Chameleon effect and the Pioneer anomaly

TL;DR

This paper investigates whether a chameleon field could explain the Pioneer anomaly, but concludes that its effect is negligible and unmodelled forces like solar radiation pressure are more likely causes.

Contribution

It explores the chameleon field as a potential explanation for the Pioneer anomaly and finds that its impact is too small to account for the observed acceleration.

Findings

Chameleon effect can cause different accelerations for small and large bodies.

Estimated chameleon contribution to Pioneer anomaly is negligible.

Unmodelled solar radiation pressure is a more plausible explanation.

Abstract

The possibility that the apparent anomalous acceleration of the Pioneer 10 and 11 spacecraft may be due, at least in part, to a chameleon field effect is examined. A small spacecraft, with no thin shell, can have a more pronounced anomalous acceleration than a large compact body, such as a planet, having a thin shell. The chameleon effect seems to present a natural way to explain the differences seen in deviations from pure Newtonian gravity for a spacecraft and for a planet, and appears to be compatible with the basic features of the Pioneer anomaly, including the appearance of a jerk term. However, estimates of the size of the chameleon effect indicate that its contribution to the anomalous acceleration is negligible. We conclude that any inverse-square component in the anomalous acceleration is more likely caused by an unmodelled reaction force from solar-radiation pressure, rather than a chameleon field effect.