Contamination concerns could mean Curiosity rover operational impact
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.
'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.
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.”
To prevent contamination, the basic standard for a spacecraft like Curiosity that touches Mars in equatorial regions such as Gale is no more than 300 bacterial spores per square meter, or 500,000 spores for the whole spacecraft (a clean terrestrial kitchen would have billions of spores). Those standards can be achieved by cleaning the spacecraft with alcohol wipes, and assaying its cleanliness by culturing samples swabbed from the hardware.
In a cold, dry equatorial region, bathed by ultraviolet light from the Sun, scientists believe that any bacteria reaching Mars would soon die. But after the Mars Phoenix lander confirmed subsurface water ice at the planet's poles, the standard was enhanced to include a requirement for heat treating the hardware to kill any spores that might thrive in highly saline underground Mars water.
That standard was not met on the rover's drill bits and wheels, which were removed from protective containment after sterilization for more work. Nor were procedures followed when insulating blankets were installed inside the heat shield that later crashed on the planet's surface. In the latter case, which left 34 sq. meters (365.9 sq. ft.) inaccessible for assaying, the hardware was cleared by sampling “a small subset of the area through the installed blankets,” according to a presentation by consultant Pericles D. Stabekis, who studied the issue for the NASA Advisory Council.
Stabekis found that planetary-protection staffing on the Curiosity program was inadequate, both at theand at NASA headquarters. That made it difficult to keep track of the compliance paperwork, and led to discovery of the non-compliant work less than three months before launch—too late in the launch preparation for corrective action. Fortunately, by then scientists had selected Gale Crater as the landing site, and Conley was able to recategorize the landing requirement from Category IVc to the less rigorous Cat. IVa, which did not require heating.
“It was a very big, complicated project,” Conley says. “There were [procedural] things that fell between the cracks.”
Teflon seals within the drill assembly are another potential source of drilling-site contamination from the Mars Science Lab mission that includes Curiosity. Although not biological, NASA Jet Propulsion Laboratory MSL project manager Richard Cook acknowledges there are scientific implications.
“While it had a noticeable impact [the analysis team] thought they could work around it essentially,” he says. “Teflon is a well-characterized substance, and so although it has potential [to skew a sample], that's not very likely since they know what Teflon will do.”
The presence of polytetrafluroethylene (the chemical name for Teflon) and another potential contaminant from the drill, molybdenum disulfide, will be detected and taken into account by the Curiosity's Sample Analysis at Mars instrument, say project scientists.
At Conley's request, the chief engineer's office at NASA is including planetary-protection lessons-learned in its review of the entire MSL project. And in her recategorization, she prohibited Curiosity from entering a “Mars Special Region” that might sustain terrestrial life, including “fluid-formed features such as recurring slope linea”—seasonal bands on the surface that may be caused by flowing water below.
“Any evidence suggesting the presence of Special Regions or flowing liquid at the actual MSL landing site shall be communicated to the planetary protection officer immediately, and physical contact by the lander with such features shall be entirely avoided,” Conley stated in the document authorizing the landing.
Preparations for the start of actual drilling will take another few weeks. “Drilling is the most significant engineering task we've done since landing,” Cook says. “We will interact with unknown surface terrain and it is the first time we've ever done that.”
Named John Klein to honor a deceased deputy project manager on the rover, the drilling site includes veins and concretions that are geological indicators of precipitation of minerals from water.
“This is why we selected it for drilling,” says Grotzinger, the project scientist. “Water went through these rocks and precipitated chemicals. It is the first time in this mission we've seen something that is not just an aqueous environment but also one which results in precipitation of minerals.”