Neutrinos are beyond doubt the weirdest particle we know. Present in abundance, 63,000,000,000 of them pass through your fingernail every second, but they are almost impossible to detect. Their existence was hypothesised in 1930 but they were only discovered in 1956. And since 1998, we know that neutrinos can spontaneously change identity, a discovery that was awarded the 2015 Nobel Prize. 

Done now? 
No! We do not know neutrino masses and neither do we know whether or not the neutrino is its own anti-particle. We enjoy studying the huge neutrino flux that accompanies a supernova explosion and we wonder how to observe the primordial neutrinos that began freely streaming through our universe approximately one second after the Big Bang!