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Thermal inertias in the upper millimeters of the Martian surface derived using Phobos' shadow

Betts, Bruce H. and Murray, Bruce C. and Svítek, Tomáš (1995) Thermal inertias in the upper millimeters of the Martian surface derived using Phobos' shadow. Journal of Geophysical Research E, 100 (E3). pp. 5285-5296. ISSN 0148-0227. doi:10.1029/95JE00226.

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The first thermal images of Phobos' shadow on the surface of Mars, in addition to simultaneous visible images, were obtained by the Phobos '88 Termoskan instrument. The best observed shadow occurrence was on the flanks of Arsia Mons. For this occurrence, we combined the observed decrease in visible illumination of the surface with the observed decrease in brightness temperature to calculate thermal inertias of the Martian surface. The most realistic of our three models of eclipse cooling improves upon our preliminary model by including nonisothermal initial conditions and downward atmospheric flux. Most of our derived inertias fall within the range 38 to 59 J m^(−2) s^(−1)/2 K^(−1) (0.9 to 1.4 10−3 cal cm^(−2) s^(−1)/2 K^(−1)), corresponding to dust-sized particles (for a homogeneous surface), consistent with previous theories of Tharsis as a current area of dust deposition. Viking infrared thermal mapper (IRTM) inertias are diurnally derived and are sensitive to centimeter depths, whereas the shadow-derived inertias sample the upper tenths of a millimeter of the surface. The shadow-derived inertias are lower than those derived from Viking IRTM measurements (84 to 147), however, uncertainties in both sets of derived inertias make conclusions about layering tenuous. Thus, near-surface millimeter versus centimeter layering may exist in this region, but if it does, it is likely not very significant. Both eclipse and diurnal inertias appear to increase near the eastern end of the shadow occurrence. We also analyzed a shadow occurrence near the crater Herschel that showed no observed cooling. This analysis was limited by cool morning temperatures and instrument sensitivity, but yielded a lower bound of 80 on eclipse inertias in that region. Based upon our results, we strongly recommend future spacecraft thermal observations of Phobos' shadow, and suggest that they will be most useful if they improve upon Termoskan's geographic and temporal coverage and its accuracy.

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Betts, Bruce H.0000-0002-4423-5800
Additional Information:© 1995 American Geophysical Union. Manuscript Accepted: 13 January 1995; Manuscript Received: 1 March 1994. Paper number 95JE00226. We thank Ken Herkenhoff and Ked Edgett for their helpful and detailed reviews, Doug Nash, Dewey Muhleman, and Andy Ingersoll for helpful comments on the manuscript; Joan Hayashi for providing digital versions of the Hayashi, et at. [this issue] inertias; and Bruce Jakosky, David Paige, and Hugh Kieffer for insightful discussions. We also than A. Selivanov, M. Naraeva, V. Kharlamov, and Y. Getkin for assistance with the data, and R. Eby, R. McLendon, K. Hudelson, and S. Welch for assistance with tasks at SJI. Funding for this research was provided by NASA grants NAGW-1426 and NAGW-2491. Division of Geological and Planetary Sciences. California Institute of Technology contribution 5384.
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Caltech Division of Geological and Planetary Sciences5384
Issue or Number:E3
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Official Citation:Betts, B. H., B. C. Murray, and T. Svítek (1995), Thermal inertias in the upper millimeters of the Martian surface derived using Phobos' shadow, J. Geophys. Res., 100(E3), 5285–5296, doi:10.1029/95JE00226.
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ID Code:46569
Deposited On:30 Jun 2014 20:27
Last Modified:10 Nov 2021 17:27

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