This artist's conception shows a hypothetical gas giant planet with an Earth-like moon similar to the moon Pandora in the movie Avatar. New research shows that, if we find such an "exomoon" in the habitable zone of a nearby star, the James Webb Space Telescope will be able to study its atmosphere and detect key gases like carbon dioxide, oxygen, and water. The key is to find a planet that transits its star, and then find a moon orbiting that planet more than one stellar radius away, so that the moon can be studied independently of the planet. Moreover, an alien moon orbiting the gas giant planet of a red dwarf star may be more likely to be habitable than tidally locked Earth-sized planets or super-Earths. (Credit: David A. Aguilar, CfA)

ScienceDaily (Dec. 18, 2009) — In the new blockbuster Avatar, humans visit the habitable — and inhabited — alien moon called Pandora. Life-bearing moons like Pandora or the Star Wars forest moon of Endor are a staple of science fiction. With NASA's Kepler mission showing the potential to detect Earth-sized objects, habitable moons may soon become science fact.

If we find them nearby, a new paper by Smithsonian astronomer Lisa Kaltenegger shows that the James Webb Space Telescope (JWST) will be able to study their atmospheres and detect key gases like carbon dioxide, oxygen, and water vapor.

"If Pandora existed, we potentially could detect it and study its atmosphere in the next decade," said Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics (CfA).

So far, planet searches have spotted hundreds of Jupiter-sized objects in a range of orbits. Gas giants, while easier to detect, could not serve as homes for life as we know it. However, scientists have speculated whether a rocky moon orbiting a gas giant could be life-friendly, if that planet orbited within the star's habitable zone (the region warm enough for liquid water to exist).

"All of the gas giant planets in our solar system have rocky and icy moons," said Kaltenegger. "That raises the possibility that alien Jupiters will also have moons. Some of those may be Earth-sized and able to hold onto an atmosphere."

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