Humble and Perplexed: NASA Scientists Seek To Understand Space Probes' Anomalous Movements

Now Jet Propulsion Laboratory astronomer John Anderson and his colleagues — who originally helped uncover the Pioneer anomaly — have discovered that five spacecraft each raced either a tiny bit faster or slower than expected when they flew past the Earth en route to other parts of the solar system.

The researchers looked at six deep-space probes — Galileo I and II to Jupiter, the NEAR mission to the asteroid Eros, the Rosetta probe to a comet, Cassini to Saturn, and the MESSENGER craft to Mercury. Each spacecraft flew past the our planet to either gain or lose orbital energy in their quests to reach their eventual targets.

In five of the six flybys, the scientists have confirmed anomalies.

"I am feeling both humble and perplexed by this," said Anderson, who is now working as a retiree. "There is something very strange going on with spacecraft motions.