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Scientists Study the Effects of Comet Linear's Breakup
By Michael Paine
Special to SPACE.com
posted: 04:03 pm ET
04 August 2000
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To the surprise of many astronomers comet Linear turned out to be extremely fragile The break-up of Comet Linear as it swept past the sun last week has shocked astronomers into rethinking theories of the origins of such rocky ice balls in ways that could reduce the threat of a collision course with Earth. Though astronomers say they need more time to analyze Hubble Space Telescope and Jacobus Kapteyn Telescope images of the disintegrating Linear, they hope to soon have a greater understanding for how cometary nuclei are put together. | Comet Linear | | Comet Linear comes from the outer reaches of the solar system, a quarter of the way to the nearest star. See an animation of the Comet Linear . | Far beyond just the interests of academia, this knowledge could affect all of humankind. If, for example, a different comet were found to be directly en route to Earth, would the rogue comet withstand a nuclear-bomb blast that would deflect it away from our planet? Earth-defense deflection methods such as nuclear blasts might not work on something as fragile as Comet Linear. Blasting a more solid object, like an asteroid or even a smushy comet, could have serious repercussions. Many of the fragments could remain on a collision course and, like the blast from a shotgun, the fragments could do up to 10 times as much damage as the original, intact object. 
Comet Linear Linear comes from the outer reaches of the solar system -- a quarter of the distance to the nearest star. Analysis of its orbit suggests it has been plunging toward the sun for millions of years. Last September, the LINEAR telescope in New Mexico detected the comet out beyond the orbit of Jupiter. With its highly sensitive automated search system, the scope is designed to detect near-Earth asteroids and observe their behavior. Occasionally, it also picks up a comet.Strange behavior Comet Linear's behavior is very strange. As it moved closer to the sun, chunks of the comet started flying off. By then, many large telescopes were pointed at the object, including the Hubble Space Telescope.~ Earlier in July, LINEAR (which stands for Lincoln Laboratory Near-Earth Asteroid Research) was about 74 million miles (120 million kilometers) from Earth. Scientists say the side-splitting event started on July 5 as LINEAR began spitting out a large amount of dust, increasing the comet's brightness by more than 50 percent in just four hours. Last week, as Linear swung around the sun, the heating effect from the solar radiation, perhaps along with solar gravity, seems to have been too intense for the fragile object, breaking it apart. Astronomer Mark Kidger was observing Linear with the Jacobus Kapteyn Telescope at La Palma in the Canary Islands. Over several nights he watched the comet elongate into a "cigar" shape. At first he thought he was seeing the development of a "string of pearls," similar to Comet Shoemaker-Levy 9, which broke up into smaller pieces before plunging into Jupiter in 1994. But Kidger soon realized that Linear was catastrophically fragmenting -- turning to dust and gas. In fact, by next week it might disappear completely, he said. A fragile comet Don Yeomans, a cometary specialist with NASA, said Linear's break-up pointed up its contrast with Shoemaker-Levy and the diversity of comets in the solar system. "The primary lesson to be learned from this one is that it was an incredible wimp -- so fragile it made Shoemaker-Levy 9 look like at tower of strength," Yeomans said. "Just goes to show you that Mother Nature's got a wide variety of comets to display -- from hard-packed iceballs [perhaps] to fragile, wimpy fluff balls like Linear." 
Comet Linear The demise of Linear may be a disappointment for amateur astronomers who were looking forward to the comet passing in front of the Sombrero Galaxy late in August. This is turning into a great year for asteroid and comet research. In addition to the Comet Linear event, the NEAR Shoemaker spacecraft continues to send detailed images and data while orbiting Asteroid Eros.
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