A team of astronomers have recently published results of observations made by Hubble of the exoplanet GJ 1214b. They didn’t discover the planet: that honour belongs to the MEarth project, which uses robotic telescopes to survey nearby M dwarf stars in search of new Earth-like exoplanets. This project spotted GJ 1214b back in 2009. What’s new is that a Hubble was used to observer the planet during transit: because the star’s light is filtered through the planet’s atmosphere, astronomers can infer what gases might be present. The best fit to the Hubble data is that GJ 1214b has a dense atmosphere of water vapour.
Various observations allow astronomers to pin down the planet’s mass, size and orbital parameters. It turns out that GJ 1214b has a radius 2.7 times that of Earth’s and a mass 6.5 times that of Earth’s, which means its average density is about twice that of water. In comparison, Earth’s average density is 5.5 times that of water. In other words, GJ 1214b holds much more water than does Earth. It’s a true waterworld.
Water … so does that mean GJ 1214b could be home to life? Well that’s unlikely, because the planet orbits just two million kilometres away from its red-dwarf star. It’s temperature will be about 230°C. However, theories of planet formation suggest that GJ 1214b will have formed at a large distance from its star and then subsequently migrated to its current position. It therefore must have passed through the habitable zone.
There might not be life there now, but it’s possible – just possible – that life may have been there once.