Comet C/2023 A3 brightens SOHO’s week

From 7 until 13 October 2024, ESA/NASA’s SOHO spacecraft recorded Comet C/2023 A3 (Tsuchinshan–ATLAS), the second brightest comet it has ever seen. Meanwhile, large amounts of material were being spewed out by the Sun (covered in the centre), and planet Mercury is visible to the left.

The comet’s nucleus is clearly visible, surrounded by a dusty coma and trailing an impressively long tail. SOHO sees the large dust tail edge-on, curving in on itself as it is pushed outward by solar wind. 

At the end of the video you can also see a rare phenomenon known as an ‘anti-tail’: a long, thin line that points towards the Sun. This tail is an optical illusion coming from SOHO getting an edge-on view of the larger cometary dust particles that accumulate in the comet’s orbital plane. 

Comet C/2023 A3 was seen for the first time early last year. It most likely came from the distant Oort cloud, and the last time this comet flew through the inner Solar System (if ever) was at least 80 000 years ago.

The comet reached an estimated peak brightness just beyond –4 magnitude. (The more negative the visual magnitude value, the brighter the object.) Of the more than 5000 comets SOHO has seen flying past the Sun, only Comet C/2006 P1 (McNaught) was brighter, with a visual magnitude of –5.5.

SOHO’s location between the Sun and Earth gave it a front-row seat, but the same comet has been visible from Earth every evening since 12 October 2024. Throughout October, as the comet moves farther away from the Sun, it will gradually grow fainter and rise higher up in the western sky.

The week that SOHO watched Comet Tsuchinshan–ATLAS was also a wild one in terms of space weather. The Sun unleashed no less than 4 X-class flares (the highest intensity type of flare), 28 medium-intensity M-class flares, and 31 coronal mass ejections – the latter being visible as white clouds of material in the video. All this activity led to two geomagnetic storms on Earth, resulting in beautiful auroras lighting up the night sky.

SOHO, short for Solar and Heliospheric Observatory, is a joint ESA-NASA mission to study the Sun. For almost 29 years now, it has been watching the Sun itself as well as the much fainter light coming from the Sun’s outer atmosphere, called the solar corona. The data shown in this video were taken by the LASCO C3 coronagraph instrument.

Special thanks to Simeon Schmauß, who processed the raw data to create this impressive video. For comparison, here is a video of the comet with more standard data processing – the comet is so bright that it partially saturated SOHO’s sensor.

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