Note on the paper by G. F. Schilling, ‘On exospheric drag as the cause of the supposed secular accelerations of phobos’

Abstract

In his recent paper, Schilling [1964] postulated that the exosphere of Mars may exert a drag on Phobos of sufficient magnitude to account for the secular acceleration in longitude of this satellite as given by Sharpless [1945]. In his examination of the problem, Schilling cited the results of Kerr and Whipple [1954], which indicated that the tide in the mantle of Mars would be about 800 times too small to account for Phobos' secular acceleration. Schilling, consequently, did not consider the tidal effect as a significant contributor to the secular acceleration. F. F. Fish and I [Redmond and Fish, 1964] have re-examined the possibility of a tidal effect being responsible for Phobos' secular acceleration. We have calculated the minimum and the maximum values for the lunitidal interval in Mars that are required to account for the secular acceleration of Phobos; these are 1.1° and 4.4°, respectively. The uncertainty of the result is due to the uncertainties in the physical constants involved in the Mars-Phobos system.