Astronomers from the University of Amsterdam have proposed a new method of planet formation for the mysterious TRAPPIST-1 system.
TRAPPIST-1 is fascinating, having an ultra-cool dwarf star orbited by seven known Earth-sized rocky planets. At least three of them may be habitable. All of these orbit within a tenth of the Earth-Sun distance (1 AU, astronomical unit), which is rather peculiar; none of our models of planet formation can really explain how they got here.
One theory we’ve got is the planets formed in the position they are now. However, that seems unlikely in this system because the initial disk from which they formed must have been very dense. If this were the case, the planets would be much larger.
Another theory suggested they migrated from further out in the system. But this theory does not explain why the planets are all roughly the same size as Earth.
So a new, third method may provide an answer. In a paper published in the journal Astronomy and Astrophysics, this team of Dutch researchers say it is actually the debris that formed the planets that migrated inwards, not the planets themselves.
"I hope that our model will help answer the question about how unique our own Solar System is compared to other planetary systems," Chris Ormel, the lead author on the study, said in a statement.
A previous video explaining the orbits of the TRAPPIST-1 planets