Discovery of OGLE 2005-BLG-390Lb, the first cool rocky/icy exoplanet

Discovery of OGLE 2005-BLG-390Lb, the first cool rocky/icy exoplanet

Microlensing observations of event OGLE 2005-BLG-390 have provided evidence that the lens star, presumably an M-dwarf with 0.2 Solar masses, is orbited by a planet with only about 5 Earth masses (uncertain within a factor of two) at 3 AU with a period of 10 years. This discovery was reported as the joint effort of three independent microlensing campaigns (PLANET/RoboNet, OGLE, and MOA) in a Letter to Nature.

The event OGLE 2005-BLG-390 was reported by the OGLE Early-Warning System (EWS) on 11-Jul 2005, and was then monitored with the telescopes constituting the PLANET/RoboNet network. The light curve initially followed the characteristic brightening expected for a single isolated lens star and a point-like source star, which in this case is a G2-4 giant, and reached a peak magnification of about 3 on 31-Jul. However, on 10-Aug, an anomalous rise by 0.15 mag was observed by PLANET/RoboNet with the Danish 1.54m at ESO LaSilla (Chile), while an OGLE point from this night showed the same trend. By succeeding in monitoring the second half of this anomaly, lasting about half a day, with the Perth 0.6m (West Australia), and previously obtaining a dense coverage of the peak region of the event, we were able to conclude that the lens star is orbited by a low-mass planet, which is designated OGLE 2005-BLG-390Lb. The MOA collaboration was able to identify the source star on its frames and confirmed the observed deviation.

Press releases The listed institutions have indicated that a press release will be issued at the time of discovery announcement.

Scientific Documentation

Figures and Animations


Full list of institutions and collaborators

The PLANET collaboration 2005 :

The RoboNet collaboration:

The OGLE collaboration:

The MOA collaboration: