A Comet From Outside Our Solar System Was Measured Three Times. This Desk Only Trusts the Last One.
Bartholomew "Bart" Pruss, Senior Cataloguer · the records desk
THE THICCC BEAT: the desk reacts to the news. The Senior Cataloguer files from the records room, where a filing error of interstellar proportions has just been corrected.
The object is called 3I/ATLAS. It is the third confirmed visitor our solar system has received from outside it, which is to say it did not form here, does not belong here, and will not be staying. Discovered last year, it has spent 2026 passing through on its way back out, watched the entire time by telescopes with better manners than most of what crosses my desk unannounced.
I want to talk about the measurement, because the measurement is the story, and because nobody else at this publication reads a correction notice with the attention it deserves. Early reports had the nucleus at seven miles across. Seven miles. Numbers like that get repeated at dinner parties by people who have never once been asked to defend a number at a dinner party. Then the Rubin Observatory did its work properly, the way work is supposed to be done, and the figure came down. Six miles, briefly. Then 5.6 kilometers, call it three and a half miles, and I will, because I do not care for kilometers in this office and never have.[^1]
I have filed three separate objections in seventeen years to numbers that were published before anyone checked them. This is not a pattern I take pleasure in. But I will say, for the record, that watching a body of professional astronomers walk their own number back by half without complaint is the single most dignified thing I have seen out of anyone, anywhere, this year. The catalogue, properly understood, could learn something from an observatory.
So: the nucleus. Three and a half miles of rock and ice, moving fast, unbothered by us, entirely unremarkable by the standards of this desk. I have certified thicker things off a loading dock. Not Thiccc. Reviewed, revised, filed, closed.
The coma is a different matter and I will not pretend otherwise. The coma is the cloud, gas, dust, ice boiling off the nucleus as the sun leans on it, and by the time 3I/ATLAS made its closest approach, that cloud had swollen past fifteen miles across. Fifteen miles of loose material, wrapped around a three-and-a-half-mile core, moving through the dark at a speed I am not equipped to make funny. That is not a number I need a second observatory to confirm. That is a number with girth.
I raised this with Teddy, who wanted to know whether a coma "counts" if it is, and I quote him exactly, "basically fog." Teddy has never filed an objection to anything in his life. A coma is not fog. A coma is committed. It has a shape. It holds formation for months at a time across empty space with nothing to lean on. I would like to see fog do that.
RULING: Split ruling, and I do not issue those lightly. The nucleus: Not Thiccc, three and a half miles, ordinary, correctly measured on the second try. The coma: Thiccc, unambiguously, fifteen-plus miles of committed material trailing an interstellar visitor sixty-six million miles from the nearest office that could object. Filed. Closed. Do not send me a third revision.
Sources: Live Science, reporting on Vera C. Rubin Observatory data, August 2026.
[^1]: Per Style Guide section II.3: measurements filed in this catalogue default to imperial. This has been the standing rule since 1979 and will remain so.
Source: www.livescience.com/space/comets/3i-atlas-is-7-miles-wide-th