NASA is back at Mars with the MAVEN spacecraft

In this artist concept provided by NASA, the MAVEN spacecraft approaches Mars on a mission to study its upper atmosphere. When it arrives on Sunday Sept. 21, 2014, MAVEN's 442 million mile journey from Earth will culminate with a dramatic engine burn, pulling the spacecraft into an elliptical orbit. It's designed to circle the planet, not land.

The Maven spacecraft arrived at the red planet late Sunday night after a 442 million-mile journey that began nearly a year ago.

NASA confirmed that the robotic explorer slipped into Martian orbit as planned.

Now the real work begins for the $671 million mission.

In this Friday, Sept. 27, 2013 file photo, technicians work on NASA’s next Mars-bound spacecraft, the Mars Atmosphere and Volatile Evolution (MAVEN), at the Kennedy Space Center in Cape Canaveral, Fla. NASA’s Maven spacecraft will reach the red planet in September 2014 following a 10-month journey spanning more than 440 million miles. If all goes well, Maven will hit the brakes and slip into Martian orbit Sunday, Sept. 21, 2014

Flight controllers will spend the next six weeks adjusting Maven's altitude and checking its science instruments. Then Maven will start probing the Martian 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.