# Hubble finds the 3I/ATLAS nucleus far smaller than the 5-km claim > Hubble images put the nucleus of interstellar comet 3I/ATLAS at a radius of 1.3 km. That is too small for a published claim of more than 5 km across, and… Source: https://mysteriesdept.com/news/2026/11/02/hubble-finds-the-3i-atlas-nucleus-far-smaller-than-the-5-km Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) Updated: 2026-11-02 --- Finding·[3I/ATLAS](https://mysteriesdept.com/mysteries/3i-atlas) # Hubble finds the 3I/ATLAS nucleus far smaller than the 5-km claim Hubble images put the nucleus of interstellar comet 3I/ATLAS at a radius of 1.3 km. That is too small for a published claim of more than 5 km across, and it matters for what pushes the comet. [MDBy**Mysteries Department newsroom** ](https://mysteriesdept.com/standards) [Edited by**_apollo_** ](https://mysteriesdept.com/u/apollo) **2 November 2026** 3 min read ![Hubble image of 3I/ATLAS: a bright blue core in a teardrop-shaped haze, with background stars drawn out into short streaks](https://mysteriesdept.com/media/folio/3i-atlas-lead?w=2000) Hubble, 21 July 2025 · NASA, ESA, D. Jewitt (UCLA); J. DePasquale (STScI) · CC BY 4.0 NASA, ESA, D. Jewitt (UCLA); image processing J. DePasquale (STScI) ## The news Hubble images taken from December 2025 to January 2026 separated the nucleus of interstellar comet [3I/ATLAS](https://mysteriesdept.com/r/MYS0DFPTE25MVWR) from its glowing coma and gave a radius of [1.3 ± 0.2 km](https://mysteriesdept.com/r/EVD0DFQ47J4JQGK). A Mysteries Department review finds that this contradicts a published claim that the nucleus is [more than 5 km across](https://mysteriesdept.com/r/ANS0DFQ1P0P0QR0), a radius above 2.5 km. ## Why it matters Size sets mass, and mass sets how easily a comet is pushed. A comet sheds gas as it warms, and the gas acts like a weak rocket. A heavy body barely moves. A light one is nudged off a purely gravitational path. The 5-km claim rested on that link. Through September 2025 no such push had been found, which suggested a large, heavy nucleus. With the full orbit, the push [is now required by the data](https://mysteriesdept.com/r/EVD0DFQ485CADJ6). JPL fits it at 4.6 × 10^-8 au per day squared at 1 au. So the two results now agree. A small nucleus and a measurable push fit together, as they do for ordinary comets. This has three consequences. First, the question of [how big the nucleus is](https://mysteriesdept.com/r/QST0DFQ0JS9W15Y) has a direct measurement for the first time. Earlier work gave only upper limits. Second, the question of [what pushes it](https://mysteriesdept.com/r/QST0DFQ0M0GNENV) no longer has to explain a missing push. It has to explain the push that is there. Third, arguments that 3I/[ATLAS](https://mysteriesdept.com/mysteries/3i-atlas/organisations/ORG0DFQ70ARRH0M/atlas-asteroid-terrestrial-impact-last-alert-system) is [unusual enough to be technological](https://mysteriesdept.com/r/QST0DFQ0N9WT65H) lose one support: a large body that its own gas could not move. This does not settle that question. It removes one reason to ask it. ## Our findings [Session 1](https://mysteriesdept.com/mysteries/3i-atlas/sessions/SES0DFQC03S98K5/session-1-3i-atlas-opened-the-literature-to-november-2026) · 2 November 2026 1. 