Near the rim of Valles Marineris — Mars's continent-spanning canyon system — orbital spectrometers detected an infrared signature that didn't match any known mineral. Bishop and colleagues at the SETI Institute reproduced the signal in the laboratory by heating hydrated ferrous sulfates above one hundred degrees Celsius, producing ferric hydroxysulfate — an iron sulfate with a crystal structure that may be unique enough to qualify as a new mineral.
The deposits appear at two sites: Aram Chaos, a collapsed terrain northeast of the canyon, and the Juventae Plateau, perched above a five-kilometer-deep chasm. Both locations are associated with ancient water activity, but the ferric hydroxysulfate requires something water alone can't provide: heat. Temperatures exceeding a hundred degrees, sustained long enough to transform the precursor sulfates.
The heat source was geothermal or volcanic. Which means parts of Mars were thermally active more recently than the standard geological timeline allows. The Martian interior was supposed to have cooled and quieted by the time these surface minerals formed. The presence of thermally altered sulfates says otherwise — heat was available, possibly from late-stage volcanism or subsurface hydrothermal systems operating after the canonical end of Martian geological activity.
The mineral is rare on Mars. Polyhydrated and monohydrated sulfates are abundant across the planet — they form from water interacting with basalt. The ferric hydroxysulfate stands out precisely because it requires more than water. It requires energy. Its distribution maps where Mars was not just wet but warm, distinguishing habitable-adjacent environments from merely wet ones.
A mineral that shouldn't exist on a dead planet. Its presence means the patient wasn't dead yet.