Water good enough to drink

CuriosityAfter just six months on Mars, Curiosity looks to have taken a significant step towards fulfilling its primary science mission: to determine whether conditions on the planet once provided a suitable environment in which life might have arisen.

Despite recently suffering a serious computer glitch – of which more later – Curiosity’s initial analysis of cuttings gathered from inside bedrock dubbed “John Klein”, so named in honour of the late John W. Klein, MSL’s former Deputy Project Manager, and which is located in the “Yellowknife Bay” region of  Gale Crater, reveals very strong evidence that ancient Mars could have supported living microbes.

Commenting on the findings, Michael Meyer, lead scientist for NASA’s Mars Exploration Programme, said, “A fundamental question for this mission is whether Mars could have supported a habitable environment. From what we know now, the answer is yes.”

The initial findings came via the rover’s Chemistry and Mineralogy (CheMin) and Sample Analysis at Mars (SAM) instruments, which each received a portion of the rock cuttings gathered from within “John Klein” on Sol 182 (February 8th / 9th). The deliveries of the samples took place on Sols 195 (February 22nd) and 196 (February 23rd) respectively, the delay between sample gathering and delivery being down to a combination of the need to “clean” the sample holding and transfer elements of dill bit and concerns over the long-term status of a filter in part of the turret-mounted sample handling mechanism (see Getting the scoop on drilling).

The area of “Yellowknife Bay” sits at the end of what mission scientists believe to be an ancient river system, and which may have been a part of a larger lake bed in planet’s ancient past. During the drive from Bradbury Landing, where it arrived on Mars in August 2012, Curiosity has come across strong evidence for liquid having once flowed freely through the region. Rock formations commonly associated with stream and river beds have been found and imaged, and the “Yellowknife Bay” area itself bears all the hallmarks of having been formed as a result of material being carried in free-flowing liquid – most likely water. These findings have supported evidence from orbit, where images taken by various spacecraft have long pointed to large parts – if not all – of Gale Crater having been subjected to aqueous activity in the distant past. This evidence includes a broad alluvial fan of water-deposited materials located close to the landing area planned for the rover, and regarded as a valuable back-up science target should post-landing issues with the rover prevent it from undertaking the long trek up onto “Mount Sharp”.

A false colour image of the MSL landing area, showing the position of the alluvial fan of water-laden material seen from orbit and which hinted that the region had a strong aqueous past. The slopes of “Mount Sharp” can be seen in the lower right-hand corner of the image,coloured light grey (click to enlarge)

The “John Klein” bedrock itself shows strong evidence on its surface for  having been formed by aqueous activity spanning numerous wet periods in the planet’s history. However, this is not what has excited scientists – evidence for water having flowed freely on Mars has been found right across the planet, both from orbit and on the ground. During their explorations of Mars, for example, both of the Mars Exploration Rovers – Spirit (before its demise) and Opportunity – came across rock formations which had most likely been formed in the presence of liquid water.

What makes the findings returned from “Yellowknife Bay” exciting for scientists is that previously, those areas of rock thought to have been formed as a result aqueous activity also showed strong signs that the water was likely to have been highly acidic and had what is referred to as a “low energy gradient”, both of which would have made the chances of life arising within it exceptionally challenging.

Wet Mars: these images both point to Mars having had a wet period of history. On the left is an image taken by the Opportunity rover of rock at Endurance Crater; on the right is rock imaged at “Yellowknife Bay” by Curiosity. Both have all the classic geological, chemical and mineralogical signs of having been formed in the presence of water. However, chemical analysis of the Endurance Crater rock strongly suggests the water there was highly acidic and with a limited energy gradient, both of which would not have been favourable to support micro-organisms. This is not the case with the rock sample gathered at “Yellowknife Bay”, which appears to have formed in a neutral or mildly alkaline pH environment, and which contains with a strong energy gradient (click to enlarge)

This is not the case with the chemical analysis of the sample gathered by Curiosity at “John Klein”. The first clue that the sample taken from inside the rock might be something special came when cutting from the bore hole in the rock were shown to be grey in colour – suggesting the interior of the rock to be only partially oxidised, as opposed to the heavy oxidation which is common to the surfaces of the rocks on Mars (and which gives them the familiar “rusty” colour). Nevertheless, scientists were surprised at the broad mix of chemical elements found within the sample delivered to SAM. Chemicals which, when taken together, provide an energy gradient of the sort many microbes on Earth exploit in order to live.

