Astronomers using the NASA/ESA/CSA James Webb Space Telescope have found evidence for the deposition of energy into the upper atmosphere of the nearby brown dwarf SIMP J013656.5+093347.3 by an aurora.
An artist’s impression of aurora on the brown dwarf SIMP-0136. Image credit: Evert Nasedkin.
SIMP J013656.5+093347.3 (SIMP-0136 for short) is a low-mass brown dwarf located just 6.12 parsecs (20 light-years) away from Earth in the constellation of Pisces.
As a member of the Carina-Near stellar association, the object is estimated to be 200 million years old.
SIMP-0136’s mass has been estimated to range from 12.7 to 17.8 Jupiter masses.
With a spectral type of T2.5 and a temperature of around 1,100 K, it shares many similar atmospheric properties to directly imaged exoplanets, such as HR 8799b or AF Lep b.
“Our observations illuminated SIMP-0136’s strong auroral activity, similar to the Northern Lights here on Earth or the powerful aurora on Jupiter, which heat up its upper atmosphere,” said Dr. Evert Nasedkin, an astronomer at Trinity College Dublin.
“These are some of the most precise measurements of the atmosphere of any extrasolar object to date, and the first time that changes in the atmospheric properties have been directly measured.”
“And at over 1,500 degrees Celsius, SIMP-0136 makes this summer’s heat wave look mild.”
“The precise observations we made meant we could accurately record temperature changes smaller than 5 degrees Celsius.”
“These changes in temperature were related to subtle changes in the chemical composition of this free-floating planet, which is suggestive of storms — similar to Jupiter’s Great Red Spot — rotating into view.”
Another surprise finding was the lack of variability of the clouds on SIMP-0136.
One might expect changes in the cloud coverage to lead to changes in the atmosphere, similar to observing patches of clouds and blue sky here on Earth.
Instead, the astronomers found that the cloud coverage was constant over the surface of SIMP-0136.
At the temperatures of SIMP-0136 these clouds are unlike those on Earth, instead composed of silicate grains, similar to sand on a beach.
“Different wavelengths of light are related to different atmospheric features,” Dr. Nasedkin said.
“Similar to observing the changes in color over the surface of the Earth, the changes in the color of SIMP-0136 are driven by changes in the atmospheric properties.”
“So by using cutting-edge models, we could infer the temperature of the atmosphere, the chemical composition, and the position of the clouds.”
“This work is exciting because it shows that by applying our state-of-the-art modelling techniques to cutting-edge datasets from Webb, we can begin to piece together the processes that drive weather in worlds beyond our Solar System,” said Trinity College Dublin’s Professor Johanna Vos.
“Understanding these weather processes will be crucial as we continue to discover and characterize exoplanets in the future.”
“While for now these types of spectroscopic variability observations are limited to isolated brown dwarfs, like this one, future observations with the Extremely Large Telescope and eventually the Habitable Worlds Observatory will enable the study of the atmospheric dynamics of exoplanets, from Jupiter-like gas giants to rocky worlds.”
The team’s findings appear in the journal Astronomy & Astrophysics.
_____
E. Nasedkin et al. 2025. The JWST weather report: Retrieving temperature variations, auroral heating, and static cloud coverage on SIMP-0136. A&A 702, A1; doi: 10.1051/0004-6361/202555370
