The nearest brown dwarf has a cloud band like Jupiter

Astronomers discovered the brown dwarf Luhman 16A surrounded by stable clouds in the atmosphere.

Graphic simulating brown dwarf Luhman 16A. Photo: Caltech.

Brown dwarfs are heavier objects than the planet, but lighter than stars and usually 13 to 80 times more massive than Jupiter. Luhman 16A, together with its "companion" Luhman 16B, create a binary star system only 6.5 light-years from Earth, closer than any other brown dwarf.

Despite having the same mass and temperature (30 times heavier than Jupiter and 1,000 ° C hot), Luhman 16A and 16B actually have markedly different weather patterns. While the outer layer of air of Luhman 16B shows up with patchy and unstable clouds, new research shows that Luhman 16A is surrounded by horizontal bands of standing clouds.

"These two brown dwarfs are twins with different weather, like Earth and Venus," said astronomer Julien Girard from the US Space Telescope Science Institute. "On Luhman 16A there may appear silicates or ammonia. It's really terrible!"

The team used the Very Large Telescope (VLT) in Chile to observe polarized light from the Luhman 16 star system. This is a property representing the oscillation direction of the light wave.

When light is reflected by atmospheric particles, such as cloud droplets, it can be tilted to a certain polarizing angle. By measuring the polarization of light from a distant star system, astronomers can infer the presence of clouds on brown dwarfs.

"Instead of trying to prevent that glare, we sought to measure it," explains lead author Max Millar-Blanchaer from the California Institute of Technology, Caltech. "Although tens of trillions of kilometers away, we can use polarization to determine what light is encountering along the way."

The team compared the observations to a range of different brown dwarf models, such as the atmosphere with only one uniform cloud, or surrounded by striped clouds, or even dwarfs. flat brown due to rapid rotation, but only an atmospheric model surrounded by stable horizontal cloud bands is suitable for Luhman 16A.

Details of the study were published in the Astrophysical Journal on 5/5.