NASA's Curiosity Rover Finds Chemical Building Blocks For Life On Mars

Jun 7, 2018
Originally published on June 8, 2018 9:24 am

For the first time, scientists say they have clear evidence that the chemical building blocks of life exist on Mars.

What they can't say yet is whether there is, or ever was, life on the Red Planet.

The new evidence comes from a pair of rocks. NASA's six-wheeled Curiosity rover drilled into the planet in late 2014 and early 2015. The two rock samples, from sites named Confidence Hills and Mojave, are at the bottom of Gale Crater.

Powder from the rocks went into an analyzer on the rover called SAM that can determine what they were made of.

But the SAM results were hard to interpret — there were a lot of extraneous signals that didn't make any sense. So NASA astrobiologist Jennifer Eigenbrode at the Goddard Space Flight Center spent the intervening years figuring out which signals were clearly junk and removing them.

Then she looked at the analyzer results again. "There were signals there that were telling us that we had detected certain types of organic molecules," she says. Organic molecules contain carbon, the chemical element central to life.

That raises the obvious question: Where did the carbon come from?

"We don't know," Eigenbrode says.

She sees three possibilities.

"It could have been from meteorites," she says. Meteorites are constant pummeling Mars, and many of them contain carbon.

"It could be from rock processes," processes that have been going on during the billions of years since Mars formed.

And then there's the most intriguing possibility. Eigenbrode says the analyzed rocks came from the bottom of what was once a lake at a time when Mars was a much warmer, wetter place.

"Because this lake had everything that organisms needed to be happy, maybe there was life in the lake," she says. If there was, then that life would have left behind organic molecules when it decayed.

Penn State astrobiologist Kate Freeman agrees the new evidence makes that interpretation possible, but "it's not standing up and waving a flag and saying, 'I'm life.' "

She isn't ruling out that possibility, however.

"I don't believe there's life on Mars at the present," Freeman says, because Mars is very dry, very cold and lacks much of an atmosphere. "Whether there was in the past or not is certainly an open question."

Freeman says finding organic molecules only a few centimeters below the surface of Mars is an encouraging sign for finding possible life. That's because the surface of Mars is constantly bombarded with radiation that can break down organic compounds. There may be more material buried deeper.

"There's a new mission in the planning where they'll be able to drill much deeper than the Curiosity rover can," Freeman says. "That gives me great hope because we can perhaps get past these surface environments that are so harsh and maybe [go] a little deeper and find better-preserved materials."

In addition to finding organic molecules in the rocks in Gale Crater, rover scientists are reporting another intriguing finding.

The rover has been seeing seasonal changes in the amount of methane in the Martian atmosphere. Methane is another organic molecule.

"We were kind of shocked to see that with the seasons, the signal changes by a factor of three, which is a huge change and completely unexpected," says Chris Webster, a rover scientist at NASA's Jet Propulsion Laboratory.

He and his colleagues think the methane is coming from underground.

"It's coming from sub-surface reservoirs" and then seeping up to the surface, Webster says.

"Once it's on the surface, the temperature on the surface regulates the way in which it holds on to the methane through 'stickiness,' or surface adsorption as we call it," he says. "So it holds it in the winter time and releases it in the summertime as temperatures get warmer."

Webster says the rover results don't say whether the methane being released has been trapped for eons or is being generated now.

The results also don't indicate whether the methane is being created by chemical processes involving rocks alone, or whether some living or formerly living bacteria generated it.

Clearly, there are more questions about Mars that need answering.

The studies on methane and on organic molecules were published Thursday in the journal Science.

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DAVID GREENE, HOST:

This seems big. Scientists say for the first time they have clear evidence that the chemical building blocks of life exist on Mars. So is this the moment we can say there is life on the red planet? Well, NPR's Joe Palca says not yet.

JOE PALCA, BYLINE: About three years ago, NASA's six-wheeled rover called Curiosity drilled into two rocks at the bottom of Gale Crater. Powder from the rocks went into an onboard analyzer to see what they were made of. But the analyzer results were garbled so NASA astrobiologist Jennifer Eigenbrode spent the intervening years removing the junk that was messing things up. Then she looked at the analyzer results again.

JENNIFER EIGENBRODE: And there was signals there that were telling us that we had detected different types of organic molecules.

PALCA: Organic molecules contain carbon, the chemical element central to life. That raises the obvious question, where was the carbon coming from?

EIGENBRODE: We don't know.

PALCA: Eigenbrode sees three possibilities.

EIGENBRODE: It could have been from meteorites.

PALCA: Meteorites are constantly pummeling Mars, and many contain organic molecules.

EIGENBRODE: It could be from rock processes.

PALCA: Processes that have been going on in the billions of years since Mars formed. And then there's the most intriguing possibility. Eigenbrode says the analyzed rocks came from the bottom of what was once a lake at a time when Mars was a much warmer, wetter place.

EIGENBRODE: Because this lake had everything the organisms needed to be happy, it could have supported life. Maybe there was life in the lake.

PALCA: And that life decayed, leaving behind the organic molecules the rover detected. Penn State astrobiologist Kate Freeman agrees the new evidence makes that interpretation possible, but...

KATE FREEMAN: It's not standing up and waving a flag saying, I'm life.

PALCA: Freeman isn't ruling out the possibility.

FREEMAN: I don't believe there's life on Mars at the present, although whether there was in the past or not is certainly an open question.

PALCA: In addition to finding organic molecules in the rocks in Gale Crater, rover scientists are reporting another intriguing finding. Chris Webster is a rover scientist at NASA's Jet Propulsion Laboratory. He says the rover has been seeing seasonal changes in the amount of methane in the Martian atmosphere. Methane is another organic molecule. Webster says he and his colleagues think the methane is coming from underground.

CHRIS WEBSTER: It's coming from subsurface reservoirs.

PALCA: So what's making the methane? Is it strictly chemical processes involving rocks alone, or could living or formerly living bacteria have generated the methane?

WEBSTER: We can't tell which one of those.

PALCA: Clearly, there are more questions about Mars that need answering. The rover results appear in the journal Science.

Joe Palca, NPR News. Transcript provided by NPR, Copyright NPR.