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Could such mass extinctions happen again? Astronomers have no doubt; the solar system is littered with flying debris, and they say it is only a matter of time before another large celestial object bears down on Earth. Reminders of that potential for disaster occur frequently. Early in January, for example, NASA released several radar images of the 6.4-km-long (4-mile) dumbbell-shaped asteroid Toutatis taken when it sped within 3.5 million km (2.2 million miles) of Earth -- a hairbreadth by astronomical standards. And while the warning that the 10-km-wide (6-mile) Comet Swift-Tuttle might slam...
Proceedings at the interception workshop were tumultuous. But there was general agreement about the basic strategy: detect the threatening object and dispatch a warhead-tipped rocket to intercept it and explode, nudging it into a new orbit that would carry it safely past Earth. For a small asteroid detected years and many orbits before its destined collision, the solution would be straightforward. "You apply some modest impulse to it at its perihelion, or closest point to the sun, using conventional explosives," explains Gregory Canavan, a senior scientist at Los Alamos National Laboratory. "The slight deflection that results will amplify during...
...scientists calculate that for objects having diameters of 100 m or more that are spotted late in the game and intercepted at a distance any closer than about 150 million km (93 million miles), only nuclear explosives pack enough wallop to avert disaster. At that distance, the energy needed to deflect a 2-km-wide (1 1/4-mile) object enough to spare Earth is about the equivalent of a 1-megaton nuclear explosion. If the object gets to about a tenth of that distance, the energy required is 100 megatons, more powerful than any nuclear device yet exploded...
Less controversial was the proposal that terrestrial defenders should know the exact nature of their target before acting. Responding early to a worrisome asteroid, they would send a "precursor mission," an instrumented spacecraft, to fly by or orbit the object and determine its size, shape and composition. One such "practice" mission, code-named Clementine, has already been budgeted by the Defense Department in coordination with NASA. It will fly an instrument package past the approaching asteroid Geographos in 1994 to test the kind of sensors and navigational devices that someday may be needed to help cope with a real threat...
Once the nature of the approaching object is determined, explains physicist Edward Tagliaferri, a U.S. space program consultant, "it becomes easier to decide if you want a standoff explosion, a surface explosion or a subsurface explosion," If the asteroid or comet is small, it can be vaporized with a subsurface explosion, but for larger bodies, says Tagliaferri, "you'll probably have to nudge them into a new orbit." For an asteroid consisting largely of iron, he says, "you'd probably want to have a surface explosion...