In one of the most significant exoplanet discoveries to date, NASA just announced that not one, but seven Earth-sized planets have been found orbiting the habitable or ‘temperate zone’ of a star just 39 light-years away. Research suggests at least the inner six planets appear to have Earth-like masses, are made of rock, and have surface temperatures ranging between a life-friendly 0 to 100°C (32 to 212°F). NASA is calling it a ‘sister solar system’ to our own, and says several of the planets could potentially host liquid water, and maybe even extraterrestrial life.
NASA made the announcement in a live press conference after triggering much speculation over their big “discovery beyond our Solar System”. The new exoplanets have been detected orbiting an ultracool dwarf star called TRAPPIST-1, which is located about 39 light-years away from our Sun in the Aquarius constellation. Astronomers led by Michaël Gillon from the University of Liège in Belgium first detected three exoplanets around the star back in May 2016, using Earth-based telescopes. But it wasn’t until the team studied it more closely using NASA’s Spitzer space telescope that they discovered an additional four planets in the system.
Initial estimates based on these observations suggest that at least five of the planets have masses similar to Earth, and follow-up observations by the Hubble Space Telescope indicate that they probably have rocky compositions. At least three also appear to fall within the temperate zone of their star – which means their surface temperatures are most likely to be between 0 and 100°C (32 and 212°F), making liquid water, and potentially even some form of extraterrestrial life, a possibility. Because of the system’s structure, it’s also possible that any of the planets have liquid water.
Before we get too excited, the researchers stress that there’s still a lot more research and analysis to be done – particularly on the seventh, outermost planet, which has only been observed orbiting the star once. Because of that, we still don’t know how long that seventh planet takes to orbit TRAPPIST-1, or how it interacts with the inner planets. And the entire system is so far away, we can’t say for sure as yet whether it hosts water, or is a good place for life to exist. But from what the researchers can tell, not only are at least three of the planets potential homes to liquid oceans, the entire system actually seems to be have a lot in common with our own.
But despite the familiarities to home, there are some big differences between our systems. Mainly the fact that TRAPPIST-1 is only a little bigger than Jupiter, and its planets orbit only a little farther apart than Jupiter’s moons. The whole system is pretty compact too, with the closest planet only taking 1.5 days to orbit its star.
The sixth planet takes 13 days. That means that if you were standing on the surface of one of these planets, the neighbouring planets in the sky would at times appear larger than our Moon does to us. Because of this, it’s thought that the planets might all affect each other, and could even be tidally locked, with one face constantly pointed towards their star, in the same way that Jupiter’s moons always have one side locked towards the giant planet.
That tidal locking could also do some strange things to the temperature gradients on the planet, which NASA says makes it possible that liquid water could exist on any of them under the right conditions. But perhaps even more exciting about this discovery is what it means for the likelihood of other Earth-like planets out there in our galaxy. “In the past few years, evidence has been mounting that Earth-sized planets are abundant in the Galaxy, but Gillon and collaborators’ findings indicate that these planets are even more common than previously thought,”