Word: asteroids
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Dates: during 1980-1989
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...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...
That could mean a direct hit or, more probably, another nerve-jangling near miss. But even if 1989FC never strikes earth, a similar asteroid is destined to do so eventually. It has happened so many times before, in fact, that the earth's surface would be as pockmarked as the moon's were it not for the cosmetic effects of erosion caused by the oceans and atmosphere. Half-mile asteroids are a dime a dozen in the solar system, and they run into the planet once every 100,000 years, on average. That means the next one could strike...
Then there are the really big asteroids -- masses of rock and iron five or ten miles across that hit every 10 million to 100 million years. The half- milers are bad enough, but these giant ones pose a threat to the entire planet. It was such an asteroid (or an equivalent-size comet) that many scientists believe caused the extinction of dinosaurs some 65 million years ago. The primary evidence, discovered by the late physicist Luis Alvarez and his son Walter, a geologist, is a layer of the element iridium laid down in sedimentary rock at about the time...
...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...