A phantom “Super-Jupiter” 13 times more massive than our solar system’s gas giant is drifting through the cosmos around 20 light-years from Earth. Although discovered in 2006, the “free-floating planetary-mass object” known as SIMP 0136 has continued to stump astronomers for nearly two decades—is it a rogue planet, failed star, or something else entirely? Thanks to an international team’s recent work utilizing NASA’s James Webb Space Telescope (JWST), newly recorded details are helping clarify the nature of SIMP 0136. The results, published on March 3 in The Astrophysical Journal Letters, depict a complicated cosmic body that continues to expand our understanding of the universe.
First detected nearly 20 years ago, SIMP J013656.5+093347 (SIMP 0136, for short) appears to be a rapidly rotating, planet-sized object situated in the Pisces constellation. It’s relatively isolated in the northern sky, and is the region’s brightest entity of its kind. Taken altogether, SIMP 0136 offers astronomers one of the best options for exo-meteorological study.
Previous examinations using ground-based tools as well as the Hubble and Spitzer space telescopes indicated SIMP 0136 was potentially a brown dwarf—a cosmic body with the makings of a star that nonetheless fails to gather enough mass to initiate nuclear fusion. Unique characteristics, however, kept astronomers perplexed: its fluctuating brightness suggested the existence of complex atmospheric conditions beyond just clouds. The more they learned about SIMP 0136, the more it appeared to be an exoplanet, albeit one lacking a star to orbit.
“We already knew that it varies in brightness, and we were confident that there are patchy cloud layers that rotate in and out of view and evolve over time,” Boston University researcher Allison McCarthy explained in a statement on March 3. “We also thought there could be temperature variations, chemical reactions, and possibly some effects of auroral activity affecting the brightness, but we weren’t sure.”
To try solving some of these mysteries, McCarthy and colleagues recently trained the JWST on SIMP 0136 for two full rotations, then gathered data using the telescope’s Near-Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI). The results generated hundreds of wavelength measurements across the infrared light spectrum that McCarthy’s team could analyze for changes over the course of its speedy rotation.
“Until now, we only had a little slice of the near-infrared spectrum from Hubble, and a few brightness measurements from Spitzer,” principal investigator and Trinity College Dublin researcher Johanna Vos added. “To see the full spectrum of this object change over the course of minutes was incredible.”
The team noticed SIMP 0136 exhibited several distinct light-curve shapes simultaneously. As some wavelengths grew in brightness, others dimmed or remained relatively stable. This implied that multiple influences trigger the variations. Co-author Philip Muirhead from Boston University likened the observations to examining Earth from very far away.
“Blue would increase as oceans rotate into view. Changes in brown and green would tell you something about soil and vegetation,” he said.
These light curves show the change in brightness of three different sets of wavelengths (colors) of near-infrared light coming from the isolated planetary-mass object SIMP 0136 as it rotated. The light was captured by Webb’s NIRSpec (Near-Infrared Spectrograph), which collected a total of 5,726 spectra — one every 1.8 seconds — over the course of about 3 hours on July 23, 2023. Credit: NASA / Space Telescope Science Institute (STScI)
Additional atmospheric modeling helped the team next assess the likely depth origins of each light wavelength, which could further clarify SIMP 0136’s details. One wavelength group located deep in the atmosphere suggests patchy clouds composed of iron particles, while higher clouds potentially contain silicate minerals. A third wavelength cluster, however, seems to exist at an extremely high altitude and correspond to temperature hot spots. Experts believe these could come from previously observed auroras, or potentially plumes of hot gas rising from deeper in the atmosphere.
Not all of the light curves can be explained just yet, and don’t relate to clouds or temperature. Researchers believe these likely depict differences in atmospheric carbon chemistry, such as pockets of carbon monoxide and carbon dioxide.
Vos admitted they “haven’t really figured out the chemistry part of the puzzle yet,” but remains excited by the latest round of discoveries. The data also underscores the diversity of exoplanets like SIMP 0136.
“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,” said Vos.
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