NASA's Maven spacecraft has entered orbit around Mars, completing a journey that lasted nearly a year and covered 442 million miles.

NASA said late Sunday that the robotic explorer had fired its brakes and slipped into orbit, successfully completing the first part of its $671 million mission.

"This is such an incredible night," John Grunsfeld, NASA's chief for science missions, told The Associated Press.

Flight controllers will spend the next six weeks adjusting Maven's altitude and checking its science instruments. Then Maven will start probing the planet's upper atmosphere. 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 moist world may have harbored microbial life, a tantalizing question yet to be answered.

The spacecraft was launched from Cape Canaveral this past November, making it 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."

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