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1994-10-05
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PHOTO RELEASE NO STScI-PRC94-43 FOR RELEASE: September 29,1994
EVOLUTION OF THE P/SHOEMAKER-LEVY 9 "GANG OF FOUR" REGION
This series of eight NASA Hubble Space Telescope "snapshots"
shows the evolution of the P-Q complex, also called the "gang of
four" region, of comet P/Shoemaker-Levy 9.
The eight individual frames chronicle changes in the comet during
the 12 months before colliding with Jupiter. The sequence shows
that the relative separations of the various cometary fragments,
thought to range in size from about 500 meters to almost 4 km
(2.5 miles) across, changed dramatically over this period. The
apparent separation of Q1 and Q2 was only about 1100 kilometers
(680 miles) on 1 July 1993 and increased to 28,000 kilometers
(17,400 miles) by 20 July 1994.
The P-Q complex demonstrates that further fragmentation occurred
after the breakup of the parent body in July 1992. Fragments Q1
and Q2 were probably together at some point in a single body.
However, it is not clear how P1 and P2, and the P and Q objects
are related.
Between 24 January and 30 March 1994, the P2 nucleus broke-up
into two separate fragments, one of which disappeared by late
June. (It might be present in the mid-May image.) The P1
nucleus had a "streaked" appearance on 24 January 1994 and then
became a barely discernible "puff" through mid-May. It was not
detected in subsequent observations.
Throughout the period, most nuclei were within a 4000
kilometer-wide (2500 miles) spherical cloud of dust, called a
coma. However, shortly before impact, the coma around each
nucleus became highly elongated along the comet's travel path due
to "stretching" by Jupiter's rapidly increasing gravity.
This stretching is dramatic in the image of the Q-complex taken
on 20 July 1994, just 10 hours before collision. Despite the
coma's changes, HST images show that the core of each nucleus
always remained concentrated. This shows that the nuclei were
probably not catastrophically fragmenting, at least not up to 10
hours before impact.
The first HST image was taken on 1 July 1993 with the Planetary
Camera before the December 1993 HST servicing mission. All other
images were taken with the WFPC-2. (The image taken on 17 May
1994 was taken in "wide-field" mode and has a lower resolution
than the other WFPC-2 images). The images were taken in visible
light. The different shades of red are a false-color
representation of the different intensities of light reflecting
off the comet's dust. Each frame covers a region 90,000 by
30,000 kilometers (56,000 by 18,600 miles).
Credit: Dr. H. A. Weaver, Mr. T. E. Smith, and Mr. K. B.
Jones (STScI), and NASA