Volcanic Comet 29P/Schwassmann-Wachmann Displays Rare Spiral Structure After Explosive Outburst
A comet known for its frequent outbursts has recently exhibited a striking spiral shape following a significant increase in brightness, captivating astronomers and astrophotographers alike. Comet 29P/Schwassmann-Wachmann (29P) is a unique object in our solar system, belonging to a group of icy bodies called centaurs.
What is Comet 29P/Schwassmann-Wachmann?
Discovered on November 15, 1927, by Arnold Schwassmann and Arno Arthur Wachmann at the Hamburg Observatory in Germany [1], 29P is approximately 37.5 miles (60.4 km) in diameter [1]. It’s classified as a cryovolcanic comet, meaning it occasionally erupts, spewing gas and ice into space. These outbursts occur when solar radiation heats the comet’s icy interior, causing a buildup of pressure that eventually releases through cracks in the nucleus.
Recent Outburst and Spiral Formation
On February 10, 2026, Comet 29P experienced a dramatic brightening event, increasing in luminosity by a factor of 100 [2]. This outburst is considered one of the comet’s top five eruptions in the last two and a half decades [2]. Following the outburst, observers noticed the comet’s coma – the cloud of gas and dust surrounding the nucleus – had expanded into an unusual spiral shape.
Astrophotographer Eliot Herman, capturing images from Chile, described the coma as resembling a fossil of an ammonoid, an extinct shelled cephalopod [2]. Another photographer, Anthony Kroes, noted its “snail-shell appearance.”
The spiral shape is believed to be caused by the internal rotation of the comet’s interior, leading to uneven ejection of cryomagma from a newly formed vent [2]. Similar patterns have been observed in other cryovolcanic comets, such as 12P/Pons-Brooks, which appeared to grow “horns” due to obstructions in the outflow of gas and dust.
Understanding Cryovolcanism on 29P
Unlike most cryovolcanic comets, which are long-period comets that only erupt when near the sun, 29P has a nearly circular orbit between Jupiter and Saturn [1]. Despite receiving less sunlight, it experiences an average of 20 eruptions per year [2]. The cause of these outbursts, particularly the larger ones releasing up to 1 million tons of cryomagma, remains a mystery to researchers [2].
Observing Comet 29P/Schwassmann-Wachmann
Whereas Comet 29P has passed its peak brightness, a smaller outburst on February 15, 2026, has reinvigorated its coma, making it potentially visible through a telescope or binoculars. [2] As of February 18, 2026, it is located in the constellation Leo [2]. Astronomers anticipate further, smaller eruptions in the coming weeks.
Other comets currently visible include C/2024 E1 (Wierzchoś), and upcoming comets C/2026 A1 (MAPS) and C/2025 R3 (PanSTARRS) are expected to be visible in April 2026.