The  Los Angeles Times said that while preparing for launch, engineers at NASA’s Jet Propulsion Laboratory just outside Los Angeles had mounted a drill bit into Curiosity’s arm in case the robot itself had trouble inserting the drill automatically after landing.

The fear is that the once-sterile drill may now be contaminated because it has been exposed to living microbes.

NASA guidelines call for the sterilization of all parts of the Curiosity that come into contact with the surface of Mars in order to avoid contaminating another planet with living microbes.

Though it’s extremely unlikely that microbes could survive through the journey and landing on Mars, contamination might occur if Curiosity discovers water on Mars, because microbes have the best chance of survival in moist areas. If that happens Curiosity would still be able to study the water from a distance with other tools such as a spectrometer and laser.

NASA officials justified the plan to insert the non-sterile drill bit, since the discovery of water is not a prime goal of the mission and is thought highly unlikely to be found in the area that Curiosity is exploring.

“Water or ice near the surface in Gale crater was not a significant probability,” David Lavery, programem executive for solar system exploration at NASA headquarters told the paper.

“We weighed that against the risks of not having a bit mounted in the drill prior to launch, and the spectre of not being able to drill any holes at all on Mars.”