The star TRAPPIST-1 is a real little thing: it is only slightly larger than the planet Jupiter and its mass corresponds to only eight percent of the mass of our sun - corresponding to faint is about 39 light years away from us red dwarf star. For a long time such ultra-cold dwarfs were considered too small to have their own planetary systems - also because no example had yet been discovered. However, that changed last year: Using the TRAPPIST (TRAnsiting Planets and Planets Illuminations Small Telescope) telescope at the La Silla Observatory in Chile, astronomers discovered an abnormality: at regular intervals, the light of this dwarf star became a tiny bit darker. From the light curves, they concluded that this dimming is caused by the transit of three roughly earth-sized planets: whenever the planets pass in front of their star, they swallow a little of its light. But the astronomers around Michaël Gillon of the University of Liège were not satisfied with this discovery. They have been following TRAPPIST-1 ever since, including three weeks with the NASA Spitzer Space Telescope, but also with various Earth-based telescopes.
Seven planets around a dwarf
Their persistence paid off, as the researchers discovered in the light curves 34 more transit signals. "The signals have a period of 4.04 days, 6.06 days, 8.1 days and 12.3 days, " Gillon and his colleagues report. The first signal corresponds to the planet TRAPPIST-d already suspected in the preliminary observations, but the three others are completely new - they must therefore belong to three other planets around the dwarf star. Thus he has at least six planets closely surrounding him. In addition, the researchers discovered yet another, one-time dimming, they attribute to a seventh planet.
The small dwarf star TRAPPIST-1 is home to no less than seven planets - and all seven are likely to be Earth-like, as the astronomers report. Accordingly, five of the planets have about the size of the earth, the other two - d and h - are of size between Mars and Earth. This is most likely a rock planet. "This planetary system is amazing - not only because we've found so many planets, but also because their sizes are all amazingly equal to Earth!" Says Gillon. With their orbital periods of between 1.5 and 12.4 days, these Earth-like planets would transmit to the Solar System all between Sun and Mercury. The miniature planetary system is more similar in size to Jupiter and its four largest moons - these moons have quite similar orbital periods around the gas giant.
Flowing water on six planets
But even more exciting is that at least three of the seven planets around TRAPPIST-1 could be in the habitable zone - and six of them could be liquid water. "The planets e, f and g could have water oceans on their surface, " the researchers report. The three inner planets b, c and d, however, are much hotter and could have a strong greenhouse effect. Nonetheless, astronomers consider it quite possible that liquid water also exists on this planet, at least in some areas of its surface. The distance of the seventh planet of the system, TRAPPIST-1h, is not yet known because the researchers could only observe one single transit from it. But they suspect that it is too far out and thus probably too cold for liquid water. display
More about the seven earth twins and their discovery (Video: Nature / NASA)
With six potentially life-friendly planets and a distance of only 39 light-years from Earth, this planetary system is almost a jackpot for planetary scientists. Because TRAPPIST-1 is close enough to be able to learn more about the planets, their atmospheres and their climate with powerful telescopes in the future. The Hubble Space Telescope has already begun to search for spectral signals of the atmospheres. "With the next generation of telescopes, such as the European Extremely Large Telescope and the James Webb Space Telescope of NASA / ESA / CSA, we will soon be able to find water and perhaps even evidence of life on this planet search, "says co-author Emmanu l Jehin of the University of L ttich.
- Micha l Gillon (University of L ttich, L ttich) et al., Nature, doi: 10.1038 / nature21360