A Volcanic Comet Blows its Top

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But what kind of volcanoes? One researcher has a theory.

Oct. 14, 2021: So you think you know what a comet is? Think again. Comet 29P/Schwassmann-Wachmann is challenging old ideas. Astronomers call it a comet, but, really, “giant space volcano” might be a better description. It’s a 60-km-wide ball of ice orbiting the Sun beyond Jupiter, and it appears to be one of the most volcanically active bodies in the entire Solar System.

Comet 29P just blew its top … again. In late September 2021, 29P erupted 4 times in quick succession, blowing shells of “cryomagma” into space. Arizona amateur astronomer Eliot Herman has been monitoring the debris:

“Initially it looked like a bright compact object,” says Herman. “Now the expanding cloud is 1.3 arcminutes wide (bigger than Jupiter) and sufficiently transparent for background stars to shine through.”

When this object was discovered in 1927, astronomers thought they had found a fairly run-of-the-mill comet, unusual mainly because it was trapped…