Observations of Phobos, Deimos, and bright stars with the Imager for Mars Pathfinder

Journal of Geophysical Research E: Planets
By: , and 



The Imager for Mars Pathfinder (IMP) was used to observe several objects during the Martian night. The satellites, Phobos and Deimos, were observed on two occasions each, through the IMP geological filters covering the wavelength range 440 nm to 1 μm. The observations were converted to geometric albedo using triaxial ellipsoid models of the satellites and phase functions derived from Viking Orbiter images. The spectral slopes over the full wavelength range were 7.9(±0.5)% (100 nm)−1 and 9.6(±0.6)% (100 nm)−1, respectively, referenced to 600 nm. In the Deimos spectra, some evidence for decreased reddening toward the trailing hemisphere was found. The geometric albedoes of Phobos and Deimos were found to be 0.065 (±0.010) and 0.068 (±0.009), respectively, averaged over 440 and 600 nm, in good agreement with previous measurements. The nighttime optical depth was investigated using observations of stars. A mean value of 0.56 (±0.09) was determined from measurements at different airmass. A possible maximum in the optical depth near 0200 local time was found, which may result from condensation during the night. A measurement of the egress of Phobos from eclipse was made. Modeling of the light curve gave a scale height for the scatterers of 10–15 km. The exact time of the eclipse reappearance over the limb could be reconstructed from the measurements and was in reasonable accord with predictions, although a small modification to the predicted position of Phobos of 6.8 (±6.0) km would have produced better agreement.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Observations of Phobos, Deimos, and bright stars with the Imager for Mars Pathfinder
Series title Journal of Geophysical Research E: Planets
DOI 10.1029/98JE02555
Volume 104
Issue E4
Year Published 1999
Language English
Publisher American Geophysical Union
Publisher location Washington, D.C.
Contributing office(s) Astrogeology Science Center
First page 9055
Last page 9068
Other Geospatial Deimos; Mars; Phobos
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