A new comet, designated SWAN25B, has appeared in the inner Solar System, first identified in imagery from the Solar Wind Anisotropies (SWAN) instrument on the Solar and Heliospheric Observatory (SOHO). The comet was detected by amateur astronomer Vladimir Bezugly in online SWAN images, leading to rapid confirmation by follow-up observers.
Comet SWAN25B was added to the Minor Planet Center (MPC) Possible Comet Confirmation Page (PCCP) on September 12, with 12 observations over an arc of 0.40 days and a provisional absolute magnitude H = 5.2. The MPC listing reports a total magnitude V ≈ 8.3, while early amateur estimates place it slightly brighter at 7.4–7.5, consistent with the broader coma being included in visual observations.
Geocentric ephemerides from the Minor Planet Center for September 12–13 give R.A. 13h 09m–13h 14m, Dec −09° 29′ to −09° 53′, elongation 29.9–30.1°, and motion 2.9–3.1″/min at P.A. 110°. The low elongation implies the comet is emerging from the Sun’s vicinity, complicating observations, especially in bright twilight and low elevation.
Early amateur images circulating on September 12 indicate a condensed coma and possible ion-tail development, but quantitative tail length estimates require additional calibrated observations.
Michael Mattiazzo of South Australia imaged the comet today, showing a 2° ion tail, noting SWAN25B appears to be in outburst after perihelion, similar to the behavior of comet C/2004 H6.
With a very short arc and provisional status, any orbit solution remains highly uncertain. More astrometry over the coming days is required before reliable predictions (including Earth-distance and brightness evolution) can be issued.
Observers are advised to consult the MPC PCCP for updated astrometry and ephemerides and to report measurements to improve the orbit.
References:
1 Possible Comet Confirmation Page (PCCP) – Minor Planet Center – Accessed September 12, 2025
2 NEO Confirmation Page – Minor Planet Center – Accessed September 12, 2025