GBT02A-042

Radar measurements of Mercury's obliquity and librations

Abstract

Evidence for a global magnetic field at Mercury has raised perplexing questions regarding the existence and nature of the planet's core. The problems related to Mercury's core are of great interest because of their implications on how planets evolve thermally and on how they generate magnetic fields. Peale showed that the measurement of four quantities, including the planet's obliquity and the amplitude of its longitude librations, could place constraints on the size and state of the putative core. In this proposal we seek to initiate a program to determine Mercury's obliquity and librations via ground-based radar measurements. Fourteen hours of antenna time distributed over four observing sessions during the May-June 2002 conjunction are requested to implement an original radar technique relying on observations of Mercury's speckle pattern at two distant sites, the GBT and the 70 m antenna in Goldstone, California. The correlation of radar echoes obtained at the two antennas will provide two observables, the time delay and the epoch associated with maximum correlation, both of which will constrain Mercury's spin state to better accuracy than expected from spacecraft missions.

**Investigators**
Name	Other *	Institution	Email	Phone
Jean-Luc Margot	PI	Caltech (Geo. and Planetary)	margot@gps.caltech.edu	626 395 6870
Stanton Peale		Dept. of Physics, U. of Calif., Santa Barbara	peale@io.physics.ucsb.edu	805 893 2977
Martin Slade		JPL	martin.a.slade@jpl.nasa.gov	818 354 2765

* PI = Principal Investigator; T = Thesis observations; S = Student

Front Ends

Gregorian X(8.2 to 10.0 GHz)

Back Ends

User supplied or new backend

Type of Observing

Imaging
Circular Polarization
High Time Resolution

Switching Type

Allocated time: 14.00 hours.

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