Mariner 9 television observations of Phobos and Deimos, 2

Abstract

Analyses of the Mariner 9 pictures of the Martian satellites have yielded much new information: improved ephemerides, estimates of their principal axes, information about the texture of their surfaces, and estimates of the structural strength of their interiors. Both satellites are found to be in synchronous rotation, as was expected from tidal theory. A close examination of the pre‐orbital satellite pictures has failed to show any unknown satellite. The photometric behavior of Phobos and Deimos indicates that they have intricate surface layers consistent with the presence of a regolith. Morphological features on Phobos and the expected collisional history of both satellites imply that both are made of well‐consolidated material.

Mars synthetic topographic mapping

“…The 18 18 mass of Phobos and Deimos are 17.4 x 10 g and 3.1 x 10 g respectively. km They are somewhat triaxial in shape with a mean radius of 10.9 and 5.7 km respectively (Pollack et al, 1973 Mars has a thin atmosphere and that the Martian surface pressure is less than 1% of that on Earth (Cunningham and Schurmeier, 1969); 2) the equatorial radius of Mars was found to be approximately 12 to 20 miles greater than the previous best estimate. The new value was indicated to be approximately 3,400 kilometers; and 3) the mass of Mars was estimated to be 1:3,098,500 of the Sun (de Vaucouleurs, 1965).…”

Physical properties of the natural satellites

“…Seen under high Sun angle, Phobos shows no albedo differences on its surface, but Deimos has a number of areas of contrasting albedo, presumably due to differences either of composition or of structure of the surface. Pollack et al (1973a) suggest that these features may have been produced by relatively recent large impacts, and are thus analogous to the lunar rays. Although the large departures from sphericity make such an analysis difficult, Pollack et aI.…”

“…The satellites of Mars are far too small to be resolved from Earth, but as a result of close-range imagery by the Mariner spacecraft (Pollack et al, , 1973a they are among the most thoroughly studied of the satellites. The best Mariner 9 pictures resolve features only 1% the linear size of the satellites.…”

“…Two papers by members of the Mariner 9 imagery team (Pollack et al, , 1973a have analyzed these data and provide most of the material for the following discussion.…”

“…Table VI lists the dimensions and volumes of the tri-axial ellipsoids found by Pollack et al (1973a) to provide the best fit to the profiles. While the absolute photometric calibration of the spacecraft images is insufficient to provide a good independent measure of the albedo, the ratio of the surface brightness of Deimos to that of Phobos under the same viewing and lighting geometry is 1.05_+ 0.05.…”