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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 110,
E07004,
doi:10.1029/2004JE002376,
2005
Improved estimate of tidal dissipation within Mars from MOLA observations of the shadow of Phobos
Bruce G. Bills
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA Scripps Institution of Oceanography, La Jolla, California, USA
Gregory A. Neumann
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
David E. Smith
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Maria T. Zuber
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
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 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.
Received 4
November
2004;
accepted 21
April
2005;
published 26
July
2005.
Keywords: Mars;
Phobos;
tides.
Index Terms: 5450 Planetary Sciences: Solid Surface Planets: Orbital and rotational dynamics (1221); 5430 Planetary Sciences: Solid Surface Planets: Interiors (8147); 5460 Planetary Sciences: Solid Surface Planets: Physical properties of materials.
Read Full Article (file size: 437165 bytes) Cited by
Citation: Bills, B. G., G. A. Neumann, D. E. Smith, and M. T. Zuber
(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.
Copyright 2005 by the American Geophysical Union.
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