Space-based and Earth-based Prospects for Measuring the Moment of Inertia of Venus
Abstract
The moment of inertia is an essential integral constraint on models of planetary interiors. Our ignorance about Venus's moment of inertia prevents us from obtaining definite answers to key questions related to the size of the core, the thermal evolution history of the planet, the absence of a global magnetic field, and the evolution of the spin state. The technical challenge and cost of Venus landers make a direct measurement of the core size with seismology unlikely in the near future. For the same reasons, lander-based measurements of the spin precession rate, which yields the moment of inertia, are improbable in the near term. Tracking of the spin axis orientation with spacecraft or Earth-based radar over a decade or more offers more promising avenues. We use a precession model and the characteristics of existing data sets to quantify measurement prospects. The best Magellan estimates of the pole orientation have uncertainties of ~15 arcseconds (Konopliv et al., 1999) and an epoch that corresponds to the mid-point of the observations (~Oct. 1993). We describe achievable measurement uncertainties for a variety of scenarios including an additional spacecraft data point (e.g., at epoch 2023) with comparable or better precision than that of Magellan. Our 14 existing Earth-based radar observations obtained in 2006-2014 are sufficient to improve upon the best Magellan values and to unambiguously detect Venus's spin precession. We describe these results and quantify the uncertainties achievable on spin precession rate and moment of inertia with additional observations in the 2016-2023 interval. The Earth-based radar technique yielded a measurement of the spin axis orientation of Mercury with <5 arcsecond precision (Margot et al., 2012) that was later validated to <1 arcsecond level agreement with an independent, MESSENGER-based estimate (Stark et al., 2015).
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #48
- Pub Date:
- October 2016
- Bibcode:
- 2016DPS....4820409M