Astronomers have discovered three Earth-like exoplanets orbiting an ultracool dwarf star, just 40 light years from Earth. Scientists say that the sizes and temperatures of these planets are comparable to those of Earth and Venus, and are the best targets found so far for the search for life outside our solar system.
Researchers focused the TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) on the ultracool dwarf star, 2MASS J23062928-0502285, now known as TRAPPIST-1, a Jupiter-sized star that is one-eighth the size of our sun and significantly cooler. Over several months starting in September 2015, the scientists observed the star’s infrared signal fade slightly at regular intervals, suggesting that several objects were passing in front of the star.
With further observations, astronomers confirmed the objects were indeed planets, with similar sizes to Earth and Venus. The two innermost 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 the Earth receives from the sun. The third planet may orbit the star in anywhere from four to 73 days, and may receive even less radiation than Earth.
Given their size and proximity to their ultracool star, researchers believe that all three planets may have regions with temperatures well below 400 kelvins, within a range that is suitable for sustaining liquid water and life.
Because the system is just 40 light years from Earth, study co-author Julien de Wit, says scientists will soon be able to study the planets’ atmospheric compositions, as well as assess their habitability and whether life actually exists within this planetary system.
“These planets are so close, and their star so small, we can study their atmosphere and composition, and further down the road, which is within our generation, assess if they are actually inhabited,” de Wit says. “All of these things are achievable, and within reach now. This is a jackpot for the field.”
From their observations, the scientists determined that all three planets are likely tidally locked, with permanent day and night sides. The two planets closest to the star may have day sides that are too hot, and night sides too cold, to host any life forms. However, there may be a “sweet spot” on the western side of both planets — a region that still receives daylight, but with relatively cool temperatures — that may be temperate enough to sustain conditions suitable for life. The third planet, furthest from its star, may be entirely within the habitable zone.