At age 85, Bethe wrote an important article about the solar neutrino problem, in which he helped establish the conversion mechanism for electron neutrinos into muon neutrinos proposed by Stanislav Mikheyev, Alexei Smirnov, and Lincoln Wolfenstein to explain a vexing discrepancy between theory and experiment. Bethe argued that physics beyond the Standard Model was required to understand the solar neutrino problem, because it presumed that neutrinos have no mass, and therefore, cannot metamorphosize into each other; whereas the MSW effect required this to occur. Bethe hoped that corroborating evidence would be found by the Sudbury Neutrino Observatory (SNO) in Ontario by his 90th birthday, but he did not get the call from SNO until June 2001, when he was nearly 95.