Solar Max spots sixth sun-grazing comet

Science News, Dec 10, 1988 by Jonathan Eberhart

Solar Max spots sixth sun-grazing comet

The number of "sun-grazing" comets discovered by the Solar Maximum Mission satellite's coronagraph now totals six. These comets' orbits carry them so close to the sun that most apparently are destroyed during the passage. Astronomers have found no sign that any of Solar Max's six comets emerged on the other side of the solar disk.

The most recent, designated SMM-6 on Dec. 3, was found by Chris St. Cyr of the NASA Goddard Space Flight Center in Greenbelt, Md., in photographs made on Nov. 18. Solar Max was not designed to hunt comets, and the coronagraph does not show the sun itself, which is masked out by a disk.

By far the most striking sun-grazer, however, is SMM-5, which St. Cyr spotted in photos (above) taken on Oct. 11. "It has the longest tail and is the brightest comet" seen by the instrument, he says. Setting it apart from other known sun-grazers is "a conspicuous bulge, almost doubling the width of the tail, on the northern side, about halfway along its length." In addition, the photos show "a wispy structure extending further north and sunward from this bulge."

Among sun-grazing comets, says Malcolm B. Niedner of Goodard, "I have never seen anything quite like that before." The bright streak heading away from the sun is probably the dust portion of the comet's tail, while the wispy feature (inset) may consist of molecules released from the comet's melting nucleus, ionized by the sun's ultraviolet light and drawn sunward along a line of the sun's magnetic field, Niedner says.