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TRAPPIST-1: A system full of possibility
Astronomers have discovered the first known system to host seven Earth-size planets around one star, and it lies just 39 light-years away from our own solar system.
Using data from the TRAPPIST telescope in Chile and other ground-based telescopes, as well as NASA's Spitzer Space Telescope, the researchers identified the sizes, orbits and masses of most of the planets — suggesting that they all may be rocky, like Earth, and that three of them are in the habitable zone, where liquid water might linger and life as we know it could find a foothold.
Come along for a tour of the remarkable TRAPPIST-1 system. [Images: The 7 Earth-Size Worlds of TRAPPIST-1]
FIRST STOP: The star
TRAPPIST-1Slide 2 of 17
TRAPPIST-1 is a dim, cool star just a little bit bigger than Jupiter. It's about 8 percent as massive as the sun and shines just 0.05 percent as brightly as Earth's star. The planets researchers have spotted huddle up close, in very tight orbits that are all closer than Mercury's around the sun.
Most of the light TRAPPIST-1 releases is in infrared wavelengths, invisible to the human eye, which is why the Spitzer telescope, which measures in infrared, was the ideal tool to scope out more details about its orbiting planets. Ultracool dwarfs like TRAPPIST-1 are extremely long-lived because of their coolness; it could potentially keep burning for another 5 trillion years, long after the sun has run out of fuel. (The sun is about halfway through its project 10-billion-year lifespan.)
Dwarf stars make up about 75 percent of the Milky Way galaxy's stellar population. Planets in their habitable zones would appear to be too close, and in danger of blasts of radiation from these stars — but models suggest that some planets could withstand the punishing conditions to have conditions amenable to life, if their atmospheres and magnetic fields are strong enough. Because dwarf-star systems are so long-lived, they could also provide plenty of time for life to develop.
NEXT STOP: The innermost planetSlide 3 of 17
TRAPPIST-1bSlide 4 of 17
The innermost of the seven planets, TRAPPIST-1b, whips around the star once every 1.51 days, according to the most recent measurements (making that the equivalent of the planet's "year"). It orbits just 0.011 astronomical units (AU) away from the star, which is 1.02 million miles, or 1.64 million kilometers — 4.27 times the average distance from Earth to the moon. (1 AU is the average distance from Earth to the sun — about 93 million miles, or 150 million km.)
TRAPPIST-1b is about 1.09 times Earth's radius, and 0.85 times its mass, according to preliminary calculations — measurements that suggest it's likely rocky. Because of its closeness, 1b (and its sister planets) are likely tidally locked with their star, like the moon is to Earth, which means they orbit with the same sides facing it at all times. Despite the star's coolness, 1b is close enough to it that any water on the world would probably boil or sublimate off as steam.
NEXT STOP: Another warm worldSlide 5 of 17
TRAPPIST-1cSlide 6 of 17
Like 1b, TRAPPIST-1c orbits close enough that liquid water likely doesn't exist on the planet's surface. It's 1.06 times Earth's radius and 1.38 times its mass, and it orbits around the star every 2.42 days. The planet orbits at a distance of 0.015 AU — that's 5.83 times the average Earth-moon distance.
Like TRAPPIST-1b, 1c was discovered orbiting TRAPPIST-1 last year, based on observations of the star's dimming as the planets passed by. It orbits five times for every eight orbits of the innermost planet — a "resonance" that suggests those planets could have moved inward from farther away at some point, researchers said.
NEXT STOP: The lightweightSlide 7 of 17
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