Computer Science – Sound
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p44b..03f&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P44B-03
Computer Science
Sound
[5450] Planetary Sciences: Solid Surface Planets / Orbital And Rotational Dynamics
Scientific paper
The Geophysical Monitoring and Sounding (GEMS) mission provides unique and critical information about the fundamental processes of terrestrial planet formation and evolutions. GEMS begins the geophysical exploration of the Martian interior using seismic and thermal measurements and rotational dynamics, providing information about the initial accretion of the planet, the formation and differentiation of its core and crust, and the subsequent evolution of the interior. One of the mission's investigations is the Rotation and Interior Structure Experiment (RISE), which uses the spacecraft X-band communication link to receive Doppler and ranging observables. The objective of RISE is to determine the mineralogy, temperature, and state of the deep interior of Mars, complementing information provided by seismology. The mineralogy and temperature of the deep interior will provide key information on the accretion of the planet, and can be used to test theories of terrestrial planet accretion and thermal evolution. The interior structure will be inferred by the effect on variations in the orientation of Mars with respect to inertial space. The precession, nutation, and polar motion of Mars result from the interaction of the interior mass distribution with the gravity of the Sun. RISE will provide improved estimates of Mars' precession and nutation, polar motion, and length-of-day variations by monitoring the Doppler shift due to the rotation of Mars on the radio signal between the spacecraft and tracking stations. RISE will reduce the uncertainty in the precession rate and therefore also in the moment of inertia by a factor of ten or more. The moment of inertia can be used as a constraint on the core size and density, core temperature and mineralogy. The improved accuracy of the moment of inertia can constraint the core size and eliminate many, if not most, possible composition ratios. In addition, the measurements of the nutation of Mars will determine whether the Martian core is fluid or solid and provide further constraints on the core density and size. The determination by RISE of a free rotational oscillation of the planet similar to the Chandler Wobble in the Earth's polar motion will yield independent constraints on the core size and density and on the elastic and inelastic behavior of the mantle. RISE determinations of seasonal polar motion and length-of-day variations will provide detailed global information on the general circulation in the atmosphere and constrain the sublimation/condensation cycle of the polar caps. In addition to the better precession rate, RISE will also improve the obliquity evolution of Mars over tens of millions of years. RISE results will therefore also be crucial for understanding the past climate of Mars, the structure of the polar layered terrain and the polar ice caps. This paper will describe the method of implementing experiments, the expected types of results and their potential scientific significance.
Asmar Sami W.
Banerdt B.
Dehant V. M.
Folkner William M.
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