Word: km
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Dates: during 1990-1999
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...ground is solid and compact and water flows down through it at a rate of less than 30 m (100 ft.) a year. But about 20% of the U.S.'s fresh water flows through the myriad cavities and pores of limestone karst, often traveling 1 km (0.6 mile) overnight, taking unpredictable turns and sometimes bubbling up to the surface through a spring. Containment of a toxic spill in such terrain is virtually impossible. Even ordinary garbage that is dumped in a sinkhole can contaminate groundwater miles away...
EVERY AUGUST THE EARTH PASSES THROUGH THE orbital path of Comet Swift-Tuttle. If the comet ever happened to be there, the 10-km-wide (6-mile) chunk of ice and rock could slam into the planet, carving an enormous crater, generating tidal waves and throwing up a worldwide pall of dust that could block sunlight for months. Plants would be largely wiped out, and so would many species that ultimately depend on plants for food -- including, perhaps, the human race. Just such a disaster, many scientists believe, killed off the dinosaurs 65 million years ago. A smaller strike...
...came in vertically, punching a hole 10 km wide through the atmosphere, generating temperatures so high that the air itself started to burn. When it hit the ground near the Gulf of Mexico, rock turned to liquid and spread outward in mountainous waves, not freezing until it had formed a crater 200 km across...
...been indirect and theoretical. At last there is something concrete. A tiny reddish spot of light recorded on a sensitive electronic detector in Hawaii last month appears to be the first component of the Kuiper belt ever observed. The body, known for now as 1992 QB1, is about 200 km (120 miles) across, and a preliminary calculation puts it at more than 5.1 billion km (3.2 billion miles) away. That doesn't necessarily make it the most remote object in the solar system, since Pluto retreats to more than 7 billion km from the sun. But it does imply that...
...study the planet Jupiter, the Galileo probe passed within 5,300 km (3,300 miles) of the asteroid 951 Gaspra, and scientists instructed it to take the first closeup ever of such an object. The irregular shape suggests that Gaspra was chipped from a larger body in a mammoth collision. (See related story on page...