Webb Detects Silicate Clouds on Nearby Brown Dwarf

by johnsmith

Using the spectral data from the NASA/ESA/CSA James Webb Space Telescope, astronomers have found evidence for silicate clouds as well as water, methane, carbon monoxide, carbon dioxide, sodium, and potassium in the atmosphere of the young brown dwarf VHS J125601.92-125723.9b (hereafter VHS J1256b).

An artist’s impression of the triple brown dwarf system VHS J1256. Image credit: Sci.News.

An artist’s impression of the triple brown dwarf system VHS J1256. Image credit: Sci.News.

VHS J1256 is a triple brown dwarf system located 72 light-years (22.2 parsecs) in the constellation of Corvus.

Also known as TIC 2470992 or SIPS J1256-1257, the system is approximately 140 million years old.

It consists of a binary brown dwarf, VHS J1256AB, and a widely separated companion, VHS 1256b.

The binary has a mass of 73 Jupiter masses, while VHS 1256b is between 11 and 19 times more massive than Jupiter.

The distant companion orbits VHS J1256AB at a distance of 150 astronomical units (AU).

First discovered in 2015, it has a radius of 1.27 Jupiter radii and an effective temperature of 1,100 K.

In a new study, University of California astronomer Brittany Miles and her colleagues aimed to obtain and analyze the detailed spectrum of VHS 1256b.

“The light observed from an exoplanet contains information about the planet’s composition, atmospheric dynamics, and other bulk physical properties,” the astronomers explained.

“This, in turn, can be used to infer how the planet formed and evolved.”

“Various parts of the planet’s spectrum contain different information,” they said.

“For example, in a 1,000-Kelvin gas-giant exoplanet or a more massive brown dwarf analog, the visible part of the spectrum contains alkali lines that can constrain metallicity and surface gravity, the near-infrared part of the spectrum contains water, carbon monoxide, and methane absorption bands that can constrain atomic ratios and turbulent mixing, and the mid-infrared part of the spectrum contains a solid state silicate feature that can be used to measure the compositions of clouds.”

“Webb provides our first opportunity to explore the spectra of brown dwarfs and exoplanets over their full luminous range.”

The spectroscopic observations of VHS 1256b were obtained using Webb’s Near-Infrared Spectrograph (NIRSpec) and the Mid-Infrared Instrument (MIRI).

“The spectrum of VHS 1256b is one of the highest signal-to-noise and broadest spectral coverage wavelength of a brown dwarf or planetary mass companion to-date,” the researchers said.

“The object’s full spectrum displays several absorption features from atmospheric gases that have been previously observed in brown dwarfs, as well as new detections of methane, water, and carbon monoxide at longer wavelengths. There is evidence for carbon dioxide as well.”

“We also directly detect silicate clouds, the first such detection reported for a planetary-mass companion.”

VHS 1256b’s properties paint a picture of a highly dynamic atmosphere, where turbulent convection drives both disequilibrium chemistry and the upwelling of condensible gasses, which form patchy silicate clouds that drive planetary variability.

“These results from Webb are groundbreaking and also obtainable for numerous other nearby brown dwarfs that will be observed in future observation cycles,” the authors said.

“This observatory will be a trailblazer, pushing our understanding of atmospheric physics in planetary-mass companions, brown dwarfs, and exoplanets for years to come.”

Their work will be published in one of the AAS journals.


Brittany E. Miles et al. 2022. The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 Micron Spectrum of the Planetary-Mass Companion VHS 1256-1257b. AAS journals, in press; arXiv: 2209.00620

Source link: https://www.sci.news/astronomy/webb-silicate-clouds-brown-dwarf-11175.html

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