Improved estimate of tidal dissipation within Mars from MOLA observations of the shadow of Phobos
Abstract
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 alongtrack 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/yr^{2}, 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) × 10^{14} Pa s.
 Publication:

Journal of Geophysical Research (Planets)
 Pub Date:
 July 2005
 DOI:
 10.1029/2004JE002376
 Bibcode:
 2005JGRE..110.7004B
 Keywords:

 Planetary Sciences: Solid Surface Planets: Orbital and rotational dynamics (1221);
 Planetary Sciences: Solid Surface Planets: Interiors (8147);
 Planetary Sciences: Solid Surface Planets: Physical properties of materials