Artwork of the extrasolar planet Drugar, also called PSR B1257+12A. This is a small rocky planet in orbit around a pulsar - a type of extremely dense, collapsed star - which is 2300 light-years away in Virgo. Drugar, which is only about twice the mass of our own Moon, is the least massive exoplanet whose mass has been accurately determined. Indeed it is not even as massive as the Solar System's smallest planet, Mercury.