MAVEN spacecraft enters Mars orbit to explore its climate change

                                                            STORY HIGHLIGHTS

• MAVEN won't land on the surface but study Mars' atmosphere from its orbit
• Why did ancient Mars change so dramatically? MAVEN sent to get answers
• MAVEN stands for Mars Atmosphere and Volatile Evolution craft
• Mars will be having plenty of other visitors: a spacecraft from India and a comet

(CNN) -- MAVEN has arrived in Mars's orbit after traveling 442 million miles in the course of 10 months to get there.

It won't land on the red planet but instead study Mars' atmosphere from above to answer questions about its climate change, NASA says.

NASA's MAVEN craft will live up to its formal name -- the Mars Atmosphere and Volatile Evolution craft -- by helping scientists figure out how ancient Mars changed so dramatically into the planet we know today.

It is the first mission devoted to studying the upper Martian atmosphere as a key to understanding the history of Mars' climate, water and habitability.

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"The evidence shows that the Mars atmosphere today is a cold, dry environment, one where liquid water really can't exist in a stable state," said Bruce Jakosky, MAVEN principal investigator, during a mission preview briefing last week at NASA headquarters in Washington. "But it also tells us when we look at older surfaces, that the ancient surfaces had liquid water flowing over it."

MAVEN to study Mars from above

 Photos: Mars MAVEN mission

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So where did the planet's water and carbon dioxide go?

Jakosky said MAVEN will help unravel that mystery by using its scientific instruments to measure the composition and escape of gases in the Martian atmosphere.

MAVEN is to study the top of the atmosphere to determine the extent to which losing gas to space might have been the driving mechanism behind climate change, Jakosky said.

MAVEN has company out near Mars, man-made and otherwise.

India's first mission to the Red Planet, the Mars Orbiter Mission, is set to arrive a few days after MAVEN does. The director of NASA's Planetary Science Division, Jim Green, says the United States and India are interested in cooperating as their crafts gather data about the planet.

There's a visitor of the cosmic kind, too.

Comet Sliding Spring, which was discovered last year, will be closest to Mars about four weeks after MAVEN arrives.

The comet is going to miss Mars by about 81,000 miles, said Jakosky.

"I'm told that the odds of having an approach that close to Mars are about one-in-a-million years," he said, adding that dust from the comet carries only a "relatively minimal" risk to the spacecraft.

MAVEN will take advantage of the rare flyby by observing the comet itself, as well as its effect on the Martian atmosphere.