Ever since Wolfgang Pauli first hypothesized their existence 60 years ago, the minute elementary particles known as neutrinos have been thought of as massless. But on June 18, representatives of the Sudbury Neutrino Observatory in Canada announced that neutrinos made by nuclear reactions in the sun's core change from one type to another during their 93-million-mile journey to Earth. And only particles with mass can change form.
The neutrino's mass is only a billionth of a proton's. But its mere existence has profound implications.
* The reigning theory in particle physics does not allow particles that change their identity to have mass. So that theory will have to be patched up to accommodate the new observations.
* Because they originate deep inside the sun, neutrinos may provide an unprecedented view of what goes on there.
* They may not weigh much individually, but adding up all the neutrinos in existence accounts for about 18% of the mysterious "dark matter" in the universe that cannot be observed by telescopes or other ordinary means.
The Sudbury researchers presented their results at a meeting of the Canadian Association of Physicists and in a paper submitted to the journal Physical Review Letters.
Compiled by Times medical writer Thomas H. Maugh II