73p/schwassmann-wachmann 3, page 6

This might or might not be irrelevant. Not for me to say. NOTE: # 1 was discovered about three years before # 3.

Going over some old notes recently I found a passage I’d forgotten about. It’s from an article titled “Saturn –Riddle of the Rings” that appeared in the Nat’l Geographic magazine (July 1981, p. 28), and it says, “One comet known as Schwassmann-Wachmann 1, whose orbit keeps it between Jupiter and Saturn, periodically explodes for no known reason. Perhaps something sparks a pocket of unstable gas within.” The full name is "29p/Schwassmann-Wachmann 1".

The reason they had for bringing up that matter in an article about Saturn is too involved to go into. It had to do with the idea that the moons of Saturn, while not geologically active, could be chemically active, which implies chemical volcanism, with explosions of gas and dust like that comet’s, rather than our kind, arising from a molten interior and sliding tectonic plates.

Moreover, ten years later, on Feb. 12, 1991, a team of Belgian astronomers noticed on a receding Comet Halley (last approach: 1985-86), which was already between Saturn and Uranus, a huge eruption that increased its luminosity about a thousandfold. By then it was tailless once again, of course, and a mere speck of light. A big cloud burst forth.

At that distance from the Sun comets have a temperature of about minus 200 degrees Cent., which made it hard to come up with an explanation. The two most plausible ones: 1) that it had collided with a meteoroid, and, more likely, 2) that a pocket of carbon monoxide (CO), a compound that can vaporize at very low temperatures, exploded under the surface.

Other sources say it’s carbon dioxide (CO2) ice and methane (CH4) ice that are involved, that the explosions are due to the solar radiation heating and vaporizing these ice deposits, and that consequently very few comets at distances greater than six astronomical units (150 million km. x 6) display this kind of activity.

…so maybe here’s an additional reason for the eventual demise of a comet, apart from its losing a lot of matter every time a star heats it up: fitful bursts.

…and a few questions for the pros: how many comets have been caught showing these bursts, when was this first seen, and can they be strong enough to destroy the comet instantly or a few hours later?
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