In 2007, the Mars Exploration Rover (MER) Spirit came across a slightly raised platform, roughly pentagonal in shape and 90 meters across, which scientists named Home Plate. The rocky outcrop had a base of solidified ash, with nearby deposits of gas-filled basalts. Next to the plateau, nubby, nodular chunks of rock showed up, and light-colored soil just beneath the surface was exposed by the rover’s wheels. Mineralogical spectra of the bright soil were beamed back to Earth, revealing, to the scientists’ surprise, that it was composed almost entirely of silica.
When the geological puzzle pieces were assembled, two main options emerged: Home Plate may have been a volcanic fumarole, spewing sulfuric acid at basaltic rocks and leaving silica behind, or it could signify the remnants of a mineral rich hot spring, whose silica-saturated water generated the knobby rocks. Either way, water and heat were likely involved, and the discovery led ...
