# Pioneer anomaly

> English word · Noun

## Definitions
1. The observed deviation from predicted accelerations of the Pioneer 10 and Pioneer 11 spacecraft after they passed about 20 astronomical units on their trajectories out of the Solar System.

## Etymology
Named after NASA space probes Pioneer 10 and Pioneer 11.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/pioneer-anomaly