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40 Light Years Away, Scientists Find Three Earth-Sized Planets Orbiting Small Nearby Sun

Two of the three planets are in the "habitable zone," meaning they could have signs of life and water

An international team of astrophysicists have discovered three Earth-sized planets orbiting near the habitable zone of a dwarf star only 40 light years away from our Earth.

The nearby discovery, detailed in the latest edition of Nature, means astronomers will one day be able to study the composition of the planets and their atmospheres in search for chemical signs of life.

“The kind of planets we've found are very exciting from the perspective of searching for life in the universe beyond Earth,” said Adam Burgasser, a professor of physics at UC San Diego’s Center for Astrophysics and Space Sciences and a key participant of the international team, in a statement.

UC San Diego (UCSD) astrophysicists worked with team members from across the globe in Chile, tracking the star’s light moment-to-moment over the course of 62 nights last September to December. Scientists used a TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) at the La Silla Observatory is Chile.

When astrophysicists look another look using larger telescopes, they found the planets orbiting the ultracool dwarf star were similarly sized to Earth.

Two of the planets have orbital periods of approximately 1.5 days and 2.4 days respectively. The third planet has an orbital period between 4.5 and 73 days.

“With such short orbital periods, the planets are between 20 and 100 times closer to their star than the Earth to the Sun,” said Gillon in a statement. “The structure of this planetary system is much more similar in scale to the system of Jupiter’s moons than to that of the Solar System.”

The star in the system, TRAPPIST-1, is cool, red, dim and so small it is invisible to most telescopes. The star is a little larger than Jupiter in diameter and half the temperature of our sun.

"While such a ‘cold’ star might sound exotic, many, if not most, of the stars in our Milky Way Galaxy are of this cool, red, small and dim variety,” Burgasser said. “If Earth-like planets around these stars turn out to be common, there may be many more habitable planets out there than current estimates predict.”

The inner planets may have rocky surfaces and, because of their close orbit to their star, only receive four times and twice, respectively, the amount of radiation received by Earth. They lie just inside the habitable zone, an orbital distance where surface water and life is likely. The outer planet may still lie within the habitable zone, but scientists do not know enough about its orbit yet.

“Fortunately, we may be able to answer these questions in the near future, as the geometry of the system makes it likely that we will be able to detect the atmospheric gases of these planets in the next decade with the launch of the James Webb Space Telescope,” Burgasser said. “This facility will allow us to search for biogenic gases--oxygen or methane for example--that would firmly indicate the presence of life, or search for other gas species that would tell us about the planets' compositions, geothermal activity and evolutionary history.”

The team is led by Michael Gilleon of the University of Liege, Belgium. It involves researchers at UCSD, MIT, NASA’s Johnson Space Center in Houston, Cavendish Laboratory in Cambridge, England, and the Indian Institute of Astrophysics in Bangalore, India.

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