The search for a far-off twin of Earth has turned up two of the most intriguing candidates yet.
Scientists say these new worlds are the right size and distance from their parent star, so that you might expect to find liquid water on their surface.
It is impossible to know for sure. Being 1,200 light-years away, they are beyond detailed inspection by current telescope technology.
But researchers tell Science magazine, they are an exciting discovery.
“They are the best candidates found to date for habitable planets,” stated Bill Borucki, who leads the team working on the US space agency Nasa’s orbiting Kepler telescope.
The prolific observatory has so far confirmed the existence of more than 100 new worlds beyond our Solar System since its launch in 2009.
The two now being highlighted were actually found in a group of five planets circling a star that is slightly smaller, cooler and older than our own Sun. Called Kepler-62, this star is located in the Constellation Lyra.
Its two outermost worlds go by the names Kepler-62e and Kepler-62f.
They are what one might term “super-Earths” because their dimensions are somewhat larger than our home planet – about one-and-a-half-times the Earth’s diameter.
Nonetheless, their size, the researchers say, still suggests that they are either rocky, like Earth, or composed mostly of ice. Certainly, they would appear to be too small to be gaseous worlds, like a Neptune or a Jupiter.
Many assumptions
Planets 62e and 62f also happen to sit a sufficient distance from their host star that they receive a very tolerable amount of energy. They are neither too hot, nor too cold; a region of space around a star sometimes referred to as the “Goldilocks Zone”.