Search for a Solution of the Pioneer Anomaly

TL;DR

This paper reviews the Pioneer anomaly, an unexplained Sunward acceleration observed in Pioneer spacecraft data since 1980, and discusses ongoing efforts to identify its cause, with radiant heat as a probable explanation.

Contribution

It provides a comprehensive review of the Pioneer anomaly and summarizes current research efforts aimed at resolving this longstanding unexplained acceleration.

Findings

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

Anomaly persists over decades with no definitive explanation

Radiant heat is a likely but unconfirmed cause

Abstract

In 1972 and 1973 the Pioneer 10 and 11 missions were launched. They were the first to explore the outer solar system and achieved stunning breakthroughs in deep-space exploration. But beginning in about 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 being in the data and not an artifact. The cause remains unknown (although radiant heat remains a likely origin). With time more and more effort has gone into understanding this anomaly (and also possibly related effects). We review the situation and describe ongoing programs to resolve the issue.