Context: Recently, a group of astrophysicists have found that the closest known brown dwarf, Luhman 16A which shows signs of cloud bands similar to those seen on Jupiter and Saturn.
Key Points

• The astrophysicists have used an idea put forth nearly two decades ago by Indian astrophysicist Sujan Sengupta that the light emitted by a cloudy brown dwarf, or reflected off an extrasolar planet, will be polarised.
• He suggested that a polarimetric technique could serve as a potential tool to probe the environment of these objects.
• The group, by using the Very Large Telescope at European Southern Observatory, Chile, found that Luhman 16A had band-like clouds in its atmosphere, whereas the same was not true of Luhman 16B.

About Luhman 16

• It is a binary star system, the third closest system to the Sun after Alpha Centauri and Barnard’s star.
• This pair of brown dwarfs referred to as Luhman 16A and Luhman 16B orbit each other, casting a dim light.
• They are at a distance of about 6.5 light years from the Sun.
• Luhman 16B shows no sign of stationary cloud bands, instead showing evidence of more irregular, patchy clouds.
• Luhman 16B, therefore, has noticeable brightness variations as a result of its cloudy features, unlike Luhman 16A which has less brightness variation due to a band of clouds.
• Understanding the cloud system over a brown dwarf can shed light on the pressure, temperature and climate on the surface of the celestial body.

About Brown Dwarfs

• They are also called failed stars, because their masses are intermediate to the largest planets and the smallest main sequence stars.
• Their masses being too small, they are unable to sustain fusion of their hydrogen to produce energy.
• It is believed that some of the more massive brown dwarfs fuse deuterium or lithium and glow faintly.

Significance

• The researchers have now found the actual structure of the clouds. It is found that they form bands over one of the pair (Luhman 16A) of brown dwarfs.
• Since brown dwarfs glow faintly, the faintness of the glow proved to be providential in finding the cloud bands.
• Unlike a star whose brightness would be too high, or an extrasolar planet orbiting a star, where the extra light from its star would have to be cut off to make the measurement, the light of the brown dwarfs was just right.
• Understanding the cloud system over a brown dwarf can shed light on the pressure, temperature and climate on the surface of the celestial body.

About Polarimetry

• It is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves. 
• Polarization is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. 
• In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave.
• Typically polarimetry is done on electromagnetic waves that have traveled through or have been reflected, refracted or diffracted by some material in order to characterize that object.
• It is used in remote sensing applications, such as planetary science, astronomy, weather radar, computational analysis of waves etc.