This illustration compares the sizes of exoplanets GJ 436b and GJ 1214b with Earth and Neptune. These so-called super-Earths have masses between gas giants, like Neptune, and smaller, rocky planets, like Earth. No such type of planet exists in our solar system. NASA Hubble Space Telescope spectroscopic observations reveal that these worlds could very likely be smothered in clouds that cloak any information about the planets' underlying chemical compositions. This artistic rendering of the exoplanets is speculative and does not necessarily reflect what their true appearance might actually be.