A 160 km crater that may once have held a lake.
Gusev Crater is a roughly 160 km-wide impact basin that NASA chose as Spirit's landing site in 2004, because a large channel called Ma'adim Vallis drains into it — a strong hint it once held standing water. Spirit spent years here uncovering exactly that kind of evidence.
Claim your plot here →Gusev was picked as a likely former lakebed: the huge Ma'adim Vallis channel cuts through the crater's southern rim, as if a river once poured in. The crater floor turned out to be mostly volcanic basalt, but when Spirit climbed the Columbia Hills, it found altered rocks and carbonates telling a wetter story.
The rover's most striking discovery came from a dragging wheel that scraped up bright soil rich in opaline silica — a mineral that on Earth forms around hot springs and volcanic vents. That pointed to ancient hydrothermal activity in Gusev, one of the more promising environments for past microbial life found on Mars.