2.6 Barnard’s Star b
In November 2018, another thrilling discovery was announced – an exoplanet orbiting the nearest single star to the Sun, six light years away. This star is called Barnard’s Star, named after the astronomer who first studied it. Like Proxima Centauri, Barnard’s Star is an M dwarf, about a tenth the mass of the Sun. There is one big difference between the planet, Barnard’s Star b, and Proxima b though – it has a much longer orbital period: 233 days compared with 11 days. Discovering a planet with such a long orbital period required the enormous task of very carefully combining many radial velocity measurements spanning 20 years from seven different instruments, and astronomers at The Open University were a key part of the team that did this.
This means that Barnard’s Star b is also much further away from its dim parent star than Proxima b is, making it an icy world predicted to experience temperatures of −150 °C. This doesn’t rule out the prospect of life completely though – a thick atmosphere creating a strong greenhouse effect could raise the surface temperature to create a more hospitable environment. Another scenario is that even if liquid water can’t exist on the surface, it could exist beneath the surface. This is akin to Jupiter’s moon, Europa, which is known to have similar icy surface temperatures but a sub-surface liquid water ocean – a tantalising potential habitat for life.