Free Astronomy Magazine September-October 2016

proven conclusively and they are un- likely to be settled without direct ob- servational evidence and characteri- sation of the planet’s atmosphere. Similar factors apply to the planets recently found around TRAPPIST-1. Two separate papers discuss the hab- itability of Proxima b and its cli- mate. They find that the existence of liquid water on the planet today cannot be ruled out and, in such case, it may be present over the sur- face of the planet only in the sun- niest regions, either in an area in the hemisphere of the planet facing the star (synchronous rota- tion) or in a tropical belt (3:2 resonance ro- tation). Proxima b's ro- tation, the strong ra- diation from its star and the formation his- tory of the planet makes its climate quite different from that of the Earth, and it is un- likely that Proxima b has seasons. This dis- covery will be the be- ginning of extensive further observations, both with current in- struments and with the next generation of giant telescopes such as the European Extremely Large Telescope (E-ELT). Some methods to study a planet’s atmosphere depend on it passing in front of its star and the starlight passing through the at- mosphere on its way to Earth. Currently there is no evidence that Proxima b transits across the disc of its parent star, and the chances of this happening seem small, but fur- ther observations to check this possi- bility are in progress. Proxima b will be a prime target for the hunt for evidence of life elsewhere in the Uni- verse. Indeed, the Alpha Centauri system is also the target of human- kind’s first attempt to travel to an- other star system, the StarShot proj- ect. Guillem Anglada-Escudé con- cludes: “Many exoplanets have been found and many more will be found, but searching for the closest poten- tial Earth-analogue and succeeding has been the experience of a lifetime for all of us. Many people’s stories and efforts have converged on this discovery. The result is also a tribute to all of them. The search for life on Proxima b comes next...” T his video takes the viewer from Earth to the closest star, Proxima Centauri. Here we can see the planet Proxima b, which orbits its red dwarf star every 11.2 days. This planet orbits within the habitable zone, shown in green, which means that liquid water could exist on its surface. [PHL @ UPR Arecibo, ESO] n