Word: orbitally
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Dates: during 2000-2009
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Denune explains that he watched the most complex juggling sequences with a mixture of rapt attention and fear that at any moment, a ball could fall from orbit...
...zone known as the Roche limit: the altitude above a planet at which the difference in gravity between the end of an object closest to the planet and the end farthest from the planet is great enough to pull the object apart while not pulling the remains out of orbit. Instead, the rubble disperses around the planet. Photographs of the debris could help confirm this phenomenon and could even turn up smaller, still undiscovered moons hiding within the rings...
Scientists already know of some moonlets that orbit inside the rings, sweeping areas clean of debris and accounting for at least two conspicuous gaps. Other tiny moons move along the outer rim of rings; these are the so-called shepherding moons that groom the ring edges and keep them sharp...
Iapetus, for example, is a two-toned world, its leading edge dark, its trailing edge white. There are many theories advanced for this--including the possibility that there are hemisphere-wide volcanoes or that the moon is picking up dust as it moves through its orbit, staining its face and leaving the other side clean. "We have all kinds of questions," says Cassini physicist Larry Soderblum. "Were there volcanoes? Were there oceans of some mystical hydrocarbon that froze...
...black hole, swallowing nearly $100 billion and delivering little of real value. President Bush's manned moon-Mars initiative will cost at least $170 billion--and that's from an agency that has never met a cost estimate it couldn't overrun. Forget the fixation with getting bodies in orbit or boots in the soil, critics say, and you could fairly blanket other planets with Cassini-quality landers and orbiters and still have billions left over. NASA administrator Sean O'Keefe, not surprisingly, disagrees: "Robotic missions are precursor missions." The most thorough exploration, he says, "requires the unique cognitive skills...