C/2024 S1 (ATLAS)

Lore & Background

The comet was discovered during the ATLAS survey using a 0.5-m reflector telescope at Haleakala, Hawaii. It is the second Kreutz comet discovered from the ground since C/2011 W3 (Lovejoy), and is likely a fragment of the same parent body that produced C/1882 R1 and C/1965 S1 (Ikeya–Seki). Upon discovery, the comet had an apparent magnitude of 15.3 and a greenish coma about half an arcminute across, later growing to three arcminutes, with a tail up to 156 arcseconds long. The green color was probably due to diatomic carbon. Visual observation with a 30-cm reflector telescope gave a magnitude of 11.7. The comet was initially in the constellation of Hydra and kept a magnitude of 12–13 throughout the next week.

On 8 October the comet was found to be elongated, lacking a central condensation, and fainter than on 3 October, suggesting possible disintegration similar to C/2019 Y4 (ATLAS). At that time it was 0.802 AU from the Sun. However, from 15 October onward, observations consistently showed a well-condensed nucleus, and the comet underwent a 2-magnitude outburst between 15 and 16 October. On 19 October the coma was triangular and 2.4 arcminutes across, with a tail 24 arcminutes long. On 20 October the magnitude was 8.2, but faded to 10 the next day, with the coma and tail shrinking, indicating another outburst. On 23 October, 4.5 degrees above the horizon, the coma was one arcminute across, magnitude 10.8, and tail 17 arcminutes long.

On 26 October 2024, Hanjie Tan, a PhD student from Guangzhou, reported a fragment ahead of C/2024 S1 in LASCO C3 images. Just a few hours before perihelion, the comet evaporated within two hours, as seen on SOHO LASCO C2 images around 28 October 07:00 UTC. It is theorized that the comet disintegrated due to combined effects of rotational instability and sublimation loss shortly before perihelion.

Reader's Guide

C/2024 S1 (ATLAS) is notable as a Kreutz sungrazer discovered from the ground, the second such discovery since C/2011 W3 (Lovejoy). Its likely origin as a fragment of the same parent body as the Great Comet of 1882 and Ikeya–Seki ties it to a historic lineage of bright sungrazers. The comet's behavior—initial signs of disintegration in early October, followed by a recovery and outbursts, then final evaporation just before perihelion—illustrates the dynamic and fragile nature of such objects. If it had survived, it could have brightened to magnitude -5 to -7, brighter than Venus, and become visible in the morning sky, especially from the southern hemisphere, possibly resembling Lovejoy. Instead, its disintegration was observed in real time by SOHO LASCO C2, providing data on the processes that destroy sungrazing comets. The discovery of a fragment by Hanjie Tan adds to the understanding of fragmentation events. The comet's green color, due to diatomic carbon, and its varying magnitude reports highlight the challenges of observing such fast-moving, disintegrating objects.

Did You Know?

• C/2024 S1 (ATLAS) was discovered on 27 September 2024 from the ATLAS–HKO in Hawaii.
• It is a member of the Population II subgroup of the Kreutz sungrazers, which includes the Great Comet of 1882 and Ikeya–Seki.
• The comet evaporated within two hours just before perihelion, as seen on SOHO LASCO C2 images around 28 October 2024 07:00 UTC.
• A fragment of the comet was reported on 26 October 2024 by PhD student Hanjie Tan in LASCO C3 images.

The Kreutz Family's Shared Ancestry

The Kreutz sungrazers represent one of the most dramatic families in the Solar System. What we observe today as individual comets are, in reality, the scattered remnants of a single enormous parent body that shattered centuries ago. Each fragment follows an orbit of extreme eccentricity, swinging from a distance roughly a hundred times Earth's orbital radius at aphelion to a closest approach less than twice the Sun's own radius. Their orbital inclinations of 139 to 144 degrees effectively shield them from close planetary encounters, while their periods stretch between five and ten centuries. This shared architecture—eccentricity approaching unity, perihelion distances under 0.01 AU, and aphelion distances near 100 AU—ties every known member to the same ancestral breakup. The family's orbits are not static; solar energy erodes the comets during each close passage, progressively reshaping their paths over successive revolutions.

Heinrich Kreutz and the Recognition of a Pattern

For nearly two centuries, astronomers puzzled over a recurring phenomenon: brilliant comets appearing near the Sun at intervals of decades or centuries. The Great Comet of 1680, which passed roughly 235,000 kilometres above the solar surface, first drew attention to these extreme orbits. Edmond Halley and his contemporaries speculated it might be a return of a comet sighted in 1106. When the Great Comet of 1843 appeared on a similar trajectory, and then the 1880 and 1882 comets followed nearly identical paths, some researchers proposed a single body whose period was being mysteriously shortened. The alternative—that these were all pieces of a shattered ancestor—was first floated in 1880 and confirmed when the 1882 comet visibly broke apart after perihelion. In 1888, German astronomer Heinrich Kreutz published the definitive paper linking the 1843, 1880, and 1882 events as fragments of one giant progenitor. The 1680 comet, though also a sungrazer, was ultimately shown to be unrelated to this particular family.

Physical Nature and the Fate of Sungrazers

Kreutz sungrazers are, for the most part, remarkably small bodies. The majority measure under 100 metres in radius, though the brightest members can reach one to ten kilometres across. Their nuclei possess irregular, diffuse shapes—sometimes star-like, sometimes trailing tails—and their material has very low tensile strength. Because most volatile ices were lost during earlier transits, these comets remain largely inert until they approach within ten to fifteen solar radii of perihelion, where solar heating finally triggers activity. Water and organic compounds evaporate first, exposing fluffy aggregates of olivine and pyroxene that form distinctive dust tails. This dust lingers in the solar corona, interacting with the Sun's magnetic field. The small comets detected by SOHO since 1995 have never survived their perihelion passage, while larger bodies like the Great Comet of 1843 and C/2011 W3 (Lovejoy) have endured the encounter. C/2024 S1 (ATLAS) disintegrated in October 2024, joining the long list of family members destroyed by their solar approach.

The Modern Era of Discovery and C/2024 S1 (ATLAS)

The launch of the SOHO satellite in 1995 transformed our understanding of the Kreutz family. Since then, more than 5,000 members have been catalogued, revealing a population far larger than the handful of great comets known from historical records. Real-time internet data has also empowered amateur astronomers to identify new Kreutz comets, democratizing a field once reserved for professional observatories. Among the most recent additions are C/2026 A1 (MAPS), scheduled for perihelion on 4 April 2026, and C/2024 S1 (ATLAS), which met its end in October 2024. The family's brightest historical members—the Great Comet of 1843, the Great Comet of 1882, and the 1106 event—were visible in daylight, and Comet Ikeya–Seki in 1965 may have been among the brightest comets of the past millennium. Researchers have suggested that another cluster of bright Kreutz comets could begin arriving in the inner Solar System within the next few decades, hinting that the family's most spectacular chapter may not yet be over.