OGLE-2005-BLG-390LB

Las Campanas, Chile (Jan 8, 2006)

This is the dome of the 1.3 meters diameter of the Warsaw telescope at Las Campanas observatory in Chile. The telescope is part of the “Optical Gravitational Lensing Experiment” (OGLE), looking for the signature of “gravitational microlensing” in the Galactic Bulge and the Magellanic Clouds. Gravitational lensing is a phenomenon predicted by Einstein’s General Relativity theory: massive objects have the properties to curve space, and thus deflects rays of light, similarly to how light is deflected by a curved piece of glass (the lenses in our cameras). Microlensing happens when a low mass object passes in front of a much farther star: the low mass object acts as a “gravitational lens” and amplifies the luminosity of the distant star which is “lensed”. Measuring the variation of the luminosity of the lensed star as the “lens” is moving in front of it makes it possible to infer the mass of the low mass object “lens”.

The objects responsible for gravitational microlensing are generally low mass dwarf stars, or brown dwarfs. The observations I performed during my last trip to Chile were about three such objects. If a micro-lens is orbited by planets, and those planets happens to pass in front of the background star themselves, an extra lensing events may happens, allowing us to detect the presence of the planet. This is exactly what happened recently while the OGLE telescopes (and the Warsaw telescope among them) were observing a star in the galactic bulge. An extra “kink” in the lightcurve revealed the presence of the smallest extrasolar planet ever detected. Named OGLE-2995-BLG-390LB, is the smalles planet discovered outside the solar system. With a mass of ~5 Earth masses orbiting its own star at a distance similar to the distance of the main asteroid belt in the Solar System, it is most probably a rocky planet covered by ice. This is very exciting because it is the most similar planet to Earth ever discovered around another star.