GBT25A-083

Moment of Inertia and Size of the Core of Venus

Abstract

We request ten sessions of 45 minutes each to measure the spin axis orientation and precession rate of Venus with the Goldstone Solar System Radar (GSSR) and the Green Bank Telescope (GBT) at X band. The spin precession rate provides a direct measurement of the polar moment of inertia, which is needed to understand the interior structure of the planet and its thermal, spin, and magnetic evolutionary histories. Our observations in 2006-2020 enabled the first estimate of this fundamental quantity with 7% uncertainties. We seek additional measurements to reduce the uncertainties to 4% with the ultimate goal of enabling the first realistic, evidence-based models of Venus's interior. These Earth-based radar observations enable singular progress because there is currently no other way of measuring the polar moment of inertia of Venus. Venus is the only terrestrial planet for which the polar moment of inertia (and therefore core size) is poorly known, yet it may be the prototype for billions of exoworlds in the Galaxy. Goldstone-GBT is requested because the observations require a planetary radar, the geometry requires an East-West baseline, and the analysis requires large apertures for SNR reasons.

Investigators

Name	Institution
Jean-Luc Margot *	California at Los Angeles, University of

* indicates the PI