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 the Jet Propulsion Laboratory and 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.