UPDATE October 28: So long, sungrazer comet Comet S1
In early October, it seemed as if we might have two bright comets this month. And – though it’s beginning to fade now – Comet A3 has performed beautifully in our evening skies. Meanwhile, we’ve heard less about the 2nd comet, C/2024 S1 (ATLAS), aka Comet S1. We knew it was supposed to reach its perihelion (closest point to the sun) on October 28, 2024. Now the latest imagery from the sun-observing SOHO spacecraft suggests that Comet S1 did not survive its run-in with the sun. On its approach to today’s perihelion, the once-promising sungrazer comet seems to vanish from the spacecraft’s field of view. Presumably, the comet has disintegrated.
While disappointing, the news comes as no surprise. Comet expert Karl Battams (@SungrazerComets on X) warned over the weekend that S1 wouldn’t survive its perihelion. And there were reports earlier this month that the comet began fragmenting as it came closer to the inner solar system.
Report of disintegration
Astronomers said on October 9, 2024, in The Astronomer’s Telegram that it appeared Comet S1 was disintegrating. They compared observations of Comet S1 from Australia’s Siding Spring Observatory on October 3 with observations from the South African Astronomical Observatory on October 8. The astronomers said the nucleus, or central ice ball of the comet, “appeared elongated and fainting” on October 8 compared to the October 3 images. They reported:
This finding suggests a possible fragmentation of the nucleus.
Despite the comet was still at a relatively ‘safe’ distance from the sun, it is possible that strong vaporization of a large amount of gas occurred which, together with the tidal or rotational forces acting on the comet’s nucleus, may have led to its fragmentation.
Announcement of the new sungrazer comet
The ATLAS survey in Hawaii discovered another new comet that could become bright in Earth’s skies on September 27, 2024. First designated A11bP7I, its name officially became C/2024 S1 (ATLAS). Predictions for the comet had it reaching as bright as magnitude -5 to -7 when it comes closest to the sun, at perihelion, on October 28. Will that still happen? We’ll have to wait and see.
The Southern Hemisphere should have the best view before perihelion. After its close encounter with the sun (if it survived) it could put on a fantastic show for the Northern Hemisphere in the morning skies. It would definitely be something to wake up early for.
But it this comet is kaput, don’t forget about the OTHER comet in Earth’s skies right now. C/2023 A3 Tsuchinshan-ATLAS should now start to appear in your evening sky just after sunset.
A BIG NEW SUNGRAZING COMET: Today, many astronomers are excited about a new comet discovered just a few days ago by the ATLAS survey. It's so new, it doesn't have a name yet, just the provisional designation "A11bP7I." What's the excitement about? A11bP7I is a sungrazer… pic.twitter.com/BeGArf7Orv
— The Watchmen Earth and Space Connection (@TWESC2023) September 30, 2024
A Kreutz sungrazer
The new sungrazing comet is part of the Kreutz sungrazers. These are comets that come perilously close to the sun, where they can disintegrate or, if we’re lucky, become fantastically bright. Many of the comets through history that have been given the name “Great” (for example the Great Comet of 1882, the Great Comet of 1106 and the Great Comet of 371 BCE) were all Kreutz sungrazers. More recently, Comet Ikeya–Seki in 1965 was a Kreutz sungrazer that became as bright as magnitude -11. That’s as bright as a 1st quarter moon.
Scientists believe Kreutz sungrazers all come from a big comet that broke up a couple of millennia ago. Most Kreutz sungrazers are small fragments, but this one may be larger than most.
Will it become as bright as Ikeya-Seki? Not likely. When the new comet was about 1 astronomical unit (AU) from the sun, it was about 4 to 5 magnitudes dimmer than Ikeya-Seki was at that distance.
Orbit of C/2024 S1 (ATLAS)
Bottom line: The new sungrazer comet gave us high hopes of a bright comet at the end of October. But it appears it has disintegrated during its close approach to the sun.