Wheel-Driven Silica Clue Reveals Mars' Hydrothermal Past

Spirit’s dead right-front wheel became a makeshift shovel, scraping a patch near Home Plate in 2007 and exposing soil about 90% silica. Measurements by the rover’s spectrometers identified opaline silica consistent with a hydrothermal setting, possibly hot springs or steam vents; while the findings stop short of proving life or a single formation path, they mark strong evidence of ancient water interacting with volcanic material on Mars.