PARIS • Researchers announced on Wednesday the stunning discovery of seven Earth-like planets orbiting a small star in Earth's galaxy, opening up the most promising hunting ground so far for life beyond the solar system.
All seven roughly match the size and mass of Earth and are almost certainly rocky, and three are perfectly perched to harbour life-nurturing oceans of water, the researchers reported in Nature journal.
Most critically, the planets' proximity to Earth and the dimness of their red dwarf star, called Trappist-1, will allow astronomers to parse each one's atmosphere in search of chemical signatures of biological activity.
"We have made a crucial step towards finding life out there," said co-author Amaury Triaud, a scientist at the University of Cambridge.
"Up to now, I don't think we have had the right planets to find out," he added at a press briefing.
RIGHT PLACE TO LOOK
We have made a crucial step towards finding life out there... Up to now, I don't think we have had the right planets to find out. Now, we have the right target.
CO-AUTHOR AMAURY TRIAUD, a scientist at the University of Cambridge.
"Now, we have the right target."
The Trappist-1 system, a mere 39 light years distant (368 trillion km), has the largest number of Earth- sized planets known to orbit a single star. It also has the most within the so-called "temperate zone" - not so hot that water evaporates, nor so cold that it freezes rock-solid.
The discovery adds to growing evidence that Earth's galaxy, the Milky Way, may be populated with tens of billions of worlds not unlike Earth's - far more than previously suspected. Remarkably, professional stargazers may simply have been looking in the wrong place.
Said lead author Michael Gillon, a professor at the University of Liege in Belgium: "The great idea of this approach was to study planets around the smallest stars of the galaxy, and close to us.
"That is something nobody did before us - most astronomers were focused on stars like our Sun."
Dr Gillon and his team began to track Trappist-1 - a dwarf star with less than 10 per cent the mass of the Sun - with a dedicated telescope in 2010, and reported last year on three planets in its orbit.
They detected the invisible exoplanets using the so-called "transit method": When an orbiting world passes between a star and an astronomer peering through a telescope, it dims the starlight by a tiny but measurable amount.
But when subsequent calculations did not tally, Dr Gillon realised there might be other stars that had escaped Earth-bound observation.
"So we requested time with Nasa's Spitzer Space Telescope," said co-author Emmanuel Jehin of the University of Liege.
"This allowed us to get 20 consecutive 24-hour periods of observation, which was crucial to discovering that we had seven transiting planets."