Interpretation of combined infrared,submillimeter, and millimeter thermal flux data obtained during the Rosetta fly-by of Asteroid (21) Lutetia |
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| Authors: | S Keihm F Tosi L Kamp F Capaccioni S Gulkis D Grassi M Hofstadter G Filacchione S Lee S Giuppi M Janssen M Capria |
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| Institution: | 1. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA;2. Istituto di Astrofisica e Planetologia Spaziali, Istitut Nazionale di Astrofisica (INAF), Via del Fosso del Cavaliere 100, I-00133 Rome, Italy |
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| Abstract: | The European Space Agency’s Rosetta spacecraft is the first Solar System mission to include instrumentation capable of measuring planetary thermal fluxes at both near-IR (VIRTIS) and submillimeter–millimeter (smm–mm, MIRO) wavelengths. Its primary mission is a 1 year reconnaissance of Comet 67P/Churyumov–Gerasimenko beginning in 2014. During a 2010 close fly-by of Asteroid 21 Lutetia, the VIRTIS and MIRO instruments provided complementary data that have been analyzed to produce a consistent model of Lutetia’s surface layer thermal and electrical properties, including a physical model of self-heating. VIRTIS dayside measurements provided highly resolved 1 K accuracy surface temperatures that required a low thermal inertia, I < 30 J/(K m2 s0.5). MIRO smm and mm measurements of polar night thermal fluxes produced constraints on Lutetia’s subsurface thermal properties to depths comparable to the seasonal thermal wave, yielding a model of I < 20 J/(K m2 s0.5) in the upper few centimeters, increasing with depth in a manner very similar to that of Earth’s Moon. Subsequent MIRO-based model predictions of the dayside surface temperatures reveal negative offsets of ～5–30 K from the higher VIRTIS-measurements. By adding surface roughness in the form of 50% fractional coverage of hemispherical mini-craters to the MIRO-based thermal model, sufficient self-heating is produced to largely remove the offsets relative to the VIRTIS measurements and also reproduce the thermal limb brightening features (relative to a smooth surface model) seen by VIRTIS. The Lutetia physical property constraints provided by the VIRTIS and MIRO data sets demonstrate the unique diagnostic capabilities of combined infrared and submillimeter/millimeter thermal flux measurements. |
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