C/2019 U5 (PanSTARRS)

Lore & Background

When first discovered in October 2019, C/2019 U5 was presumed to be a hyperbolic asteroid. Later observations from September 2020 revealed weak cometary activity that increased as it approached the Sun. A persistent coma observed from Hawaii, Japan, and other European nations confirmed its nature as a comet.

Optical photometry obtained from the Sanglokh Observatory between May and September 2022 gave an absolute magnitude of 6.84±0.02, with color indices suggesting quasi-steady activity within its coma. Morphological observations while the comet was 4.63–4.03 AU from the Sun showed no signs of jet-like or other structural features within the coma. The nucleus is estimated to be about 60–95 km in diameter.

Barycentric osculating parameters from HORIZONS show that C/2019 U5 is a dynamically new comet from the Oort cloud. It reached perihelion on 29 March 2023 at a distance of 3.624 AU from the Sun and is expected to leave the Solar System on its outbound trajectory.

Reader's Guide

C/2019 U5 (PanSTARRS) is significant as a dynamically new comet from the Oort cloud, meaning it has likely never passed close to the Sun before. Its large nucleus, estimated at 60–95 km, makes it one of the larger known comets. The comet's retrograde orbit and non-periodic nature indicate it will leave the Solar System permanently after its perihelion passage. The detection of cometary activity only after a year of observations, and the confirmation of a persistent coma from multiple observatories, highlight the challenges of identifying distant comets. The lack of jet-like features in its coma suggests a relatively uniform outgassing process. Its discovery by the Pan-STARRS survey underscores the survey's role in finding distant solar system objects.