3I/ATLAS Still Single

ATel #17490; David Jewitt, Jane luu
on 11 Nov 2025; 19:55 UT
Credential Certification: David Jewitt (djewitt@gmail.com)

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Images from the Nordic Optical Telescope on UT 2025 November 11 show that 3I/ATLAS continues as an active, single body, with no evidence for breakup following the recent perihelion passage. Asymmetries in the coma project to position angles 106+/-10 degrees and 301+/-1 degrees. The former is close to the projected orbit (110 degrees) and sunward direction (115 degrees), suggesting that it is the sunward fan observed on the inbound leg of the orbit and consisting of large and slowly launched particles projected sunward by dayside sublimation (c.f. 2025 Ap. J. Letters, 994 L3). The latter is close to the projected antisolar direction (295 degrees) on this date, identifying it as a normal dust tail. Plasma structures evident in recent wide field pictures taken by others are not evident in our data presumably because we used an R filter to isolate the dust, so excluding most gaseous emission lines. The heliocentric, geocentric distances and phase angle on UT 2025 November 11 were 1.43 au, 2.16 au and 22 degrees, respectively. Linked images show 3I/ATLAS with North to the top, East to the left, and a region approximately 0.5 million km wide. The projected antisolar direction (-S) and negative heliocentric velocity vector (-V) are marked. The diffuse object to the upper left of 3I is a galaxy. Other discrete objects are stars. The images are 1) linear stretch 2) contoured 3) color contoured 4) spatially filtered within a 0.13 million km radius region by subtracting the median signal in concentric annuli centered on the brightest pixel. The faint diagonal line from upper left to lower right is an "Elon".

3I UT 2025 Nov 11 -- NOT ALFOSC