http://www.economist.com/science/displaystory.cfm?story_id=10804075

So-called "slingshot" maneuvers produce a tiny amount more speed than current known gravity models allow for... 4mm/sec... and the deep space and other probes that have used the maneuver have all seen the effect.

Unexplained little gravity phenomenon. Very interesting.

-- Nate Duehr, WY0X nate@natetech.com