Free Astronomy Magazine January-February 2018

34 JANUARY-FEBRUARY 2018 SPACE CHRONICLES elaborate planetary system, and not just a single planet, around the star closest to our Sun.” Dust belts are the remains of mate- rial that did not form into larger bodies such as planets. The particles of rock and ice in these belts vary in size from the tiniest dust grain, smaller than a millimetre across, up to asteroid-like bodies many kilome- tres in diameter. Dust appears to lie in a belt that extends a few hundred million kilometres from Proxima Centauri and has a total mass of about one hundredth of the Earth’s mass. This belt is estimated to have a temperature of about –230 de- grees Celsius, as cold as that of the Kuiper Belt in the outer Solar Sys- tem. There are also hints in the ALMA data of another belt of even colder dust about ten times further out. If confirmed, the nature of an outer belt is intriguing, given its very cold environment far from a star that is cooler and fainter than ALMA discovers cold dust around nearest star by ESO P roxima Centauri is the closest star to the Sun. It is a faint red dwarf lying just four light- years away in the southern constel- lation of Centaurus (The Centaur). It is orbited by the Earth-sized tem- perate world Proxima b, discovered in 2016 and the closest planet to the Solar System. But there is more to this system than just a single planet. The new ALMA observations reveal emission from clouds of cold cosmic dust surrounding the star. The lead author of the new study, Guillem Anglada, from the Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain, explains the signif- icance of this find: “The dust around Proxima is important because, fol- lowing the discovery of the terres- trial planet Proxima b, it’s the first indication of the presence of an