Seeking a solution of the Pioneer Anomaly

TL;DR

This paper reviews the Pioneer Anomaly, an unexplained Sunward acceleration observed in Pioneer spacecraft data, discussing potential causes and ongoing efforts to resolve this longstanding mystery.

Contribution

It provides a comprehensive review of the Pioneer Anomaly and outlines current programs aimed at identifying its origin.

Findings

Unmodeled acceleration of ~8×10^{-8} cm/s^2 observed in Pioneer data

The anomaly is confirmed not to be an artifact of data processing

Radiant heat is a likely but unconfirmed cause

Abstract

The 1972 and 1973 launched Pioneer 10 and 11 were the first missions to explore the outer solar system. They achieved stunning breakthroughs in deep-space exploration. But around 1980 an unmodeled force of \sim 8 \times 10^{-8} cm/s^2, directed approximately towards the Sun, appeared in the tracking data. It later was unambiguously verified as not being an artifact. The origin remains unknown (although radiant heat remains a likely cause). Increasing effort has gone into understanding this anomaly. We review the situation and describe programs to resolve the issue.