2023 A3 Tsuchinshan-ATLAS: a Bright Comet for the End of 2024?

New Comet C/2023 A3 Tsuchinshan-ATLAS may put on a show at the end of next year.

Could this one be the next great comet? Though caution is always warranted when it comes to icy interlopers from the Oort Cloud, a recent discovery has given us pause, and a reason to take notice. We’re talking about the recent discovery of Comet C/2023 A3 Tsuchinshan-ATLAS, just announced last week.

The discovery announcement came out of CBAT (The Central Bureau for Astronomical Telegrams) Number 5228 released on February 28th. The comet was sighted independently by the ATLAS (Asteroid Terrestrial-impact Last Alert System) automated sky survey, and earlier data from the Tsuchinshan (Zijinshan or ‘Purple Mountain’) observatory in China, hence the double moniker. The comet turned up in earlier observations from Purple Mountain Observatory’s XuYi Station going back all the way to January 9^th, 2023, that’s why it ended up with an A3 designation, which is usually reserved for comets discovered in early January.

The specifics for the comet are certainly interesting: the comet was discovered as a faint +19^th magnitude fuzzball, and currently shines at +18^th magnitude in the constellation Serpens Caput. Its current distance is 7.2 AU (670 million miles/1.08 billion kilometers) from the Sun, out beyond the orbit of Jupiter.

On an 80,660 year retrograde orbit with a 139 degree inclination relative to the ecliptic plane, the comet will reach perihelion on September 28th, 2024 at 0.39 AU from the Sun… though it will also only be 22 degrees as seen from the Earth, and lost in the Sun’s glare. Things get a bit better in the succeeding weeks, as the comet makes its closest Earth approach of 0.476 AU on October 13^th. Best views are expected around this time as the comet emerges from the Sun’s glare low in the dawn sky, post perihelion. The comet may reach a brilliant magnitude 0, through +3 or so is more conservative. A phenomenon known as forward scattering may work in the comet’s favor, increasing its apparent brightness.

First though, several caveats are in order. Yes, the discovery circumstances for this comet shares a few characteristics with one of the great comets of the 20^th century: C/1995 O1 Hale-Bopp. That historic comet was discovered when it was still 7.2 AU distant as a +10.5 fuzzball, the same distance (but much brighter) than A3 Tsuchinshan-ATLAS. Hale-Bopp reached perihelion 0.914 AU from the Sun on April 1^st, 1997 (over twice the expected distance for A3 Tsuchinshan-ATLAS), and passed 1.315 AU from Earth the month prior on March 22^nd, 1997, and reached a brilliant maximum of magnitude -1.8. Hale-Bopp actually lingered in naked-eye visibility range for northern hemisphere observers for months as it headed outbound, not to return for another ~2,500 years. We actually had a good study in naked eye comets in the late 90s, as C/1996 B2 Hyakutake snuck up on Earth as a fine comet close up, while we were all anticipating Hale-Bopp as a large comet farther out.

Of course, we’ve been burned by anticipated great (and not so great) comets of yore. Just a decade ago, we were all awaiting the apparition of Comet C/2012 S1 ISON… which promptly disintegrated at perihelion. If Comet A3 Tsuchinshan-ATLAS is large and dynamically new, we could be in for a show. If, however, it’s smaller than expected and inactive, it could be yet another under-performer.

For now, it’s a wait and see situation, as more observations are made. Comets often seem to have minds of their own, and fail to read and heed online prognostications. One thing is for sure: we’re definitely ‘due’ for this generation’s next great comet.