|Discovery date||26 July 2021|
|Orbit type||Oort cloud|
|Eccentricity||1.00005 (epoch 1950)|
1.002 (epoch 2021)
1.0001 (epoch 2100)
|Last perihelion||21 April 2022|
|Earth MOID||0.062 AU|
|Jupiter MOID||2.16 AU|
C/2021 O3 (PanSTARRS) was 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. While near perihelion the comet was dimmer than expectations. It was faintly visible in STEREO/SECCHI COR2-A on 27 April 2022. 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 disintergrated during perihelion. C/2021 O3 made its closest approach to Earth on 8 May 2022 at a distance of 0.60 AU (90 million km). As a dynamically new comet from the Oort cloud there was a high risk of disintegration.
With a short observation arc of 7 days, the Minor Planet Center used an assumed eccentricity of 1.0 for the orbit solution. 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. With an observation arc of 53 days, JPL Horizons shows both an inbound and outbound eccentricity greater than 1.
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.