NASA has announced the discovery of a family of 7 Earth-like exoplanets that are orbiting a nearby star, an ultracool dwarf called TRAPPIST-1. The observations were made using NASA’s Spitzer Space Telescope, building on earlier findings announced last year by a team from the University of Liège in Belgium, using observations from the TRAPPIST (Transiting Planets and Planetesimals Small Telescope) telescope at the La Silla Observatory in the Atacama desert, Chile. Not only is the TRAPPIST-1 system rich in earth-sized, rocky planets, ripe for comparatively easy study, but also three of these planets lie within their star’s habitable zone.
TRAPPIST-1 is a small star, only 1/12th the mass of the Sun, that is located 39.13 light-years away in the constellation of Aquarius. The sheer number of rocky planets found there, and especially the number of planets within the Goldilocks zone, allows for a significantly larger chance of finding signs of life around this star. The star’s relative dimness also allows for easier observations of the planets as they cross TRAPPIST-1’s face, as the light from brighter stars tend to overwhelm the shadows cast by their planets.
The three planets orbiting in the habitable zone, where the temperature is just right for liquid water to form, are designated TRAPPIST-1e, TRAPPIST-1f and TRAPPIST-1g. TRAPPIST-1e is roughly Earth-sized, and is estimated to have a similar surface temperature to that of Earth. TRAPPIST-1f is slightly larger, and receives about the same energy from its star as Mars does from the Sun. TRAPPIST-1g is roughly 13 percent larger than Earth, and would receive an amount of energy somewhat similar to a planet that would be positioned partway between Mars and Jupiter. Despite the amount of energy that the planets receive, most of it is in the infrared part of the spectrum, so the local star would only appear to be one-half of a percent as bright as our own Sun.
However, the sun in their sky would appear very large, due to the small size of the planetary system: from the surface of TRAPPIST-1e, the star would appear to be three times larger than our own Sun. In regards to its size, the Trappist-1 system is being likened to Jupiter and its moons, with the diameter of the outtermost planet’s orbit being smaller than that of Mercury’s. This means that, while none of the planets are likely to have their own moons, each of the other planets would appear very prominent in the sky to anyone standing on the surface of one, similar to how the moon appears in our own sky.
Spectral analysis is being undertaken to determine the composition of any atmospheres that Trappist-1’s planets might host. So far, the innermost two planets have been found to not have a hydrogen signature around them, a key component of water, but this still leaves five more candidates to be searched. And even if the analysis comes up dry, such an abundant amount of planets around an easily-observed star will add an immeasurable amount of knowledge to the search for life outside of the Solar System.
“The Trappist-1 planets make the search for life in the galaxy imminent,” said Sara Seager, an astronomer at the Massachusetts Institute of Technology. “For the first time ever, we don’t have to speculate. We just have to wait and then make very careful observations and see what is in the atmospheres of the Trappist planets.”
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