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Astronomers eye 'giant space volcano' comet spewing 'cryomagma'

The comet is about as weird as one can get and is more active than it's been in decades.

Comet 29P as seen by the Spitzer Space Telescope.
NASA/JPL/Caltech/Ames Research Center/University of Arizona

One of the most bizarre objects in our solar system might be the comet 29P/Schwassmann-Wachmann, which is cruising around space at around 26,000 miles per hour (41,836 kilometers per hour) and repeatedly erupting with so-called "cryomagma" as it goes. 

"In fact, it strains the definition of 'comet,'" writes astronomer Tony Phillips at "Really, 'giant space volcano' might be a better description."

Phillips describes comet 29P as a huge ball of ice 37 miles (60 kilometers) across that "appears to be festooned with ice volcanoes which erupt (around) 20 times a year."

The comet was originally discovered in 1927 orbiting the sun on a planet-like path between Jupiter and Saturn. Its explosive behavior has been well known for decades, but the object has recently entered a phase of apparent eruptive hyperactivity. 

Because it never comes very close to the sun, the comet doesn't have the same distinctive tail we expect from such space snowballs, but instead appears surrounded by a fuzzy coma, as if traveling in a fog of its own making. 

"The current outburst, which began on Sept. 25, appears to be the most energetic of the past 40 years," Richard Miles of the British Astronomical Association tells Phillips. "Within a span of only 56 hours, four eruptions took place in quick succession, creating a 'superoutburst.'"

Miles has been studying comet 29P for years and believes it contains no magma, but instead erupts with a chilled combination of methane, ethylene and other liquid hydrocarbons like those present on the surface of Saturn's moon Titan. 

"In Miles' model, the cryomagma contains a sprinkling of dust and it is suffused with dissolved gases nitrogen and carbon monoxide, all trapped beneath a surface which, in some places, has the consistency of wax," Phillips explains. "These bottled-up volatiles love to explode when a fissure is opened -- hence some of 29P's more spectacular eruptions."

The current superoutburst has increased the comet's brightness from Earth more than 200-fold. If you have access to a powerful backyard telescope, Sky and Telescope magazine has a brief guide on how to try to spot the restless comet. 

Miles has also studied not just the comet itself, but the possibility that a spacecraft could be sent to investigate it up close in the future. NASA has so far declined to fund a proposed mission to 29P.