3.3 Earth mass planet detected by microlensing

The Centauri Dreams blog wrote:But note the play in the numbers from this microlensing detection, which suggests the mass could actually be as low as 1.7 Earth masses or as high as 8.2.

Steinn wrote:It is very hard to draw a robust conclusion from a single data point, the formal uncertainties are infinite; but, this is a small corner of the observing parameters space, low mass stars have low cross-sections for microlensing, we only see them because there are so many of them.

We present the analysis of two epochs of JHKs band data obtained with ESO's AO system NACO on the planetary microlensing event MOA-2007-BLG-192. By separating the microlens event from unrelated ambient stars in the crowded field, thanks to the high spatial resolution of NACO we improve the constraints on the mass and distance of the MOA-2007-BLG-192Lb system. To calibrate our AO photometry with respect to the standard 2MASS system we follow a two-step approach. We first align IRSF JHKs photometry with the 2MASS catalog and then finally gauge the NACO photometry with the calibrated IRSF data. We detect light from the host star of MOA-2007-BLG-192Lb, which significantly reduces the uncertainties in its characteristics from previous analyses. We find that MOA-2007-BLG-192L is most likely a very low mass late type M-dwarf (0.084 ^{+0.015}_{-0.012} Sol mass) at a distance of 660^{+100}_{-70} pc orbited by a $3.2^{+5.2}_{-1.8} Earth mass super-Earth at 0.66^{+0.11}_{-0.06} AU.