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Asteroids have always been the proletariat of the solar system. It's not just that most of them are nothing more than very big rocks, it's that there are so darn many of them — more than a million in the 1-km or larger range. It's hard to get excited about what's little more than a celestial rubble stream.

But asteroids are getting their moment to shine. The Dawn spacecraft just arrived in orbit around Vesta — the second largest asteroid in the solar system — and will later make a similar visit to Ceres, the 900-km-diameter granddaddy of them all. Ceres is so large that it's spherical and has been officially accorded the honorific "dwarf planet," putting it on the same footing as the recently demoted Pluto.

Now there's word out of NASA's Jet Propulsion Laboratory that astronomers have just discovered Earth's first Trojan asteroid — a rock that shares our own solar orbit, leading us around the sun like a tugboat pulling an ocean liner. That's big news not just because such an object had never been spotted before, but also because a Trojan could make such an easy and nifty place for astronauts to visit.

Trojan asteroids have been seen in the solar system before: Mars has one, so does Jupiter, so does Neptune and so do two of Saturn's moons. There was no reason Earth couldn't have one too, but they're not easy to detect because of both their small size and the telescope-swamping effects of the sun. (Through a complicated — and unfortunate — interplay of Trojans' Earth-leading position and the rotation of the planet itself, the asteroids tend to appear in the skies mostly during daylight hours.) More at http://www.time.com/time/health/article/0,8599,2085982,00.html

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