A brilliant show and a fateful end: comet C/2024 G3 (ATLAS) disintegrated after perihelion

Comet C/2024 G3 (ATLAS) has long been a rather unremarkable object. But in January it appeared in all its glory: a bright nucleus and a fluffy fibrous tail on the shimmering colors of the western horizon – a breathtaking sight. However, fresh images from different astrophotographers clearly and unambiguously show signs of disintegration.

C/2024 G3 (ATLAS) from Australia on January 19. Photo: Blake Estes

A daytime comet

C/2024 G3, discovered last April, was a dark horse for a long time. Its orbit is located so that, for an Earth observer, the comet moves close to the Sun. More often it began to be photographed in December, expecting a rapid increase in brightness before passing perihelion on January 13. However specific peak luminosity values varied from -3.5m to -5.5m.

On January 11, the comet entered the field of view of the SOHO space solar telescope. The LASCO C3 coronograph takes pictures of anything no farther than 8° from the Sun. Although the comet was approaching Sirius in brilliance, it was a difficult object to observe. LASCO C3 is a sensitive instrument, so such bright objects appear over-lit. The comet’s head develops “whiskers” called blooms, which are related to the architecture of the camera’s sensor. You can roughly estimate the object’s brilliance from them: the longer and thicker the “whiskers”, the brighter the comet. Below you see an animation of the motion of comet C/2024 G3 (ATLAS) in the field of view of the SOHO LASCO C3 coronograph from January 11 to 15. You can see that after January 14, the comet increases in brightness.

Despite the difficult observing conditions near perihelion, some photographers managed to shoot it in the daytime sky – literally from 8:00 a.m. – to 12:00 p.m. UST (3 a.m. – 7 a.m. EST). Such attempts can safely be classified as “extreme astronomy” because of the danger of damaging the equipment with focused solar radiation. The telescope should be stationary from the night and be able to point to the desired object by coordinates. In addition, it should be equipped with a special hood that will protect the instrument and camera from the oblique rays of the Sun.

C/2024 G3 (ATLAS) between thin clouds in the afternoon sky. Photo: Lionel Majzik
Comet in the daytime sky on January 14 at 12:00 p.m. UST (7:00 a.m. EST). The sum of 25 short exposures. Photo: Martin Bree
While this image is not extremely impressive, the technique of taking it is without a doubt the most sophisticated of all the images shown here. On January 14, Maja Kraljik (an astrophotographer from Croatia) covered part of the camera lens with a special film to show both the Sun (lower right corner) and the comet itself, just to the left and above the bird

Too close to the Sun

At perihelion, the distance from the comet to the Sun was only 0.0935 astronomical units, a very close neighborhood. The comet’s nucleus consists mainly of frozen gases and solid pebbles. As it approaches the Sun, the mixture of ice vaporizes intensely, turning at once into gas. Usually, the solid part of a comet is not dense, especially if this comet is visiting the central part of our system for the first time. The active outgassing stimulates a rise in pressure in the nucleus. During perihelion, the core temperature of C/2024 G3 (ATLAS) reached hundreds of degrees, and not every comet can withstand that kind of heat stress. Add to this the Sun’s gravitational influence and the nucleus is at risk of disintegration.

Near-solar comets, in general, tend to become brighter after perihelion. In addition, as they fly away from the Sun, they turn their tails forward, which can make them extremely spectacular. When C/2024 G3 returned to observers in the southern hemisphere after a hot solar embrace, it showed itself in all its glory. In the image below you can see how bright it is and how magnificent its tail has become. Even with a fairly bright sky after sunset, it was still visible to the naked eye. Particularly amazing images came from January 17-19.

C/2024 G3 (ATLAS) near the Paranal Observatory in Chile (South America) on January 18.
Photo: Yuri Beletsky

Finita la comedia

Since the discovery of C/2024 G3 (ATLAS) after the parameters of its orbit were determined, the debate in scientific circles has been ongoing: will the “tailed” survive or disintegrate? Comets, especially those approaching the Sun for the first time, are rather unpredictable. Oil in the fire of the debate was fueled by a sharp increase in light on January 2, which observed Terry Lovejoy, as well as observations on January 12, conducted by Takaaki Oribe: in his pictures, he saw allegedly the comet has two nuclei, not one. However further studies did not confirm the breakup.

A comparison of detailed images for January 18 and 19 caused some concern among astronomers. Lionel Majzik (Hungary) was the first to point out that the comet’s head in the photo from the 19th seems much dimmer and tentatively suspected the beginning of the nucleus disintegration. These observations were confirmed by Gabriel Zaparolli (Brazil): literally in one day – January 18 – the comet’s appearance changed dramatically.

A sequence of images showing the aftermath of the decay. Photo: Lionel Majzik
The changing appearance of the comet’s head and tail over a day. Photo: Gabriel Zaparolli

It is impossible to observe the nucleus of a comet directly. But usually, its brightest part, the so-called pseudo-nucleus, stands out in the head. If it is point-like, the comet is considered “enormous”. In the latest images obtained by different observers, the pseudo-nucleus is absent, or rather, it has stretched into an extended structure inside the tail – a plume of dust particles enveloped in gas.

What’s next? Did the comet disappear without a trace immediately after defragmentation? So far, no. A similar situation occurred in April 2020 after the breakup of comet C/2019 Y4 (ATLAS), discovered by the same observatory. That disintegration was observed in detail by the Hubble Space Telescope which saw the individual fragments surrounded by a coma, which for some time still moved next to each other in similar orbits, feeding the comet’s tail.

As for C/2024 G3 (ATLAS), its nucleus has now almost certainly fragmented into many pieces, revealing a “stash” of primordial cometary matter. It was probably the increase in the total surface area of the nucleus that made the comet so bright. In a few days, the fragments will completely vaporize, and we will be left with an incredible collection of stunning images.

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