It could be argued that methane emissions are the universe’s answer to the old saying, “One man’s trash is another man’s treasure.”
Here on Earth, methane—which is expelled during the production and transportation of coal and natural gas and, yes, by burping cows—is the world’s second largest contributor to global warming, according to the Climate & Clean Air Coalition.
But when discharged from one specific and isolated brown dwarf (a substellar object bigger than a planet but smaller than a star) located 47 light-years away, methane emissions are probably an indication of something far more positive: luminescent bands (similar to Earth’s northern lights) in the object’s atmosphere, according to Daniella Bardalez Gagliuffi, assistant professor of astronomy. Such aurorae, as they are called, could in turn suggest that the aforementioned brown dwarf—named CWISEP J193518.59–154620.3 or W1935, in hardly charismatic shorthand—is orbited by a yet-to-be-seen moon.
“If this does indicate the existence of a moon, it would be momentous, because scientists haven’t yet confirmed a moon outside of our solar system,” said Bardalez Gagliuffi. “Continued research on this object could have truly historic implications.”
As described in a paper they co-authored and published by the prestigious journal Nature in April, Bardalez Gagliuffi and 23 scientists from the American Museum of Natural History, California Institute of Technology, Goddard Space Flight Center, National Optical-Infrared Astronomy Research Laboratory and University of Texas at Austin, among other institutions, discovered the first signature of what is called “methane in emission” in the infrared spectrum of W1935 using NASA’s powerful NIRSpec instrument on board the James Webb Space Telescope (JWST). The team was studying W1935 as part of a larger JWST program gathering information about it and 11 other extremely cold brown dwarfs.
NIRSpec collected infrared light from W1935—which is only slightly hotter than Earth—and spread it through a prism to look at an infrared rainbow of colors. When a color goes missing from the rainbow, explained Bardalez Gagliuffi, it’s because a molecule has absorbed light with that wavelength in the atmosphere of a world outside of the solar system.
In this case, though, the team of scientists saw the opposite: a very bright emission in a part of the spectrum that corresponds to methane.
“This emission suggests there is methane ‘shining’ in the brown dwarf’s atmosphere, which is a phenomenon similar to the northern lights the world experienced in May,” Bardalez Gagliuffi said. “On Earth, the sun provides the charged particles that interact with our planet’s magnetic field, and those particles can glow in auroral events. However, W1935 is not in orbit around a star that can provide a so-called ‘stellar wind’ to produce aurorae on it. That means the culprit might be a hidden active moon.”
Some aurorae on Jupiter are generated when charged particles spewed from volcanoes on Io, one of the planet’s moons, interact with Jupiter’s magnetic field. Bardalez Gagliuffi and her colleagues think that a similar process also involving a moon might be causing the methane in emission in the spectrum of W1935.
While the possibility that she and the team may have found evidence of a still-concealed moon is extremely exciting, the observation of methane in emission on W1935 itself is notable, said Bardalez Gagliuffi. “We typically see a methane absorption feature in objects as cold as W1935,” she noted. “But this is the first time we are seeing it as an emission like we see in Jupiter during auroral events, and in an object that more or less is like an extrasolar Jupiter. That alone is an incredible discovery.”
The fact that the scientific community can see ultracold atmospheres in amazing detail at all and for the first time ever makes it an exciting time for brown dwarf science, Bardalez Gagliuffi added.
“It’s like we’ve finally put on glasses, and everything looks sharp,” she said. “Now we are working to understand this new world we’re seeing.”