Astronomers from NASA and the European Southern Observatory announced Wednesday that four new Earth-sized exoplanets have been discovered orbiting a star about 40 light-years away, and that three may contain liquid water and be able to sustain life.

This star's small grouping of planets now boasts the most Earth-sized worlds of any system astronomers have discovered, and the most exoplanets that may be able to support surface life and water.

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A Belgian-led team was able to spy these planets using space- and ground-based telescopes as each passed in front of its host, a red dwarf star known as TRAPPIST-1. These so called transits created dips in the Jupiter-sized star's light output that helped astronomers determine the sizes, compositions, and orbits of each of the celestial bodies.

"Whether or not TRAPPIST-1 has inhabitants, its discovery has underlined the growing conviction that the universe is replete with real estate on which biology could both arise and flourish," says Seth Shostak of the SETI Institute, an expert in the search for extraterrestrial life. "If you still think the rest of the universe is sterile, you are surely singular, and probably wrong."

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These four exoplanets join three others circling TRAPPIST-1 that were discovered by the same team early in 2016, after which the group said it intensified follow-up efforts.

"This is an amazing planetary system, not only because we have found so many planets, but because they are all surprisingly similar in size to Earth," said Michaël Gillon, astronomer from the University of Liège in Belgium and lead author of the paper about the discovery published in the journal Nature.

All seven planets that surround the ultra cool star — which has only about 8 percent the mass of our own sun — orbit more tightly to their host than any of the planets in our system are to the sun.

“They would fit within the orbit of Mercury with oodles of room to spare," Shostak says. "A year on any of these worlds would be less than three weeks, and in the case of the innermost planet, only 36 hours. You’d have a hard time keeping up with birthdays."

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TRAPPIST-1 doesn't put out much energy, but the inner six exoplanets are in such tight orbit around their host that they have temperatures comparable to those on Venus, Earth, and Mars.

The scientists observations and measurements suggest the inner six planets have rocky compositions, and that three of TRAPPIST-1's surrounding bodies may orbit within a habitable zone that represents the "holy grail for planet-hunting" as they could be warm enough to host surface water and oceans.

The team believes this discovery could mean that similar dwarf stars are able to host Earth-sized planets in tight orbits, making them "promising targets" in the search for extraterrestrial life.

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