Comet and Asteroids

[Gaby]

This one put up a show 9 days ago

City-size, cold-volcano comet transforms into a glowing 'snail shell' after major explosive outburst

Following a massive cryovolcanic eruption, the mysterious Comet 29P/Schwassmann-Wachmann has been morphed into a giant spiral and is now shining 100 times brighter than normal.

The cryovolcanic comet 29P/Schwassmann-Wachmann experienced a massive outburst on Feb. 10 and subsequently morphed into a giant spiral, similar to a snail shell or an ammonoid fossil. (Image credit: Eliot Herman)

On Feb. 10, Comet 29P experienced a sudden brightening event, roughly equivalent to a 100-fold increase in its luminosity, signaling that it had undergone a major eruptive event, according to Spaceweather.com.

This outburst is one of the comet's "top five" eruptions of the past two and a half decades, experts told Spaceweather.com, and it's the most powerful event since a quadruple eruption in October 2024, which caused Comet 29P to shine 300 times brighter than normal.

However, in the days following the explosive outburst, researchers began to notice something unusual about 29P's expanding coma: The reflective cloud was not evenly distributed around the comet as it typically would be. Instead, the cloud appeared to have stretched out into a rare spiral shape.

The unusual shape likely results from an internal rotation of the comet's interior relative to its nucleus, which causes cryomagma to unevenly spew out of a newly formed vent on its icy surface, according to Spaceweather.com.

This is very similar to the "devil comet," 12P/Pons-Brooks, which appeared to grow demonic horns during the initial eruptions of its solar flyby in late 2023, likely due to a notch on its surface that partially blocked the outflow of cryomagma, experts said at the time.

The interstellar comet 3I/ATLAS, which made headlines as it zoomed through the inner solar system last year, also displayed evidence of cryovolcanism and likely leaked cryomagma through multiple jets.

Though the shapes are very well described by the plasma discharge comet theory, including the horns.

Here is where it was when it got discharged: