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Coldest known brown dwarf shows evidence of water clouds

Artist's illustration of how the nearby brown dwarf WISE 0855 might appear if viewed close-up in infrared light. Credit: Joy Pollard, Gemini Observatory/AURA

Infrared spectral data obtained by researchers provides strong evidence that the coldest known brown dwarf star has water clouds in its atmosphere.

WISE 0855, discovered in 2014 only 7.2 light years from Earth, is a brown dwarf, or failed star, formed via the gravitational collapse of gas and dust but not massive enough to sustain hydrogen fusion in its core.

Some brown dwarfs fuse deuterium, an isotope of hydrogen or experience fusion for only a brief time. Because  fusion is what makes stars luminous, brown dwarfs are very dim and often visible only in infrared wavelengths.

The coldest object discovered outside our solar system, WISE 0855 has about five times the mass of Jupiter and a temperature of about 250 degrees Kelvin or minus 10 degrees Fahrenheit.

Jupiter’s temperature is about 130 degrees Kelvin.

“WISE 0855 is our first opportunity to study an extrasolar planetary-mass object that is nearly as cold as our own gas giants,” said UC Santa Cruz assistant professor of astronomy and astrophysics Andrew Skemer, who is also first author of a paper that will be published in Astrophysical Journal Letters.

“We would expect an object that cold to have water clouds, and this is the best evidence that it does.”

Skemer and his research team used the Gemini North telescope in Hawaii to obtain the spectral data on WISE 0855 that has yielded details about its chemistry and composition.

An object’s spectrum separates its light into component wavelengths and therefore makes it possible to determine that object’s composition.

Earlier observations of WISE 0855 suggested the presence of water clouds.

Skemer’s team observed the brown dwarf for 13 nights over a total of 14 hours using both the Gemini North telescope and the Gemini Near Infrared Spectrograph.

“It’s five times fainter than any other object detected with ground-based spectroscopy at this wavelength,” Skemer said of WISE 0855. “Now that we have a spectrum, we can really start thinking about what’s going on in this object. Our spectrum shows that WISE 0855 is dominated by water vapor and clouds, with an overall appearance that is strikingly similar to Jupiter.”

The brown dwarf’s atmosphere is less turbulent than Jupiter’s, as evidenced by a lack of the compound phosphine in its atmosphere.

Phosphine forms in the hot interiors of gas giants and reacts in their cooler outer atmospheres, in the process forming other compounds.

Atmospheres containing phosphine experience turbulent mixing not seen in those lacking this substance.

Laurel Kornfeld

Laurel Kornfeld

Staff Writer
Laurel Kornfeld is a freelance writer and amateur astronomer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science in astronomy from Swinburne University’s Astronomy Online program.
About Laurel Kornfeld (980 Articles)
Laurel Kornfeld is a freelance writer and amateur astronomer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science in astronomy from Swinburne University’s Astronomy Online program.