Brown dwarf may someday harbour habitable planets

The construction site of a miniature solar system has been spotted but, unusually, its central star is a tiny brown dwarf. The star is so small it could be mistaken for a giant planet and it is surrounded by a disc of material chunky enough to form several planets the size of Earth or Mars. The discovery calls for a rethink of how diverse planetary systems can be, says Kevin Luhman of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, US. 'We always just think of planets forming around stars about the mass of our Sun,' he says. 'But they could form in more exotic situations around very small brown dwarfs - there might be mini solar systems out there.' Brown dwarfs are 'failed' stars with masses of about 15 to 70 times that of Jupiter. They are thought to form like ordinary stars, from a collapsing cloud of gas and dust. But unlike ordinary stars, they do not generate enough heat to trigger the sustained nuclear fusion of hydrogen nuclei that makes stars burn bright. Earlier studies had shown that several medium-sized brown dwarfs are surrounded by discs of material that could clump together to form planets, just as planets like Earth emerged in a disc of debris around the young Sun. Astronomers spotted telltale signs of the cool discs around these dwarfs using ground-based infrared telescopes. But it is often hard to study the discs because they were faint in comparison to the infrared glare from the brown dwarf itself. Now a team led by Luhman has found compelling evidence for a disc surrounding a much smaller, cooler brown dwarf, weighing in at just 15 times the mass of Jupiter - an exceedingly small mass for a star." [New Scientist]