Mariner 9 television observations of Phobos and Deimos

Physical properties of the natural satellites

“…Both the disappearance and reappeaiance of the star were essentially instantaneous. Smith and Smith (1972) use the occultation photometry to set upper limits of 0.9 • 10 -7 and 1.3 • 10 -7 for the surface partial pressure of CH 4 and N2, respectively, and slightly larger values result from a similar analysis by Bartholdi and Owen (1972). More recently, Carlson et al (1973) have reported photometric observations of an occultation of SAO 186800 by Ganymede on 7 June 1972.…”

“…Because of their very irregular shapes (discussed further in Section 5), it is meaningful to speak of their radii only in the sense of the radius of a sphere whose projected area equals the average projected area of the satellite. Using this definition, Pollack et aL (1972) obtain radii of 5.7+_0.5 km for Deimos and 10.9+_1.5 km for Phobos. Combining these radii with the photometry of Kuiper (Harris, 1961), Pollack et al arrive at geometric visual albedos of about 0.05 for these two satellites.…”

“…(b) Deimos; range 5465 km, phase angle 65 ~ The sharp crater below center has diameter ~1 kin, and the diffuse crater above it ~2 km, From Pollack et al (1972), Phobos and Deimos have been molded in part by impacts that have excavated craters and apparently chipped away large pieces to produce the present irregular profiles. It is important to inquire into the fate of this excavated and spallated material fm satellites of such low surface gravity, as well as to try to reconstruct the history of the impacts 9 Figure 4 (taken from Pollack et al, 1972) shows the frequency distribution of craters on Phobos and Deimos compared to mean distributions for the lunar uplands and for the Martian surface 9 The density if small craters on these satellites is an order of magnitude greater than on heavily cratered terrain on the planet, but it is similar to that on the lunar highlands, which represents a state of saturation in which old craters are eliminated as fast as new ones are formed 9 A lower limit to the age of the surfaces of Phobos and Deimos is the time needed to arrive at a saturated crater density 9 Although the rate of impacts in the past is not known, Pollack et al conclude that this age is probably measured in eons. From the size distribution of craters it is possible to estimate the present thickness of the regoliths on these satellites.…”

“…The most extensive recent search for satellites both interior and exterior to the known systems was made by Kuiper (1961), who also reviewed earlier surveys. Since that time, additional unsuccessful searches have been made for new satellites of Uranus by Sinton (1972) and of Mars by Pollack et al (1972), and one additional satellite of Saturn * The 195 references cited in the bibliography clearly show the rapid increase in publications in the field of satellite studies in the past three years: 39 ~ are dated 1973 or 74; 16~ are 1972; 14~ are 1971, and all previous years contribute only 31 ~. Of these references, 84 % are journal publications, with two journals clearly dominating: Icarus, with 37 ~ of the journal citations, and The Astrophysical Journal with 16 ~.…”

The prospects for life on Mars: A pre-Viking assessment

“…High resolution photography of Phobos by Mariner 9 has shown conclusively that it is an entirely natural and ancient satellite (Pollack et al, 1972). In addition, the most recent reduction of the celestial mechanical data shows that there may be no large secular acceleration; and what secular acceleration there is can be understood in terms of body tides (Smith and Born, 1976;Pollack, 1976).…”