Extra Solar Planets
Gliese 1214 is a faint red dwarf star of type M4.5. It is about 42 light years from Earth, and is about 21% the diameter and 16% the mass of the Sun. It is thought to be a little older than the Sun at around 6 billion years, but will survive for much longer due to its low mass.
The MEarth Project observed a slight dimming of the star GJ1214 in early 2009. Following up with more detailed observations showed the star dimming very slightly once every 1.58 days. Because the star system is close to us, and the planet passes directly in front of the star as it orbits, astronomers are able to study and analyze the atmosphere of the planet using spectroscopy.
The planet is about 2.7 times the diameter of the Earth but with only between about 5.6 to 7.5 times its mass. One suggestion for the low density is that the planet comprises mainly water; about 25% rock to 75% water, in fact. Recent observations by the Hubble Space Telescope indicate that this may well be the case.
The planet orbits very close to its parent star, at a distance of about 2.14 million km (1.33 million miles) once every 38 hours or so. Being so close to its primary means that the surface temperature is in the region of 520K (247°C or 477°F) resulting in it having an incredibly damp atmosphere.