Webb’s Infrared Scan Found Methane on Interstellar Comet 3I/ATLAS
In an achievement unprecedented even among modern advances in space science, NASA’s James Webb Space Telescope has chemically characterized an object that didn’t originate in the solar system. Specifically, the Mid-Infrared Instrument (MIRI) onboard Webb picked up methane emissions from interstellar comet 3I/ATLAS as the object journeyed outward through the solar system following its close approach to the Sun.
There are two key takeaways from this discovery. Firstly, the identification of methane is said to be the first chemical fingerprint ever obtained from a true interstellar object, and the first time methane has been observed around an interstellar comet. Secondly, it showcases the exact reason why mid-infrared sensors represent such a powerful technology for spacecrafts to use when characterizing objects.
These results are outlined in a publication from The Astrophysical Journal Letters. Data was collected via Webb in late December and early January around two months after perihelion (closest approach) to the Sun. In other words, the comet had already completed its passage through the inner regions of the solar system, allowing astronomers a chance to observe changes in the chemistry resulting from solar irradiation of the comet.
The latter detail is crucial for understanding the methane observation. In contrast to most gasses, methane is highly volatile meaning that it sublimates from frozen forms easily and quickly. Given that Webb identified methane in a stage post-perihelion, it is theorized that the gaseous compound likely resided beneath the surface of 3I/ATLAS and only became detectable after deeper layers melted from solar warming.
Methane wasn’t the only compound detected by MIRI. The telescope also observed carbon dioxide and water surrounding the comet. The relative concentrations of all three components provided insight into differences between this interstellar object and solar system comets. In particular, Webb found a much higher methane to water ratio in 3I/ATLAS than any comet originating from our system, while earlier observations found similarly high levels of carbon dioxide in this comet.
All of the above strongly suggests that 3I/ATLAS was chemically dissimilar to comets from the solar system. Accordingly, the European Space Agency (ESA) has concluded: “Both these findings point to a very different formation environment and chemistry than the vast majority of comets that formed within our Solar System.”
Technologically speaking, this serves as a prime example of a successful mission for Webb. The MIRI payload contains the Medium Resolution Spectrometer (MRS), which separates incoming infrared light into constituent wavelengths and analyzes their spectrum (at every point on an astronomical target). That allows researchers to determine both the composition of an object’s atmosphere and to create a map of atmospheric gases’ distribution. This capability is especially valuable when studying transients and fleeting visitors to the solar system, as such events don’t give many opportunities for repeated observations over long periods.
Finally, this study highlights the advantages of using space infrared instruments compared with ground telescopes. Observations of 3I/ATLAS continue to be conducted with ground-based telescopes, however, Webb is uniquely positioned to identify and analyze volatiles via infrared spectroscopy in objects like 3I/ATLAS, which already passed perihelion and are starting to leave the inner solar system.
Despite the above, it is too early to make definitive claims about the nature of the methane observation. Notably, the hypothesis that methane existed buried under the surface doesn’t imply any physical proof and remains a purely scientific guess based on time considerations. However, in combination with other evidence, the findings allow researchers to paint a more complete picture. While being foreign to our Solar System alone is a defining characteristic of 3I/ATLAS, it turns out to be foreign in terms of volatile compounds as well.
From an American perspective, the significance of this study is primarily illustrative in nature. This is one of the first times that a U.S.-linked space infrared telescope successfully identified and analyzed volatiles of an interstellar object. If further discoveries in similar events occur, the next question might be whether the observation infrastructure will be able to respond quickly enough. Here, Webb demonstrated just how effectively this can be done.
David Whitaker is an associate editor for AMI’s aerospace and drone systems desk, covering advancements and development of aircraft and drones.
