HOST: NASA says there is no reason to worry that the Mars Curiosity rover may be contaminating the Martian surface with microbes from Earth. The agency wants to dispel concerns raised by a Los Angeles Times story, as KQED's Amy Standen reports.

AMY STANDEN: Here's the problem: If Curiosity were to find evidence of life on Mars, how would we know we weren't just picking up Earthly microbes that we had brought over by mistake?

That's one reason Curiosity landed on what's thought to be a completely dry spot, near the equator. Life, it's believed, needs water. So, no water means less chance that any Earthly stowaways could survive there.

Still, as the LA Times reported, NASA scientists have had some explaining to do about a drill bit that wasn't sterilized when it was installed on Curiosity.

Catherine Conley, NASA's Planetary Protection Officer, says as long as Curiosity encounters no ice, there is no cause for concern. But:

CATHERINE CONLEY: If they do find ice, they have to step back and talk to me before they touch it.

STANDEN: Curiosity landed on August 5. Next month, it's expected to start drilling into Martian rock.

I'm Amy Standen, KQED News.