Word: asteroids
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Some 130 terrestrial impact craters had been identified, but none of them near the age of 65 million years was large enough to qualify as the Crater. Yet if a comet or asteroid massive enough to cause the extinction had struck the earth, it would have left a crater hundreds of kilometers wide. Some traces would still exist, despite the intervening millenniums of erosion, sedimentation and tectonic-plate movement...
...Chicxulub, on the northern tip of Mexico's Yucatan Peninsula, and extending out under the Gulf of Mexico. The nature of the basin, its location and a preliminary estimate of its age suggest that it is the Crater, the one gouged into the earth by the comet or asteroid that killed the dinosaurs...
...contrast, Triton, which is about the size of earth's moon, orbits in the opposite direction. That has led astronomers to guess that Triton might be a large asteroid that was captured by Neptune's gravity. Such an intrusion should have disrupted the paths of any existing moons. This would explain tiny Nereid's highly elongated and tilted orbit. But 1989-N1 is just "sitting there," says Voyager project scientist Torrence Johnson, of the Jet Propulsion Laboratory. Johnson expects that the probe will discover more moons, shedding light on Triton's origins. "All of the outer planets have lots...
...most reasonable date for a Mars mission is 2020. That allows plenty of time for a measured approach and spreads the expenditure over a sensible period. It also gives NASA ample opportunity to choose the next goal after Mars -- exploration of the asteroid belt, for example, or a manned trip to the outer planets. Robot probes would have to study the Red Planet in depth first. One, the Mars Observer, is scheduled for a 1992 launch, and others would have to follow...
...there any way to avoid collisions with asteroids and comets? Perhaps. A nuclear warhead aimed right at a small asteroid could vaporize it, says Alan Harris, an astronomer at the Jet Propulsion Laboratory in Pasadena, Calif. But the warhead might also simply break the rock into pieces that would hit the earth anyway. A better plan, proposed by concerned scientists in the early 1980s, would be to use explosives to deflect an asteroid rather than destroy it. Properly positioned, a bomb could nudge a threatening object enough to make it miss the planet. The catch, says Harris, is that there...