Comet Tsuchinshan–ATLAS

Lore & Background

The comet was first detected as an asteroidal object of magnitude 18.1 by ATLAS on 22 February 2023, and later matched to an 18.7 magnitude object reported by Purple Mountain Observatory on 9 January 2023. It had been removed from the confirmation list on 30 January 2023 after being considered lost. Pre-discovery images from the Zwicky Transient Facility on 22 December 2022 showed a coma and tail, indicating cometary activity at 7.9 AU from the Sun. The comet received its name from both observatories.

By January 2024, the comet had brightened to magnitude 13.6, visible through 15-inch telescopes. In May and June, the brightening rate slowed, leading astronomer Zdenek Sekanina to suggest the nucleus was fragmenting, predicting disintegration before perihelion. The comet was recovered in September 2024, and by 23 September it was visible to the naked eye at magnitude 3.3. Perihelion occurred on 27 September, and the comet peaked at magnitude −4.9 on 9 October, becoming the brightest comet observed from the Northern Hemisphere since Hale–Bopp. It was also the second-brightest comet viewed by SOHO since 1995, after Comet McNaught in 2007.

Earth crossed the orbital plane on 14 October, producing an anti-tail. The comet faded quickly, dropping below naked-eye visibility by 2 November. NASA formally dubbed it the Great Comet of 2024 on 21 October and again on 11 November.

Reader's Guide

Comet Tsuchinshan–ATLAS is significant as the brightest comet observed from the Northern Hemisphere since Comet Hale–Bopp in 1997, reaching a peak apparent magnitude of −4.9 on 9 October 2024. It was the second-brightest comet viewed by the SOHO coronagraph since its launch in 1995, after Comet McNaught in 2007. Its legacy includes being formally dubbed the Great Comet of 2024 by NASA. The comet displayed a prominent dust tail that reached over 20 degrees in length photographically, and an anti-tail was observed after Earth crossed its orbital plane. Its spectrum showed strong sodium lines and carbon depletion. The comet's brightness exceeded early predictions, which had estimated a magnitude of +3 at perihelion. It was observed from the International Space Station by astronauts Matthew Dominick and Donald Pettit. The comet's discovery involved two independent observatories and pre-discovery images from ZTF, highlighting the collaborative nature of modern comet detection. Its fragmentation was suggested by Sekanina, but the comet survived perihelion and became a spectacular object.

Did You Know?

• The comet was independently discovered by Purple Mountain Observatory on 9 January 2023 and by ATLAS South Africa on 22 February 2023.
• It peaked at an apparent magnitude of −4.9 on 9 October 2024, the brightest Northern Hemisphere comet since Hale–Bopp in 1997.
• Astronaut Matthew Dominick photographed the comet from the International Space Station on 20 September 2024.
• Earth crossed the comet's orbital plane on 14 October 2024, producing an anti-tail.