What can auroras on a rogue planet teach astronomers about planetary formation and evolution? This is what a recent study published in Astronomy & Astrophysics hopes to address as an international team of researchers investigated the atmospheric composition of a nearby rogue planet, including its atmospheric temperature and auroras. This study has the potential to help astronomers better understand rogue planets, along with additional planetary atmospheric formation and evolutionary traits.
For the study, the researchers used NASA’s James Webb Space Telescope (JWST) to examine SIMP-0136, which is a rogue planet located approximately 20 light-years from Earth while being approximately 12.7 times the mass and approximately 1.2 times the radius of Jupiter. Additionally, SIMP-0136 only has a rotational period of 2.4 hours, enabling the researchers to observe all aspects of the rogue planet. Additionally, the researchers used a series of computer models to better understand their observations.
In the end, the researchers made a few surprise discoveries, including that SIMP-0136’s atmosphere exhibits what’s called thermal inversion, meaning the atmospheric temperature is colder near the surface and hotter as the altitude increases. This is in stark contrast to traditional atmospheric compositions, as Earth, for example, exhibits warmer temperatures near the surface while gradually decreasing in temperature with increasing altitude.
The team found that SIMP-0136’s auroras were responsible for heating up the rogue planet’s upper atmosphere, along with discovering constant global cloud coverage, which contrasts planets like Earth that experience constant break in cloud coverage across the globe. Finally, the team discovered the clouds were composed of silicate grains like beach sand, as opposed to water droplets or ice crystals as seen on Earth.
“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. Evert Nasedkin, who is a Postdoctoral Fellow at Trinity College Dublin and lead author of the study. “And at over 1,500°C, 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 °C. 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.”
This research builds on JWST data that was analyzed in a March 2025 study published in The Astrophysical Journal Letters that discovered atmospheric clouds, hot spots, and carbon chemistry variances. While that study was unable to ascertain the processes responsible for the atmospheric variances, this most recent study successfully identified that the auroras were responsible for them, along with the thermal inversion, as noted above. With an average temperature of more than 1,500°C, this makes SIMP-0136 far hotter than Jupiter and Saturn at -145°C (-229°F) and -178°C (-288°F), respectively.
First discovered in 2000, rogue planets have grabbed the attention of astronomers worldwide due to their unique characteristic of not having a star to orbit, as their “rogue” name implies. There are several hypotheses regarding their formation and evolution, including being ejected from their original star systems or being sub-brown dwarf stars. It is currently estimated that there could be between billions to trillions of rogue planets throughout the Milky Way Galaxy. However, astronomers are quick to note the extremely unlikely chance that a rogue planet will enter our solar system, let alone pose a threat to life on Earth. Going forward, the upcoming Nancy Grace Roman Space Telescope, which is scheduled to launch in May 2027, will help filter this number down.
What new discoveries regarding rogue planet auroras will astronomers make in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!