3 Gravity Science and Planetary Interiors
3.1 Overview
Planetary bodies have influence inherent to their mass that extends into space as gravitational fields that is detectable by objects in the vicinity such as spacecraft on scientific missions. One of the earliest applications of radio science (RS) techniques was in the study of planetary gravitational fields for the purpose of deducing planetary properties, such as bulk mass (radio scientists weigh the planets), mass/density distribution, internal density gradients, and interior structures and composition. This research is referred to in the scientific literature as gravity science, planetary gravimetry, planetary geodesy, or celestial mechanics investigations. Table 3.1 lists completed and selected planned gravity experiments from spacecraft radiometric data.
Table 3.1 Summary of gravity experiments from spacecraft radiometric data (and selected planned future experiments).
| Planetary body | Mission | Year |
|---|---|---|
| Mercury | Mariner 10 | 1974 |
| MESSENGER | 2011–2015 | |
| BepiColombo | Planned for 2025 | |
| Venus | Mariner 2 | 1962 |
| Mariner 10 | 1974 | |
| Pioneer Venus | 1978 | |
| Magellan | 1991 | |
| Moon | Luna 10 | 1966 |
| Lunar Orbiters I-V | 1966–1967 | |
| Apollo 15/16 subsatellites | 1971–1972 | |
| Clementine | 1994 | |
| Lunar Prospector | 1998–1999 | |
| SELENE | 2007–2009 | |
| Chang’E-1 | 2007–2008 | |
| GRAIL | 2011–2012 | |
| Mars | Mariner 9 | 1971 |
| Viking 1, 2 | 1976 | |
| Mars Global Surveyor | 1997–2006 | |
| Mars Pathfinder | 1997 | |
| Mars Express (targets) | 2003–present |
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