An anonymous reader sends this quote from a press release at CERN: "An international team at the ISOLDE radioactive-beam facility at CERN has shown that some atomic nuclei can assume asymmetric, 'pear' shapes (abstract). The observations contradict some existing nuclear theories and will require others to be amended. ... Most nuclei have the shape of a rugby ball. While state-of-the-art theories are able to predict this behaviour, the same theories have predicted that for some particular combinations of protons and neutrons, nuclei can also assume asymmetric shapes, like a pear. In this case there is more mass at one end of the nucleus than the other."