Fine structures of 2025 Ursids peak and the rotation of the binary comet 8P/Tuttle

ATel #17675; Costantino Sigismondi (ICRANet Pescara and APRA-ISF Rome), Federico Manzini (Stazione Astronomica di Sozzago), Virginio Oldani (Stazione Astronomica di Sozzago), Paolo Ochner (UniPd; INAF-OAPd), Maria Salvatori Buzzanca (Liceo Morgagni, Roma)
on 12 Feb 2026; 12:51 UT
Credential Certification: Costantino Sigismondi (sigismondi@icra.it)

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The alternance of intense with low meteors' activity within some hours around the peak of a meteor's shower is a well documented phenomenon. In ATel #17629 we advanced the hypothesis –for the Geminids- that the peak's structure may reflect the action of a jet from an active source on the parent nucleus, in rotation. To avoid cancelling fine space structures by averaging all over the Earth's hemisphere exposed to the meteoroids, we analyzed the meteor shower's peak from a single location. We observed the peak of the 2025 Ursids on 21-22 December from Ely, Minnesota. During that new-Moon night, the radiant was in or near the 40 x 90 square degrees webcam's field of view centered above the Northern horizon and the limiting magnitude was 5.3 all night long. The link to the video of the whole night is available at https://www.imo.net/members/imo_photo/view?photo_id=4375 The Ursids are characterized by a population index of 2.6, with a relatively lower number of bright meteors, with respect to faint ones. Nevertheless a fireball was visible in that relatively narrow field of view (near 1/5 of the sky's dome). In 10.5 hours of continuous observations we detected a robust peak of activity at the solar longitude 270.75 +/- 0.04 deg. FWHM, in fair agreement with the Ursids' history available in literature. The whole ZHR curve shows three bumps, compatible with a rotating contact-binary nucleus of the comet 8P/Tuttle with an active jet on each side.

Structures of Ursids meteor shower's peak in 2025