Last week, NASA's Mars Atmosphere and Volatile Evoluton (Maven) spacecraft successfully entered orbit around Mars. Now, the agency is releasing the first photos taken by the spacecraft of the planet's upper atmosphere.

Maven took these images with its ultraviolet spectrograph instrument from about 22,000 miles above the planet's surface after about its first eight hours in Mars' orbit. These images are "false-color" photos showing Mars' atmosphere within three ultraviolet wavelength bands.

"Blue shows the ultraviolet light from the sun scattered from atomic hydrogen gas in an extended cloud that goes to thousands of kilometers above the planet's surface,"  writes NASA. "Green shows a different wavelength of ultraviolet light that is primarily sunlight reflected off of atomic oxygen, showing the smaller oxygen cloud. Red shows ultraviolet sunlight reflected from the planet's surface; the bright spot in the lower right is light reflected either from polar ice or clouds."

These photos show how Mars' gravity holds oxygen close to the planet, while hydrogen, which weighs less, is farther away in the atmosphere. These gases are the result of water and carbon dioxide breaking down.

Maven is the first spacecraft in Mars' orbit with the mission of examining its upper atmosphere. Data from Maven's three scientific instrument packages will give scientists an idea of how much water once existed on the planet and provide details about not just Mars' atmosphere, but also its climate and whether it was ever habitable.

Over the next six weeks, Maven will test those scientific instruments, while controllers on Earth position it for its primary mission. From there, Maven's one-year mission begins, including a small dive that will allow measurements of the layers that make up the planet's atmosphere.

"Maven's orbit through the tenuous top of the atmosphere will be unique among Mars missions," says Bruce Jakosky, principal investigator for Maven at the University of Colorado in Boulder. "We'll get a new perspective on the planet and the history of the Martian climate, liquid water and planetary habitability by microbes."

Maven isn't alone in orbit around the red planet. It joined NASA's Mars Odyssey and Mars Reconnaissance Orbiter and the European Space Agency's Mars Express. India's Mars Orbiter Mission also recently joined the group, after a successful entry into the planet's orbit this week.

On the ground, NASA's Opportunity and Curiosity are studying the composition of the planet's surface.