Comet Hale-Bopp Update
COMET HALE-BOPP UPDATE
Sky & Telescope News Bulletin
May 30, 1997
RETURN OF THE MINI-COMETS
Based on newly released images, Earth is being pelted more or less
continuously by small comet-like objects. A camera on the orbiting spacecraft
called Polar recorded the intruders has they sliced through Earth's uppermost
atmosphere. The interlopers are thought to weigh 20 to 40 tons and consist of
almost pure ice. They begin to break up at altitudes at least 10,000 km above
Earth, so they never reach Earth's surface. Their water creates neutralized
"holes" in the ionosphere that are seen by Polar's cameras. The comets strike at
rates of five to 30 *per minute.* If this rate has been steady over billions of
years, they have contributed much of Earth's water and perhaps a large
proportion of its organic constituents.
Physicist Louis Frank (Univ. of Iowa) first called attention to these
mini-comets in 1986, based on their appearance in other spacecraft data.
But his idea was widely criticized at the time because there was no other
observational evidence for the comets' existence.
BOTTOM'S UP FOR HALE-BOPP
Observers in the Southern Hemisphere are finally getting to enjoy Comet Hale-Bopp.
The comet is still near magnitude 2, but the views from down under are a
weak imitation of what Northerners were treated to earlier this year. The
comet is some 22 deg from the Sun, so it can only be seen well up while still
in twilight, and its magnificent dust tail has shrunk to just a couple degrees
in length. In fact, when S&T Contributing Editor Steve O'Meara saw it from
Hawaii last week, no tail was visible with his unaided eyes. "In binoculars,"
he reports, "there was just a dinky fan of dust and a stubby jet of ion tail."
He adds that the coma has become more diffuse.
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