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Like any other spacecraft, Dawn will have to be muscled off its launchpad by a conventional rocket burning conventional propellant. Once it climbs to near Earth space, however, everything will change. Of all the things that add weight to a spacecraft, fuel presents the most problems. The farther you're going, the more propellant you need, but every pound of it you add means more mass the engine must propel, which requires more fuel still, and on and on. A spacecraft like Dawn, which is designed not just to fly by its two targets but also to settle into orbit...
There's good reason to spend so much time and money--Dawn carries a $446 million price tag--getting to Ceres and Vesta. The composition and reflectivity of the bodies suggest they were formed within the first 3 million years of the solar system's life, whereas Earth was something of a late arrival, coming along about 27 million years later. A close look at Ceres and Vesta, then, is a close look at a local cosmos that our planet wasn't even around to see. "These two objects are our best opportunity for going back into time," says Christopher...
...only are the little worlds old, but they're also odd. Vesta, which measures about 330 miles (531 km) at maximum diameter, or roughly the width of Arizona, is thought to account for 1 out of 20 meteorites that strike Earth, while Ceres, which is closer to us, provides none. One reason might be simply that Vesta is made of denser stuff, material that when it breaks away can remain intact through the long journey to Earth. "Ceres is not very thick," says Russell, "and whenever there's an impact, it knocks off ice and a lot of dust that...
This summer's record-breaking heat has put global warming at center stage - with the slew of Live Earth concerts and inescapable pontifications by Al Gore. Most Republicans, however, seem to be watching from the wings. But Florida's new G.O.P. Governor, Charlie Crist, hopes to erase that impression starting today with a major international summit in Miami on climate change, featuring California Governor Arnold Schwarzenegger and Robert Kennedy...
...alarm members of minority religions or secular voters. It has become an article of faith among party leaders that it was sheer strategic stupidity to cede the values debate to Republicans for so long; that most people want to reduce abortion but not criminalize it, protect the earth instead of the auto industry, raise up the least among us; and that a lot of voters care as much about the candidates' principles as about their policies. "What we're seeing," says strategist Mike McCurry, "is a Great Awakening in the Democratic Party...