05-03-2025
James Webb Space Telescope Spots Mysterious, Free-Floating Mass
The James Webb Space Telescope is helping scientists study a strange mass about 20 light-years from Earth. Traveling unpredictably through the cosmos, the mass is thought to be either a rogue planet or a "failed star," also known as a brown dwarf. Only a close examination of the body's atmosphere will determine which it is.
Astronomers first found SIMP 0136 back in 2003 using Sondage Infrarouge de Mouvement Propre (SIMP), a French term that translates to "infrared proper motion survey." This technique uses two telescopes on opposite hemispheres to capture the movement of a cosmic body in infrared. Strangely, SIMP 0136 appeared to be traveling freely and without a central star around which it could orbit. It also spun very quickly, despite being roughly the same size as Jupiter, making a single SIMP 0136 day only 2.4 hours on Earth.
This led astronomers to believe SIMP 0136 was a rogue planet, or a planet that floats freely through space. But there's a chance the mysterious mass could be something else entirely. Brown dwarfs, otherwise known as failed stars, are the result of gas clouds that have collapsed without gaining enough mass to initiate nuclear fusion—an essential step required to become a "true" star. Brown dwarfs have a minimum mass of 13 Jupiter masses (MJ) and SIMP 0136 has 12.7. SIMP 0136 also emits very little light, though these emissions seem to fluctuate, causing astronomers to be unsure about whether it fits within the brown dwarf category.
Credit: NASA/JPL-Caltech
Webb could help nail down SIMP 0136's classification once and for all. In a paper published Monday in The Astrophysical Journal Letters, researchers in the United States, Canada, and the United Kingdom share their initial findings from Webb observations over two SIMP 0136 rotations. During those rotations, Webb's Near-Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI) examined the body's atmosphere in a wide range of infrared wavelengths, revealing a highly detailed map of SIMP 0136's changes in brightness.
The team used atmospheric models to determine which circumstances might cause the body's light emissions to fluctuate in such a way. From one part of the body, a particular band of infrared light seemed to emanate from deep within the atmosphere; the astronomers think iron particles could be to blame. Emissions within another wavelength are meanwhile thought to come from the upper atmosphere, where clusters of silicates could linger. Still other, brighter patches of light could constitute SIMP 0136's very own version of an aurora.
The jury is still out on whether SIMP 0136 is a rogue planet or a failed star, but these initial Webb findings bring astronomers a bit closer to categorizing the celestial oddball.
"We haven't really figured out the chemistry part of the puzzle yet," Johanna Vos, the study's principal investigator, told NASA. "But these results are really exciting because they are showing us that the abundances of molecules like methane and carbon dioxide could change from place to place and over time. If we are looking at an exoplanet and can get only one measurement, we need to consider that it might not be representative of the entire planet."
