2023 March 4

Comet C/2023 A3 (Tsuchinshan-ATLAS)

Nick James

This recently discovered comet, announced on CBET 5228, may become a bright object in October next year but it is far too early to tell. It has been the subject of a lot of speculation on social media and the mainstream media are likely to pick this up soon.

The comet was detected by the ATLAS 0.5-m, f/2 Schmidt at Southerland, South Africa on Feb 22. At the time it was an 18th magnitude, apparently asteroidal object in Serpens. It was placed on the PCCP as object A10SVYR and a number of observers reported it to be cometary. The MPC linked it to a previous object that had been reported by the Purple Mountain Observatory XuYi station in China on 2023 January 9 hence the name Tsuchinshan-ATLAS.

The comet is currently 7.5 au from the Sun but it will come to a perihelion distance of only  0.39 au in late 2024 September. It is this that has started the speculation since a comet which is 18th magnitude at 7.5 au could become quite bright when it gets that close to the Sun. Since the comet has only been under observation for a few weeks it would be wise not to get caught up in the hype. We have no idea how its activity will change as it moves in towards perihelion. Let’s observe it over the next year and see how it behaves. We can then start making more detailed predictions as to how bright it may become.

We do know its orbit pretty well. It spends the next  year moving slowly through Serpens, Virgo and Libra staying within a few degrees of the celestial equator. Around perihelion, even if it is bright, it will be at small solar elongations and so will only be visible in a bright sky.  The best prospects, if it survives, are after perihelion as it emerges into the evening twilight in 2024 October but it has a long journey ahead of it and, being a comet, it is unlikely to do what we expect. 

You can follow its progress through images posted to the Comet Section archive here.