Planetary science. NASA weighs asteroids: cheaper than moon, but still not easy.

Planetary ScienceRather than first returning astronauts to the moon before heading off to Mars, NASA will be aiming for near-Earth asteroids (NEAs) as steppingstones in the human exploration of deep space. The new approach has disappointed lunar scientists, naturally enough, but planetary scientists who study the small bodies of the solar system are delighted. For them, the redirection promises a bonanza of new data that had seemed beyond their reach for decades to come. And astronomers looking for that next catastrophic impacter would get a boost just as their ongoing search gets a lot harder ([see sidebar][1]). But the same planetary scientists who would most benefit from an NEA-studded "flexible path" to Mars are warning that the new route looks bumpy. So far, no one knows of even one NEA that would clearly serve as a practical first target for astronauts. And no one knows what the first visitors will find at a tiny, nearly gravity-free body, except that it could be both bizarre and dangerous. [1]: http://www.sciencemag.org/content/331/6019/843.summary