For the last 10 years physicists have been puzzled by a mysterious force acting on space probes. There have been various slight anomalies detected in how spacecraft move which don't seem to be moving quite as we would predict them to.
One of the first anomalies was noticed on the pioneer spacecraft that visited the outer solar system in the 1970s and are still heading off into space. They seem to be slowing down slightly faster than we would predict using our present understanding of physics. This effect is minute, about a ten billionth as strong as the force of gravity on the surface of the earth but it is measurable. This effect could just be due to some physics we already understand, like a gas leak or we don't understand how the probe is radiating heat.
Now a team from the jet propulsion laboratory in California have found another anomaly which seems to appear when some spacecraft make a flyby of earth. For examble when the NEAR spacecraft flew past the earth on its way to visit an asteroid, it left moving at 13mm/s slower than it should have done, and the Galileo probe was speeded up by 4mm/s these are tiny effects as the probes are moving more than a million times faster than this, but it is well within our ability to measure their speeds.
Some probes have this effect and others don't, Frank Jordan who is part of the team which was looking at this effect and trying formulae to try and model these results and found one that works nicely. It seems to suggest that probes which approach and leave the earth at a similar angle to the equator won't feel an effect, but probes which enter and leave at different angles feel this strange extra force.
This doesn't say anything about what could be causing the force, but the fact that the equator is important could indicate that the earth's rotation is affecting it somehow. Einstein's theory of general relativity suggests some effects related to rotating massive objects, but they should be much smaller than this, so it is just possible that these may be some hints at some interesting new physics.