via National Geographic, the smallest exoplanet yet found orbitting a star has been discovered by a team using the relatively novel gravitational lensing technique. Gravitational lensing utilzies the bending of light around large gravitational objects to focus on distant objects. The planet, called MOA-2007-BLG-192Lb, is only three earth masses and orbits what is thought to be a brown dwarf.
"The planet is 3,000 light-years from Earth and has a close-in orbit similar to Venus's. But because the newfound body's parent is so much cooler than our sun, MOA-2007-BLG-192Lb is most likely to be even colder than Pluto. Even so—and despite almost no solar heating—there's a slim chance that the planet could maintain a habitable temperature if the atmosphere is as thick with molecular hydrogen as researchers think it could be, according to study leader David Bennett."
The fact we've discovered such a small mass planet orbiting a rather small failed star leads researchers to believe there are many more such objects in the cosmos. The new planet is only the seventh such exoplanet discovered by the gravitational lensing technique.