An Update on the Habitable-Zone Planet Gliese 581g

Steven S. Vogt (UCO/Lick Observatory, UC Santa Cruz)

The nearby M-dwarf star Gliese 581 has been known since 2009 to host four exoplanets, all discovered by the Swiss HARPS team. Two of these planets, GJ 581c and 581d are Super-earths orbiting respectively near the inner and outer edges of the star's habitable zone. In 2010, we combined published HARPS precision radial velocity data with a comparable set of HIRES precision velocities, finding evidence for yet two more planets in the system. One of these, GJ 581g, is a Super-earth orbiting squarely in the star's habitable zone. Soon after, the HARPS team reported that they were unable to confirm GJ 581g, but presented no new data or analysis. A year later, the Swiss team reiterated their claim, with certainty, that no more than the original four planets exist in this system. Their preprint included twice the amount of HARPS data and a detailed Keplerian model. This talk will present an independent review of their Keplerian model, reaching a completely different conclusion regarding evidence for a Super-earth in the star's habitable zone.