Koshiba devised the construction of giant underground chambers to detect neutrinos, elusive particles that stream from the sun.
Neutrinos offer a unique view of the sun’s inner workings because they are produced in its heart by the same process that causes the sun to shine.
He shared the prize with two other scientists — the late Raymond Davis Jr. of the University of Pennsylvania, who also worked on neutrino detectors, and the late Italian-born scientist Riccardo Giacconi, who was cited for X-ray telescopes that provide sharper images of the universe.
Koshiba worked at the Kamiokande neutrino detector, a huge facility built in the mountains in central Japan. He confirmed and extended Davis’ work, and also discovered neutrinos coming from distant supernova explosions, some of the brightest objects in the universe.
Koshiba's contribution led to subsequent discoveries. His student, Takaaki Kajita, won the Nobel Prize in physics in 2015 for research at the Super-Kamiokande facility that found neutrinos have mass.
Koshiba was active in science education for young people, and established a basic science foundation using his Nobel Prize award to provide learning experiences for high school and college students.