“Why are we trying to detect Earthlike planets around the smallest and coolest stars in the solar neighborhood? The reason is simple: Systems around these tiny stars are the only places where we can detect life on an Earth-sized exoplanet with our current technology,” Michaël Gillon, an astronomer from the University of Liège in Belgium, said in a news release from the European Southern Observatory. “So if we want to find life elsewhere in the universe, this is where we should start to look.”
The discoveries are detailed in a study published today by the journal Nature.
The star in question, known as TRAPPIST-1 in the constellation Aquarius, is ultracool not only because it’s cool to think about extraterrestrial life: It’s just on the edge of starhood, with 8 percent of our sun’s mass and 0.05 percent of its luminosity.
The dwarf star’s proximity to Earth is one of the big reasons why little TRAPPIST-1 could be detected by a robotic observatory known as the Transiting Planets and Planetesimals Small Telescope, or TRAPPIST. The 23-inch (0.6-meter) telescope is located at ESO’s La Silla Observatory in Chile, but it’s operated from a control room in Liège. The focus of the TRAPPIST project is to look for dim stars and the not-quite-stars known as brown dwarfs in our celestial neighborhood.
TRAPPIST’s observations registered subtle dips in the brightness of the star’s light – a tip-off that exoplanets might be passing in front of TRAPPIST-1’s disk. Follow-up observations by several other telescopes confirmed the sizes and orbits of the three planets. All three are roughly Earth’s size, but they orbit 20 to 100 times closer to their parent star than Earth does.
If TRAPPIST-1 were as hot as our sun, those planets would be cooked. But because the star is ultracool, there’s a chance that the planets are on the edge of the star system’s habitable zone – that is, the region where water can exist as a liquid on the surface. That condition is considered key for the presence of life as we know it on Earth, and it may hold true for exoplanets as well. It’s not a slam-dunk: Two of the planets might be a little too hot, and the other one might be a little too cold. But the potential for them to be just right, at least on some regions of the planet, is enough to get exobiologists excited.
The timing of the research published today is fortuitous. It turns out that two of TRAPPIST-1’s planets are expected to cross the star’s disk on Wednesday. The Hubble Space Telescope and other instruments are set to track the event, and there’s a chance the resulting data could tell astronomers whether the planets’ atmosphere’s contain water vapor.
NASA’s Kepler space telescope is also scheduled to observe TRAPPIST-1’s planetary transits during one of its planet-hunting K2 campaigns, starting in December and winding up in March 2017. By combining the data from Kepler and TRAPPIST, astronomers should be able to figure out the exoplanets’ density and whether they’re rocky, Earthlike worlds.
In a news release, NASA said the TRAPPIST-1 system is an ideal target for the James Webb Space Telescope, which should be able to detect water vapor, methane, carbon dioxide and other chemicals of astrobiological interest in exoplanetary atmospheres. ESO is also planning to follow up on the TRAPPIST survey with a more ambitious project called SPECULOOS at its Paranal Observatory in Chile.
“Thanks to several giant telescopes currently under construction, including ESO’s E-ELT and the NASA/ESA/CSA James Webb Space Telescope due to launch for 2018, we will soon be able to study the atmospheric composition of these planets and to explore them first for water, then for traces of biological activity,” said study co-author Julien de Wit, an astronomer at the Massachusetts Institute of Technology.
Gillon and de Wit are among 15 authors of the Nature study, titled “Temperate Earth-