Brown University planetary geologists have identified a spot on Mars which they say could have been one of the most recent habitable microenvironments on the planet.
The team has discovered mounds of hydrated silica - proof that water was once present - deposited on a volcanic cone less than 3.5 billion years ago. The mounds' location on the volcanic cone provide the best evidence yet for a hydrothermal environment — a steam fumarole or a hot spring.
Such environments may have provided habitats for some of Earth's earliest life forms.
"The heat and water required to create this deposit probably made this a habitable zone," said JR Skok, a graduate student at Brown and lead author of the Nature Geoscience paper. "If life did exist there, this would be a promising spot where it would have been entombed — a microbial mortuary, so to speak."
The finding adds to evidence that - at some times and in some places - Mars hosted favorable environments for microbial life. The newly-found deposit is located in the zone known as Syrtis Major and is believed to have been left during the early Hesperian period, when most of Mars was already turning cold and arid.
"Mars is just drying out," Skok said, "and this is one last hospitable spot in a cooling, drying Mars."
Concentrations of hydrated silica have been identified on Mars previously, including a nearly pure patch found by NASA's Mars Exploration Rover Spirit in 2007. However, this is the first found in an intact setting that clearly shows the mineral's origin.
"You have spectacular context for this deposit," Skok said. "It's right on the flank of a volcano. The setting remains essentially the same as it was when the silica was deposited."
Cameras on the Mars Reconnaissance Orbiter detected patches of bright deposits near the summit of the cone, fanning down its flank, and on flatter ground nearby. It appears that hot springs or fumaroles fed by underground heating created these deposits; the closest parallel on Earth would probably be silica deposits around hydrothermal vents in Iceland.
"The habitable zone would have been within and alongside the conduits carrying the heated water," Murchie said.