Blasting Rock and Hunting for Martian Life

ChemCam in action, in an artist’s view.

Early on Monday, after a tricky parachute descent, a hovering spacecraft will lower the new Mars rover, Curiosity, to the planet’s surface with long cables. If the nail-biting, never-before-tried maneuver works, the remote-controlled vehicle will begin searching for signs of water—and life. Bethany Ehlmann, an assistant professor at Caltech, will play a key role. From a control room in Pasadena, Calif., she will blow holes in rocks with a laser on the rover, creating clouds of atoms that could hold evidence of water. She spoke with The Chronicle about the quest.

Bethany Ehlmann

Q. This sounds like a point-and-shoot game, something in a video arcade.

A. I can see that. This is the first time anyone has zapped rocks with lasers on another planet. But it’s a serious scientific instrument called ChemCam.

Q. Do you pull the trigger?

A. Well, the rover pulls the trigger. I’m part of a science team that decides to take an image of a particular rock. We snap it with a telescopic camera. Then the engineers prepare the rover to shoot the laser, usually overnight. Curiosity takes the shot the next morning.

Q. What does all this have to do with water and life on Mars?

A. Mars is cold and dry now. But when we look at rock formations from 3.5 billion years ago, they look like they were part of hydrothermal systems like Yellowstone Park or parts of lake beds. If we were looking at these things on Earth, we’d find signs of microbial life there. So we want to get a closer look. If you were a geologist, you’d chip off some samples and take them back to the lab. Curiosity is our geologist.

Q. A geologist with a laser cannon?

A. It’s our way of getting a closer look. The laser vaporizes a patch of surface, creating a plasma. Light reflecting off the plasma forms a “fingerprint” based on the particular atoms that made up the rock. We can tell from the ratios of these elements if they may have been formed by upwelling groundwater or by settling sediments in a lake. Some rocks are more intriguing than others. If they have a large amount of carbonate in them, for example, they are crying out, “Look at me!” Or a small amount of potassium relative to other minerals is interesting because potassium gets flushed out from rock first if you run water through it.

Q. Then what does Curiosity do?

A. If the rock is just like one we already looked at, say, six days ago, then we’ll move on. But if it’s novel, then we’ll stay in the area and investigate further. We have very limited time and power. So we are always doing triage.

Q. How often will you fire ChemCam?

A. At the beginning, perhaps just a handful of shots each day as we see how the instrument behaves many millions of miles away. As we grow more confident, perhaps 10 or 15 times a day.

Q. Speaking of confidence, are you sure you’ll get a chance to use ChemCam? A lot of people are worried about this new parachute-and-cable landing technique for Curiosity. It could crash.

A. Mars does eat spacecraft. So I’m both nervous and excited. But our engineers are really, really good. Therefore, on Monday, I plan to be working on the planet’s surface.

(Images: J-L. Lacour/CEA/French Space Agency; courtesy Bethany Ehlmann)

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