Cloud reflection modelling for impact flashes on Jupiter

A new constraint on the bulk properties of the impact objects

¹ The Hakubi Center/Astronomical Observatory, Graduate School of Science, Kyoto University Kitashirakawa-oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
e-mail: arimatsu.ko.6x@kyoto-u.ac.jp
² Department of Natural Science, Faculty of Science and Engineering, Tokyo City University, 1-28-1, Tamazutsumi, Setagaya, Tokyo 158-8557, Japan
³ Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan
⁴ Public Relations center, National Astronomical Observatory of Japan 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

Received: 8 May 2023
Accepted: 28 July 2023

Abstract

Aims. We investigate the optical characteristics of flashes caused by the impact of metre- to decametre-sized outer Solar System objects on Jupiter, and the contributions of reflected light from surface clouds at visible wavelengths, in order to estimate more accurate bulk parameters, such as the luminous energy of the flash, the kinetic energy, the mass, and the size of the impact object.

Methods. Using the results of recent reflectivity studies of the Jovian surface, we developed a cloud reflection model that calculates the contribution of the reflected light relative to that directly from the flash. We compared the apparent luminous energy of the previously reported flashes with the expected cloud reflection contributions to obtain their revised bulk parameters.

Results. We find that cloud reflection contributions can make up to 200% of the flux directly from the flash, and thus can be the most significant uncertainty in the measurement of the bulk parameters. The reflection contributions strongly depend on wavelength. With our cloud reflection correction, we obtained revised bulk parameters for the previously reported flashes.

Conclusions. Our cloud reflection correction enables us to better understand the properties of objects impacting Jupiter and is crucial for ongoing detailed investigations using high-sensitivity and multi-wavelength observation systems, such as PONCOTS. It will also be useful for understanding other optical transients in Jupiter’s upper atmosphere, such as the recently discovered sprite-like events.