Identification of Carbonate-Rich Outcrops on Mars by the Spirit Rover

TLDR

Mars’ early warmer, wetter climate and denser CO₂ atmosphere are thought to have produced carbonate‑rich outcrops, but evidence has been sparse; the Gusev carbonate likely formed from hydrothermal, near‑neutral solutions during the Noachian. The Spirit rover identified magnesium‑iron carbonate outcrops (16–34 wt %) in Gusev’s Columbia Hills, matching the composition of carbonate globules in meteorite ALH 84001.

Abstract

Decades of speculation about a warmer, wetter Mars climate in the planet's first billion years postulate a denser CO2-rich atmosphere than at present. Such an atmosphere should have led to the formation of outcrops rich in carbonate minerals, for which evidence has been sparse. Using the Mars Exploration Rover Spirit, we have now identified outcrops rich in magnesium-iron carbonate (16 to 34 weight percent) in the Columbia Hills of Gusev crater. Its composition approximates the average composition of the carbonate globules in martian meteorite ALH 84001. The Gusev carbonate probably precipitated from carbonate-bearing solutions under hydrothermal conditions at near-neutral pH in association with volcanic activity during the Noachian era.