Free Astronomy Magazine May-June 2021

42 MAY-JUNE 2021 ASTRO PUBLISHING words, they are in resonance. This means that there are patterns that repeat themselves as the planets go around the star, with some planets aligning every few orbits. A similar resonance is observed in the orbits of three of Jupiter’s moons: Io, Eu- ropa and Ganymede. Io, the closest of the three to Jupiter, completes four full orbits around Jupiter for every orbit that Ganymede, the fur- thest away, makes, and two full or- bits for every orbit Europa makes. The five outer exoplanets of the TOI-178 system follow a much more complex chain of resonance, one of the longest yet discovered in a sys- tem of planets. While the three Jupiter moons are in a 4:2:1 reso- nance, the five outer planets in the TOI-178 system follow a 18:9:6:4:3 chain: while the second planet from the star (the first in the resonance Six-exoplanet system challenges theories of how planets form T he first time an ESO team ob- served TOI-178, a star some 200 light-years away in the constellation of Sculptor, they thought they had spotted two plan- ets going around it in the same or- bit. However, a closer look revealed something entirely different. “Through further observations we realised that there were not two planets orbiting the star at roughly the same distance from it, but rather multiple planets in a very special con- figuration,” says Adrien Leleu from the Université de Genève and the University of Bern, Switzerland, who led a new study of the system pub- lished in Astronomy & Astrophysics . The new research has revealed that the system boasts six exoplanets and that all but the one closest to the star are locked in a rhythmic dance as they move in their orbits. In other by ESO - Bárbara Ferreira