We've covered the Pioneer space probe mystery a couple of times in the past. Now it would appear scientists have figured out a new way to test for this anomaly, and cheaply:

Gary Page of George Mason University in Fairfax, Virginia, and his colleagues have identified 15 asteroids that might also be subjected to the mysterious force. The asteroids' orbits all stretch far into the outer solar system. This is crucial because the Pioneer anomaly only shows up beyond about twice the distance from the sun to Saturn.

So, no need for an expensive, risky space probe, just some telescope time. Some preliminary observations already seem to indicate something is acting on these big rocks. More as it develops...