A small, cool star in distant space plays host to something amazing. Scientists have discovered that at least seven Earth-sized worlds circle the star TRAPPIST-1, a ultracool dwarf star only about 40 light-years (235 trillion miles) from Earth. The planetary haul — which includes at least six rocky planets total, three of which were first discovered last year — is detailed in a new study published in the journal Nature on Wednesday. SEE ALSO: Stop describing a planet as 'Earth-like' unless it really is This marks the first time so many Earth-sized worlds have been found orbiting the same star. It's possible that some of those exoplanets (worlds orbiting stars outside of our solar system) could play host to liquid water on their surfaces, boosting the chance that alien life might be lurking there. "We can expect that within a few years we will know a lot more about these planets," Amaury Triaud, a co-author of the new study said during a press conference, adding that if there is life on one of these worlds, we could find it within a decade. Before you go running off to plan your trip to TRAPPIST-1, it's important to remember that the system isn't exactly an analogue to our own. A star system like Jupiter The best way to think about TRAPPIST-1 and its worlds is to compare it to Jupiter and its many moons. Just like Jupiter's moons, the planets orbiting TRAPPIST-1 all interact with one another, meaning that their orbits are influenced by one another. The seven planets in the system closely orbit their star, so that if TRAPPIST-1 were in place of our sun in the solar system, the planets surrounding it would all be within the orbit of Mercury, according to the study's authors. The planets are thought to be tidally locked to their star, meaning that, like the moon, the same sides of the exoplanets' faces always point toward the host star. If you were to stand on the surface of one of the planets, the salmon-colored star would look about 200 times dimmer than our own sun, giving off about the same amount of light as our star does at the tail end of a sunset, Triaud said. Artist's representation of the planets around TRAPPIST-1. Image: NASA/JPL-Caltech "The spectacle would be beautiful because every now and then, you would see another planet — maybe about as big as twice the moon — in the sky depending on which planet you're on and which planet you look at," Triaud said. A special solar system Because the star system is so close (in cosmic terms) to Earth, it's ideal for any scientist hoping to check out these worlds for themselves, and they already have. The same team behind this Nature study announced the discovery of three planets orbiting TRAPPIST-1 in May 2016. Since then, the researchers did many followup observations on the system to try to better characterize the planets orbiting the faint star light-years from home. The new study details the four other planets orbiting the star using multiple ground-based telescopes and NASA's Spitzer Space Telescope. Scientists used the transit method to find the exoplanets, meaning that they had to wait for the worlds to pass in front of their star, causing a dip in the light of the dwarf star. Because the orbits of each planet influence the others, such observations also allowed the researchers to ascertain the masses and diameters of the planets, Triaud said. The planets orbiting TRAPPIST-1 compared to worlds in our solar system. Image: NASA/JPL-Caltech The fact that they transit their star also means that scientists will be able to do plenty of followup observations that will characterize the atmospheres of the worlds thanks to the light shining on them from the star. "This is just the neatest system," NASA exoplanet scientist Steve Howell, who is not affiliated with the new study, said in an interview. "While there was much hoopla about the Proxima Centauri planet — well, okay, that's cool too, don't get me wrong — that planet doesn't transit, and so there just won't be a lot of followup work you can do on that planet." Hunting for life It's still unclear whether or not life exists on any of these worlds. All of the planets are far enough from their star that they could conceivably host liquid water on their surfaces, according to the researchers. Four of the worlds in particular are thought to be in the "habitable zone" of the star, which means they could be our best chances for life outside the solar system. However, none of this is a sure thing. Figuring out the habitable zone of a dwarf star isn't exactly easy. Because TRAPPIST-1 and stars of its ilk are much smaller and dimmer than our sun, it's unclear exactly where the habitable zone lies. We have a relatively good understanding of the habitable zone around sunlike stars, but ultracool dwarfs are trickier, in part because they are very active in their early days, possibly stripping worlds that would be in the habitable zones of their atmospheres. That said, these stars do live a long time, possibly allowing advanced life time to evolve on worlds surrounding stars like TRAPPIST-1, which is thought to be at least 500 million years old. Follow ups a-plenty The Hubble Space Telescope characterized the atmospheres of TRAPPIST-1B and TRAPPIST-1C, finding that the two worlds probably aren't encircled by hydrogen and helium rich atmospheres, meaning their atmospheres could resemble our own. Researchers will be able to get an even better look at these worlds in the future. NASA's James Webb Space Telescope (JWST) — Hubble's telescope successor expected to launch in 2018 — should be able to peer deeply into the atmospheres of alien planets to try to see if they really could be like our own. By learning more about the atmospheres enveloping on these worlds, it's possible that we'll be able to figure out if we are alone in the universe. The JWST might be able to pick out oxygen, carbon dioxide, methane and other molecules in exoplanet atmospheres to find any biosignatures that might be present. While there isn't a silver bullet molecule that indicates whether life is definitely present on an alien world, certain elements could give scientists pause if found in a planet's atmosphere. If, for example, JWST found "molecular oxygen, or if it found carbon compounds that on the Earth we assign to pollution — like burning of fossil fuels — that would be pretty cool," Howell said. "Those would be things that you'd have to scratch your head and say, 'wow, that would be a pretty good sign.'" BONUS: Could massive solar 'superflares' help us find life on other planets?
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