Solar System Constraints on f(G) Dark Energy

Corrections to solar system gravity are derived for f(G) gravity theories, in which a function of the Gauss-Bonnet curvature term is added to the gravitational action. Their effects on Newton's law, as felt by the planets, and on the frequency shift of signals from the Cassini spacecraft, are both determined. Despite the fact that the Gauss-Bonnet term is quadratic in curvature, the resulting constraints are substantial. It is shown that they practically rule out f(G) as a natural explanation for the late-time acceleration of the universe. Possible exceptions are when f(G) reduces to something very close to a cosmological constant, or if the form of the function f is exceptionally fine-tuned.