We will (or should) remember the planet GJ1214b if it is, in fact, the first planet we have discovered outside of our solar system to definitely have water. Is it an ‘Earth-like’ planet? No, not really. It has been measured as 2.7 times the size of Earth and 6.5 times the mass. That makes it about half-way in size between Earth and the ice giants in our system (Neptune and Uranus). It has been given the tag: super-Earth. This may, or may not be apropos.
GJ1214b was discovered during the work of the MEarth project, the current champ of small planet hunting. MEarth uses the eight 16 inch telescope array at Mount Hopkins (Arizona, USA). This time, the planet is almost ‘in the neighborhood’ – only 40 light years away in the constellation Ophiuchus. It was visible during a transit in front of the dim red star GJ1214 (M class dwarf). As one of the smaller planets yet found, the MEarth observation was confirmed using the full precision of the HARPS spectrograph, attached to ESO’s (European Southern Observatory) 3.6-metre telescope at La Silla, Chile.
Astronomers believe GJ1214b has water by inference. Compared to another recently discovered planet, Corot-7b, GJ1214b is considerably larger but much less dense. It has been thought that Corot-7b is a rocky or iron-cored planet, which would mean GJ1214b could be a larger but less dense frozen-water (ice) planet. The planet also has a size-profile much larger than predicted by a model of exoplanets, which led astronomers to believe that much of what was blocking the sun’s light during transit was a water-vapor atmosphere. As yet there is no directly measured confirmation for water.
Although GJ1214b may have water, astronomers believe that it is too close to its sun, about 70 times closer than Earth is to our Sun, to retain water for long. It’s also not a good place to find life.
When the astronomers compared the measured radius of GJ1214b with theoretical models of planets, they found that the observed radius exceeds the models’ predictions: there is something more than the planet’s solid surface blocking the star’s light — a surrounding atmosphere, 200 km thick. “This atmosphere is much thicker than that of the Earth, so the high pressure and absence of light would rule out life as we know it,” says Charbonneau, “but these conditions are still very interesting, as they could allow for some complex chemistry to take place.”
It’s also possible that instead of a water vapor atmosphere, GJ1214b has a denser core and a thinner gas atmosphere. We should soon learn more. GJ1214b is close enough to Earth that ground-based telescopes – even amateur – can see it. However, it will probably be the Hubble telescope that gets the best shots of it. As only the second ‘super-Earth’ planet yet discovered, it’s a good bet that in the coming year (or two) we’re in for finding a lot more; and a true water-planet would not be surprising.