  Despite its remarkable agreement with gravity tests in the solar system,
general relativity is challenged at larger scales. Large scale tests performed
in the solar system by the Pioneer 10/11 probes have failed to confirm the
expected gravity laws. We discuss here extensions of general relativity which
preserve its geometrical nature while showing an ability to conciliate the
Pioneer anomalies with other gravity tests. Further testable phenomenological
consequences are also briefly discussed.
