If you're an astronomy buff, you know about the Pioneer anomaly: that two NASA space probes have been drifting slightly off course for decades in a way that goes against everything we know about how gravity works. Now we may finally have the answer, and it's a doozy: a brand new fundamental force.
For the last 40 years or so, space probes Pioneer 10 and 11 have been steadily pulled toward the Sun by an unknown force. Scientists eliminated all possible causes — gravity, radiation, equipment problems — and have now apparently concluded that the craft have been affected by a previously unknown force that's about 10 billion times weaker than the gravitational force.
What is this new force, and how is it we haven't encountered it before? Explanations aren't forthcoming just yet, but the research is due to be published in an upcoming issue of The Physical Review, a physics journal (actually a past issue — note the update below). After that, expect a lot of arguing among researchers about how to verify this force, why it exists and what to call it. Or as scientists call it: fun!
Update: It appears the NineMSN article referenced in this story was mistakenly based on this eight-year-old article from the Telegraph. While the existence of a new fundamental force is still possible — and certainly worthy of lively discussion — we don't remember all of physics being up-ended back in 2002. Nonetheless, the Pioneer Anomaly remains a stubbornly unsolved scientific mystery, and new physics may indeed be needed to explain it fully.