Free Astronomy Magazine September-October 2016

O n 24 August 2016 at 13:00 CEST, ESO hosted a press con- ference at its Headquarters in Gar- ching, near Munich, Germany. In this image, Prof. Dr. Ansgar Reiners speaks. [ESO/M. Zamani] T his infographic compares the or- bit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System. Proxima Centauri is smaller and cooler than the Sun and the planet orbits much closer to its star than Mercury. As a result it lies well within the habita- ble zone, where liquid water can exist on the planet’s surface. [ESO/M. Kornmesser/G. Coleman] Radial velocity data taken when the star was flaring were excluded from the final analysis. Although Proxima b orbits much closer to its star than Mercury does to the Sun in the Solar System, the star itself is far fainter than the Sun. As a result Proxima b lies well within the habitable zone around the star and has an estimat- ed surface temperature that would allow the presence of liquid water. Despite the temperate orbit of Prox- ima b, the conditions on the surface may be strongly affected by the ul- traviolet and X-ray flares from the star — far more intense than the Earth experiences from the Sun. The actual suitability of this kind of planet to support water and Earth- like life is a matter of intense but mostly theoretical debate. Major concerns that count against the presence of life are related to the closeness of the star. For exam- ple gravitational forces probably lock the same side of the planet in perpetual daylight, while the other side is in perpetual night. The plan- et's atmosphere might also slowly be evaporating or have more com- plex chemistry than Earth’s due to stronger ultraviolet and X-ray radia- tion, especially during the first bil- lion years of the star’s life. However, none of the arguments has been of 11.2 days. Careful analysis of the resulting tiny Doppler shifts showed that they indicated the presence of a planet with a mass at least 1.3 times that of the Earth, orbiting about 7 million kilometres from Proxima Centauri — only 5% of the Earth-Sun distance. Guillem Anglada-Escudé comments on the excitement of the last few months: “I kept checking the consis- tency of the signal every single day during the 60 nights of the Pale Red Dot campaign. The first 10 were promising, the first 20 were consis- tent with expectations, and at 30 days the result was pretty much de- finitive, so we started drafting the paper!” Red dwarfs like Proxima Centauri are active stars and can vary in ways that would mimic the presence of a planet. To exclude this possibility the team also monitored the chang- ing brightness of the star very care- fully during the campaign using the ASH2 telescope at the San Pedro de Atacama Celestial Explorations Ob- servatory in Chile and the Las Cum- bres Observatory telescope network.