New ‘Devil’ Comet Erupts in Series of Violent Volcanic Explosions

A volcanic comet orbiting within the inner solar system, known as 29P/Schwassmann-Wachmann (or 29P), has recently become exceptionally active, erupting four times over a 48-hour span. This burst of energy has made it almost 300 times brighter than usual, puzzling scientists who are unsure what triggered this sudden surge. Measuring about 60 kilometers across, 29P belongs to a rare group called centaurs—icy bodies that spend their lives racing around the inner solar system. Its recent eruptions mark the most intense activity seen in over three years.

29P is unique not only as a centaur but also as a cryovolcanic, or “cold volcano” comet, one of only a few hundred known in the universe. These comets have icy exteriors filled with ice, gas, and dust. When they approach the sun, radiation causes their frozen interiors to heat up. As pressure builds, the comet’s shell cracks, releasing an icy mixture, or cryomagma, into space. This process makes the comet shine brighter due to an expanding coma—a cloud of reflective cryomagma that amplifies sunlight.

The British Astronomical Association (BAA) reported 29P’s first major eruption on November 2, followed by three more within two days. BAA astronomers monitoring 29P noted that these four eruptions released a cloud of debris that reflected nearly 289 times more light than the comet’s nucleus.

Last year, another comet, 12P/Pons-Brooks, drew attention with similar explosions that gave it a horned shape, earning it the nickname “devil comet.” Experts believe 29P may also take on unusual forms after these outbursts, as explosions often lead comets to develop irregular shapes.

This isn’t the first instance of violent activity for 29P. Its last eruption was in November 2022, releasing over a million tonnes of debris, and in September 2021, it experienced five major outbursts in quick succession. The recent eruptions have been even more intense than those previous events.

Cryovolcanic comets like 29P travel in elliptical orbits around the sun, sometimes venturing to the far edges of the outer solar system for centuries before returning. When they re-enter the inner solar system, they often undergo explosive activity before being pushed back out to the outer reaches of the solar system.