An article published in the journal “Astronomy & Astrophysics” describes a study of the internal structure and tidal warming of the 7 planets of the ultra-cool dwarf star TRAPPIST-1 system. Amy C. Barr, Vera Dobos, and László L. Kiss created models of those 7 planets, concluding that two of them are most likely to be habitable because the temperatures on their surface could allow the presence of liquid water.