By Earth standards, Tharsis Tholus is a giant, towering nearly 4 miles above the surrounding terrain (the height of Mount Everest), with a base stretching 20 times that. On Mars, it is just so-so in size. The shield volcano, Olympus Mons, which also rests in the vast upland region Tharsis is, at 26 km, the highest known mountain in the Solar System, but the condition of Tharsis Tholus is what interests researchers more than its size. At least two large sections have collapsed around its eastern and western flanks during its four-billion-year history and these catastrophes are now visible as scarps up to a few miles high. The main feature of Tharsis Tholus is the caldera in its center.
It has an almost circular outline, about 32 x 34 km, and is ringed by faults that have allowed the caldera floor to subside by as much as 2.7 km. It is thought that the volcano emptied its magma chamber during eruptions and, as the lava ran out onto the surface, the chamber roof was no longer able to support its own weight. So, the volcano collapsed, forming the large caldera.
Tharsis Tholis image was created using a Digital Terrain Model (DTM) obtained from the High Resolution Stereo Camera on ESA’s Mars Express spacecraft. Elevation data from the DTM is colour coded: purple indicates the lowest lying regions and beige the highest. The scale is in metres. In these images, the relief has been exaggerated by a factor of three. Credits: ESA/DLR/FU Berlin (G. Neukum)
NASA's upcoming mission is the Mars Science Laboratory, a large rover known as Curiosity, with experiments designed to detect organic molecules, past or present, on the Red Planet.
Also worth noting is the simulated Mars mission, Mars500, which ended on Friday when the hatch was opened for the first time since June 2010. For 520 days, the international crew had been working in a simulated spacecraft in Moscow.
Perhaps one of them will become John Carter, or perhaps even Dejah Thoris.