Two Earth-size planets orbiting a nearby star are now confirmed to be rocky, strengthening the case that they might be habitable, a new study finds.
The atmospheres of these worlds may range from vanishingly thin, like that of Mars, to hellishly dense, like Venus' air — and, possibly, comfortably in between, like Earth's, the researchers said.
In May, astronomers reported the discovery of three Earth-size planets orbiting a dim, cold, red star named TRAPPIST-1. This "ultracool dwarf" is located in the constellation Aquarius, about 39 light-years from Earth. (For comparison, Alpha Centauri, the nearest star system to our own, is about 4.3 light-years from Earth.)
Previous research found that TRAPPIST-1 is 2,000 times dimmer than the sun, a bit less than half as warm as the sun, about one-twelfth the sun's mass, and less than one-eighth the sun's width, making it only barely larger in diameter than Jupiter.
Ultracool dwarfs such as TRAPPIST-1 are very common in the Milky Way galaxy, making up about 15 percent of the stars near the sun. TRAPPIST-1's discoverers suggest that these kinds of stars may be the first places to look for life elsewhere in the universe, because they may be the only places where scientists using current technology can detect life on distant Earth-size planets.
Judging from the size and temperatures of the three planets around TRAPPIST-1, researchers previously suggested that regions on each world could be habitable — that is, have surfaces with just the right temperatures to harbor liquid water, a key ingredient of life as it is known on Earth. However, it was uncertain if these three planets were rocky worlds like Earth.
Now, TRAPPIST-1's discoverers have found that the star's two innermost worlds, TRAPPIST-1b and TRAPPIST-1c, are indeed primarily rocky planets.
The scientists made this new discovery by pointing NASA's Hubble Space Telescope at TRAPPIST-1 to catch a rare event on May 4: a double transit, when two planets — in this case, TRAPPIST-1b and TRAPPIST-1c — pass in front of their star at nearly the same time.
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http://www.interstellar-news.net/2016/07/2-nearby-exoplanets-confirmed-to-be.html
