On 27 Sept., 2024, a new comet having temporary designation A11bP7I (now officially designated as C/2024 S1 ATLAS), was discovered by the ATLAS survey from Hawaii and almost immediately it revealed to likely be a very interesting one: a member of the Kreutz sungrazing family, reaching perihelion next 28 October and potentially able to put on a marvelous show. We did some follow-up, hoping for the best.

Comet A11bP7I, imaged on 29 Sept. 2024 at dawn.

The image above comes from the sigma clipping combination of 25, 30-second unguided exposures, remotely taken with the ARTEC250+Paramount ME+C3Pro61000EC robotic unit available as part of the Virtual Telescope Project facility in Manciano, Italy. The object was at just 13 degrees of altitude above the E horizon, with the Sun 14 deg. below it.

The comet is really obvious and displays an hint of tail spanning in the W direction. A couple of satellites crossed the field of view while we were imaging.

The next morning we managed to look at this comet again, using the same robotic telescope.

Comet A11bP7I, imaged on 30 Sept. 2024 at dawn, with a possible second fragment visible.

This time we managed to sigma combine 35, 30-second unguided exposures, under similar circumstances as in the image above. Again we see the comet very clearly, with possible evidence of a secondary component/fragment, as in the upper right insert in the image itself.

Median combination (left) vs average (right) of the 30 Sept. frames.

Because the target is low on the horizon, the signal is limited, so that can be noise, but Kreutz sungrazers are used to fragment (after all, they are the outcome of a major fragmentation event several centuries ago), so this possible detection is worth some follow-up.

Since researches suggested this could likely be a member of the Kreutz sungrazers family, excitement is increasing as the comet brightens, as such an object like A11bP7I can offer us a stunning performance. But as with every comet, patience and prudence are in order.

A comet belonging to the Kreutz family mentioned above is reason of excitement, under the right circumstances like in tthis case, as many great comets of the past are members of that family. This includes the legendary C/1965 S1 Ikeya-Seky, one of the greatest comets of the past millennia.

Using all the data publicly available from the Minor Planet Center, including the ones from our two nights and rejecting observations with too large residuals, I managed to compiute an orbit using the Find Orb software by Bill Gray, getting a the perihelion date of 28,6 Oct. 2024

Orbital elements: A11bP7I
Perihelion 2024 Oct 28.62008 +/- 0.0177 TT; Constraint: e=1
Epoch 2024 Sep 30.0 TT = JDT 2460583.5 Earth MOID: 0.5123 Find_Orb
q827738.112 +/- 39261 (J2000 ecliptic)
H 13.5 G 0.15 Peri. 64.59960 +/- 0.57
Node 339.64014 +/- 0.9
e 1.0 +/- 0 Incl. 140.63984 +/- 0.18
68 of 79 observations 2024 Sept. 27-30; mean residual 0″.60

UPDATES (2 October. 2024): on 1 October, the Minor Planet Center issued the MPEC T22 circular, including our astrometry, with the official designation of the comet: C/2023 S1 ATLAS.

Let’s hope this comet will survive and will offer us a great show in a few weeks! Soon, we will investigate the potential visibility of this new icy world.

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