Our solar system's latest and only third known interstellar visitor is becoming more fascinating by the week.
Spotted in early July, the object, dubbed 3I/ATLAS, is widely believed to be a comet. It's traveling so fast that one look at its speed was enough to let astronomers know that it came from untold thousands of light years away. And it may even be older than our entire solar system.
Now, the James Webb Space Telescope has turned its mighty eye — specifically, its Near-Infrared Spectrograph instrument — towards the object, furnishing us with more details about its size and composition to back up what other observatories, including the Hubble Space Telescope, had found previously.
These findings were published in a new study by researchers at NASA and a host of universities, currently awaiting peer review. And one detail in it is especially tantalizing, as highlighted by Space.com: 3I/ATLAS has among the highest ever ratio of carbon dioxide to water ever observed in a comet. And it also appears that the ice entombed within the comet may have been exposed to higher levels of radiation than comes from our solar system, the authors found.
It's a pristine sample of the greater cosmos delivered, serendipitously, right to our doorstep.
"Continued spectroscopic observations of interstellar objects have the potential to reveal crucial details on the physics and chemistry of planet formation in planetary systems other than our own," reads the paper.
Comets are believed to form in large numbers during the formation of a planetary system, and can get ejected by gravitational encounters with larger objects, like planets, the authors explain. A mixture of rock, ice, and dust, these cosmic snowballs heat up as they near a star like our Sun, causing them to release a glowing cloud of gas called a coma, giving them their distinctive appearance.
The previous interstellar visitor, Borisov, was also believed to be a comet. Both have shown clear signs of cometary activity, such as possessing a coma. But Borisov was largely similar to the well-studied comets in our solar system, the authors wrote, save for unusual levels of carbon monoxide.
With its extreme imbalance of water and carbon, 3I/ATLAS appears to be a far more remarkable object. One scenario that the unprecedentedly high ratio of carbon suggests is that the comet first formed in the circumstellar cloud of gas and dust that surrounds a nascent star called a protoplanetary disk — specifically, near a region called the CO2 ice line, where temperatures are low enough that CO2 molecules can freeze into a solid.
Alternatively, something could be preventing the Sun's warmth from reaching deep into the comet's nucleus, suppressing the sublimation of water ice into water vapor, the authors speculated.
As we speak, 3I/ATLAS is storming towards the solar system's center at over 138,000 miles per hour. Its speed, coupled with its trajectory, point to it originating from the center of the galaxy, possibly in a star system low in heavy elements. And to build up to such an incredible pace, it would have to be unimaginably ancient: perhaps 3 to 11 billion years old, previous research has estimated. The latest James Webb findings could help fill in more blanks about its origins and history.
3I/ATLAS is expected to reach perihelion, its closest distance to the Sun, around October 30 this year, coming within Mars' orbit. Along the way, it'll travel behind the Sun from our perspective — meaning for a while, it'll be impossible to observe.
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