A new “Halloween comet” could become as bright as Venus and even be visible in daylight next week, but astronomers are concerned that it may break up and fade before that happens, calling it an “all or nothing” event.
In the wake of comet C/2023 A3 (Tsuchinshan-ATLAS) being bright in the post-sunset night sky, astronomers are closely monitoring the comet, officially called C/2024 S1 (Atlas) as it approaches the sun on Oct. 28, with some astronomers reporting that it’s been fragmenting. However, it’s still uncertain whether the nucleus will survive the encounter with the sun.
“Only if the nucleus survives past that point will there be any sort of display worth mentioning,” said astronomer Dr. Qicheng Zhang at Flagstaff, Arizona’s Lowell Observatory, who has been monitoring the comet. “In other words, it’s almost a binary all-or-nothing event.”
When To See The ‘Halloween Comet’
“We’ve been observing C/2024 S1 fragmenting in the last couple of weeks,” said Zhang. “The fragmentation process seems to still be ongoing, meaning the comet has not yet fully disintegrated.” However, it’s too early to completely write off comet S1. “It’s still not clear, however, if what’s left the left of the nucleus is enough to survive the encounter with the sun,” said Zhang.
That won’t bother observers in the Southern Hemisphere. Comet S1 will make its closest approach to Earth on Wednesday, Oct. 23. In the days after, from Thursday, Oct. 24 to Monday, Oct. 28, it could dramatically brighten and become visible to the naked eye, according to StarWalk. It will be best seen just before sunrise as it gets closer to the sun each morning.
It will make its perihelion with the sun — the closest it will get to our star — on Monday, Oct. 28, and in theory, then be visible from the Northern Hemisphere after sunset from Tuesday, Oct. 29 through December.
It could theoretically reach a brightness of magnitude -8.3. That’s brighter even than Venus, the brightest object in the sky aside from the sun and moon, so comet S1 could be visible in daylight.
But there’s a problem.
What Could Happen To The ‘Halloween Comet’
Only discovered on Sept. 27 by astronomers at the ATLAS survey in Hawaii, comet S3 is likely a Kreutz sungrazer comet, which means it will get much closer to the sun than most comets — within around 1,500,000 kilometers (900,000 miles), according to astronomer Graham Jones at Timeanddate.com. “Comets are notorious for being highly unpredictable, and the latest indications are discouraging,” writes Jones.
Best And Worst Case ScenarioS For Comet S1
Kreutz sungrazer comets can be the best and brightest comets of all — if they survive. “The best case scenario for it is it could produce a very long but also very tenuous tail that emerges into the morning sky in early November,” said Zhang, who thinks it could resemble 2011’s bright comet C/2011 W3 (Lovejoy), also a Kreutz sungrazer. “It probably can’t get too much brighter than that given what we see of it now, but C/2024 S1 would at least be visible from the Northern Hemisphere if it does do that.”
The worst case for comet-watchers is that comet S1 falls apart before its close encounter with the sun this week. “That would result in virtually nothing being visible afterward in November,” said Zhang, adding that in that scenario, it probably won’t be anything impressive to look at in October while it’s close to the sun.
Astronomers should know more about the probable fate of comet S1 in the coming days. They’ll be looking to see “if there’s anything solid of the comet left that’s remotely large enough to survive the solar encounter,” said Zhang. “But even if there is, we probably won’t know until Oct. 28 if it actually does survive.”
Wishing you clear skies and wide eyes.