“The range of chemical ingredients we have identified in the sample is impressive,” said Paul Mahaffy, principal investigator of the SAM suite of instruments, “And it suggests pairings such as sulfates and sulfides that indicate a possible chemical energy source for micro-organisms.”

First clue: the grey colour of the cutting gathered by Curiosity’s drill was the first clue as to the possible nature of the rock’s chemical signature

Evidence of Smectitec clay minerals has also been also found within the samples, accounting for at least 20% of their composition. Such clays general form from the reaction between relatively fresh water with igneous minerals, such as olivine, also present in the sediment. These further suggest that the mudstone rock comprising “John Klein” was laid down is a freshwater environment, while the discovery of calcium sulfate along with the clay suggests the soil is a neutral or mildly alkaline pH environment.

“We have found a habitable environment that is so benign and supportive of life that probably, if this water was around and you had been there, you would have been able to drink it,” said John Grotzinger, Curiosity’s Principal Investigator. “We have characterized a very ancient, but strangely new ‘grey Mars’ where conditions once were favorable for life.”

Nor does the evidence for Mars once having conditions favourable to life end there. The initial analyses by both CheMin and SAM have also identified sulphur, nitrogen, hydrogen, oxygen, phosphorus and carbon present in the sample – all of which are the key chemical elements for life. These, and the range of oxidised chemical states in the sample, suggest that if there were any primitive micro-organisms on Mars, they could have derived sufficient energy to survive just by feeding off the rocks.

“Just like on [a] battery,” Grotzinger explained, “You hook up the wires and it goes to a lightbulb and the lightbulb turns on. That’s kind of what a micro-organism would have done in this environment, if life had ever evolved on Mars and it was present here.”

An analysis of a drilled rock sample from NASA’s Curiosity rover shows the presence of water, carbon dioxide, oxygen, sulfur dioxide, and hydrogen sulfide released on heating. The results analysing the high temperature water release are consistent with smectite clay minerals. On Earth, similar environments found on exposed lake beds have proven to be richly habitable for micro-organisms

As a result of these findings, it now appears as though Curiosity will remain within the Yellowknife Bay area for an extended period to allow for a more thorough examination and analysis of the area. This work will include a further drilling operation to obtain a further sample, however, with a period of Solar conjunction looming in April, this will not take place until the latter part of that month. This is because that during time, when the Earth and Mars will be on opposite sides of the Sun, both electromagnetic interference generated by the Sun and the bulk of the sun itself will interrupt direct Earth-Mars communications, and so Curiosity will be largely “fending for itself” during a period of some 11 days during April, reliant on instructions from Earth uploaded in advance and stored in memory.

The Road to Recovery

Work at “Yellowknife Bay” has been further slowed by ongoing efforts to both restore Curiosity’s full computer capabilities following the recent corruption with its on-board “A-side” computer and to discover the cause for the original glitch as well as providing a means of preventing it recurring.

Despite being somewhat interrupted by a solar eruption last week, which saw Curiosity effectively “put back to sleep” as a precaution against elevated surface radiation levels on Mars, work has continued in testing and assessing the “A-side” computer’s memory.

“These tests have provided us with a great deal of information about the rover’s A-side memory,” said Jim Erickson, deputy project manager for the MSL mission at NASA’s Jet Propulsion Laboratory. “We have been able to store new data in many of the memory locations previously affected and believe more runs will demonstrate more memory is available.”

While the “B-side” computer has now taken over managing most of Curiosity’s onboard systems and activities, the all-clear has yet to be given on resuming mission operations in full. This is unlikely to happen until after two software packages have been uplinked to the rover. One is  targeted at onboard memory allocation and the other focused on vehicle safing procedures – both of which will play an important role in the upcoming period of solar conjunction. These should be uploaded later this week. Once they have been installed and tested, the mission team will reassess when to resume full mission operations.

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All images courtesy NASA / JPL