The search for 'Earth 2.0' – another watery planet with life – has come a step closer with the discovery of 715 planets orbiting stars beyond our own solar system, NASA scientists have said.
Four of the new planets lie within the habitable 'Goldilocks' zone of their own suns, meaning they orbit at a distance that is neither too hot nor too cold for water to exist in liquid form – considered to be an essential precondition for life to exist.
The latest results from NASA's programme to find "exoplanets" lend further support to the idea that the Milky Way – which is just one galaxy of many billions – is teeming with planets, many of which are similar to our own.
Scientists identified the new planets using a new statistical method to analyse data gathered by the €438m Kepler telescope, which was launched in 2009. This has almost overnight boosted the total number of confirmed exoplanets in the Milky Way to about 1,700 – with another 3,500 candidate planets waiting to be confirmed. The total number of habitable exoplanets has now reached nine.
The very first extra-solar planet was identified about 20 years ago and since then, there has been a revolution in the way that astronomers can identify the tiny perturbations in starlight they create as they orbit their own stars.
"We almost doubled just today the number of planets known to humanity," said planetary scientist Jack Lissauer of NASA's Ames Research Centre in Moffett Field, California, who led the study of the Kepler data. "We've now developed a process to verify multiple planet candidates in bulk to deliver planets wholesale, and have used it to unveil a veritable bonanza of new worlds.
"These results are based on the first two years of Kepler observations and with each additional year, we'll be able to bring in a few hundred more."
The four potentially habitable planets within the new batch are all less than 2.5 times the size of Earth and orbit at the right distance from their suns to allow water to exist in liquid form – although it is impossible to know yet whether they really do have water, let alone life. Nasa said that one of these planets, called Kepler-296f, orbits a star that is half the size and 5pc as bright as our own Sun. It is twice the size of Earth, but it may be a gaseous world with a thick hydrogen-helium envelope, or a water world with a deep ocean.
The 715 new exoplanets were found by analysing the light patterns of 305 stars, meaning that they exist in multi-planet solar systems similar to our own. All the planets were closer in size to the Earth than to gas giants like Jupiter where life is considered less likely than on a small, rocky planet.
The Kepler telescope, which is now crippled, gathered vast amounts of data for scientists to analyse before it went defunct. The latest study used a technique called "verification by multiplicity" which gets round the problem of trying to verify planets on a planet-by-planet basis. Douglas Hudgins, an exploration programme scientist at Nasa, said that the latest study was a significant step towards the ultimate goal of finding Earth 2.0. (© Independent, News Service)