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Five things to know about neutrinos:

What are they?

Neutrinos are one of the fundamental particles that make up the universe, but they're also among the least understood and for decades remained hypothetical. Neutrinos are minuscule and created in nuclear reactions, such as in the sun and the stars. They are similar to the electron, but they don't carry an electric charge. Because they're electrically neutral, they are unfazed by electromagnetic forces that act upon electrons.

What does affect them?

Neutrinos are affected only by a "weak" sub-atomic force of much shorter range than electromagnetism, and are therefore able to pass through great distances in matter without being affected by it. If neutrinos have mass, they also interact gravitationally with other massive particles, but gravity is by far the weakest of the four known forces.

How many types of neutrinos are there?

There are three types and they oscillate from one type to another, dispelling the long-held notion that neutrinos are massless. Neutrinos are so small that about a billion neutrinos pass through a human thumb every second.

What did Canada discover about neutrinos?

In 2001, while working at the Sudbury Neutrino Observatory, Canadian Nobel Prize winner Arthur McDonald found that neutrinos coming from the sun didn't disappear — some just changed identities. He and Takaaki Kajita, a Japanese colleague with whom he shares the Nobel Prize, gave rise to the conclusion that neutrinos have mass.

Fun fact: Neutrino means "little neutral one" in Italian.

Source: The University of California, Arthur McDonald, Tony Noble