Spin state and moment of inertia of Venus
arXiv:2103.01504 · doi:10.1038/s41550-021-01339-7
Abstract
Fundamental properties of the planet Venus, such as its internal mass distribution and variations in length of day, have remained unknown. We used Earth-based observations of radar speckles tied to the rotation of Venus obtained in 2006-2020 to measure its spin axis orientation, spin precession rate, moment of inertia, and length-of-day variations. Venus is tilted by 2.6392 0.0008 degrees () with respect to its orbital plane. The spin axis precesses at a rate of 44.58 3.3 arcseconds per year (), which gives a normalized moment of inertia of 0.337 0.024 and yields a rough estimate of the size of the core. The average sidereal day on Venus in the 2006-2020 interval is 243.0226 0.0013 Earth days (). The spin period of the solid planet exhibits variations of 61 ppm (20 minutes) with a possible diurnal or semidiurnal forcing. The length-of-day variations imply that changes in atmospheric angular momentum of at least 4% are transferred to the solid planet.
20 pages, 7 figures, supplementary information. Submitted to Nature Astronomy on October 14, 2020