The team speculates that the planet is covered with water, although the system is too far away to take the measurements needed to estimate the planet's mass. Researchers need that measurement to determine the planet's density, a major clue as to its bulk composition.
Instead, modeling studies have indicated that planets ranging from 1.5 to two times Earth's size tend to be far more watery than planets closer to Earth's size. Thus, while the nature of the planet remains speculative for now, "the fascinating idea is that we've actually found the first ocean planet, the first water world out there," said Lisa Kaltenegger, an astronomer with the Max Planck Institute for Astronomy in Germany and the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., during a mission briefing Thursday afternoon.
(Sorry "Waterworld" fans, no post-apocalyptic planet here. It was born that way.)
The system's age is of no small interest. Assuming that the two planets are indeed habitable and that their stellar system has been at least as kind to them as the solar system has been to Earth over its 4.5 billion-year history, 7 billion years in principle is plenty of time for life to emerge and evolve into ever-more-complex forms.
The second of the new habitable-zone planets is the fifth, most distant planet yet detected in the Kepler 62 system. It orbits Kepler 62 once every 267 days. The planet, Kepler 62-f, is about 40 percent larger than Earth.
Here, too, the team has no true mass estimate. The researchers have inferred the planet's composition based on studies of other extra-solar planets of comparable size for which mass estimates exist. Those planets are rocky.
While it falls within its star's habitable zone, 62-f would have to build up an overabundance of carbon dioxide to provide enough of an atmospheric greenhouse effect to warm the planet's surface.