https://www.planetary.org/sci-tech/the-pioneer-anomaly
The Pioneer Anomaly | The Planetary Society
Something strange was happening to the Pioneer spacecraft in the outer reaches of the solar system. The Planetary Society helped solve the mystery.
the pioneer anomalyplanetarysociety
https://www.universetoday.com/articles/the-pioneer-anomaly-a-deviation-from-einstein-gravity
The Pioneer Anomaly: A Deviation from Einstein Gravity? - Universe Today
the pioneer anomalydeviationeinsteingravityuniverse