Long range gravity tests and the Pioneer anomaly

TL;DR

This paper discusses the Pioneer anomaly as a potential sign of modified gravity at solar system scales, emphasizing the importance of testing gravity theories with new experiments and data analysis.

Contribution

It explores metric extensions of general relativity that could explain the Pioneer anomaly without conflicting with existing gravity tests.

Findings

Metric extensions can account for the Pioneer anomaly.

Existing experiments are compatible with modified gravity theories.

New mission designs are suggested for further testing.

Abstract

Experimental tests of gravity performed in the solar system show a good agreement with general relativity. The latter is however challenged by the Pioneer anomaly which might be pointing at some modification of gravity law at ranges of the order of the size of the solar system. As this question could be related to the puzzles of ``dark matter'' or ``dark energy'', it is important to test it with care. There exist metric extensions of general relativity which preserve the well verified equivalence principle while possibly changing the metric solution in the solar system. Such extensions have the capability to preserve compatibility with existing gravity tests while opening free space for the Pioneer anomaly. They constitute arguments for new mission designs and new space technologies as well as for having a new look at data of already performed experiments.