Webb Telescope captures auroras on a rogue planet as it zips through the galaxy

Astronomers have spotted auroras on a planet-sized object called SIMP 0136, which is currently roaming around our Milky Way galaxy without a star.

The auroral activity seems to be warming the objects upper atmosphere, creating a steady blanket of sand like clouds.

The scientists were able to track the weather on SIMP 0136 using the James Webb Space Telescope as it spins rapidly on its axis, completing one Earth day every 2.4 hours.

The team measured tiny brightness changes as the object rotated and turned those signals into temperature, cloud, and chemistry maps.

They caught signs of a heated upper layer and weather shifts tied to chemistry, with clouds that stay oddly uniform.

Studying rogue world SIMP 0136

Lead author Dr. Evert Nasedkin, Trinity College Dublin, and colleagues focused on SIMP 0136, a nearby brown dwarf that resembles a giant planet but does not orbit a star.

It is young and fast spinning, which makes its atmosphere a sharp test for weather physics beyond our solar system.

Rogue objects like this radiate leftover heat rather than sunlight reflected from a star.

That clean glow makes them perfect targets for spectroscopy, the method of spreading light into colors to read temperature and gases.

How Webb reads exoplanet weather

Webb’s near infrared spectrograph, NIRSpec, recorded one full rotation in Bright Object Time Series (BOTS) mode designed for steady, time stamped spectra of bright targets.

The setup catches subtle flickers caused by features rotating in and out of view.

Webb’s mid infrared instrument, MIRI, added low resolution time series from 5 to 14 microns, a range rich in methane and ammonia features that probe different heights.

Combining both instruments let the team track changes from the deep atmosphere up into the thin air above.

Weather forecast on SIMP 0136

SIMP 0136 shows a thermal inversion in its stratosphere, with temperatures rising again higher up rather than falling.

The inversion peaks a few thousandths of a bar above the main clouds and is about 250 Kelvin stronger than if the air stayed flat with height, a signature the spectra demand.

“These are some of the most precise measurements of the atmosphere of any extra-solar object to date, and the first time that changes in the atmospheric properties have been directly measured,” said Dr. Nasedkin.

Over a full spin, the hemisphere averaged temperature shifts by roughly 5 Kelvin while the object stays very hot overall at more than 1,500 degrees Celsius (2,732 degrees Fahrenheit). 

Methane and other gases probe different layers of the atmosphere, with their absorption features marking changes in pressure. The wavelengths of light correspond directly to distinct atmospheric properties.

Auroras as a heat source

Auroras are a natural suspect for that upper air heating, because energetic particles streaming along magnetic field lines dump power where they collide with gas.

On Jupiter, global upper atmosphere heating has been tied to the polar aurora redistributing energy across the planet.

SIMP 0136 itself pulses at radio wavelengths, evidence for strong magnetically driven currents that can produce auroras and heat, has been found using sensitive radio and spectroscopic measurements.

The new Webb results fit that picture: the inversion sits where methane lines are most sensitive to upper air temperatures, and its strength changes with rotation.

Why rogue clouds stay steady

At these blistering temperatures, clouds on SIMP 0136 are not water-based. They are silicate grains, chemically akin to sand, that condense deep down.

The spectra require a patchy silicate cloud deck near the base of the photosphere, but the coverage stays essentially constant as the world turns.

That steadiness runs against the old idea that flickering brightness near the L/T transition is mostly clouds drifting around. Here, temperature structure does the heavy lifting while the cloud map barely budges.

Carbon dioxide and hydrogen sulfide change slightly with phase and anticorrelate with the temperature shifts, a hint of small scale storms that tug on chemistry as they move.

Other dominant molecules, including water, methane, and carbon monoxide, look uniform across the disk at this precision.

Those chemical clues matter because they set the elemental ratios that track how the object formed. The retrieved carbon to oxygen ratio sits near solar and the overall metal content is only mildly enriched.

Why rogue planets matter

An independent Webb analysis earlier this year linked SIMP 0136’s variability to multiple pressure levels and mechanisms, showing that brightness changes do not come from a single layer.

The new time resolved retrievals sharpen that view by tying specific spectral features to temperature and chemistry changes through depth.

Put simply, multiple dials are turning at once: deep temperature wiggles set the object’s overall brightness, while higher, aurora warmed layers imprint patterns on methane bands.

Weather is physics in motion. On worlds like SIMP 0136, it plays out with exotic materials, fast spins, and powerful magnetic fields, yet the same core rules apply: heat moves, gases mix, light encodes the story.

Time resolved spectra are the key to reading that story. Webb can now watch a world change in minutes and trace cause, effect, and altitude with enough precision to separate temperature from clouds and chemistry.

Next steps for SIMP 0136

Bigger telescopes on the ground will map similar objects in finer detail and test for ion driven glow that proves auroras outright.

Future space missions tuned to habitable planets will borrow these tricks to read winds, clouds, and heat flows on smaller, cooler targets.

SIMP 0136 shows that even without a star, a world can run a lively weather system powered by its own heat and magnetism.

The upper air lights up, the deep air breathes, and the clouds hold steady as the planet sized object spins.

The study is published in Astronomy & Astrophysics.

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