On Mars: It's Curiosity's moment to shine, but MAVEN is in the works (+video)

Orbiters currently at Mars have shown that atoms are being stripped from the atmosphere today – swept off as the solar wind, solar storms, and their magnetic fields flow past the planet. During its year-long primary mission, MAVEN will collect data on space weather's influence on Mars' upper atmosphere.

MAVEN also will measure extreme-ultraviolet radiation reaching Mars from the sun. This radiation breaks up molecules in the upper atmosphere, liberating lighter atoms, especially hydrogen, which then can easily be swept into interplanetary space.

Finally, MAVEN will measure the ratios of different forms, or isotopes, of five elements in the upper atmosphere – hydrogen, nitrogen, carbon, oxygen, and argon.

Typically planetary atmospheres are awash with normal hydrogen, the lightest atom, compared with its rarer, heavier sibling, deuterium. On Mars, however, the relative abundance of deuterium in the atmosphere is much higher than anywhere else in the solar system.

"That means that a lot of hydrogen has escaped," Jakosky says, since the heavier deuterium is less likely to leave the planet.

"By understanding something about the escape processes, and by measuring those ratios today, and measuring the ratios as they escape, we can get something that allows us to directly extrapolate back to learn how much of that atom was lost over time," he says.

Curiosity will be a crucial teammate for several kinds of measurements.

For instance, one of the rover's main instruments – known as SAM – will provide high-precision measurements of the atmosphere's composition at the surface, in addition to its analysis of soil and rock samples. Indeed, Jakosky is on the team that will analyze and interpret SAM data. SAM's information on the atmosphere at ground level, combined with similar, top-of-the-atmosphere measurements from MAVEN, will directly gauge the amounts and types of elements that Mars' atmosphere loses over time.

Once MAVEN ends its science mission, it will serve as a communications relay between spacecraft on the Martian surface and Earth. The US and European orbiters at Mars are getting a bit long in the tooth.

So far, the project, approved in 2008, is proceeding a bit ahead of schedule and on budget, notes David Mitchell, MAVEN project manager at NASA's Goddard Space Flight Center in Greenbelt, Md. If it makes its 20-day launch window next year, Maven would arrive in 2014.

"We're all so excited to see Curiosity on the ground there safely," he says. "I'm not a scientist, but I'm really excited to see what happens with the synergism" between Curiosity, MAVEN, the still-roving Mars veteran Opportunity, and other missions, he says.

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