Artist's impression of a rotating galaxy
Life around other stars
Is our Solar System special? Probably not. Scientists think that there are planets going around many stars in our galaxy.
Spacecraft such as the NASA-ESA Hubble Space Telescope have found many disks of gas and dust around stars – places where new planets are being born. Since 2009, ESA's Herschel spacecraft has been carrying out the most detailed studies yet of these dust clouds.
More than 400 planets have already been discovered around distant stars. Most of these are giant gas worlds like Jupiter and Saturn. Most of them also orbit very close to their stars – often closer than Mercury is to our Sun.
It is extremely difficult to actually see these small, faint objects. Only a few planets in orbit around distant stars have been imaged by Hubble and other powerful telescopes. We can usually only tell the planets are there by the way they make a nearby star wobble.
In a few cases, we see a dip in the brightness of a star when a large planet moves in front of it. Europe’s CoRoT space telescope has discovered 9 planets as they cross in front of stars. The smallest of these is less than twice the size of Earth and orbits a Sun-like star. Its temperature is so high that it may be covered in lava.
One day, scientists expect to discover small, Earth-like planets around other stars. ESA also hopes to launch future space telescopes to look for signs of life on these planets.