Gravity of Mars noted that older regions on Mars are isostatically compensated when the younger region are usually only partially compensated. Different volcanic constructs could behave differently in terms of gravity anomalies. Large volcanoes Olympus Mons and the Tharsis Montes produce the largest positive free-air gravity anomalies in the solar system. Alba Patera, also a volcanic rise, north of the Tharsis Montes, however, produces negative Bouguer anomaly, though its extension is similar to that of Olympus Mons. And for the Elysium Mons, its center is found to have slight increase in Bouguer anomalies in an overall broad negative anomaly context in the Elysium
Olympus Mons gradient and residual heat from the volcano's magma chamber. Potential springs or seeps around the volcano would offer exciting possibilities for detecting microbial life. Olympus Mons and a few other volcanoes in the Tharsis region stand high enough to reach above the frequent Martian dust-storms recorded by telescopic observers as early as the 19th century. The astronomer Patrick Moore pointed out that Schiaparelli (1835–1910) "had found that his "Nodus Gordis" and "Olympic Snow" [Nix Olympica] were almost the only features to be seen" during dust storms, and "guessed correctly that they must be high". The Mariner 9 spacecraft arrived in