Comet Shoemaker-Levy 9 Collides with Jupiter
Comet Shoemaker-Levy 9, discovered in March 1993, was a unique celestial object that became notable for its dramatic collision with Jupiter between July 16 and July 22, 1994. After being torn apart by Jupiter's gravity, over twenty fragments of the comet entered the planet's atmosphere, resulting in massive impacts that released energy surpassing that of all nuclear arsenals combined. Observed from Earth and space, these collisions generated bright fireballs and created dark scars in Jupiter's atmosphere, offering astronomers an unprecedented opportunity to witness such a cosmic event. The fragments, which ranged from half a mile to about a mile in size, moved at incredible speeds, leading to explosive effects equivalent to millions of tons of TNT. This event marked a significant moment in astronomy, as it allowed scientists to study the implications of cosmic impacts, enhancing models of how similar events might affect Earth. The aftermath of the collision not only advanced understanding of planetary atmospheres and dynamics but also sparked increased efforts to detect near-Earth objects. Overall, the Shoemaker-Levy 9 event underscored the importance of monitoring potential threats from space, shaping future astronomical research and planetary defense initiatives.
Comet Shoemaker-Levy 9 Collides with Jupiter
Date July 16-22, 1994
When more than twenty fragments from Comet Shoemaker-Levy 9 collided with the upper atmosphere of Jupiter, the event offered scientists the opportunity to witness the consequences of the collision of extraterrestrial objects and provided insights into the likely effects of asteroid or comet impacts on Earth.
Also known as D/1993 F2; SL9
Locale Jupiter
Key Figures
Eugene Merle Shoemaker (1928-1997), American geologist and codiscoverer of Comet Shoemaker-Levy 9Carolyn Shoemaker (b. 1929), American astronomer and codiscoverer of Comet Shoemaker-Levy 9David H. Levy (b. 1948), Canadian astronomer, science writer, and codiscoverer of Comet Shoemaker-Levy 9Brian G. Marsden (b. 1937), British astronomer who showed that Shoemaker-Levy 9 was in orbit around Jupiter
Summary of Event
From July 16 to July 22, 1994, more than twenty fragments of Comet Shoemaker-Levy 9, which had been ripped apart by Jupiter’s gravity during an earlier encounter with the planet, collided with the atmosphere of Jupiter. These collisions deposited more energy into the atmosphere of Jupiter than would be produced by all of the nuclear weapons in the military arsenals around the world. These impacts, which were observed from Earth and from spacecraft, provided astronomers with their first opportunity to witness a cosmic collision of a size capable of causing global consequences. The impacts produced bright fireballs in Jupiter’s atmosphere and new cloud features visible from Earth.
Comet Shoemaker-Levy 9 was discovered by Eugene Merle Shoemaker, Carolyn Shoemaker, and David H. Levy in photographs taken on March 24, 1993. These photographs were taken using a 0.46-meter diameter Schmidt camera, a low-power telescope with a high light-gathering capability, at the Mount Palomar Observatory in Southern California. A Schmidt camera is designed so that it can see dim objects, and it has a wide field of view, making it an ideal instrument to search a large area of the sky for faint objects such as comets and asteroids. Shoemaker-Levy 9 was the ninth comet discovered by this group of researchers.
The comet was very dim—having a brightness of 13.8, much fainter than the dimmest object that can be seen with the human eye or with binoculars—when it was discovered. Still, it appeared unusual in the photographs, being slightly elongated. Once the position of Shoemaker-Levy 9 was determined, other observers looked at it with telescopes having higher magnification. Photographs taken by John Scotti, an astronomer using the Spacewatch telescope on Kitt Peak, Arizona, showed that Shoemaker-Levy 9 was not a single object but was actually several distinct objects spread out along the same path in space. Astronomers referred to the comet as “a string of pearls” because its bright fragments were distributed in a line along its orbital path. Astronomers wondered what caused Shoemaker-Levy 9 to break into pieces. Other comets had been seen breaking up when they came close to the Sun, but the initial determination of the orbit of Shoemaker-Levy 9 showed that it had not passed close to the Sun.
Within days of its discovery, the comet had been observed by astronomers at the University of Hawaii and the McDonald Observatory in Texas. By April, 1993, these and other observations allowed Brian G. Marsden to determine that Shoemaker-Levy 9, instead of orbiting the Sun as is typical for comets, was actually in orbit around Jupiter.
Other researchers were able to trace the history of the comet’s orbit. They determined that the comet passed only 15,500 miles above the clouds of Jupiter, within 1.4 Jupiter radii of the planet’s center, on July 7, 1992. They suggested that during this close approach, the difference between the gravitational force Jupiter exerted on the near and far sides of the comet had ripped the weak comet into many pieces.
