For 20 days, Spitzer observed the TRAPPIST-1 system, watching the star’s brightness decline, then rise again as planets passed by.Ĭombining the Spitzer data with more ground-based measurements, the researchers observed 34 different transits, from which they teased out not three planets but seven. So the researchers turned to the Spitzer Space Telescope, which observes the solar system in infrared light-light with wavelengths longer than the human eye can see. Last year, the researchers spotted the three outermost planets but suspected there were more because previous exoplanet discoveries from the Kepler mission “show that multiplanet systems are very common,” said Katherine Deck, an astronomer at the California Institute of Technology in Pasadena and coauthor of the paper. Instead, many scientists began to wonder: Why not look where our current technology can clearly see? This would be around small, ultracool dwarf stars like TRAPPIST-1, which is one ninth the diameter of our Sun and only half as bright.įollowing this logic, the researchers used the ground-based Transiting Planets and Planetesimals Small Telescope ( TRAPPIST) at the European Southern Observatory’s La Silla site in Chile. Michaël Gillion, lead author of the new paper, said that this is because the light from Sun-like stars often drowns out any signal from small, rocky, Earth-sized planets. Recently, exoplanet hunters have focused attention away from observing stars like our Sun-large and bright-to the smallest, coldest stars to look for planets.

A periodic dip in the star’s brightness means that something moves between the star and Earth on a regular basis, like a planet. The scientists observed the star, called TRAPPIST-1, via ground-based and space-based telescopes, looking for dips in its brightness. To find the seven bodies, the team used the most common method by which scientists find exoplanets: the transit method. Get the most fascinating science news stories of the week in your inbox every Friday. They offer observers a “winning combination” of revealing information because they regularly pass between the star and Earth, throwing doors wide open for detailed atmospheric studies, he continued. The seven planets serve as “true Rosetta Stones” for studying exoplanets, de Wit added. There might even be enough internal heat to generate strong volcanic activity on some of the planets, de Wit said. In addition, the planets’ orbits do not dip very much below or above the plane of the star, which would allow for the star’s gravity to push and pull the planets enough to perhaps produce internal heat. These exoplanets, four of them previously unknown, “are the best targets so far to search for signs of life” outside our solar system, said Julien de Wit, a planetary scientist at the Massachusetts Institute of Technology in Cambridge and coauthor of a paper about the planets published today in Nature.Īll of these remote worlds orbit close to their dim star, meaning that enough energy may reach the outermost planets to provide liquid water. Forty light years away, seven Earth-sized planets circle a small, dim, “ultracool” dwarf star, some completing their orbits as fast as three or four times per Earth month.

Space art view from a planet surface