Tootfinder

Simultaneously NASA and ESA have published new spacecraft images of #3IATLAS, https://science.nasa.gov/blogs/3iatlas/2025/12/04/nasas-hubble-space-telescope-revisits-interstellar-comet/ from the Hubble Space Telescope on 30 November (just the inner coma with a central condensation) and https://www.esa.int/ESA_Multimedia/Images/2025/12/Comet_3I_ATLAS_shows_activity_in_Juice_navigation_camera_teaser from Juice's NavCam on 2 November with an early sighting of the plasma tail - more contributions to understanding the behavior of the interstellar visitor.

All the NASA s/c images of #3IATLAS shared today (and some more) can be found at https://science.nasa.gov/solar-system/comets/3i-atlas/comet-3i-atlas-image-gallery/ now - including this spectrum from the Imaging Ultraviolet Spectrograph on MAVEN taken on 28 September, showing hydrogen emitted from different sources, namely the comet (dim spot on the far left), hydrogen from Mars (bright emission on the right), and hydrogen flowing through our solar system between the planets (dim emission in the middle).

And here is now also a spectrum of #comet #3I/ATLAS taken during the #ShadowTheScientists session on 26 November, from https://www.astronomerstelegram.org/?read=17561 - CN (388 nm), C3 (402 nm) and C2 (474 nm/517 nm) are detected. Meanwhile the paper https://arxiv.org/abs/2512.18341 concludes from the non-gravitational acceleration that the diameter of the comet's nucleus is 820 to1050 m.

The size of #3I/ATLAS from non-gravitational acceleration: https://arxiv.org/abs/2512.18341 -> "we find diameters between 820 meters and 1050 meters [...] reliable estimates of the mass loss rate at other stages of the comet's trajectory will substantially reduce the systematic uncertainty in this estimate."

Finally an RGB image of comet #3IATLAS from images taken by #GeminiNorth during the 26 November #shadowTheScientists session: https://noirlab.edu/public/news/noirlab2532/ - the coma has become bluer due to more gas emission. Also published today: an X-ray image by XMM-Newton at https://www.esa.int/ESA_Multimedia/Images/2025/12/XMM-Newton_sees_comet_3I_ATLAS_in_X-ray_light with explanations in http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET005646.txt which also contains more 3I news.
Meanwhile the paper https://iopscience.iop.org/article/10.3847/2515-5172/ae2915 claims an upper limit for 3I's nucleus diameter of only some 750 meters from the measured non-gravitational acceleration (NGA) parameters: that would be waaay more stringent than the 5.6 km upper limit from early Hubble observations reported in https://iopscience.iop.org/article/10.3847/2041-8213/adf8d8 (where also a lower limit of 440 meters is stated).

Comparative Analysis of Polarization in Interstellar Comet #3I/ATLAS with Distant Solar System Comets: https://iopscience.iop.org/article/10.3847/2515-5172/ae0d91 > interview with the first author: https://www.youtube.com/watch?v=F30vaWKywpA

X-ray observation of the cometary interloper C/2025 N1 (3I/ATLAS) by XRISM/Xtend: #3IATLAS from beyond the solar system: https://www.xrism.jaxa.jp/en/topics/news/1208/