NASA’S MAVEN SPACECRAFT entered orbit around Mars for an unprecedented study of the red planet’s atmosphere following a 442 million-mile journey that began nearly a year ago.

The robotic explorer successfully slipped into orbit around the red planet late Sunday night.

“I think my heart’s about ready to start again,” Maven’s chief investigator, Bruce Jakosky of the University of Colorado, said early Monday. “All I can say at this point is, ‘We’re in orbit at Mars, guys!’”

Now the real work begins for the $671 million mission, the first dedicated to studying the Martian upper atmosphere and the latest step in NASA’s bid to send astronauts to Mars in the 2030s.

Flight controllers in Colorado will spend the next six weeks adjusting Maven’s altitude and checking its science instruments, and observing a comet streaking by at relatively close range. Then in early November, Maven will start probing the upper atmosphere of Mars. The spacecraft will conduct its observations from orbit; it’s not meant to land.

Scientists believe the Martian atmosphere holds clues as to how Earth’s neighbor went from being warm and wet billions of years ago to cold and dry. That early wet world may have harbored microbial life, a tantalizing question yet to be answered.

NASA launched Maven last November from Cape Canaveral, the 10th U.S. mission sent to orbit the red planet. Three earlier ones failed, and until the official word came of success late Sunday night, the entire team was on edge.

“I don’t have any fingernails any more, but we’ve made it,” said Colleen Hartman, deputy director for science at Goddard Space Flight Center in Greenbelt, Maryland. “It’s incredible.”

The spacecraft was clocking more than 10,000 mph when it hit the brakes for the so-called orbital insertion, a half-hour process. The world had to wait 12 minutes to learn the outcome, once it occurred, because of the lag in spacecraft signals given the 138 million miles between the two planets Sunday.

“Wow, what a night. You get one shot with Mars orbit insertion, and Maven nailed it tonight,” said NASA project manager David Mitchell.

Maven joins three spacecraft already circling Mars, two American and one European. And the traffic jam isn’t over: India’s first interplanetary probe, Mangalyaan, will reach Mars in two days and also aim for orbit. Jakosky wished the team well.

Jakosky, who’s with the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder, hopes to learn where all the water on Mars went, along with the carbon dioxide that once comprised an atmosphere thick enough to hold moist clouds.

The gases may have been stripped away by the sun early in Mars’ existence, escaping into the upper atmosphere and out into space. Maven’s observations should be able to extrapolate back in time, Jakosky said.

Maven will spend at least a year collecting data. That’s a full Earth year, half a Martian one. Its orbit will dip as low as 78 miles above the Martian surface as its eight instruments make measurements. The craft is as long as a school bus, from solar wingtip to tip, and as hefty as an SUV.

Maven will have a rare brush with a comet next month as Comet Siding Spring pass 82,000 miles from Mars

This is NASA’s 21st shot at Mars and the first since the Curiosity rover landed on the red planet in 2012.

Read: ‘It’s not like Star Trek’: This is a big weekend for NASA’s plans to land a human on Mars >

Read: ‘It’s not like Star Trek’: This is a big weekend for NASA’s plans to land a human on MarsHere’s why you really should be following the International Space Station online >