Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.arcetri.astro.it/~palla/ANDREAIMMAGINI/sistemasolare/Comete/halebopp.txt Дата изменения: Wed Dec 11 20:00:57 2002 Дата индексирования: Sat Dec 22 12:20:03 2007 Кодировка: Поисковые слова: arp 220

These NASA Hubble Space Telescope pictures of comet Hale-Bopp show
a remarkable "pinwheel" pattern and a blob of free-flying debris
near the nucleus. The bright clump of light along the spiral (above
the nucleus, which is near the center of the frame) may be a piece
of the comet's icy crust that was ejected into space by a combination
of ice evaporation and the comet's rotation, and which then
disintegrated into a bright cloud of particles.

Although the "blob" is about 3.5 times fainter than the brightest
portion at the nucleus, the lump appears brighter because it
covers a larger area. The debris follows a spiral pattern outward
because the solid nucleus is rotating like a lawn sprinkler,
completing a single rotation about once per week.

Ground-based observations conducted over the past two months have
documented at least two separate episodes of jet and pinwheel
formation and fading. By coincidence, the first Hubble images of
Hale-Bopp, taken on September 26, 1995, immediately followed one
of these outbursts and allow researchers to examine it at
unprecedented detail. For the first time they see a clear separation
between the nucleus and some of the debris being shed. By putting
together information from the Hubble images and those taken during
the recent outburst using the 82 cm telescope of the Teide Observatory
(Tenerife, Canary Islands, Spain), astronomers find that the debris
is moving away from the nucleus at a speed (projected on the sky)
of about 68 miles per hour (109 kilometers per hour).

The Hubble observations will be used to determine if Hale-Bopp is
really a giant comet or rather a more moderate-sized object whose
current activity is driven by outgassing from a very volatile ice
which will "burn out" over the next year. Comet Hale-Bopp was
discovered on July 23, 1995 by amateur astronomers Alan Hale
and Thomas Bopp. Though this comet is still well outside the orbit
of Jupiter (almost 600 million miles, or one billion kilometers
from Earth) it looks surprisingly bright, fueling predictions that
it could become the brightest comet of the century in early 1997.

The full-field picture on the left, taken with the Wide Field Planetary
Camera 2 (in WF mode), shows the comet against a stellar backdrop in the
constellation Sagittarius. The stars are streaked due to a combination
of Hubble's orbital motion and its tracking of the nucleus, which is
now falling toward the Sun at 33,800 miles per hour (54,000 km/hr). In
the close-up picture on the right, the stars have been subtracted
through image processing. Each picture element is nearly 300 miles
(480 km) across at the comet's distance. In this false color scale the
faintest regions are black, the brightest regions are white, and
intermediate intensities are represented by different levels of red.

Even more detailed Hubble images will be taken with the Planetary Camera
in late October to follow the further evolution of the spiral, look for
more outbursts, place limits on the size of the nucleus, and use spectroscopy
to study the enigmatic comet's chemical composition.

Credit: H.A. Weaver (Applied Research Corp.), P.D. Feldman
(The Johns Hopkins University), and NASA.