Since Curiosity’s stunning debut on Mars last August we’ve been blessed with wondrous new data from NASA’s latest intrepid rover. About the size of a small car, Curiosity is a self-contained science laboratory that has already achieved one of its chief aims - to find evidence of a habitable environment where microbial life could survive. Curiosity landed in 96-mile-wide Gale Crater where in March of this year it hit pay dirt while drilling into its first rock. According to John Grotzinger, California Institute of Technology geology professor and principal investigator for the NASA mission, “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 on the planet, you would have been able to drink it.”
Today the Red Planet is a cold, dry place, with high levels of radiation, but it wasn’t always so. Several billion years ago it had abundant water and a thicker atmosphere to keep it warm and shield it from radiation. About three billion years ago, things began to change. With only one tenth the mass of Earth, and therefore much weaker gravity, Mars was unable to maintain most of its atmosphere. Also, as the inside of the planet cooled, Mars lost most of its magnetic field that had helped protect its atmosphere from depletion by the scouring effects of the solar wind. In addition, the cooling of the planet meant that volcanoes, a source of water in the form of steam, stopped erupting. The water on Mars froze or evaporated, escaping into space. However, evidence of liquid water in the past still exists on Mars in the form of dry river and lake beds, and ice both above and below its surface, not just at the poles.
NASA’s rovers, Spirit and Opportunity, had previously provided strong evidence of liquid water on the Martian surface, but in places that were highly acidic and salty. However, the rock examined by Curiosity, found in the Glenelg region of Gale Crater, not far from the landing site, showed evidence of an environment far more conducive to life. Scientists found clays, which form in water that has a neutral pH (neither acidic nor alkaline), and were able to identify the elements hydrogen, oxygen, nitrogen, carbon and phosphorus, all important ingredients of life. In addition, minerals such as sulfates and sulfides were found that could provide food, or an energy source, for primitive microbes. According to Dr. Grotzinger, very primitive organisms can derive energy just by feeding on rocks.
The question remains, however: Were there ever microbes on Mars? We know they could exist, but did they? And if so, are they still there? It is possible that life could still exist, shielded from radiation, beneath the planet’s surface. Unfortunately, Curiosity is not equipped to detect life on Mars. It can identify organic molecules, the precursors of life, but many nonliving chemical reactions produce organic molecules too, so their presence would not be conclusive. So far, some simple organic molecules have been found but it has yet to be determined whether these are the result of contamination from Earth, were created during chemical reactions as the sample rock powder was heated, or in fact came from the Martian rock itself.
Meanwhile, in early July, Curiosity left the Glenelg region of Gale Crater where the ancient wet environment conducive to life had been found. It has now begun the five-mile long trek to the base of its main mission destination, the three-mile high Mount Sharp, in the middle of the crater. Along the way, in a journey lasting nine months to a year, it will take photos and make stops, digging in the rocks and dirt for yet more discoveries. Mount Sharp’s slopes have many exposed layers where scientists hope to find evidence of how the ancient Martian environment changed and evolved. These layers include clays, detected earlier by orbiting spacecraft, that, like those already found in the Glenelg area, might be prime candidates in the search for organic molecules.
Looking to the future, NASA plans to send another rover to the Red Planet in 2020. Its goals will be to look for signs of past life, to collect samples for future return to Earth, and to demonstrate technology for future human exploration of Mars. This mission could, in turn, bring us closer to meeting President Obama’s challenge to send humans to Mars in the 2030’s.
Copyright © Amanda Jermyn