Are Super-Earths Actually Mini-Neptunes?

In the last two decades astronomers have found hundreds of planets in orbit around other stars. One type of these so-called 'exoplanets' is the super-Earths that are thought to have a high proportion of rock but at the same time are significantly bigger than our own world. Now a new study led by Helmut Lammer of the Space Research Institute (IWF) of the Austrian Academy of Sciences suggests that these planets are actually surrounded by extended hydrogen-rich envelopes and that they are unlikely to ever become Earth-like. Rather than being super-Earths, these worlds are more like mini-Neptunes.