¹B.E.Clark et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115563]
Department of Physics and Astronomy, Ithaca College, Ithaca, NY, USA
Copyright Elsevier

This paper summarizes the evidence for the optical effects of space weathering, as well as the properties of the surface that control optical changes, on asteroid (101955) Bennu. First, we set the stage by briefly reviewing what was known about space weathering of low-albedo materials from telescopic surveys, laboratory simulations, and sample return analysis. We then look at the evidence for the nature of space weathering on Bennu from recent spacecraft imaging and spectroscopy observations, including the visible to near-infrared and thermal infrared wavelengths, followed by other measurements such as normal albedo measurements from LIDAR scans. We synthesize these different lines of evidence in an effort to describe a general model of space weathering processes and resulting color effects on dark C-complex asteroids, with hypotheses that can be tested by analyzing samples returned by the mission.

A working hypothesis that synthesizes findings thus far is that the optical effects of maturation in the space environment depend on the level of hydration of the silicate/phyllosilicate substrate. Subsequent variations in color depend on surface processes and exposure age. On strongly hydrated Bennu, in color imaging data, very young craters are darker and redder than their surroundings (more positive spectral slope in the wavelength range 0.4–0.7µm) as a result of their smaller particle sizes and/or fresh exposures of organics by impacts. Solar wind, dehydration, or migration of fines may cause intermediate-age surfaces to appear bluer than the very young craters. Exposed surfaces evolve toward Bennu’s moderately blue global average spectral slope. However, in spectroscopic and LIDAR data, the equator, the oldest surface on Bennu, is darker and redder (wavelength range 0.55–2.0
µm) than average and has shallower absorption bands, possibly due to dehydration and/or nanophase and/or microphase opaque production.

Bennu is a rubble pile with an active surface, making age relationships, which are critical for determining space weathering signals, difficult to locate and quantify. Hence, the full story ultimately awaits analyses of the Bennu samples that will soon be delivered to Earth.

¹A.Dugdale et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115568]
¹AstrobiologyOU, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
Copyright Elsevier

The phyllosilicate-bearing martian plain, Oxia Planum, is the proposed landing site for the Rosalind Franklin rover mission, scheduled to launch in 2028. Rosalind Franklin which will search for signs of past or present life on Mars. Terrestrial analogue sites and simulants can be used to test instruments analogous to those on Rosalind Franklin, however no simulant for Oxia Planum currently exists. In anticipation of this mission, a simulant – SOPHIA (Simulant for Oxia Planum: Hydrated, Igneous, and Amorphous) – representative of the local mineralogy at Oxia Planum has been developed for biosignature and mineralogy experiments, which will assist in interpreting data returned by the rover. The simulant is derived from orbital observations of Oxia Planum and its catchment area. As no in situ data is available for Oxia Planum, mineralogy from other comparable sites on Mars was used to design the simulant including orbital data from Arabia Terra and Mawrth Vallis and in situ data collected from Gale crater. The mineralogy, chemistry and physical properties of the simulant were characterised using standard laboratory techniques (SEM-EDS, XRF, XRD).Techniques analogous to rover instruments (Raman spectroscopy, Near-IR spectroscopy analogous to the Raman laser spectrometer and ISEM and MicrOmega instruments) were also used. The simulant is rich in Fe/Mg phyllosilicates with additional primary igneous and other alteration minerals and is an appropriate spectral and mineralogical analogue for Oxia Planum.