Moons, rather than planets, could star in the first images of habitable worlds outside our solar system. Once taken, such images would offer unprecedented clues to the moons' ability to support life by providing the chemical signatures carried in their light.
"If we can direct-image them, we can take their spectra, which means we can determine what sort of molecules are in their atmosphere," says Mary Anne Peters of Princeton University.
So far, more than 800 planets outside our solar system, or exoplanets, have been found using indirect methods, such as picking up the dimming of a star's light when a planet passes in front of it. But spectra from rocky planets similar in size to Earth have been tough to collect with these methods. The planetary photo album is even slimmer: only 4 systems have been imaged
.
One challenge is that stars are bright whereas planets are dim, so a planet has to be far enough from its star to avoid being outshined. That means those worlds that have been imaged orbit outside the habitable zone, the region around a star that's warm enough for liquid water. Also, planets shining bright enough to appear in pictures must be glowing from the heat of formation and so are too young to host life.
To read more, click here.