Astronomers have discovered three Earth-sized planets orbiting a small red sun, just 40 light-years away. Researchers say all three worlds are potentially habitable and could represent the best targets yet in the search for life beyond the solar system.”These are not massive, hot, super exotic worlds,” said Julien de Wit, a postdoctoral associate in planetary science at MIT who worked on the study describing the find. “All three of them are close to one Earth (radius), and each of them could be suitable for life.” The system’s host star, called TRAPPIST-1, is what is known as an ultracool dwarf. It is about one-tenth the size of our sun and just a bit bigger than Jupiter.
Its two innermost planets orbit extremely close to the star, taking just 1.5 and 2.4 Earth days respectively to complete a turn around the ultracool dwarf. The third planet’s orbital period is less certain: Current observations suggest its orbital period could range anywhere from 4 to 73 days. The star is just .05 per cent as bright as our sun, but scientists say it could still give off enough radiation to warm all three planets such that liquid water could exist on their surfaces. A planet that is neither too hot nor too cold to sustain liquid water on its surface is generally considered to have the potential for life. Ultracool dwarfs make up about 15 per cent of the astronomical objects in our immediate neighbourhood, but until now, no one had ever discovered a planet orbiting one. That’s probably because no one was looking, De Wit said. Most exoplanet searches, like those involving NASA’s Kepler telescope, target hotter, bigger stars. For a while, there was some debate in the astronomy community about whether it was possible for planets to form around such tiny and dim stars. “The team took a big risk even looking for planets around these stars,” De Wit said. “But it has really paid off.” The research, published Monday in the journal Nature, was led by Michael Gillon and Emmanuel Jehin of the University of Liege in Belgium. The scientists say the discovery provides a unique opportunity to look for signs of life on the three Earth-sized planets that would not be possible if the bodies were orbiting brighter stars. “Systems around these tiny stars are the only places where we can detect life on an Earth-sized exoplanet with our current technology,” Gillon said in a statement. “If we want to find life elsewhere in the universe, this is where we should look.” To determine if a planet might harbour life, scientists usually analyse the makeup of its atmosphere. Biomarkers like methane, oxygen and water could indicate that life is present ( via watoday.com.au ). “This is only the beginning,” De Wit said. “There is a big adventure ahead of us.”
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