By comparing the observed spectrum before and during transits, the spectrum of the planetary atmosphere can be inferred. In December 2010, a study was published showing the spectrum to be largely featureless over the wavelength range of 750–1000 nm. Because a thick and cloud-free hydrogen-rich atmosphere would have produced detectable spectral features, such an atmosphere appears to be ruled out. Although no clear signs were observed of water vapor or any other molecule, the authors of the study believe the planet may have an atmosphere composed mainly of water vapor. Another possibility is that there may be a thick layer of high clouds, which absorbs the starlight. Further observations are necessary to determine the composition of its atmosphere. Because of the estimated old age of the planetary system and the calculated hydrodynamic escape rate of 9×105 kg s−1, scientists conclude that there has been a significant atmospheric loss during the lifetime of the planet and any current atmosphere cannot be primordial. GJ 1214 b may be cooler than any other known transiting planet prior to the discovery of Kepler-16b in 2011 by the Kepler mission. Its equilibrium temperature is believed to be in the range of , depending on how much of the star's radiation is reflected into space. While very little is known about GJ 1214 b, there has been speculation as to its specific nature and composition. On the basis of planetary models it has been suggested that GJ 1214 b has a relatively thick gaseous envelope. It is possible to propose structures by assuming different compositions, guided by scenarios for the formation and evolution of the planet. GJ 1214 b could be a rocky planet with an outgassed hydrogen-rich atmosphere, a mini-Neptune, or an ocean planet. If it is a waterworld, it could possibly be thought of as a bigger and hotter version of Jupiter's Galilean moon Europa. While no scientist has stated to believe GJ 1214 b is an ocean planet, if GJ 1214 b is assumed to be an ocean planet, i.e. the interior is assumed to be composed primarily of a water core surrounded by more water, proportions of the total mass consistent with the mass and radius are about 25% rock and 75% water, covered by a thick envelope of gases such as hydrogen and helium (c. 0.05%). Water planets could result from inward planetary migration and originate as protoplanets that formed from volatile ice-rich material beyond the snow-line but that never attained masses sufficient to accrete large amounts of H/He nebular gas.