C/2024 S1 (ATLAS) (previously had the temporary designation A11bP7I) was a sungrazing comet that was discovered by ATLAS-HKO in Hawaii on 27 September 2024. The comet passed its perihelion on 28 October 2024, at a distance of about 0.008 AU (1.2 million km; 0.74 million mi) from the barycenter of the Solar System,[1] and disintegrated. The comet had a similar orbit to the Kreutz sungrazers, which were created by the fragmentation of a large comet.
The comet was discovered during the ATLAS survey, using a 0.5-m reflector telescope located at Haleakala, Hawaii. The comet then was estimated to have an apparent magnitude of 15.3 and featured a coma about a half arcminute across. Further observations reported the coma was as large as three arcminutes across and the tail up to 156 arcseconds long.[1] The comet had upon discovery a greenish color, probably due to the presence of diatomic carbon.[3] The apparent magnitude of the comet was variously reported to range from magnitude 16.9 up to 11.5.[1] The presence of the green coma indicated that it was closer to 11.5. A visual observation was reported with a 30-cm reflector telescope, with a reported magnitude of 11.7.[3] The comet upon discovery was located in the constellation of Hydra.[4] The comet kept to a magnitude of 12–13 throughout the next week.[5]
Animation of C／2024 S1 around Sun C/2024 S1· Sun· Mercury· Venus· Earth· Mars
On 8 October the comet was found to be elongated and to lack a central condensation, and to be overall fainter than it was on 3 October, indicating that the comet possibly disintegrated, similarly to C/2019 Y4 (ATLAS) in 2020. The comet on 8 October was located 0.802 AU from the Sun, which although not too close, could be enough for gases to have vaporized and in combination with tidal or rotational forces may have led to the fragmentation of the nucleus.[6] However, later observations from October 15 onwards consistently showed a well-condensed nucleus, and the comet underwent a 2-magnitude outburst between October 15 and 16.[7] On 19 October the coma was reported to be triangular in shape and 2.4 arcminutes across while a tail 24 arcminutes long was observed. On 20 October the comet was reported to have an apparent magnitude of 8.2 but the next day it was reported it had faded to 10, while the coma and tail decreased in size, indicating another outburst had taken place.[8] On 23 October, with the comet being 4.5 degrees above the horizon, the coma was one arcminute across, had a total magnitude of 10.8 and the tail was 17 arcminutes long.[8]
On October 26th, PhD student from Guangzhou, Hanjie Tan, has discovered leading fragment in front of ATLAS comet using LASCO C3 images.[9]
Animation of C/2024 S1 (ATLAS) disintegrating during perihelion from SOHO LASCO C2
Just a few hours before reaching perihelion the comet evaporated within two hours which could be seen on images from SOHO LASCO C2 around 28 October 07:00 UTC.[10][11] The comet was predicted to be visible in the morning sky before perihelion, with better visibility from the southern hemisphere. During perihelion, if the comet had not disintegrated, it could have brightened to a magnitude of -5 to -7, which is brighter than the planet Venus.[12] If it had survived perihelion it would be visible again before dawn, more favorably located for the southern hemisphere,[4] and could have looked like C/2011 W3 (Lovejoy), another Kreutz sungrazer.[13]
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