NASA’s new course (if Congress permits) is to put astronauts on an asteroid. Two goals can be achieved by landing on such a piece of solar system debris: first to find out how to disarm such a projectile when it’s flying in the direction of Earth, and second to function as a first stage to Mars. Problem is you have to find an asteroid quite close to Earth, else you could better fly to Mars directly. Turns out there are very few of those critters flying around. NASA only found two so far:

NASA may appear to have its pick of thousands of known asteroids for a manned mission, but only two are good targets within the next 20 years.

An asteroid mission requires a large-enough destination that astronauts could reach within a few months of launch from Earth, says Lindley Johnson, head of NASA’s Near-Earth Object program in Washington. Other limits to such an ambitious undertaking include the viewing range of ground-based telescopes.

“They don’t come all that close all that often,” Johnson said at a NASA workshop on NEOs three weeks ago.

While NASA admits more knowledge about objects that pass within 28 million miles (45 million km) of Earth could increase the number of possible destinations, only two currently meet the guidelines set out by the space agency in its attempt to send a manned mission to an asteroid by 2025, a goal set by President Barack Obama. One of the asteroids could be reached in 2020 and the other in 2025.

A third candidate would not be within range until 2045. (SPACE.com)

Well, for the time being one is enough, methinks.