Comet Shoemaker-Levy 9
The First Observed Impact on a Planetary Body
The impact of comet Shoemaker-Levy 9 showed that the solar system is still a very volatile place.
On July 16th 1994, comet Shoemaker-levy 9 began to collide with Jupiter. This was the first comet impact ever observed by humans, and most optical telescopes in the world were trained on Jupiter. The recently repaired Hubble Space Telescope, the Galileo spacecraft that was en route to Jupiter at the time, and several other spacecraft were also set to observe. It was an unprecedented event in astronomy.
String of Pearls
Shoemaker-Levy 9 was discovered on March 24th 1993 by Carolyn and Gene Shoemaker, and David Levy at the Palomar Observatory owned by the California Institute of Technology. It was the first comet observed that orbited a body other than the Sun. It was thought to have been captured by Jupiter's gravity sometime in the 1960s or 1970s from a solar orbit.
Its dance with Jupiter had been a dangerous one. The strong gravitational pull from Jupiter had broken the comet up into 22 fragments on a previous pass, inside the orbit of the planet's closest moon. It was later calculated that the fragments would collide with Jupiter over the course of a week. No one knew what would happen.
Impact
Each of the fragments were designated with a letter of the alphabet. Fragment A was the first to collide, traveling at a speed of 60 m/s. It produced an impact plume ejecting debris 3000 km above the atmosphere of Jupiter, and raised the temperature of the atmosphere in that area to 24,000 degrees Kelvin or over 23,000 degrees Celsius and nearly 43,000 degrees Fahrenheit.
Each of the impacts produced distinct dark spots that blemished the surface of Jupiter for months afterward. Impact G was the largest, hitting Jupiter on July 18th. It produced a dark spot 12,000 km in diameter, an released nearly 1000 times the energy of all Earth's stockpile of nuclear weapons. If any comet impacted the Earth it would clearly wipe out all complex life.
Results
Comet Shoemaker-Levy 9 helped to redefine our view of the volatility of the solar system. It brought the threat of planetary impact into broader public awareness, spawning a new crop of factually questionable disaster films in the process.
The impact also indicated that gas giants like Jupiter, in our star system and others, act as cleanup machines that suck in stray bodies, making the inner terrestrial planetary system safer. Life on Earth may have had a chance to form and evolve in relative peace because of the presence of gas giants in the solar system.
