Borderline hyperbolic comet C/2021 O3 (PANSTARRS) was fading as it approached the Sun

TL;DR

This study combines observational data and numerical analysis to investigate the activity, brightness, and orbital history of comet C/2021 O3, revealing its unusually low activity and potential origin within the Solar system.

Contribution

It provides new observational evidence of the comet's low activity and analyzes its orbital evolution, suggesting it may be a dynamically old or new comet originating from the Solar system.

Findings

Comet C/2021 O3 showed lower activity than typical long-period comets.

Brightness decreased as the comet approached the Sun.

Spectral slope increased as dust in the coma decreased.

Abstract

We present an observational and numerical study of the borderline hyperbolic comet C/2021 O3 (PANSTARRS) performed during its recent passage through the inner Solar system. Our observations were carried out at OASI and SOAR between 2021 October and 2022 January, and reveal a low level of activity relative to which was measured for other long-period comets. In addition, we observed a decrease in brightness as the comet got closer to the Sun. Our photometric data, obtained as C/2021 O3 approached perihelion on 2022 April 21, show that the comet was much less active than what is usually expected in the cases of long-period comets, with $Af\rho$ values more in line with those of short-period comets (specifically, the Jupiter Family Comets). On the other hand, the observed increase in the value of the spectral slope as the amount of dust in the coma decreased could indicate that the smaller dust particles were being dispersed from the coma by radiation pressure faster than they were injected by possible sublimation jets. The analysis of its orbital evolution suggests that C/2021 O3 could be a dynamically old comet, or perhaps a new one masquerading as a dynamically old comet, with a likely origin in the Solar system.