Water Production Rate of C/2020 F3 (NEOWISE) from SOHO/SWAN over Its Active Apparition

TL;DR

This study measures the water production rate of comet C/2020 F3 (NEOWISE) using SOHO/SWAN data over its active period, revealing asymmetries around perihelion and providing insights into its activity and history in the solar system.

Contribution

First detailed water production rate analysis of NEOWISE using SOHO/SWAN data over a four-month period, showing asymmetry and activity levels around perihelion.

Findings

Water production rate varies with heliocentric distance as r^-2.5 before perihelion and r^-3.5 after.

Maximum water production rate reached 5.27 x 10^30 s^-1.

Water activity suggests previous passages through the planetary region.

Abstract

C/2020 F3 (NEOWISE) was discovered in images from the Near Earth Object program of the Wide-Field Infrared Survey Explorer (NEOWISE) taken on 27 March 2020 and has become the Great Comet of 2020. The Solar Wind ANisotropies (SWAN) camera on the Solar and Heliospheric Observatory (SOHO) spacecraft, located in a halo orbit around the Earth-Sun L1 Lagrange point, makes daily full-sky images of hydrogen Lyman-alpha. Water production rates were determined from the SWAN hydrogen Lyman-alpha brightness and spatial distribution of the comet measured over a 4-month period of time on either side of the comet's perihelion on 3 July 2020. The water production rate in s^-1 was moderately asymmetric around perihelion and varied with the heliocentric distance, r, in au as (6.9+/-0.5) x 10^28 r^-2.5+/-0.2 and (10.1+/-0.5) x 10^28 r^-3.5+/-0.1 before and after perihelion, respectively. This is consistent with the comet having been through the planetary region of the solar system on one or more previous apparitions. A water production rates as large as 5.27 x 10^30 s^-1 were determined shortly after perihelion, once the comet was outside the solar avoidance area of SWAN, when the comet was 0.324 au from the Sun.