Home=Current Comets: C/2021 S3
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On Sep. 24, 2021 the PANSTARRS team discovered a 19.5 mag comet in the constellation Lepus, which showed a 2" coma. Additional observations of comet C/2021 S3 (PANSTARRS) showed that this comet was still at a distance of 9 AU from the Sun, displaying a compact, 6" coma. It will pass perihelion on Feb. 18, 2024 at the solar distance of 1.33 AU, predicted to become as bright as 9 mag (CBET 5051 / MPECs). It should be brighter than 16 mag between February 2023 and January 2025. During this period it will move through the constellations Columba, Lepus, Canis Major, Puppis, Circinus, Antlia, Centaurus, Lupus, Scorpius, Ophiuchus/Serpens (perihelion), Aquila, Sagitta, Vulpecula towards the border of Cygnus/Draco, where it will display an opposition loop. It should be brighter than 12 mag between November 2023 and July 2024, when it will move from Centaurus to Cygnus/Draco. At mid-European locations it will appear above the southern morning horizon in February 2024, will then climb up and culminate at altitudes of 75° in June/July 2024. Thereafter it changes to the whole-night and evening sky, at which it will sink slowly down.
For a temporary analysis 55 observations from 13 observers can be taken into account on the start of January 2024. These indicate a brightness development significantly below-average, which can be represented by the parameters
m0 = 8.3 mag / n = 2indicating a maximum brightness of 9.5 mag at the beginning of March 2024. The comet was of magnitude 15.5 at the start of the apparition, brightening slowly at first, but ever more rapidly during the following months. At the beginning of February 2024 the comet was of magnitude 10.0.
Total Brightness and Coma DiameterThe apparent diameter of the comet increased from 0.3' to 1.3' between the end of 2022 and the end of 2023, reaching 2.5' at the beginning of February 2024. The absolute diameter measured about 100,000 km until the end of 2023, and 175,000 km at the beginning of February 2024. The degree of condensation appears to have slowly decreased from DC 5 to DC 3 until fall 2023, only to increase slightly thereafter, reaching DC 4 in February 2024. Since November 2023 a tail of up to 5' (800,000 km) length can be observed, which is directed towards Southwest.
Andreas Kammerer