Support for temporally varying behavior of the Pioneer anomaly from the extended Pioneer 10 and 11 Doppler data sets

TL;DR

This study confirms the Pioneer anomaly's presence over extended data spans, suggests it may decay over time, and finds no definitive direction, challenging previous assumptions about its nature.

Contribution

The paper provides the first evidence of a temporally decaying Pioneer anomaly using extended Doppler data sets from Pioneer 10 and 11.

Findings

Anomalous acceleration is confirmed with longer data spans.

Data favor a decaying acceleration over a constant one.

No strong evidence supports a Sun-pointing direction.

Abstract

The Pioneer anomaly is a small sunward anomalous acceleration found in the trajectory analysis of the Pioneer 10 and 11 spacecraft. As part of the investigation of the effect, analysis of recently recovered Doppler data for both spacecraft has been completed. The presence of a small anomalous acceleration is confirmed using data spans more than twice as long as those that were previously analyzed. We examine the constancy and direction of the Pioneer anomaly, and conclude that: i) the data favor a temporally decaying anomalous acceleration (~2\times 10^{-11} m/s^2/yr) with an over 10% improvement in the residuals compared to a constant acceleration model; ii) although the direction of the acceleration remains imprecisely determined, we find no support in favor of a Sun-pointing direction over the Earth-pointing or along the spin-axis directions, and iii) support for an early "onset" of the acceleration remains weak in the pre-Saturn Pioneer 11 tracking data. We present these new findings and discuss their implications for the nature of the Pioneer anomaly.