Two ‘Earth-like’ planets among eight found that could hold life

Eight more planets have been discovered that could possess watery oceans and sustain life, including two of the most Earth-like yet found.

The discovery of the new worlds doubles the number of small exo-planets believed to be circling their stars in the “habitable zone”, the narrow region in which temperatures are mild enough to allow liquid surface water.

By small, astronomers mean planets with less than twice Earth’s diameter.

"Most of these planets have a good chance of being rocky, like Earth," said lead scientist Dr Guillermo Torres, from the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts.

The two most Earth-like planets, known as Kepler-438b and Kepler-442b, both orbit red dwarf stars that are smaller and cooler than the sun.

With a diameter just 12 per cent bigger than Earth’s, Kepler-438b has a 70 per cent chance of being rocky, scientists calculate. Kepler-442b is about a third larger than Earth, and the likelihood of it being rocky is about 60 per cent.

To be in the habitable zone, also known as the “Goldilocks zone”, a planet must be not too hot or too cold and must receive roughly as much sunlight as Earth.Too much heat from its star, and any water would boil away as steam. Too little, and the water would freeze solid.

“For our calculations we chose to adopt the broadest possible limits that can plausibly lead to suitable conditions for life,” Dr Torres said.

Kepler-438b receives about 40 per cent more light than Earth, giving it a 70 per cent probability of having a habitable zone orbit. In comparison, baking-hot Venus has twice as much. Kepler-442b gets about two-thirds as much light as Earth and is 97 per cent likely to be in the habitable zone.

Dr David Kipping, also from the Centre for Astrophysics, said: "We don't know for sure whether any of the planets in our sample are truly habitable. All we can say is that they're promising candidates."

The planets are not our close neighbours. Kepler-438b is 470 light years from Earth, and Kepler-442b more distant still.

The team studied planetary candidates first identified by US space agency Nasa’s Kepler space telescope. All the planets were too small to confirm by measuring their masses. Instead, they were validated using a computer program that determined their likeliness to be planets. After the analysis, follow-up observations showed that four of the planets were in multiple star systems. The research is published in the Astrophysical Journal.

– (PA)