WASHINGTON — Microbial life could have thrived on Mars billions of years ago, researchers from NASA’s Curiosity mission reported March 12. An analysis of the rover’s first drill sample on the Red Planet revealed a nonacidic, slightly salty aquatic environment with plenty of energy-rich minerals. There is no evidence of past life, the researchers said, but the sample revealed the most hospitable environment ever detected beyond Earth.
“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,” said Curiosity project scientist John Grotzinger of Caltech.
Curiosity has been very busy since its arrival on Mars last August. It landed in Gale Crater with plans to explore Mount Sharp, the 5-kilometer-high mountain at the crater’s center. But early in Curiosity’s adventures the rover encountered the remains of what appears to be an ancient stream emptying into a lake.
That region, called Yellowknife Bay, is where researchers decided to drill into a rock — the first time that has ever been done on another planet. “Mars has written its autobiography in the rocks of Gale Crater,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program. “Chapter One is Yellowknife Bay.”
Curiosity’s drill is one of its most important features because the Martian surface can be deceiving. Radiation pelts the soil, altering its chemistry, and winds carry material far from where they formed. But by drilling down a mere 6 centimeters, Curiosity hit bedrock. “You know the stuff formed there,” said David Blake of NASA’s Ames Research Center in Moffett Field, Calif.
Scientists got excited the moment they saw the powder from inside the rock. It was gray, evidence that it was at least partially protected from the harsh environment that gives the Martian surface its familiar rusty appearance. Once Curiosity extracted the drilled sample, two of the rover’s onboard tools, the Chemistry and Mineralogy and Sample Analysis at Mars instruments, took a closer look.
The instruments detected chemicals, such as calcium sulfate, that can form only in nonacidic environments, a pivotal attribute for life on Earth. The rocks also contained clays that formed in water that was only slightly salty, meaning Yellowknife Bay wasn’t a Dead Sea–like environment that would suck the water out of any microbial life.
Curiosity did not find any of the organic carbon compounds that form the basis of amino acids and sugars — pivotal ingredients for complex life on Earth. However, Grotzinger points out that many single-celled organisms on Earth thrive in inorganic environments. The drilled powder contained hydrogen, carbon, sulfur, nitrogen, phosphorous and oxygen — elements that could have served as a chemical energy source for microbial life, he said.
While NASA researchers are confident with the analysis, the scientists stressed that another sample or two is needed to confirm the results and make sure none of the chemicals came from contaminants on the rover itself. Unfortunately, a problem with one of Curiosity’s two onboard computers is keeping the rover from doing any more exploring for now. And in April, Mars will cross behind the sun, blocking scientists’ lines of communication with the rover for about a month. The researchers hope to take another drilling sample in May before directing the rover toward Mount Sharp.
From there, scientists can start putting all the pieces together to reconstruct Mars as it appeared a few billion years ago, when it was far warmer and more hospitable than it is today. Additional drilling by Curiosity will turn up more chemicals, while lab tests will determine how different compounds degrade over time. Meanwhile a probe called MAVEN, scheduled for launch later this year, will detect gases escaping from the Martian atmosphere that may have once persisted on the surface.
The long-term goal, Grotzinger says, is to compare the geology and climate of ancient Mars with that of early Earth. It could turn out that Earth and Mars started on similarly biologically friendly paths before diverging into the worlds we see today.