3.3 Earth mass planet detected by microlensing

The lowest mass exoplanet detected so far and orbiting a (possible) brown dwarf too

http://exoplanet.eu/planet.php?p1=MOA-2007-BLG-192-L&p2=b

Ahh... this is good. This is very very good. It sets the record as the lowest mass planet found around a normal-ish star. Probably inhospitable though. The paper does mention that it may be possible for the planet to have a sufficiently thick atmosphere in addition to an abundance of radioactive elements in the interior, to keep the temperature above the freezing point of water. I don't think that it's very likely that this planet is habitable, though.

Doing an approximate calculation, assuming a "host brown dwarf" temperature around <2000 K (an L-dwarf) and a radius of 0.9 Jupiter radii, I should get a very low luminosity (obviously, about 1.09x10^-4 Solar luminosities) and the water zone appears located within 0.011 AUs. Thus the planet is located really beyond system's snowline, within Pluto's orbital zones (i.e 56.4 AUs).

However yeah, with a mass which is three times the Earth, some kind of "cryo-tectonic" or "cryo-volcanism" may occur but these speculations require a proper subforum

It would seem there's quite a bit of ambiguity as to the true mass of the planet.

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.

Some people got excited thinking to have found the 1st Earth-like planet beyond Solar System. They do this silly math:

*Mass similar to Earth + orbital separation similar to Earth=Earth-like planet*

Even assuming a very hot and young brown dwarf, with a water zone around 0.03-0.05 AUs (very very forced), such a planet would be made entirely of ices alike Enceladus (in the warmest case).

A frozen super-Earth orbiting a star at the bottom of the Main Sequence
http://arxiv.org/abs/1009.5665

Quote :

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.