If there’s life beyond our solar system, our best bet for finding it may lie in three temperate, Earth-size exoplanets nearby.
For the first time, an international team of astronomers from MIT, the University of Liège in Belgium, and elsewhere has detected three planets orbiting an ultracool dwarf star, just 40 light-years from Earth. Comparable in size and temperature to Earth and Venus, these planets are the best targets found so far in the search for life outside the solar system. The results are published in the journal Nature.
The scientists discovered the planets using TRAPPIST (Transiting Planets and Planetesimals Small Telescope), a 60-centimeter telescope operated by the University of Liège and based in Chile. TRAPPIST is designed to focus on 60 nearby dwarf stars—very small, cool stars that are so faint they are invisible to optical telescopes. It is a prototype for SPECULOOS (Search for Habitable Planets Eclipsing Ultra-Cool Stars), a set of four one-meter telescopes that will be installed later this year in Chile, to monitor 500 of the nearest ultra-cool stars and brown dwarfs in the southern sky. Belgian scientists designed TRAPPIST and SPECULOOS to monitor dwarf stars at infrared wavelengths and search for planets around them.
The team focused the telescope on 2MASS J23062928-0502285, now known as TRAPPIST-1, a star that is one-eighth as big as our sun and significantly cooler. Over several months starting in September 2015, the scientists saw its infrared signal fade slightly at regular intervals, suggesting that several objects were passing in front of the star.
With further observations, the team confirmed that the objects were indeed planets, similar in size 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, that 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, all three planets may have regions with temperatures well below 126.85 °C, within a range that is suitable for sustaining liquid water and life.
Because the system is just 40 light-years from Earth, says coauthor Julien de Wit, PhD ’14, a postdoc in the Department of Earth, Atmospheric, and Planetary Sciences, scientists will soon have an unprecedented opportunity to evaluate their potential for supporting life.
“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 explains. “All of these things are achievable and within reach now. This is a jackpot for the field.”