TRAPPIST-1 alien system was not bombarded by space rocks like early Earth
TRAPPIST-1 would be an unremarkable star if not for the scientific interest generated by its seven planets. Located some 40 light years away from the Sun in the constellation of Aquarius, TRAPPIST-1 is a cool, dim star called a red dwarf, the type that is most common in our galaxy, the Milky Way. Around the star, seven exoplanets about the size of Earth – referred to by simple letters from TRAPPIST-1 b to h based on their distance from the star – orbit in a way that astronomers call ‘resonant.’ Resonance means that although each planet takes a different amount of time to complete one orbit, pairs regularly meet again at the same starting point.
For example, for every eight orbits completed by planet TRAPPIST-1 b, which is closest to the star, planet c makes five laps, planet d four and planet e two orbits. Scientists argue that this strangely regular orbital dance wouldn’t be possible if those planets were subjected to too much hammering by space rocks after their birth in the protoplanetary disc that surrounded the newly formed TRAPPIST-1 star some 7 billion years ago.
“We figured out that after these planets formed, they weren’t bombarded by more than a very small amount of stuff,” said astrophysicist Sean Raymond of the University of Bordeaux in France. “That’s kind of cool. It’s interesting information when we’re thinking about other aspects of the planets in the system.” The model suggests that planets in the TRAPPIST-1 system must have formed very early and very fast, in about one-tenth of the time that it took our Earth to form.