RISC DISC 2/RISC_DISC_2.iso/resources/nasa/shoemaker/info/comet_to_collide_with_jupiter

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Comet Freight Train to Collide with Jupiter

Comet Impact '94
Fact Sheet

Significance

The impact of comet Shoemaker-Levy 9 onto Jupiter represents the first time in
human history that people have discovered a body in the sky and been able to
predict its impact on a planet more than seconds in advance.  The impact will
deliver more energy to Jupiter than the largest nuclear warheads ever built,
and up to a significant fraction of the energy delivered by the impact which is
generally thought to have caused the extinction of the dinosaurs on Earth.
roughly 65 million years ago.  Earth-bound observers are taking this
opportunity to observe and study the comet's collision with a planet to gain
more understanding of one of the fundamental physical processes within the
solar system, impacts.  The discovery has spawned scientific thinking about the
frequency with which comets fragment and implications related to the inventory
of small bodies in the Solar System and how they modify the surface and
atmospheres of the planets.

Introduction

The fast approaching collision of segmented Periodic Comet Shoemaker-Levy 9
with the planet Jupiter has peaked the interest of professional and amateur
astronomers worldwide.  Scientists expect a spectacular 5 1/2-day event from
July 16-22 and anticipate some observations.  For the first time in history,
scientists have advance notice of such a collision and the technological
capabilities to observe it.

Astronomers predict the comet's 20+ segments will hit Jupiter's dark night
side, where they will be hidden from telescopes on Earth. Some observers may be
able to view the phenomenon indirectly in light reflected from Jupiter's inner
moon or off ring particles. Other observers anticipate viewing the impacts and
expected explosions through observations from NASA's Galileo and other
spacecraft or by studying the aftereffects on Jupiter's atmosphere.

Thousands of planet-watchers are readying observatories on the ground and in
space for what they hope will be a remarkable encounter. For comet experts and
planetary specialists around the world, this may be the most important event of
their careers because of the discoveries they may make about the nature of
comets and the makeup of Jupiter's atmosphere and magnetosphere. This knowledge
may help them explain similar high-energy events on Earth.

Background The fragmented comet was discovered by Gene and Carolyn Shoemaker
and David Levy on March 24, 1993. It was the ninth periodic comet found by this
team of professional and amateur astronomers. They identified the comet through
a photograph taken with the 18-inch Schmidt telescope at Mt. Palomar
Observatory near Los Angeles, California. Subsequent imaging conducted by James
Scotti at the Spacewatch Telescope on Kitt Peak in Arizona, and by Jane Luu and
David Jewitt at the Mauna Kea Observatory in Hawaii revealed the comet's
peculiar form: it is actually a string of numerous fragments of comet, "a
string of pearls."

P/Shoemaker-Levy 9 probably split apart during July 1992, when scientists think
it traveled within 113,000 kilometers of Jupiter's center. During this pass in
its orbit around Jupiter, the planet's tidal forces tore it apart. The comet is
designated, "P," for "periodic," because even before its capture in a death
grip by Jupiter, its original orbit around the Sun was closed and contained
within our solar system.

Its fragments vary in size, with about six relatively large pieces, a dozen
medium-sized ones, and assorted smaller debris. The average chunk is estimated
to be two kilometers in diameter, although no one knows for certain. The size
or mass of the fragments however, will determine the nature of their impact on
Jupiter's atmosphere.

Predicted Effects on Jupiter

As the comet string nears Jupiter, its associated dust coma will be bombarded
by charged particles trapped in Jupiter's magnetosphere. Gas and dust ejected
from the comet may be swept up by Jupiter's magnetic field, possibly causing
large changes in the density and composition of Jupiter's aurora. The comet
fragments will plummet into the planet one by one, like a freight train falling
off a bridge. The explosions within Jupiter's atmosphere may inject atmospheric
ingredients into the magnetosphere, altering Jupiter's radio emissions.

As the comet fragments enter Jupiter's stratosphere, they will be heated and
lose some mass and energy by aerodynamic forces. Because they are fragile, they
may break up after penetrating about 300-400 kilometers into the atmosphere.
The largest and strongest fragments will descend another 50-200 kilometers. At
this point, the fragments will release the majority of their kinetic energy in
a spectacular explosion in a little over a second. This explosion may create a
fireball, like a nuclear burst, that could rise above Jupiter's cloud tops in a
matter of minutes.

Ordinarily, events occurring 150-200 kilometers below visible cloud tops would
be invisible beyond the planet. In this case, however, the shock wave from the
airburst may blow through the planet's atmosphere carrying the gases far above
Jupiter's clouds. This deeper gas contains volatile materials that ultimately
will condense high in the atmosphere. The gas may form unusual clouds, which
could last a long time if the comet's ice particles are small. The impacts
could create a thermal anomaly or a tremendous storm, similar to Jupiter's Red
Spot but not as big. This new turbulence or spot might be visible through the
most powerful Earth-based telescopes.

When these comet fragments dissipate in the atmosphere, they could be very
bright - possibly as bright or brighter than Jupiter itself. The light from the
impact of the largest fragments could brighten a well-placed inner moon of
Jupiter enough to be detected by powerful Earth telescopes. The Hubble Space
Telescope is scheduled to make more pictures of Jupiter during the days of
impact. Thousands of Earthbound astronomers throughout the world will point
their telescopes towards Jupiter to look for some evidence of the crash.

World-Wide Effort

In the United States, NASA and The National Science Foundation have jointly
funded a coordinated program to support research efforts for this event, using
many ground-based observatories and several spacecraft: Galileo, Hubble Space
Telescope, the International Ultraviolet Explorer, the Extreme Ultraviolet
Explorer, Ulysses, and Voyager 2. The program includes listening for radio
signals, visible and thermal imaging, modeling, theory, and data analysis.

Since 1993, an electronic bulletin board on the Internet, organized by
astronomer Michael A' Hearn at the University of Maryland, has kept the world's
planetary-scientific research community advised of the latest information on
the pending collision. In January 1994, 175 astronomers from the United States
and Europe met to identify the specific physical phenomena they would try to
observe to gain the most knowledge from the event. They established a
continuous worldwide series of Jupiter observations during the collision's
six-day time frame. They also agreed to disseminate their scientific
information within three to six months after obtaining it. Throughout the
planning process, scientists in varied U.S. and international organizations
have displayed a spirit of cooperation in their quest for discoveries.

Astronomers hope to gain more knowledge about the composition of comets and the
make up of Jupiter's atmosphere. Analysis of the new data may teach us more
about the role of comets, meteors, and other space objects in the disappearance
of the dinosaurs more than 65 million years ago. Additional measurements and
observations may test theories of other mass extinctions on Earth, the behavior
of high-energy shock waves and cloud formation in planetary atmospheres, the
makeup of comets, and even the origin of planets.


Comet Levy References

Foley, Theresa M., "Comet heads for collision with Jupiter," Aerospace America,
pp 24-29, April

Levy, David H., "Pop! Pow! Smash!," The Sciences, pp 31-35, May/June 1994.

Smith, Douglas L., "When a Body Hits a Body Comin' Through the Sky,"
Engineering & Science, pp 3-13, Fall 1993.