Abstract
In 2017, 2018, and 2019, comets 46P/Wirtanen, 45P/Honda-Mrkos-Pajdusakova, and 41P/Tuttle-Giacobini-Kresak all had perihelion passages. Their hydrogen comae were observed by the Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyman-alpha camera on the SOlar and Heliospheric Observer (SOHO) satellite: comet 46P for the fourth time and comets 45P and 41P for the third time each since 1997. Comet 46P/Wirtanen is one of a small class of so-called hyperactive comets whose gas production rates belie their small size. This comet was the original target comet of the Rosetta mission. The Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyman-alpha camera on the SOlar and Heliospheric Observer (SOHO) satellite observed the hydrogen coma of comet 46P/Wirtanen during the apparitions of 1997, 2002, 2008, and 2018. Over the 22 years, the activity decreased and its variation with heliocentric distance has changed markedly in a way very similar to that of another hyperactive comet, 103P/Hartley 2. Comet 45P/Honda-Mrkos-Pajdusakova was observed by SWAN during its perihelion apparitions of 2001, 2011, and 2017. Over this time period the activity level has remained remarkably similar, with no long-term fading or abrupt decreases. Comet 41P/Tuttle-Giacobini-Kresak was observed by SWAN in its perihelion apparitions of 2001, 2006, and 2017 and has decreased in activity markedly over the same time period. In 1973 it was known for large outbursts, which continued during the 2001 (2 outbursts) and 2006 (1 outburst) apparitions. However, over the 2001 to 2017 time period covered by the SOHO/SWAN observations the water production rates have greatly decreased by factors of 10-30 over corresponding times during its orbit.
Highlights
Comet 46P/Wirtanen was discovered in 1948 by Carl Wirtanen (Klemola 1991)
Expected total uncertainties in water production rates determined from Solar Wind ANisotropies (SWAN) images of the hydrogen coma resulting from a combination of calibration and model description and parameters are expected to be on the order of ∼30%
In the SWAN 61-comet survey (Combi et al 2019), power laws of water production rate versus heliocentric distance were fitted to three different pre- or post-perihelion set of individual apparition data sets; most did not lend themselves to being represented by a power law
Summary
Comet 46P/Wirtanen (hereafter 46P) was discovered in 1948 by Carl Wirtanen (Klemola 1991) It is a Jupiter Family Comet (JFC) with a current orbital period of 5.4 yr and a perihelion distance of 1.0 au. Comet 45P/Honda–Mrkos–Pajdusakova (hereafter 45P) was discovered by Minoru Honda, Antonín Mrkos, and Ludmila Pajdušáková on 1948 December 3 It is a JFC with a perihelion distance of only 0.53 au, so it is quite active at perihelion despite being a relatively small object with an effective diameter of only ∼0.8 km. In this paper we concentrate more on determining the change in activity as measured by the water production rate over typically long periods of time of several apparitions
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