Shoemaker-Levy 9 had been in a rapidly changing orbit around Jupiter for several decades. The comet did not fragment during earlier encounters with Jupiter because it had approached no closer than about five million miles in its previous orbits. Analysis of high-resolution photographs taken by the National Aeronautics and Space Administration (NASA) Hubble Space Telescope in July, 1993, as well as images taken after the Hubble repair mission, which greatly improved the resolution, showed at least twenty-three discrete fragments, which were assigned letters A through W. The brightness of the Hubble images suggested that the visible fragments ranged in size from one-half mile to about one mile, with the fragments G and H being the largest. These visible fragments were embedded in a cloud of debris with material ranging from boulder-sized to microscopic particles.
By late May, 1993, it appeared that Shoemaker-Levy 9 was likely to hit Jupiter in 1994, and the fragments would be moving at a speed of about 130,000 miles per hour relative to the planet. At that point, the comet became the subject of intense study by astronomers around the world, since a cosmic collision of that magnitude had never been observed before. Based on the size and speed of each of the fragments, the impacts were expected to produce an explosive effect equivalent to between 6 million and 250 million megatons of TNT.
In the two-year period between the breakup of the comet and the collision with Jupiter, the fragments had spread out along the comet’s orbit. The impacts, which took place over a one-week period from July 16 through July 22, 1994, caused enormous fireballs in the atmosphere of Jupiter and produced large, dark storms. Fragments G and H, each about 1.5 miles in diameter, caused the most destruction.
The first two impacts occurred on a part of Jupiter that was facing away from the Earth, so the impacts were not directly observable from Earth. However, astronomers were able to see the bright clouds of debris as they rose over the edge of the planet. An hour later, as Jupiter rotated, the impact sites became visible, and the extent of the damage was clear. The impacts had left dark scars in the atmosphere of Jupiter.
The observation of Shoemaker-Levy 9’s impact with Jupiter was a once-in-a lifetime event for astronomers. The disruption of a comet into many fragments is an unusual event. Capture of a comet into an orbit around Jupiter is even more unusual, and the collision of a large comet with a planet is extremely rare, estimated to occur only once in a thousand years.
Significance
Sixty-five million years ago, Earth was struck by a large asteroid, an event which may have brought about the extinction of the dinosaurs. However, exactly what took place as the object passed through Earth’s atmosphere has only been modeled, never verified, by experiment. The enormous release of energy into the atmosphere cannot be produced by humans, even with the use of nuclear bombs. Thus the Shoemaker-Levy 9 impacts into the atmosphere of Jupiter provided the first opportunity to observe this type of event and to validate the models, allowing scientists to determine with better accuracy the likely effects of impacts of asteroids or comets on Earth.
Shoemaker-Levy 9’s impact on Jupiter provided graphic visual evidence of the destructive power of comet and asteroid impacts on a planet. Governments around the world began to recognize the consequences such an event would have if it occurred on Earth. The event resulted in a more ambitious effort to discover and track asteroids and comets that approach Earth.
The impacts also allowed scientists to study Jupiter. The dark spots in the atmosphere were quickly distorted in shape, serving as a tracer to map the winds on Jupiter. Ultraviolet observations from the Hubble Space Telescope showed the debris sinking into Jupiter’s atmosphere, providing the third dimension in the motion of Jupiter’s winds. Observations also led to the suggestion that linear chains of craters, previously observed on two of Jupiter’s moons, Ganymede and Callisto, might have formed by the impact of bodies disrupted in the same way as Shoemaker-Levy 9.
Bibliography
Levy, David H. Impact Jupiter: The Crash of Shoemaker-Levy 9. New York: Basic Books, 2003. Well-illustrated, nontechnical account of the impact of Comet Shoemaker-Levy 9 into Jupiter. Discusses how the event changed the understanding of comets and cosmic cataclysms.
‗‗‗‗‗‗‗. Shoemaker by Levy: The Man Who Made an Impact. Princeton, N.J.: Princeton University Press, 2000. Account of the life of Eugene Shoemaker, including the events that led to the discovery of Shoemaker-Levy 9, and Shoemaker’s work on the effects of comet and asteroid collisions with Earth and other heavenly bodies.
Noll, Keith, Harold A. Weaver, and Paul D. Feldman, eds. The Collision of Comet Shoemaker-Levy 9 and Jupiter. New York: Cambridge University Press, 2006. A 388-page collection of scientific reports presenting the major scientific results from observation of the impacts.
Shoemaker, Gene, Carolyn Shoemaker, John R. Spencer, and Jacqueline Mitton. The Great Comet Crash: The Collision of Comet Shoemaker-Levy 9 and Jupiter. New York: Cambridge University Press, 1995. Collection of images from telescopes around the world showing Comet Shoemaker-Levy 9 and the effects of its collision with Jupiter.