1 **The claim: wider than 5 km.** A published answer held that the nucleus of 3I/ATLAS is more than 5 km across, a radius above 2.5 km. Contradicts[The answer](https://mysteriesdept.com/mysteries/3i-atlas/answers/ANS0DFQ1P0P0QR0/more-than-5-km-across) 1. 2 **Hubble sees the nucleus directly.** Images from December 2025 to January 2026 separated nucleus from coma, giving a radius of 1.3 ± 0.2 km for an albedo of 0.04. Finding[The evidence](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ47J4JQGK/hubble-detects-the-nucleus-radius-1-3-0-2-km) 1. 3 **The missing push is there.** With the full orbit the data require a non-gravitational acceleration, which JPL fits at 4.6 × 10^-8 au per day squared at 1 au. Finding[The evidence](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ485CADJ6/the-missing-acceleration-turned-up) 1. 4 **Two telescopes set lower ceilings.** Before perihelion Hubble put the radius below 2.8 km and SPHEREx below 2.5 km, both under the claimed size. Finding[The evidence](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ48E606F6/two-telescopes-put-the-radius-below-2-8-km) [All findings on 3I/ATLAS](https://mysteriesdept.com/mysteries/3i-atlas) ## Room for disagreement The strongest objection comes from the measurement itself. Hubble sees reflected light, so the radius depends on how dark the surface is. The 1.3 km figure assumes an albedo of 0.04, meaning the surface reflects 4 per cent of the light. A darker surface would mean a bigger body. Reaching the claimed size would need a surface far darker than comets usually have. Two earlier limits also stand against the claim. [Before perihelion](https://mysteriesdept.com/r/EVD0DFQ48E606F6), Hubble put the radius below 2.8 km and SPHEREx below 2.5 km. ## What's next A heat measurement of the nucleus would fix its darkness independently and settle the size. Repeat imaging as the comet leaves would test whether the 1.3 km radius holds. A better fit of the push, combined with the size, would show how much gas the comet must shed to move as it does. Avi [Loeb](https://mysteriesdept.com/records/FIG0CSKBRJJ6DGG/abraham-avi-loeb) answered questions about the comet [a week before its closest approach to Jupiter](https://news.google.com/rss/articles/CBMiqAFBVV95cUxOU2tuN2NZT2w2ZWVJT3drM2JUenBwWnUzY2JTYnNWdTllT0Nhb1BLVVJyVDRSOVkwVkljRnJxM0xtZDhPOTR5WU9BUnFUMUtscWVLdzlfN0NoalNNZ2ltaEphOUl6c3ZDUFdseFpfSF9wXzNqallnYmg5ZXNydGdxM053eWpZTXlUQi1fdFhSMUFSUHN0NzdwVm1IWGlOa2prdE1YV2ZJcWE?oc=5). Observations from that pass may add to the record. ## Reported elsewhere Avi Loeb – Medium[Q&A About 3I/ATLAS, a Week Before Its Closest Approach to Jupiter](https://news.google.com/rss/articles/CBMiqAFBVV95cUxOU2tuN2NZT2w2ZWVJT3drM2JUenBwWnUzY2JTYnNWdTllT0Nhb1BLVVJyVDRSOVkwVkljRnJxM0xtZDhPOTR5WU9BUnFUMUtscWVLdzlfN0NoalNNZ2ltaEphOUl6c3ZDUFdseFpfSF9wXzNqallnYmg5ZXNydGdxM053eWpZTXlUQi1fdFhSMUFSUHN0NzdwVm1IWGlOa2prdE1YV2ZJcWE?oc=5) 10 Mar 2026 Avi Loeb answers questions about 3I/ATLAS a week before its closest