An exoplanet in orbit around τ1 Gruis

We report the detection of a new candidate exoplanet around the metal-rich star tau(1) Gruis. With M sin i=1.26+/-0.18 M-Jup, a period of 1391+/-300 d and an orbit with an eccentricity of 0.14+/-0.14 it adds to the growing population of long-period exoplanets with low-eccentricity orbits. This population now comprises more than 20 per cent of known exoplanets. When the companion to tau(1) Gruis is plotted together with all exoplanets found by radial velocity searches we find evidence for a peak in the number of short-period exoplanets, followed by a minimum of planets between approximately 5 and 50 d and then an apparent rise in the number of planets per unit radius that seems to set in by 100 d, indicating more planets further from the host star. This is very different from the Gaussian-like period distribution found for stellar companions. This lends support to the idea that once a clearing in the inner protoplanetary disc develops, it halts the inward migration of planets. In particular, the smooth distribution of exoplanets arising from planetary migration through a disc is altered by an accumulation of exoplanets at the point where the disc has been cleared out.