News in Science

Cloudy with a chance of molten iron

Exo-meteorology The first weather map of an unusual type of star called a brown dwarf has revealed a world where it rains molten iron.

The research reported in separate studies in Nature and Astrophysical Journal Letters, has provided astronomers with their clearest view yet of the complicated atmospheric processes occurring in these strange worlds.

A brown dwarf is a low-temperature star that has failed to accumulate enough mass to reach the core temperatures and pressures needed to ignite. Some astronomers suggest brown dwarfs bridge the gap between the largest planets and the smallest stars.

Astronomers used the European Southern Observatory's Very Large Telescope in Chile to directly map out lighter and darker patches on the surface of a brown dwarf known as Luhman 16B.

Located just 6.5 light years away, in the southern constellation of Vela the Sail, Luhman 16B is one half of a pair of brown dwarfs discovered last year.

To map its atmosphere, astronomers monitored changes in brightness at different latitudes and depths as Luhman 16B rotated.

The found a searingly hot atmosphere of patchy clouds made up of droplets of liquid iron and other minerals in an atmosphere of hydrogen at temperatures of over 1000°C .

"Our brown dwarf map helps bring us one step closer to the goal of understanding weather patterns in other solar systems," says Dr Ian Crossfield of the Germany's Max Planck Institute, who is lead author of the paper in Nature.

Complex systems

Previous observations suggested that brown dwarfs might have mottled surfaces, but this new work has allowed scientists to actually map them.

"Soon, we will be able to watch cloud patterns form, evolve, and dissipate on this brown dwarf - eventually, exometeorologists may be able to predict whether a visitor to Luhman 16B could expect clear or cloudy skies," says Crossfield.

The University of Edinburgh's Dr Beth Biller who is the lead author of the study appearing in Astrophysical Journal Letters, examined the clouds at different altitudes within the atmosphere.

"We learned that the weather patterns on these brown dwarfs are quite complex," says Biller.

"The cloud structure varies, depending on atmospheric depth. We are definitely dealing with more than one layer of cloud."

According to Biller these studies are only the start.

"With new generations of telescopes, such as the forthcoming European Extremely Large Telescope, astronomers will likely see surface maps of more distant brown dwarfs, and eventually, surface maps for young giant planets," says Biller.