On May 2, 2016, a team of astronomers from the Massachusetts Institute of Technology (MIT) announced in the journal Nature an unusual finding : They had detected three Earth-like exoplanets around the ultracool dwarf known as TRAPPIST-1 , a little star. larger than Jupiter whose brightness represents only 0.05% that of the Sun. Never before have objects of this type been hunted accompanying such a small star. And they are very close, 40 light years from us . At the time of that announcement, it was said that one of them seemed to be in the habitable zone of the system, a region in which the necessary conditions exist for there to be water in a liquid state on its surface . Perhaps it could even harbor life.
Well, the discovery has been not only confirmed but expanded. There were not three but seven . Thanks to the use of several telescopes both on the ground and in space, including ESO’s VLT (Very Large Telescope) and the one on the island of La Palma, in the Canary Islands, the exoplanets were detected one by one, like models of a catwalk galactic, as they passed in front of their star , the ultracool dwarf star TRAPPIST-1. According to the new article, which also appears in Nature , there are not one but three planets that are in the habitable zone and could host oceans of water on their surfaces , increasing the possibility that the system could host life. It is the system found so far that has both the largest number of Earth-sized planets and the largest number of worlds that could have liquid water on their surfaces.
Thanks to the TRAPPIST – Sur telescope, installed at the La Silla Observatory, the Very Large Telescope (VLT), in Paranal, and NASA’s Spitzer Space Telescope, as well as other telescopes around the world, the international team of astronomers has confirmed the existence of the seven small planets that orbit the cool red dwarf star TRAPPIST-1. The planets, named TRAPPIST-1b, c, d, e, f, g, and h, in increasing order of distance from their star, are similar in size to our Earth .
The astronomers observed changes in the star’s light emission caused by each of the seven planets passing in front of it – an event known as a transit – which allowed them to extract information about their sizes, compositions and orbits. They found that at least the six inner planets are comparable to ours in size and temperature .
The lead author of the research, Michaël Gillon, from the STAR Institute at the University of Liege (Belgium) believes that “this is an amazing discovery , not only because we have found so many planets, but because they are all similar in size to Earth” .
At just 8% the mass of the Sun, TRAPPIST-1 is very small in stellar terms (only slightly larger than Jupiter) and, although relatively close to us, in the constellation Aquarius, it emits a very dim light. Astronomers hoped that these types of dwarf stars could host many Earth-sized planets in tight orbits, making them prime targets for the search for extraterrestrial life, but TRAPPIST-1 is the first such system to have existed. been confirmed.
Amaury Triaud, another of the astronomers involved, says that ” the emission of energy from dwarf stars like TRAPPIST-1 is much weaker than that of our Sun. For there to be water on their surfaces, the planets would have to be in much closer orbits. than we have in the Solar System. Fortunately, it seems that this kind of compact configuration is what we are seeing around TRAPPIST-1. ” All the planets in the system are similar in size to Earth and Venus or slightly smaller. Density measurements suggest that at least the six innermost planets are probably rocky in composition.
Planetary orbits are smaller than Mercury’s orbit in the Solar System. However, TRAPPIST-1’s small size and low temperature mean that the energy it provides to its planets is similar to that received by the inner planets of our Solar System. So TRAPPIST-1c, d, and f receive similar amounts of energy as Venus, Earth, and Mars, respectively.
The seven planets discovered in the system could potentially have liquid water on their surfaces, although their orbital distances make this more likely in some than others. Climate models suggest that the innermost planets, TRAPPIST-1b, c and d, are probably too hot to host liquid water , except for perhaps a small fraction of their surfaces. The outermost planet in the system, TRAPPIST-1h, is probably too distant and cold to host liquid water. But TRAPPIST-1e, f, and g have all the ballots to become the holy grail for planet-hunting astronomers, as they orbit in the star’s habitable zone and could host oceans of water on their surfaces.
This finding makes the TRAPPIST-1 system a very important target for future studies. The NASA / ESA Hubble Space Telecope is already looking for atmospheres around the planets . Astronomer Emmanuël Jehin believes that “with the next generation of telescopes such as the E-ELT (ESO’s European Extremely Large Telescope) and the JWST space telescope (NASA / ESA / CSA James Webb Space Telescope) we will soon be able to search for water and even evidence of life on these worlds. “
Illustration: shows the view from the surface of one of the planets in the TRAPPIST-1 system. At least seven planets orbit this ultracool dwarf star 40 light years from Earth and all are roughly the same size as Earth. They are at the right distance from their star so that several of them harbor liquid water on their surfaces.
Credit: ESO / M. Kornmesser / spaceengine.org
