NASA’s Kepler mission was launched five years ago and has revolutionised our view of exoplanets, finding planets of all sizes and compositions.
The most numerous size of exoplanet seems to be between two to four times the radius of Earth, a planet size we do not have in our Solar System. Therefore we know little about this type of planet, how it forms and what it’s made of.
Other planets discovered have sizes larger than Earth with the density of styrofoam or in the case of two small planets just slightly larger than Earth orbiting the same star but with densities a factor of eight apart. There is even a disintegrating exoplanet, orbiting close to its host star and being evaporated. Discovery is forever dawning, so I’d be amiss to say we will not find new types of exoplanets.
Answered by Steve Howell, Kepler Space Telescope Project Scientist
Image Credit: NASA