Jupiter-like cloud belt discovered on brown dwarf binary only 6.5 light-years away

[Mobile software: Bo Ke Yuan] Astronomers have discovered that the closest known brown dwarf, Luhman 16A, shows signs of cloud belts similar to those of Jupiter and Saturn. This is the first time that scientists have used polarimetry to determine the characteristics of atmospheric clouds outside the solar system (or exoclouds). Brown dwarfs are objects heavier than planets but lighter than stars, typically with masses 13 to 80 times that of Jupiter. Luhman 16A is part of a binary star system that includes a second brown dwarf, Luhman 16B, which is 6.5 light-years away from the solar system and is the third closest star system to us, after Alpha Centauri and Barnard's Star.

Both brown dwarfs are about 30 times more massive than Jupiter, and although Luhman 16A and Luhman 16B have similar masses and temperatures (about 1,900°F or 1,000°C) and likely formed at the same time, they display markedly different weather. Luhman 16B shows no signs of stationary cloud bands, and instead shows evidence of more irregular clouds. As a result, unlike Luhman 16A, Luhman 16B has significant brightness variations due to its cloudy features. Julien Girard of the Space Telescope Science Institute at Mount Sinai, one of the research team, said:

Like Earth and Venus, these bodies are twins with very different climates. They might rain things like silicates or ammonia. In fact, the weather is pretty bad. The researchers used an instrument on the Very Large Telescope in Chile to study polarized light from the Luhman 16 system. Polarization is a property of light that indicates the direction in which the light waves oscillate. Polarized sunglasses block out one direction of polarization to reduce glare and improve contrast. "Instead of trying to block out this glare, we tried to measure it," said lead author Max Millar-Blanchaer of the California Institute of Technology (Caltech) in Pasadena, California.

When light reflects off particles, such as cloud droplets, it may be biased toward a certain polarization angle. By measuring the polarized light from distant systems, astronomers can infer the presence of clouds without having to directly resolve the brown dwarf's cloud structure. Even from light-years away, polarization can be used to determine what the light encountered on its path. "To determine what the light encountered along the way, we compared our observations to models of different properties," said Theodora Karalidi of the University of Central Florida in Orlando, one of the research team:

Brown dwarf atmospheres with solid clouds, striped cloud bands, and even brown dwarfs that are flattened due to rapid rotation. The study found that only the atmospheric model with cloud bands matched the observations of Luhman 16A. The polarimetry technique is not limited to brown dwarfs, it can also be applied to exoplanets orbiting distant stars. Hot, gas giant exoplanet atmospheres are similar to brown dwarfs. Although measuring the polarization signal of exoplanets will be more challenging because they are relatively faint and close to their stars, the information obtained from brown dwarfs may provide information for future studies.

NASA's upcoming James Webb Space Telescope, due to launch in 2021, will be able to study systems like Luhman 16 for signs of brightness variations in infrared light that indicate the signature of clouds. NASA's Wide Field Infrared Survey Telescope (WFIRST) will be equipped with a coronagraph that can perform polarimetry, perhaps enabling the detection of giant exoplanets in reflected light and, ultimately, signs of clouds in their atmospheres, the study was published in the Astrophysical Journal.

Bo Ke Yuan | Research/From: European Space Agency/Hubble Information Center

The research was published in the journal Astrophysics

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