospheric greenhouse warming than analogous processes on Earth.