Detecting Extrasolar Moons

Finding planets orbiting other stars is still quite a challenge-- though 300 have been discovered so far. Still, some scientists are already looking at the next step: How might we find extrasolar moons?

The question has a bearing on the search for life. Virtually all exoplanets discovered to date, for example, are huge worlds that could easily have moons of substantial size. They are also mostly "hot Jupiters," orbiting their suns tightly. A giant planet only a bit farther out could have a moon-- a Titan, or even a Mars or an Earth-- that could support life.

Finding exomoons now could be done by building up an infrared picture of an exoplanet. Slowly, a body the size of Earth's Moon might make itself known as its own infrared signature was built up. A better option will come next decade, when NASA puts its space-based planet finders into operation. They will be able to image nearby Earth-sized planets directly, and, therefore, might also be able to directly detect very large moons. They may also be able to observe transits of moons-- that is, moons moving across the disk of their parent planet.