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Two more sun-grazing comets discovered.

The Air Force satellite that was deliberately destroyed Sept. 13 in a test of the U.S. anti-satellite system (SN: 9/28/85, p. 197) was probably best known for its discovery of three previously unknown comets whose orbits took them so close to the sun that they failed to reappear on the other side -- presumably due to the sun's heat -- following the initial observations. Now two more sun-grazing comets have been reported in later images from the same satellite.

All five were discovered by the P78-1 satellite's coronagraph/polarimeter, a Naval Research Laboratory instrument named SOLWIND, which had been monitoring the sun's corona since the craft was launched on Feb. 24, 1979. It found its first sun-grazer only six months later (SN: 10/17/81, p. 244), and two more in January and July of 1981 (SN: 8/21/82, p. 117).

SOLWIND's data are not processed immediately, however, and one of the two new finds was actually photographed on Nov. 4, 1981. The other showed up on July 28, 1984. Both appeared in the coronagraphic images as they approached the sun, which was masked by the instrument's occulting disk, but neither emerged on the disk's other side in subsequent frames. The assumption has been that the comets either collided with the sun or were destroyed by its heat.

The sun-grazing comets are named SOLWIND 1 through 5 (though SOLWIND 4 and 5 are so far only tentative names, pending International Astronomical Union approval). None has been reported by ground-based observers. SOLWIND 5, however, was also photographed by the coronagraph aboard the Solar Maximum Mission satellite, or Solar Max. Solar Max was not launched until Feb. 14, 1980, so it was unavailable to see SOLWIND 1, and it missed the next three chances because blown fuses kept its coronagraph and several other instruments shut down until space shuttle astronauts administered repairs in April of 1984, just three months before SOLWIND 5 came by the sun.

The only other comet seen by Solar Max, says Robert MacQueen of the High Altitude Observatory in Boulder, Colo., was Comet Machholz, photographed last summer to try aiming the coronagraph away from the solar disk in preparation for similar studies of Comet Halley when it is near the sun early next year.

Meanwhile, more than two years of SOLWIND's data remain to the processed, with more sun-grazers perhaps to be found.
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Title Annotation:SOLWIND 4 and 5
Author:Eberhart, Jonathan
Publication:Science News
Date:Nov 23, 1985
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