Hubble Discovers Missing Pieces of Comet LINEAR
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The Missing Pieces of Comet LINEAR
Astronomers using the Hubble Space Telescope have
spotted at least a half-dozen mini-comets with tails inside the
fading coma of Comet LINEAR.
August
7, 2000 -- To the surprise and delight of astronomers, NASA's
Hubble Space Telescope has discovered a small armada of "mini-comets"
left behind by what seemed to be a total disintegration of the
explosive comet LINEAR.
Hubble's powerful vision has settled the fate of the mysteriously-vanished
solid nucleus of the comet, which disappeared
from the view of Earth-bound telescopes following its passage
around the Sun on July 26
Above: (lower right) This Hubble picture of comet
LINEAR's core shows that the icy nucleus has been reduced to
a shower of glowing "mini-comets." (upper left)
A ground-based telescopic view (2.2-meter telescope) of Comet
LINEAR taken at nearly the same time as the Hubble observations
shows a diffuse elongated cloud of debris without any visible
nucleus. The inset box corresponds to the HST field of view.
[more
information]
On July 27, ground-based observers lost sight of the bright core
of the comet and suggested that the nucleus disintegrated into
a pile of dust. Astronomers at the Space Telescope Science Institute
(STScI) in Baltimore, MD, quickly reprogrammed Hubble to search
for the missing nucleus. Johns Hopkins University astronomer
Hal Weaver said he was stunned when the Hubble image popped up
on his computer screen. "My first thought was Hubble Space
Telescope does it again! We caught the fish! This is amazing,
very exciting, very neat."
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Some astronomers think that the fragments now being seen in LINEAR may be the primordial building blocks of the original nucleus, the so-called cometesimals, which theory predicts should be several tens of feet across. The breakup of a comet tells scientists how it was put together in the first place. The cometesimals were built up from micron-sized grains of dust as it collected in the early solar system, roughly 4.6 billion years ago.
On Weaver's screen were at least a half dozen "mini-comets"
with tails, resembling the shower of glowing fireballs from fireworks.
They were clustered in the lance-head tip of an elongated stream
of dust. An isolated brighter piece in front of the cluster may
be the parent nucleus for the smaller fragments. Hubble's exceptional
resolution and sensitivity allowed it to reveal the nuclei as
separated bodies at a level of detail never before seen in a
disintegrating comet. 
Some
astronomers find it hard to imagine how an object the size of
a mountain could totally disintegrate in only two weeks. "Actually,
I would have been more amazed if Hubble saw no pieces,"
adds co-investigator Carey Lisse, of STScI. "The comet's
breakup was too violent and fast for it to completely vaporize.
How do you pulverize something the size of a mountain?"
In hindsight Comet LINEAR began falling apart in June when the comet unexpectedly brightened, indicating an outburst of dust. Powerful gas jets nudged the comet along a chaotic path, another indication of a very volatile activity. Hubble fortuitously caught a piece blowing off on July 5 - which may have been the first of the cometesimals or a piece of crust. Another comet brightening happened on July 20. When the comet went around the Sun on July 26, the Sun's heat made the comet come unglued.
Above: This 3-frame sequence of Hubble Space Telescope
images spanning July 5th through 7th shows the brightness of
comet LINEAR increasing by 50% and then subsiding again as it
blows off a piece of its crust, like a cork popping off a champagne
bottle. [more
information]
Weaver says it will be important for the largest ground-based
telescopes to try and see the mini-comets as they spread apart.
This may yield further clues on the structure of the original
nucleus and the sizes of the remaining fragments.
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Some astronomers believe this was Comet LINEAR's first visit
to the inner solar system, after traveling for nearly the distance
of one light-year (six trillion miles) from the vast comet storehouse
called the Oort cloud. Other astronomers suggest that LINEAR
may have been a fragile piece that broke off of a larger comet
that visited our solar system more than 10 million years ago.
Scientists think that 20-30 percent of comets are so fragile
they completely disintegrate when they pass the Sun.
The Space Telescope Science Institute is operated by the Association
of Universities for Research in Astronomy, Inc., for NASA, under
contract with NASA's Goddard Space Flight Center, Greenbelt,
MD. The Hubble Space Telescope is a project of international
cooperation between NASA and the European Space Agency (ESA).
Orbital
Elements of C/1999 LINEAR S4
- from the Harvard Center for Astrophysics
Daily
Ephemeris for C/1999 LINEAR S4 - from the Harvard Center
for Astrophysics
C/1999
S4 (LINEAR) -- images and historical highlights from
Gary Kronk's popular Comets
& Meteors web site.
CometLinear.com -- images, updates and a discussion forum -- all about Comet LINEAR!
Recent Science@NASA Stories about Comet LINEAR
Here Comes Comet LINEAR -- July 5, 2000
Comet LINEAR Misbehaves -- July 28, 2000
Meltdown! -- July 31, 2000
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Source: NASA
HQ press release 00-122 Production Editor: Dr. Tony Phillips Curator: Bryan Walls Media Relations: Steve Roy Responsible NASA official: John M. Horack |