Mariner Meteor Mystery, Solved?

For almost 40 years the source of the shower remained a mystery. But now, meteor expert Paul Wiegert of the University of Western Ontario may have cracked the case. The culprit, he believes, is a "dark comet" named D/1895 Q1 (Swift) or "D/Swift" for short.

Photo courtesy of NASA A picture of Comet 73P/Schwassmann-Wachmann 3 falling apart in April 2006, taken by the Hubble Space Telescope. Perhaps the same thing happened to D/Swift in the 19th century.

"Comet D/Swift was first seen in August 1895 by the prolific comet hunter Lewis A. Swift," says Wiegert. Swift discovered or co-discovered more than a dozen comets, including 109P/Swift-Tuttle, the source of the well-known Perseid meteor shower. Unlike his other comets, however, "D/Swift quickly vanished. The comet was last spotted in February 1896 heading out of the inner Solar System, and it has never been seen since, even though its orbit indicates it should come back and brighten every 5 years or so."

"Comet D/Swift was first seen in August 1895 by the prolific comet hunter Lewis A. Swift," says Wiegert. Swift discovered or co-discovered more than a dozen comets, including 109P/Swift-Tuttle, the source of the well-known Perseid meteor shower. Unlike his other comets, however, "D/Swift quickly vanished. The comet was last spotted in February 1896 heading out of the inner Solar System, and it has never been seen since, even though its orbit indicates it should come back and brighten every 5 years or so." (Note that the prefix D/ indicates a lost or broken-up comet, one that was well-observed on one or more occasions, but which failed to reappear as expected.)

What happened to D/Swift? "The comet may have disintegrated," says Wiegert. Comets are notoriously fragile and sometimes a little sunlight is all it takes to make them crumble. Comet D/Swift probably overheated when it passed by the sun in 1895 and later fell apart.

D/Swift was mostly forgotten until last year when Bill Cooke wondered if "some old D/ comet" might be responsible for the Mariner 4 episode. Comets, especially disrupted comets, leave a stream of debris in their wake as they orbit the sun. If Mariner 4 passed through such a stream, "it would have been sandblasted."