It’s crazy how sometimes science can just surprise you. Think about how an apple falls or a chocolate bar melts—just little moments that lead to big discoveries, even if the stories sound odd. A fresh paper on arXiv sheds light on a fascinating instance: Vera Rubin captured high-res images of the interstellar comet 3I/ATLAS before anyone really knew it was there, and that’s pretty incredible!
So here’s the scoop: when Rubin was doing her Science Validation phase with her telescope, she just happened to be pointing at the right part of the sky. That was between June 21 and July 7, which is actually 10 days before the official discovery of 3I/ATLAS. Just think, three days before iconic “First Look” images went public on June 23. Talk about luck!
This discovery is super vital because those are the earliest snapshots we’ve got from such a powerful telescope. With Rubin’s 8.4-meter Simonyi Survey Telescope combined with the Legacy Survey of Space and Time (LSST), they got the most detailed images of the comet so far! Since the data was gathered before everything was officially set up, it went through customer data processes instead of the usual one used for the megabytes of data Rubin normally collects every night.
In total, there were 49 images analyzed, although some had to be dropped because they got messed up during telescope calibrations, got jumbled with other stars, or were out of focus. Interestingly, 19 of them were actually taken purposefully during those validation operations.
What these images show is a comet that behaved pretty much as expected. They provided solid proof that 3I/ATLAS wasn’t just any object—it really is a comet, featuring that distinct coma of gas and dust around it. As it zoomed in closer to the sun, the size of that coma actually expanded by about 58% during the observation period. Oh, and it even had a tail aimed towards the sun!
Now, why did it have a tail like that? Turns out, this could be explained as “anisotropic dust emission,” which isn’t something you see all the time. Some theories put forward include slow-motion ejection of larger particles that don’t get pushed away from the sun as quickly or that the comet’s rotation is pretty much lined up with its orbital path.
Though here’s where it gets slightly less exciting: unlike 1I/Oumuamua, 3I/ATLAS isn’t showing any signs of weird acceleration not caused by gravity. That doesn’t mean it’s completely off the hook—there’s still a chance it might show that acceleration effect when it hits its perihelion in October. However, the sad part? We won’t be able to see this comet then, as it’s going to be blocked by the sun from September till December.
Rubin will start to lose sight of it right before that on August 22, as it moves out of her viewing area. But here’s a hopeful thought! Between the last captured photo and then, the team expects to snap at least 100 more pictures of the comet. Many might actually be better quality since they weren’t realizing yet they had such a remarkable sight in front of them. A more detailed study will definitely be coming out, albeit without that same surprise element!
More information: Colin Orion Chandler et al, NSF-DOE Vera C. Rubin Observatory Observations of Interstellar Comet 3I/ATLAS (C/2025 N1), arXiv (2025). DOI: 10.48550/arxiv.2507.13409
Provided by Universe Today
This story was originally published on Phys.org.
