Astronomers have discovered about 80 planets outside our own solar system. These planets orbiting stars other than our own Sun are called extra-solar planets. Now astronomers have, for the first time, detected an atmosphere on one of these alien worlds.

This planet is 900 quadrillion miles away, 250,000 times farther away than Pluto, so it can't be seen from Earth. But we know it's there because it exerts a tiny gravitational tug on its star. This planet is unique among extra-solar planets because as it orbits its star, the planet passes in front of the star, as viewed from Earth. When this so-called "transit" occurs, the star dims very very slightly, and by analyzing this filtered starlight, it's possible to detect not only that the planet has an atmosphere, but also some of the gases in it.

This observing technique opens a new phase in the exploration of extra-solar planets. It could potentially provide the first direct evidence for life beyond Earth, because living organisms often leave their mark in a planet's atmosphere.