Comet 46P/Wirtanen is a short-period comet with an orbital period of 5.4 years. The comet is relatively small in size with an estimated diameter of just 1.2 kilometres. It was the original target for ESA’s Rosetta spacecraft but the launch window was missed so 67P/Churymov-Gerasimenko was Rosetta’s target in the end.
Comet 46P/Wirtanen was discovered by Carl A. Wirtanen in 1948 at the Lick Observatory, California via photographic plate. The plate was exposed on 17 January 1948 during a stellar proper motion survey at the observatory. It took over a year before the object was recognised as a short-period comet due to a lack of observations.
46P/Wirtanen belongs to a small family of comets that boast a higher level of activity than expected for their nucleus size. They emit more water vapour than they should. This is one of the reasons for added interest in this regular visitor to the proximity of Earth’s orbit .
The next perihelion passage of comet Wirtanen will be on 16 December 2018 when it will pass 0.078 AU (7,220,000 mi) from Earth. The icy space rock is expected to reach magnitude 3. This is the brightest prediction of known and future passes of this comet. This is also currently the brightest prediction for all comet passes in 2018 unless a new discovery is made after time of writing (we can but hope!).
Comet Wirtanen is currently dimmer than magnitude 20 making it well out of observing or even decent photographic reach unless you have a considerably powerful telescope. The comet will gradually brighten through 2018. Throughout the summer months, the comet will move from Aquarius in the Cetus brightening to magnitude 12 by the end of August. The comet will then dip further South where the icy rock will struggle to rise above 20 for observers in the UK (or any location above 50 deg latitude). Throughout the Autumn, the comet will begin to increase in brightness quite considerably but sinks ever lower as it reaches the midway point between Fornax and Sculptor making observation difficult for observers above 50 degrees in latitude. Things begin to improve through November after dramatic U-turn moving swiftly North through Eridanus towards Taurus. This is where the comet will reach closest approach on 16 December 2018, right at the point when positioned between the Pleiades and Hayades clusters. From here on it, the comet remains in a much more favourable position for northern sky observers high up in the sky by after sunset.
46P Wirtanen Visualisation
Associated Meteor Shower
A meteor shower was forecast by Mikhail Maslov, a Russian forecaster using computer models of crossings of comet Wirtanen’s debris stream. He predicted four crossings in total between December 10th and 14th, 2012. Even though, the comet had passed close to the Earth’s orbital plane on many occasions in the past, Earth has not run directly in to the comet’s debris streams before. Although the shower was overshadowed by the coinciding Geminid meteor shower, Maslov’s prediction proved correct.