Is there life beyond our solar system? If yes, our best bet would be to search out three nearby, Earth-like exo-planets. It is for the first time that international teams of astronomers from MIT, the University of Liège in Belgium and elsewhere have spotted 3 planets orbiting an ultracool dwarf star that is just 40 light years from Earth.
The sizes and temperatures of these worlds are similar to those of Earth and Venus. They are the best targets found so far for the search for life beyond the solar system.
The scientists discovered the planets using TRAPPIST, a 60-centimeter telescope developed by the University of Liège, based in Chile. TRAPPIST is designed to focus on 60 nearby dwarf stars — very small and cool stars which are so faint that they are invisible to optical telescopes. Belgian scientists designed TRAPPIST to observe dwarf stars at infrared wavelengths and hunt for planets around them.
The team directed the telescope on the ultracool dwarf star,2MASS J23062928-0502285, currently known as TRAPPIST-1, a Jupiter-sized star that is one-eighth the size of our sun and considerably cooler. Over several months starting in September 2015, the scientists observed the star’s infrared signal weakens slightly at regular intervals, suggesting that several objects were passing in front of the star. With additional observations, the team established that the objects were indeed planets, with similar sizes to Earth and Venus.
The two closest planets orbit the star in 1.5 and 2.4 days, though they receive only four and two times the amount of radiation respectively as compared to what the Earth receives from the sun. The third planet orbits the star in somewhere from four to 73 days, and may get even less radiation than Earth. Given their size and proximity to their star, all three planets may have areas with temperatures well below 400 kelvins, within a range that is appropriate for sustaining liquid water and life.
Today’s exo-planetary missions have been dedicated on finding systems around bright, sun-like stars. These stars produce radiation in the visible band most often at yellow wavelengths and can be observed with optical telescopes. However, since these stars are very bright, their light can subdue any signal coming from a planet.
Cold dwarf stars, in contrast, are dim stars that emit radiation in the infrared band. Because they are so dim, these tiny red stars would not suppress a planetary signal, giving scientists a better chance of detecting orbiting planets. However, most missions today are not optimized to observe such stars.
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