Jonathan Amos, Science Correspondent for BBC News reports on the stunning findings relayed to scientists by NASA’s Curiosity rover.
The ancient lake environment found in Mars’ Gale Crater could have supported microbes called chemolithoautotrophs – if they had been present. Known as Yellowknife bay, this topographic low has been shown through the drilling and chemical analysis of rock samples to contain ancient mudstones. Today, they are cold, dry and dusty, but their sediments were originally laid down in water that flowed in streams and eventually pooled into a lake. It is clear the conditions at the time of deposition would have been more than suitable for a wide range of microbial lifeforms. The scientists can tell that water – the “lubricant” of life – was significant and persistent in Gale, and that it must have been broadly neutral in pH, and not at all briney. Much of this is evident from the presence of clay minerals, which tend to form only under particular conditions. “I think what’s very important here is that we’ve now made the case that these clay minerals were formed in situ,” said Prof Grotzinger. “They were not detrital; they were not blown in. They are representative of the aqueous environment that is suggested by the [look of the rocks], and that environment would have been a habitable one.” Key to this habitability is the availability of essential elements, such as carbon, hydrogen, oxygen, sulphur, nitrogen and phosphorous. Curiosity has found them all to be present, and in a form that microbes could have accessed. The robot also detects minerals and compounds in various states of oxidation, which organisms could have exploited in simple reactions to obtain the energy needed to drive metabolism. The depression where Curiosity found the mudstones is only about 60m across, but the geologists on the science team believe this is just one small exposed area, and that the rock member (it has been dubbed “Sheepbed”) may extend up to 30 square km or more, hidden beneath other sediments. The thickness of the mudstone layer also hints at the length of time the water might have been present. Curiosity scientists estimate this to be perhaps hundreds to thousands of years, just based on the visible Sheepbed layers. When the other rocks lying on top of the mudstones are taken into account – rocks that unmistakably also have been touched by water at some point – it is entirely plausible the wet environments in Gale persisted from millions to tens of millions of years.