Researchers Reveal How Climate Change Killed Mars : The Two-Way Mars used to be much warmer and wetter than it is today. Scientists are unraveling the mystery of why it dried out.

Researchers Reveal How Climate Change Killed Mars

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KELLY MCEVERS, HOST:

There's some new research out today about climate change. Not on Earth, but on Mars. At one time Mars was warm and wet, and scientists have been trying to figure out why it dried out. NPR's Geoff Brumfiel reports on the mystery that's being unraveled.

GEOFF BRUMFIEL, BYLINE: Back in the day, about 3.8 billion years ago, Mars was actually a reasonably pleasant place. It had a thick atmosphere filled with carbon dioxide that kept it warm. Rivers trickled into lakes across its surface. Some researchers think there might've even been an ocean.

BRUCE JAKOSKY: It seemed to have been a much more clement climate, a climate more suitable to perhaps sustaining life at the surface.

BRUMFIEL: Bruce Jakosky is a researcher at the University of Colorado at Boulder. Nobody knows if there was life on Mars back then but today it's a hostile place. The water's mostly gone. So is a lot of that cozy atmosphere. Jakosky and other scientists are trying to figure out what went wrong. And to help, they've sent a spacecraft to Mars called MAVEN.

JAKOSKY: MAVEN is the Mars Atmosphere and Volatile Evolution Mission.

BRUMFIEL: With each swing around Mars, MAVEN actually dips into the atmosphere gathering data. The results are published today in two journals, Geophysical Research Letters, and Science. They reveal something remarkable.

JAKOSKY: What we're seeing is that the Mars atmosphere is escaping to space today. It's leaving at a rate of about a hundred grams per second. That doesn't seem like much, but you add it up over a couple of billion years, and it's enough to remove the entire atmosphere.

BRUMFIEL: And it's leaving for a surprising reason - the sun. Our friendly neighborhood star is constantly shooting out high-energy particles. It's called the solar wind, though wind doesn't really do it justice.

JAKOSKY: It streams outward as a gas flow at about a million miles an hour.

BRUMFIEL: When the solar wind reaches Mars, it strips away the atmosphere. Now, if the solar wind can do this to Mars, you might be wondering, uh-oh, is Earth at risk? The answer, fortunately, is no because Earth has a magnetic field.

(SOUNDBITE OF PARTICLES IN SPACE)

BRUMFIEL: That's the sound of particles in the solar wind getting trapped in our planet's field. It protects the atmosphere from destruction. Back when Mars was warm and wet, it had a magnetic field too, but that field ran out. That's when the atmosphere began to bleed into space. The water probably followed.

JAKOSKY: It would've taken a couple of hundred-million years.

BRUMFIEL: Mike Liemohn, a planetary scientist at the University of Michigan, says this new MAVEN data firms up the long standing theory about what happened to Mars.

MIKE LIEMOHN: I think that we are onto something new here with the MAVEN results.

BRUMFIEL: But Liemohn says there are still plenty of questions about why Mars's atmosphere disappeared. Did a comet or asteroid impact blow part of it away? Did rocks on the surface suck up vital gases? Perhaps most important of all, what happened to Mars's magnetic field? MAVEN continues to orbit, looking for answers. Geoff Brumfiel, NPR News.

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