(AP Photo/NASA)
(AP Photo/NASA)

It's not the first space probe to Mars but it may be the most critical. A NASA craft, prepares to go to work.

FOX News Radio's Bill Vitka reports: 

It took 442 million miles -- but a new NASA spacecraft has finally reached its destination.

(Jakosky) "All I can say at this point is, we're in orbit at Mars, guys." 

NASA's Bruce Jakosky.

The spacecraft is called Maven -- and its mission is to study the mystery of what happened to the planet's air.

Denser atmosphere would be needed for there to be water on Mars. While there's no water today, Mars is covered with river channels, lake beds and evidence of a warmer, wetter past.

The answer to the question of where the air went may help answer the question of where the water went.

Bill Vitka, FOX News Radio.

(AP Photo/John Raoux, File)
(AP Photo/John Raoux, File)

NASA's Maven spacecraft has arrived at Mars.

Flight Program Manager Guy Beutelschies (BOY-tell-SHEE's) says the mission was incredibly complex: