Much of our solar system operates like clockwork. This routine can become a bit monotonous at times; moon phases can be forecast, oppositions occur regularly, and even solar eclipses are predictable. However, it is the occasional intruder that disturbs this calm and can result in a better understanding of our astronomical neighborhood.
The final trip of the Shoemaker-Levy Nine comet through the solar system upset this clockwork. Fortunately for our existence on Earth, Jupiter was the planet which stood in the comet's way. Astronomers were lucky as well, since the Hubble Space Telescope and the Galileo interplanetary probe were in position to take full advantage of the first comet-planet collision ever to be observed.
One of the most successful comet hunting teams in history, Carolyn and Eugene Shoemaker and David Levy, discovered the comet in March 1993. At first they believed that the comet was squashed, but its orbit prior to its fateful final trip passed so close to Jupiter the planet's gravity tore it into 21 fragments.
Photo. Fragments of the Shoemaker-Levy Nine comet before colliding with Jupiter. Courtesy Space Telescope Science Institute, NASA
Jupiter's gravity also altered Shoemaker-Levy Nine's orbit, ensuring a collision after its next trip around the Sun. Before the first piece of the comet struck on July 16,1994, astronomers knew the collisions would be out of view on Earth-on the dark side of Jupiter. Most predictions about the coming incident were conservative.
The first fragment ended all doubt about the spectacle the impacts were to come. Hubble captured collision after collision. Some fragments burned up in Jupiter's atmosphere, while another left a dark blotch more than twice the diameter of Earth. The relative size of this Shoemaker-Levy Nine splotch can be more easily put into perspective when it is considered that some 1300 Earths could fit inside a hollow Jupiter.
Lined up around the southern hemisphere of the planet, several impact sites were visible for months after the comet had smashed into the surface. Shoemaker-Levy Nine left its mark not only on Jupiter but also on the field of astronomy, which held its breath for the remarkable encounter between comet and planet and which renewed its excitement about the glorious possibilities of the Hubble Space Telescope in observing other rare sights.
Illustration. The Shoemaker-Levy Nine hits Jupiter. This is a NASA artist's rendering of the trail of fragments from the comet shows that many were glowing hot as they entered Jupiter's atmosphere. Notice the bright illumination where the first fragments actually made contact with the planet. Courtesy Space Telescope Science Institute, NASA.
Perhaps the lessons learned from Shoemaker-Levy Nine can someday help scientists remove the threat of such a collision on Earth. Scientists also hope that this can provide insight into a similar event that may have occurred millions of years ago on Earth, resulting in the extinction of the dinosaurs.