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Washington DC [USA], May 6 (ANI): A team of astronomers discovered that the closest known brown dwarf, Luhman 16A, shows signs of cloud bands similar to those seen on Jupiter and Saturn.
This is the first time that scientists have used the polarimetry technique to determine the properties of atmospheric clouds outside the solar system or exoclouds.
Brown dwarfs are objects heavier than planets but lighter than stars, and are typically 13 to 80 times the mass of Jupiter.
Luhman 16A is part of a binary system that contains a second brown dwarf, Luhman 16B. At a distance of 6.5 light years, it is the third closest system to our Sun after Alpha Centauri and Barnard’s Star. Both brown dwarfs weigh approximately 30 times more than Jupiter.
Despite the fact that Luhman 16A and 16B have similar masses and temperatures (approximately 1,900 ° F or 1,000 ° C), and presumably formed at the same time, they show markedly different weather. Luhman 16B shows no signs of stationary cloud bands, rather than exhibiting evidence of more irregular jagged clouds. Luhman 16B, therefore, has noticeable brightness variations as a result of its cloudy characteristics, unlike Luhman 16A.
“Like Earth and Venus, these objects are twins with a very different climate,” said Julien Girard of the Space Telescope Science Institute in Baltimore, Maryland, a member of the discovery team.
“It can rain on things like silicates or ammonia. It’s pretty awful weather, actually,” Girard added.
The researchers used an instrument at the Very Large Telescope in Chile to study polarized light from the Luhman 16 system. Polarization is a property of light that represents the direction in which the light wave oscillates. Polarized sunglasses block a polarization direction to reduce glare and improve contrast.
“Instead of trying to block that glare, we are trying to measure it,” said lead author Max Millar-Blanchaer of the California Institute of Technology (Caltech) in Pasadena, California.
When light is reflected off particles, like cloud drops, it can favor a certain angle of polarization. By measuring the preferred polarization of light from a distant system, astronomers can deduce the presence of clouds without directly solving the cloud structure of brown dwarfs.
“Even light years away, we can use polarization to determine what light found in its path,” Girard added.
“To determine what light found in its path, we compared observations against models with different properties: brown dwarf atmospheres with solid cloud covers, striped cloud bands, and even brown dwarfs that are Oblate due to their rapid rotation. We found that only models of atmospheres with cloud bands could match our observations of Luhman 16A, “explained Theodora Karalidi of the University of Central Florida in Orlando, Florida, a member of the discovery team.
The polarimetry technique is not limited to brown dwarfs. It can also be applied to exoplanets orbiting distant stars. The atmospheres of hot gaseous exoplanets are similar to those of brown dwarfs. While measuring an exoplanet polarization signal will be more difficult, due to its relative fainting and proximity to its star, information obtained from brown dwarfs may potentially inform those future studies.
NASA’s upcoming James Webb Space Telescope could study systems like Luhman 16 to look for signs of brightness variations in infrared light that are indicative of cloud characteristics. NASA’s Wide Field Infrared Reconnaissance Telescope (WFIRST) will be equipped with a coronagraph instrument that can perform polarimetry and can detect giant exoplanets in reflected light and eventual signs of clouds in their atmospheres.
This study has been accepted for publication in The Astrophysical Journal.
The Space Telescope Science Institute (STScI) is expanding the frontiers of space astronomy by hosting the Hubble Space Telescope scientific operations center, the science and operations center for the James Webb Space Telescope, and the scientific operations center for the future widefield infrared. Survey Telescope (WFIRST).
STScI also houses the Mikulski Archive for Space Telescopes (MAST), which is a NASA-funded project to support and provide the astronomical community with a variety of astronomical data files and is the data repository for the Hubble, Webb, Kepler missions , K2, TESS and more. (AND ME)
