Ultraviolet and Visible Reflectance Spectra of Phobos and Deimos as Measured by the ExoMars‐TGO/NOMAD‐UVIS Spectrometer.
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| Title: | Ultraviolet and Visible Reflectance Spectra of Phobos and Deimos as Measured by the ExoMars‐TGO/NOMAD‐UVIS Spectrometer. |
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| Authors: | Mason, J. P.1 (AUTHOR) jon.mason@open.ac.uk, Patel, M. R.1,2 (AUTHOR), Pajola, M.3 (AUTHOR), Cloutis, E. D.4 (AUTHOR), Alday, J.1,5 (AUTHOR), Olsen, K. S.6 (AUTHOR), Marriner, C.1 (AUTHOR), Holmes, J. A.1 (AUTHOR), Sellers, G.1 (AUTHOR), Thomas, N.7 (AUTHOR), Almeida, M.7 (AUTHOR), Read, M.7 (AUTHOR), Nakagawa, H.8 (AUTHOR), Thomas, I. R.9 (AUTHOR), Ristic, B.9 (AUTHOR), Willame, Y.9 (AUTHOR), Depiesse, C.9 (AUTHOR), Daerden, F.9 (AUTHOR), Vandaele, A. C.9 (AUTHOR), Lopez‐Moreno, J. J.10 (AUTHOR) |
| Source: | Journal of Geophysical Research. Planets. Dec2023, Vol. 128 Issue 12, p1-18. 18p. |
| Subject Terms: | Visible spectra, Asteroids, Martian meteorites, Ultraviolet spectra, Origin of planets, Spectrometers, Ultraviolet spectrometers |
| Abstract: | Spectroscopic measurements are a powerful tool to investigate the surface composition of airless bodies and provide clues of their origin. The composition and origin of Phobos and Deimos are still unknown and are currently widely debated. We present spectroscopic measurements of Phobos and Deimos at ultraviolet and visible wavelengths (250–650 nm) made by the NOMAD‐Ultraviolet and Visible Spectrometer (UVIS) on the ExoMars TGO mission. These new spectra cover multiple areas on Phobos and Deimos, and are of generally higher spectral resolution and signal‐to‐noise than previous spectra, and extend to lower wavelengths than most previous measurements. The UVIS spectra confirm a red‐sloped spectrum lacking any strong absorption features; however, we confirm the presence of a previously identified absorption feature near 0.65 μm and tentative absorption near 0.45 μm. The observed Phobos and Deimos spectra are similar to D‐ and T‐type asteroids, adding weight to the captured asteroid hypothesis for the moons' origins. We also find, however, that the UVIS Phobos reflectance spectra of Phobos' red unit is a relatively close match to the olivine‐rich, highly shocked Mars meteorite NWA 2737, with a low overall reflectance, a red‐sloped spectrum, and lack of olivine‐associated absorption bands in the UVIS spectral range. This meteorite, however, exhibits spectral features at longer wavelengths that not observed in the Martian moon spectra, indicating a need for further investigation at longer wavelengths to interpret whether this material could inform our understanding of Phobos' origin. Plain Language Summary: Whether the Martian moons Phobos and Deimos are captured asteroids that originated outside the Mars system or formed from a debris disk around Mars during its formation or following a large impact on Mars is widely debated. Measurements of reflected sunlight from the surfaces of Phobos and Deimos can provide pivotal information on their composition as well as clues to their origins. In this study, we present a comparison between observations of Phobos and Deimos made with the NOMAD Ultraviolet and VIsible Spectrometer (UVIS) on the ExoMars Trace Gas Orbiter (TGO) and previous spectral measurements from other missions. The UVIS spectra show a good agreement with previous observations, with the Phobos and Deimos spectra showing a red‐sloped spectrum similar to primitive carbonaceous chondrite asteroids. A change in the spectral slope at wavelengths longer than 0.53 μm is shown to be consistent with the previously identified 0.65 μm absorption feature. The similarity between the measured Phobos ultraviolet and visible spectrum and highly‐shocked olivine from the Mars meteorite NWA 2737 entices the question of whether Phobos and Deimos surfaces could be composed of a similar dark olivine matrix and formed within the accretion disk created from a giant impact on Mars. Key Points: Phobos and Deimos reflectance spectra have been obtained from the ExoMars NOMAD spectrometer covering 250–650 nmUVIS measurements confirm the spectral similarity of Phobos and Deimos to primitive carbonaceous chondrite asteroidsThe spectrum of Phobos is analogous to some features of shock‐produced dark olivine which could support an alternative planetary origin [ABSTRACT FROM AUTHOR] |
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| Database: | GreenFILE |
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