Do the Voyager spacecraft orbits exactly obey Newtonian mechanics?

[edpell]

I seem to remember hearing that there is some question about the orbits of the voyager spacecraft and weather they obey Newtonian mechanics exactly. Can someone please fill me in on the details? Thanks.

 

[mgb_phys]

It's more noticable for the pioneer probe and is called the Pioneer anomaly - http://en.wikipedia.org/wiki/Pioneer_anomaly