Improved estimate of tidal dissipation within Mars from MOLA observations of the shadow of Phobos
Article first published online: 26 JUL 2005
Copyright 2005 by the American Geophysical Union.
Journal of Geophysical Research: Planets (1991–2012)
Volume 110, Issue E7, July 2005
How to Cite
2005), Improved estimate of tidal dissipation within Mars from MOLA observations of the shadow of Phobos, J. Geophys. Res., 110, E07004, doi:10.1029/2004JE002376., , , and (
- Issue published online: 26 JUL 2005
- Article first published online: 26 JUL 2005
- Manuscript Accepted: 21 APR 2005
- Manuscript Revised: 4 JAN 2005
- Manuscript Received: 4 NOV 2004
 We report on new observations of the orbital position of Phobos, the innermost natural satellite of Mars, and show that these observations provide an improved estimate of the rate of tidal dissipation within Mars. The observations were made with the Mars Orbiter Laser Altimeter instrument on the Mars Global Surveyor spacecraft. The secular acceleration in along-track orbital motion is conventionally expressed in terms of a quadratic term in mean orbital longitude, which yields s = (dn/dt)/2 = (136.7 ± 0.6) × 10−5 deg/yr2, where n is the mean motion. The corresponding fractional rate of change in orbital angular velocity is (dn/dt)/n = (6.631 ± 0.029) × 10−9/yr, the highest measured for any natural satellite in the solar system. The energy dissipation rate is (3.34 ± 0.01) MW. Because Phobos is so close to Mars, there are nonnegligible contributions to the tidal evolution from harmonic degrees 2, 3, and 4. However, the elastic tidal Love numbers are observationally constrained only at degree two. The observed acceleration is consistent with that for a homogeneous Maxwell viscoelastic model of Mars with effective viscosity of (8.7 ± 0.6) × 1014 Pa s.