Monday, June 2, 2008
STOP PRESS: Smallest planet of smallest star (or sub-star) found
A press conference is still underway in St. Louis at the 212th AAS Meeting in which D. Bennett has just announced the discovery of a planet of roughly 3 Earth masses orbiting a star or brown dwarf of 6±3 percent of a solar mass; with a high probability the mass is < 8%, so it's probably a brown dwarf. The discovery was made with a new wide-field telescope by the MOA collaboration in New Zealand which images the whole galactic bulge every hour, looking for microlensing events and signatures of planets in these. The detailled paper is rather cautious, though: "the observational coverage of the planetary deviation is sparse and incomplete, and the radius of the source was estimated without the benefit of a source star color measurement. As a result, the 2-sigma limits on the mass ratio and the finite source measurements are weak. Nevertheless, the microlensing parallax signal clearly favors a sub-stellar mass planetary host, and the measurement of finite source effects in the light curve supports this conclusion." This would be the 7th exoplanet detection via microlensing, though the mass of the planet is ill-defined at 3.3 (+4.9/-1.6) Earth masses and does not necessarily set a new record.