Written by Lucas McClure, NAU PhD student in Astronomy and Planetary Science

On July 1st, scientists in Chile discovered what later became known as 3I/ATLAS, the 3rd interstellar object to ever be captured by our telescopes. Within 24 hours, astronomers from all around the world used other telescopes to observe 3I/ATLAS in wavelengths that inform us about composition. Overall, observational data indicate that 3I/ATLAS is a comet-like object. That is, it's sublimating its ices to generate an all-encompassing "cloud" of materials, which is called a coma. Lines of evidence from a variety of research teams seem to be converging on the idea that this object is composed of similar materials found on objects in our own outer Solar System. This is particularly interesting because interstellar objects are “vagabonds” in a sense. They inform us about the distant solar system which they originated (and were ultimately expelled) from. 

We’ll be able to monitor 3I/ATLAS for the next few months until it starts becoming dimmer and dimmer from our viewpoint here on Earth, leaving our Solar System just as fast as it entered it. While the object is still bright enough, we’ll observe it — numerous times — with world-class telescopes located all around the Earth. In addition, the James Webb Space Telescope (JWST) will provide us with even higher resolution data that will in turn inform us even more about its composition. Ground-based data are good for telling us about 3I/ATLAS's most prominent surface component(s), but JWST will be able to show us specific molecules, which are certain to be investigated for a long while after 3I/ATLAS is gone.

What's great is that this is only the beginning of a new field in planetary astronomy. In a few years time, the Vera C. Rubin Observatory is likely to discover these kinds of objects with a regular cadence as it begins scanning the sky, night after night. In a way, the study of interstellar objects is at the same stage that the study of exoplanets (planets orbiting other stars) was at during the 90s. It's an exciting time for astronomy, which in turn means it's an exciting time for humanity.

As an aside... Also on July 1st, I was flying into the Big Island of Hawaii from Arizona to be trained on how to use the Infrared Telescope Facility (IRTF) atop Mauna Kea. I had intended to go there to observe some really small asteroids in the asteroid belt that I (and a handful of people in the world) care about a lot. I got off the plane, turned my plane off "airplane mode," drove to Mauna Kea, took a long nap after a long travel day, and then woke up to a dozen or so emails informing me about 3I/ATLAS. Given I had two full nights of time on the telescope, I just happened to be at the right place at the right time for a once-in-a-lifetime opportunity. The whole experience was surreal. I was part of a handful of scientists who took the first data on this object in the infrared wavelength range, which -- again -- can help us understand composition. We didn't note any direct detection of water-ice in our observations, but we suggested that the presence of water-ice could indirectly help to explain the spectrum we retrieved, giving an estimated relative abundance of < 7%. Interestingly, a different group (using the same telescope) looked at the object 10 days later, and they claim to detect water-ice directly, giving a relative abundance estimate of ~30%! Though more observations will be needed to really determine the presence of water-ice, the detection is still tenable and might be underscoring the evolution of the object's coma. That is, more and more water-ice may be detected as it nears the Sun, which will sublimate more and more of 3I/ATLAS's ices into its coma that we'll see with further telescopic observation. Again, exciting times!!

Read the scientific publication: https://arxiv.org/abs/2507.12234

Lucas McClure is a PhD Candidate in Astronomy and Planetary Sciences at NAU. He was born in West Tennessee and after graduating from the University of Tennessee, he moved to Northern Arizona in 2021 for graduate school at NAU. In his free time, he enjoys running long distances, listening to the music of Jimmy Buffett, and watching the theatrics & acrobatics of professional wrestling. He is a Lawson scholar.