An article published in the journal “Nature Astronomy” reports a study on the formation of the planets of the ultra-cool star TRAPPIST-1’s system. A team of researchers exploited the particular configuration of the seven rocky planets to calculate how long their formation may have taken, obtaining a maximum value of a few million years, only a tenth of the time it took for the Earth to form. That’s because the resonance that exists between the planets can only have been maintained in the absence of a late bombardment of the kind that occurred in the solar system that completed its planets’ formation. One consequence is that water must have been absorbed by TRAPPIST-1’s planets during their formation in the protoplanetary disk.