The space agency said the TRAPPIST-1 star is "quite old: between 5.4 and 9.8 billion years." In comparison, our own solar system was formed around 4.5 billion years ago.
The age of a solar system's star is an important factor affecting whether life could survive there.
"Young stars have frequent releases of high-energy radiation called flares that can zap their planets' surfaces," NASA said. "If the planets are newly formed, their orbits may also be unstable. On the other hand, planets orbiting older stars have survived the spate of youthful flares, but have also been exposed to the ravages of stellar radiation for a longer period of time."
NASA said it's "unclear" what TRAPPIST-1's old age means for the planets' habitability. On the plus side, older stars flare less often than younger ones. On the down side, the planets are so close to their star that they have "soaked up billions of years of high-energy radiation, which could have boiled off atmospheres and large amounts of water." Because they're so close, it's possible that the equivalent of an ocean has evaporated from each TRAPPIST-1 planet, except for the two farthest from the star.
On the other hand, NASA that TRAPPIST-1 planets have lower densities than Earth, so "it is possible that large reservoirs of volatile molecules such as water could produce thick atmospheres that would shield the planetary surfaces from harmful radiation."
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In other words, they're saying there's a chance.
"If there is life on these planets, I would speculate that it has to be hardy life, because it has to be able to survive some potentially dire scenarios for billions of years," Adam Burgasser, an astronomer at the University of California, San Diego said in a statement. Burgasser worked with Eric Mamajek, deputy program scientist for NASA's Exoplanet Exploration Program, to calculate TRAPPIST-1's age. The duo's findings are slated to be published in The Astrophysical Journal.
Unveiled in February, TRAPPIST-1 is 40 light-years away from Earth, or about 325 trillion miles, which is "relatively close" in the grand scheme of things, NASA said. Three of these planets are located in what NASA calls the "habitable zone," meaning the area around the parent star where a rocky planet is most likely to have water. All seven planets in TRAPPIST-1 could have liquid water under the right atmospheric conditions, but the three in the habitable zone are most promising.