Using the James Webb Space Telescope (JWST), astronomers have peered into the atmosphere of a cosmic body that could be a rogue planet or a “failed star.” Either way, the world wanders the cosmos without a parent.
The cosmic orphan, or “free-floating planetary-mass object,” designated SIMP 0136 drifts through the universe around 20 light-years from Earth — and it does so without a stellar anchor. SIMP 0136 has a mass that’s around 13 times the mass of Jupiter, but it is around the same size as the solar system gas giant. Discovered in 2003, SIMP 0136 rotates so rapidly that a day on this rogue world lasts just around 2.4 Earth hours.
There is a possibility that SIMP 0136 isn’t a planet at all but is an object called a “brown dwarf,” a stellar body that forms like a star but fails to gather enough mass to trigger the nuclear fusion of hydrogen to helium in its core. The confusion arises from the fact that these “failed stars” have a lower mass limit of around 13 times the mass of Jupiter — right around the mass of SIMP 0136, in fact.
Because SIMP 0136 is relatively bright for an isolated planetary mass object and its light isn’t contaminated by the light of a parent star, it has been a popular target for astronomers.
Thus, even before the JWST examined this object, a range of ground-based instruments as well as the Hubble and Spitzer space telescopes had studied it. These investigations, however, left astronomers with some puzzles surrounding SIMP 0136.
Astronomers had previously discovered that SIMP 0136 fluctuates in brightness. It was reasoned that these changes couldn’t simply be the result of clouds on the Jupiter-size world alone, but rather have to do with a complex combination of atmospheric factors.
Using the JWST, the team was able to monitor infrared light from SIMP 0136 for two full rotations, observing variations in the world’s cloud layers, temperature and even its chemistry. Many of the details the scientists observed were previously hidden from view.
“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,” Allison McCarthy, study team leader and a researcher at Boston University, said in a statement. “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.”
Thousands of invisible rainbows
Observing SIMP 0136 with the JWST over two rotations allowed the team to use the telescope’s Near-Infrared Spectrograph (NIRSpec) as well as its Mid-Infrared Instrument (MIRI). This meant the researchers could collect data in a wide range of wavelengths of infrared light.
The result was hundreds of highly detailed light curves showing how each wavelength of infrared light changed in brightness as SIMP 0136 rotated.
“To see the full spectrum of this object change over the course of minutes was incredible,” Johanna Vos , the team’s principal investigator and a researcher at Trinity College Dublin, said in the statement. “Until now, we only had a little slice of the near-infrared spectrum from Hubble, and a few brightness measurements from Spitzer.”
The researchers noticed that the infrared light from SIMP 0136 had distinct light curve shapes, with some wavelengths brightening while others dimmed; the rest did not change at all.
They reasoned there must be various factors influencing these variations.
“Imagine watching Earth from far away. If you were to look at each color separately, you would see different patterns that tell you something about its surface and atmosphere, even if you couldn’t make out the individual features,” Philip Muirhead, study team member and a researcher at Boston University, said in the statement. “Blue would increase as oceans rotate into view. Changes in brown and green would tell you something about soil and vegetation.”
To assess what is causing the light variations of SIMP 0136, the team developed atmospheric models to determine which regions of the atmosphere were responsible for which wavelength of light.
“Different wavelengths provide information about different depths in the atmosphere,” McCarthy said. “We started to realize that the wavelengths that had the most similar light-curve shapes also probed the same depths, which reinforced this idea that they must be caused by the same mechanism.”
One band of infrared wavelengths originated from deep into the atmosphere of SIMP 0136 where the team suspects patchy clouds of iron particles lurk. Another wavelength grouping is thought to come from higher in the atmosphere and patchy clouds of silicates.
The final set of wavelengths are theorized to originate from high above these clouds in relation to the temperature of SIMP 0136. Brighter areas could correspond with auroras detected around SIMP 0136 in radiowaves.
Alternatively, these bright patches could be the result of hot gas traveling upwards through the atmosphere of SIMP 0136.
There are light curves that the JWST saw from SIMP 0136 that can’t be explained by either the object’s clouds or its temperature.
These could be influenced by the carbon chemistry of SIMP 0136’s atmosphere, as pockets of carbon dioxide and carbon monoxide rotated in and out of the JWST’s view. Another explanation could be chemical reactions causing changes in the atmosphere of SIMP 0136.
“We haven’t really figured out the chemistry part of the puzzle yet, 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,” Vos said. “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.”
The team’s research was published on Monday (March 3) in the Astrophysical Journal Letters.
