The change in the light of a star as it streams through an exoplanet's atmosphere can reveal details about the air's composition. Different molecules absorb light in distinct ways, resulting in patterns known as spectra that allow scientists to identify what they are. [Gallery: The Strangest Alien Planets]
Now scientists have for the first time analyzed the atmosphere of an exoplanet that, like most such alien worlds, does not pass between its star and Earth.
The planet in question is Tau Boötis b, one of the first exoplanets to be discovered back in 1996 and one of the nearest exoplanets to Earth known, at about 51 light-years away. The world is a "hot Jupiter" — a gas giant orbiting very close to its parent star.
The exoplanet's parent star, Tau Boötis, is easily visible with the naked eye, but the planet is not. Up to now, Tau Boötis b was only detectable through its gravitational pull on the star.
"We were able to study the spectrum of the system in much more detail than has been possible before," study lead author Matteo Brogi, of Leiden Observatory in the Netherlands, said in a statement. "Only about 0.01 percent of the light we see comes from the planet, and the rest from the star, so this was not easy."