The European Space Agency has selected two candidate asteroids for a future mission to study how to alter an asteroid's orbit by crashing a spacecraft into it. Such a deflection may one day be needed to prevent a catastrophic impact on Earth.
The proposed Don Quijote mission will involve a pair of spacecraft - one will be used for the impact itself while the other observes the results.
The observing craft, called Sancho, would go into orbit around the asteroid several months ahead of time in order to determine the object's precise orbit before the companion craft, called Hidalgo, smashes into it.
The two asteroids selected by ESA's Advanced Concepts Team are called 2002 AT3 and 1989 ML. Only one would actually be targeted by the mission, with the final selection being made in 2007, along with the spacecraft design.
The potential danger from asteroids was illustrated in December 2004 by the discovery of 2004 MN4 (now named Apophis), which will come very close to Earth in 2029 and could end up on an orbit that would impact Earth in 2036 or later.
ESA is not the only organisation examining how to deflect asteroids. The US-based B612 Foundation, set up by former Apollo astronaut Rusty Schweickart, aims to launch a similar mission by 2015.
Both missions would target asteroids that have no possibility of an Earth impact, since the consequences of a nudge in the wrong direction could create the very danger the tests are designed to prevent.
Computer simulations and laboratory tests have shown that the effect of an impact on an asteroid depends on its composition, density and internal structure, all of which are very poorly understood. So real-world tests are essential.
While the ESA mission would use a simple, direct impact, the B612 Foundation is studying several ways to deflect an asteroid: landing thrusters on it to alter its orbit very gradually, or even just using the spacecraft's gravitational attraction to do the same.
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11:17 21 August 2008
