NASA’s Curiosity rover has scored several remarkable successes since touching down in the vast, yawning bowl of Mars’ 96-mile-wide Gale Crater. The $2.5 billion, six-wheeled vehicle made landfall on the surface of the Red Planet last August, with the aid of a revolutionary “Sky Crane,” and almost immediately began exploring its desolate surroundings. It has performed the first X-ray diffraction analysis of a soil sample on another world and recently drilled its first rock specimen. Yet its most dramatic discoveries may lie just around the corner, for NASA yesterday released details of tantalizing new results which hint at a suitable environment for microbial life in Mars’ ancient past.
The possibility of life on the Red Planet—whether in the present or in the millions of years ago—has exerted a strong tug on humanity for more than a century, although five decades of robotic exploration have done little to reveal any “smoking gun” proof. Last November, NASA’s announcement of an embargoed news conference to discuss the progress of the Curiosity mission provoked a flurry of public and media speculation that traces of microbial life had been found. The space agency’s assertion to the contrary, and President Barack Obama’s somewhat glib remark that NASA should advise him immediately if Martian microbes are found, has done little to dissuade proponents of life on the planet.
Five weeks ago, on 8 February, the drill on Curiosity’s robotic arm bored a 2.5-inch hole into a sedimentary rock named in honor of former Mars Science Laboratory Deputy Project Manager John Klein, who died in 2011, and extracted powdery material from its interior. The rock lies about one third of a mile to the west of Bradbury Landing, where the rover touched down, and occupies a site thought to represent the end of an ancient river system or an intermittently wet lake bed. Moreover, the site is notable in that its ancient conditions were not harshly oxidizing, acidic, or extremely salty. By extension, such an environment may have provided the chemical energy and other favorable conditions for microbes. It became clear that the region boasted elevated levels of calcium, sulfur, and hydrogen, and the presence of vein-like features and nodules was strongly suggestive that multiple periods of wet conditions may have been involved in their formation. After extracting material from John Klein, the sample was sieved and examined by the rover’s Chemistry and Mineralogy (CheMin) and Sample Analysis at Mars (SAM) instruments.
Their ongoing work has borne surprising fruit. Evidence of sulfur, nitrogen, hydrogen, oxygen, phosphorus, and carbon—several key chemical ingredients for life—were detected in the powder. “A fundamental question for this mission is whether Mars could have supported a habitable environment,” said Michael Meyer, lead scientist for the Mars Exploration Program at NASA Headquarters in Washington, D.C. “From what we now know, the answer is yes.” David Blake, principal investigator for CheMin at NASA’s Ames Research Center in Moffett Field, Calif., added that upwards of 20 percent of the sample is composed of clay minerals, indicating a product of the reaction of relatively fresh water with igneous minerals, such as olivine, which was also found.
Researchers were initially puzzled to find a mixture of oxidized, less-oxidized, and even non-oxidizer chemicals providing an energy gradient similar to the sort that Earth-based microbes exploit in order to survive. This partial oxidation was hinted when the drill sample was revealed to be gray, rather than red. “The range of chemical ingredients we have identified in the sample is impressive, and it suggests pairings such as sulfates and sulfides that indicate a possible chemical energy source for micro-organisms,” explained Paul Mahaffy, SAM principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Md. Further investigation is expected to expand the picture of Mars’ wet past significantly, and MSL Project Scientist John Grotzinger of the California Institute of Technology in Pasadena, Calif., noted that the Curiosity “mission of discovery and exploration” is certain to make “many more exciting discoveries … in the months and years to come.”