C/2021 O3 (PanSTARRS) is perhaps an Oort cloud comet, discovered on 26 July 2021 by the Pan-STARRS sky survey. It came to perihelion on 21 April 2022 at 0.287 AU (42.9 million km). from the Sun.

The comet was expected to reach apparent magnitude 5 by late April 2022, while being only 15 degrees from the Sun.^[3][4] While near perihelion the comet was dimmer than expectations. It was faintly visible in STEREO/SECCHI COR2-A on 27 April 2022.^[5] Observations by Lowell Discovery Telescope on April 29 in the twilight detected a diffuse glow with a magnitude of 9 where the comet was expected to be, indicating that the comet nucleus disintegrated during perihelion.^[6] C/2021 O3 made its closest approach to Earth on 8 May 2022 at a distance of 0.60 AU (90 million km).^[7] As a dynamically new comet from the Oort cloud there was a high risk of disintegration.^[8]

The comet was recovered by multiple observatories after perihelion at magnitudes not too different from those observed pre-perihelion.^[9] Calculations carried out using the pre- and post-perihelion orbits indicate that although the comet is probably dynamically old, it may also be a fragment of a dynamically new comet that was released during the first perihelion passage of its parent comet.^[9]

Orbit

With a short observation arc of 7 days, the Minor Planet Center used an assumed eccentricity of 1.0 for the orbit solution.^[10] Due to statistics of small numbers, with a short 10 day arc JPL had an eccentricity of 0.99595±0.00444 which could be as high as 1.00039 or as low as 0.99151.^[11] With an observation arc of 53 days, JPL Horizons shows both an inbound and outbound eccentricity greater than 1.^[2]

C/2021 O3 probably took millions of years to arrive from the outer Oort cloud and, had it survived, may have been fated to be ejected from the Solar System.^[2] This is also the most likely scenario when considering the post-perihelion orbit determination of the surviving object.^[9]