An apparent lack of rigor in maintaining cleanliness on the Curiosity rover while it was being assembled may one day force a hiatus in its use to explore Mars, if its instruments detect the possibility that life-supporting water exists nearby.

NASA's planetary protection officer, the scientist in charge of ensuring U.S. terrestrial probes do not contaminate celestial bodies, certified Curiosity for landing only because it was targeted on an equatorial crater that is unlikely to harbor subsurface water. Had planetary scientists chosen another landing site, mishandling of the rover's wheels and drill bits on Earth might have forced a two-year slip in launching until the next planetary window.

NASA officials, including Planetary Protection Officer Catharine Conley, stress that Curiosity is “fully compliant” with international protocols dating back to the Viking missions. Those standards were designed to ensure that any life found on Mars originated there, and did not arrive on the lander that found it or an earlier robotic visitor from Earth.

However, if Curiosity turns up evidence of contemporary water or ice as it explores Gale Crater, it may be commanded to back off from the potentially life-sustaining area while astrobiologists and planetary scientists ponder whether the rover could “forward contaminate” Mars.

“We have data that suggest [Gale Crater] should be very dry,” Conley says. “If somehow we discover something that means we have misinterpreted those data, before the project does anything about contacting those interesting places, they have to tell me, and I will convene my advisory committee, a subcommittee of the NASA Advisory Council, and I may even ask the Space Studies Board [of the U.S. National Academies of Science]—that's within my mandate—and we will actually get a good scientific review of all of the information the mission has collected, and doing that review, we will decide how to go forward.”

The problem is a little more acute now that the science team controlling the rover has selected an area of flat-lying rock containing a target-rich environment of fractures, veins and mineral concretions for the first use of its drill to collect subsurface samples. The drill bit is one of the items that was exposed to possible contamination during the rover's assembly, requiring Conley to accept the lower cleanliness standard.

The target area lies within a shallow depression called “Yellowknife Bay,” which lies around 500 meters (1,640 ft.) to the east of the rover's landing site. It was originally identified from orbital observations of fractured ground that cooled more slowly each night than nearby terrain. To the untrained eye, it strongly resembles a dry lakebed (see photo, p. 32).

“The orbital signal drew us here, but what we found when we arrived has been a great surprise,” says Mars Science Laboratory (MSL) project scientist John Grotzinger, of the California Institute of Technology in Pasadena. “This area had a different type of wet environment than the streambed where we landed, maybe a few different types of wet environments.”