First weather map of a brown dwarf
January 31, 2014
ESO‘s Very Large Telescope has been used to create the first ever map of the weather on the surface of the brown dwarf* nearest to Earth.
An international team has made a chart of the dark and light features on WISE J104915.57-531906.1B (“Luhman 16B”) — one of two recently discovered brown dwarfs forming a pair only six light-years from the Sun.
Ian Crossfield (Max Planck Institute for Astronomy, Heidelberg, Germany), the lead author of the new paper published in the January 30, 2014 issue of the journal Nature., sums up the results: “Previous observations suggested that brown dwarfs might have mottled surfaces, but now we can 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.”
To map the surface the astronomers used a clever technique. They observed the brown dwarfs using the CRIRES instrument on the VLT. This allowed them not just to see the changing brightness as Luhman 16B rotated, but also to see whether dark and light features were moving away from, or towards the observer. By combining all this information they could recreate a map of the dark and light patches of the surface.
The atmospheres of brown dwarfs are very similar to those of hot gas giant exoplanets, so by studying comparatively easy-to-observe brown dwarfs astronomers can also learn more about the atmospheres of young, giant planets — many of which will be found in the near future with the new SPHERE instrument that will be installed on the VLT in 2014.
“Our brown dwarf map helps bring us one step closer to the goal of understanding weather patterns in other solar systems,” said Crossfield.
* Brown dwarfs are in between giant gas planets, such as Jupiter and Saturn, and faint cool stars. They do not contain enough mass to initiate nuclear fusion in their cores and can only glow feebly at infrared wavelengths of light. The first confirmed brown dwarf was found 20 years ago and only a few hundred of these elusive objects are known.
Abstract of Nature paper
Brown dwarfs — substellar bodies more massive than planets but not massive enough to initiate the sustained hydrogen fusion that powers self-luminous stars — are born hot and slowly cool as they age. As they cool below about 2,300 kelvin, liquid or crystalline particles composed of calcium aluminates, silicates and iron condense into atmospheric ‘dust’, which disappears at still cooler temperatures (around 1,300 kelvin). Models to explain this dust dispersal include both an abrupt sinking of the entire cloud deck into the deep, unobservable atmosphere and breakup of the cloud into scattered patches(as seen on Jupiter and Saturn). However, hitherto observations of brown dwarfs have been limited to globally integrated measurements, which can reveal surface inhomogeneities but cannot unambiguously resolve surface features. Here we report a two-dimensional map of a brown dwarf’s surface that allows identification of large-scale bright and dark features, indicative of patchy clouds. Monitoring suggests that the characteristic timescale for the evolution of global weather patterns is approximately one day.