approach to Jupiter. Medium[The Dust Mass Shed by 3I/ATLAS. In my latest essay — accessible here, I…](https://news.google.com/rss/articles/CBMie0FVX3lxTE9PalpWUndzNnlTYUtjUUVlRWh4WU0yd2F3ZGhBX0VLaFdrZzRncW80MFdIYUZaZ2pTSVMwMGd0ZVB6UjJDZC1KX2lBbTRPVGZpTmttcDJZNmZacWJ1MnBocWtaV2JZWnVyZFRwU1FCQV9zcGVDRW5lMzZpcw?oc=5) 26 Dec 2025 An essay on how much dust 3I/ATLAS has shed. Futurism[3I/ATLAS Still Showing Strange Protrusion as It Approaches Earth](https://news.google.com/rss/articles/CBMiYkFVX3lxTE5TdmpQMTF3NjJUaGVVWUg3bnhEa3RXcDlKcWhLbXV4UEkwNGpUd1B4UlNHZ3BLYXZ6NkRQNU1vWThDeVBDMlJBR2M5bUZ0TWpjSEdkUFpyMUU5OTNwQUhqRlJB?oc=5) 15 Dec 2025 Futurism reports that 3I/ATLAS still showed a protrusion as it approached Earth. Avi Loeb – Medium[The Inspiration Delivered by 3I/ATLAS to Our Doorstep](https://news.google.com/rss/articles/CBMimgFBVV95cUxNcWk3ZDFQelpHYmhjVnhhRmhWV1BEd2c0SVFldVlSbFVENVdaYTlyS3NYRVJJMVR6NUdoU1BsT0NYSzA1NUFucmYzR09vUkdiM2Z4TmtBblMyeDEtTDFxWllrcXN3NGl6UFFNZXBDSHA4WW5SQjRUTUlnWUVWeEJpbl91ZzRsZEJreGpqeFdub3hYX184VFl1d2RB?oc=5) 6 Nov 2025 Avi Loeb's essay on what 3I/ATLAS has inspired. ## Go deeper [3I/ATLASThe mystery, its questions and evidence](https://mysteriesdept.com/mysteries/3i-atlas)[How big is the nucleus of 3I/ATLAS?Question · open · 2 answers](https://mysteriesdept.com/mysteries/3i-atlas/questions/QST0DFQ0JS9W15Y/how-big-is-the-nucleus-of-3i-atlas)[Abraham (Avi) LoebPerson](https://mysteriesdept.com/mysteries/oumuamua/people/FIG0CSKBRJJ6DGG/abraham-avi-loeb)[ATLAS (Asteroid Terrestrial-impact Last Alert System)Organisation](https://mysteriesdept.com/mysteries/3i-atlas/organisations/ORG0DFQ70ARRH0M/atlas-asteroid-terrestrial-impact-last-alert-system) Cite or reference this article ``` Mysteries Department. (2026, November 2). Hubble finds the 3I/ATLAS nucleus far smaller than the 5-km claim (apollo, Ed.). https://mysteriesdept.com/news/2026/11/02/hubble-finds-the-3i-atlas-nucleus-far-smaller-than-the-5-km ``` Permanent link`mysteriesdept.com/r/NWS0DFS3AM91HCC`[Copy citation][Press kit](https://mysteriesdept.com/news/2026/11/02/hubble-finds-the-3i-atlas-nucleus-far-smaller-than-the-5-km/press-kit) By the numbers **1.3 ± 0.2 km** radius of the nucleus measured by Hubble, for an albedo of 0.04 **above 2.5 km** radius in the published 5-km claim **below 2.5 km** SPHEREx limit on the radius before perihelion **4.6 × 10^-8 au/day²** non-gravitational acceleration at 1 au, JPL fit Edited by **apollo** Founder and editor founder and keeper of the Mysteries Department [Profile and articles](https://mysteriesdept.com/u/apollo) Share [Copy link](https://mysteriesdept.com/news/2026/11/02/hubble-finds-the-3i-atlas-nucleus-far-smaller-than-the-5-km) For journalists #### Press kit The release, the figures and the data, free to use with credit. - [Press releaseText · 1 page](https://mysteriesdept.com/news/NWS0DFS3AM91HCC/press-release.txt) - [How to citeAPA, BibTeX] [Open the press kit](https://mysteriesdept.com/news/2026/11/02/hubble-finds-the-3i-atlas-nucleus-far-smaller-than-the-5-km/press-kit) Questions: [contact the newsroom](https://mysteriesdept.com/standards#contact)