Around 40 light-years away, seven Earth-sized planets have been spotted orbiting closely around a small, ultra-cool star. It’s one of the largest solar systems that’s ever been discovered outside of our own, and it’s a particularly enticing find in the ongoing search for extraterrestrial life. Six of the planets in the system may have the right temperatures for liquid water to exist on their surfaces, and astronomers are confident they’ll be able to get a more in-depth look at these seven worlds with future space telescopes.
A PARTICULARLY ENTICING FIND IN THE ONGOING SEARCH FOR EXTRATERRESTRIAL LIFE
The solar system, detailed today in a study in Nature, isn’t a completely new find. In fact, the discovery of this system was announced last year by the same researchers. But at the time, they thought they had only found three planets around the star, named TRAPPIST-1. When the researchers took a closer look at the system with more precise telescopes, including NASA’s Spitzer Space Telescope, they found more planets nearby.
“We got plenty of new data, and we went from three to four to five planets,” Michaël Gillon, a research associate for the Belgian Funds for Scientific Research and lead author of the Nature study, tells The Verge. “Then we got this Spitzer data that showed there were, in fact, seven planets.”
Since these planets are roughly the same size as Earth, the researchers think they may be rocky like our own world. And three orbit within the star’s habitable zone, where temperatures are just right that there could be whole oceans on the planets’ surfaces. Given that liquid water is such an essential ingredient for life here on our planet, astronomers are eager to find it on other worlds outside our Solar System. The presence of liquid water on an exoplanet could mean that life has thrived there as well, so that makes these seven planets now top candidates in the search for alien life.
The astronomers say there’s a good chance they’ll get some answers, since they’ll be able to study these exoplanets and their atmospheres in greater detail. In the grand scheme of the Universe, 40 light-years is a relatively short distance, which makes observing this system a bit easier with our telescopes. Plus, peering into the planets’ atmospheres is less challenging since these planets orbit around a star that’s much smaller and fainter than our yellow Sun. If they orbited a star the size of ours, the intense starlight would make the worlds and their atmospheres difficult to see. “Of course it’s super exciting, but what makes the system so special is that all these seven planets are suited for detailed atmospheric characterization,” says Gillon.
This is why small, super-cool stars — known as red dwarfs — have become popular targets for exoplanet hunters; it’s easier to study the planets around them. Over the past couple of years, Gillon and his team have been focused on looking for worlds around red dwarfs using the TRAPPIST telescope at the La Silla Observatory in Chile. Less than a couple years ago, their search led them to TRAPPIST-1, a star just a little bigger than Jupiter.
They found three worlds orbiting TRAPPIST-1 by watching the planets as they passed in front of the star — a process known as transiting. Whenever a planet transits in front of its host star, it slightly dims the star’s light. That dimming is incredibly small, but with the right instruments, astronomers can sometimes pick up these minute light changes from Earth. Through this process, astronomers can use the dimming to calculate the size, mass, and orbit of a passing planet.
The astronomers decided to keep observing the system and have spent more than 1,000 hours spying on the star and its planets with other telescopes. The new data has helped bring the rest of the planets into view, with NASA’s Spitzer Telescope revealing two planets that could not have been seen from telescopes on the ground. (The telescope’s location in space allows it to bypass Earth’s noisy atmosphere and gather more precise data.) The follow-up observations also revealed that some of the scientists’ original findings had been misinterpreted. One of the original three planets the team had identified turned out to be multiple planets.