C/2025 R3 (PanSTARRS)

Lore & Background

The comet was discovered by PanSTARRS in images obtained on 8 September 2025, appearing diffuse with a head about 2.5 arcseconds across and no tail. Follow-up images by the Canada-France-Hawaii Telescope revealed a broad tail 10 arcseconds long. By January 2026 the comet was around magnitude 17, then brightened quickly, reaching magnitude 9 in mid-March. On 20 March 2026 it became visible in 10x50 binoculars, detected visually by Alan Hale. By 21 March the tail was about one degree long. On 4 April the comet had magnitude about 6 and a coma 3 arcminutes across. On 7 April it reached its maximum elongation of 33 degrees from the Sun. On 8 April its ion tail was at least 7 degrees long, with little dust tail visible. The comet was first spotted with the naked eye on 11 April at magnitude 5.1. It reached perihelion on 19 April 2026 at 0.499 AU from the Sun, then moved between the Sun and Earth, with its dust tail brightness enhanced by forward scattering. It reached solar conjunction on 25 April 2026 at 05:23 UT, 3.5 degrees from the Sun. It passed 0.489 AU from Earth on 26 April. It entered SOHO's LASCO C3 field of view on 23 April and CCOR-1 on 24 April. By May 5–6 it was barely visible to the naked eye, low in the twilight sky. As of May, the comet had faded, moved into southern skies, and required binoculars or a camera. By the end of July it had faded to magnitude 17 as it headed out of the Solar System.

Reader's Guide

C/2025 R3 (PanSTARRS) is significant as a hyperbolic comet with a 91% probability of extrasolar origin, based on backward orbital integration over the last 3 million years. If confirmed, it would be only the second known extrasolar comet candidate within the Solar System, after C/2018 V1 (Machholz–Fujikawa–Iwamoto). Its orbit indicates it will be ejected from the Solar System. The comet passed within 1.58 AU of Uranus on 23 November 2019. Radio observations by FAST on 7–8 April 2026 detected 18-cm hydroxyl emission lines, and spectroscopic analysis from the Asiago Astrophysical Observatory on 15 April 2026 detected H-alpha and H2O+ emission lines. The comet was widely observed and featured in multiple NASA Astronomy Picture of the Day entries from April to June 2026. Its legacy includes providing a rare opportunity to study a likely interstellar object during a close passage through the inner Solar System.

Did You Know?

• The comet was discovered by PanSTARRS on 8 September 2025 at an apparent magnitude of about 20.
• There is a 91% probability that the comet originated outside the Solar System.