An astrophysicist in the US has proposed using one of Jupiter's moons to detect high-energy particles such as neutrinos. Peter Gorham of the University of Hawaii says that detectors on this scale will be needed to identify particles with energies as high as 1021 electron volts (arXiv.org/abs/astro-ph/0411510).
Low-energy neutrinos from the Sun have already been observed in a number of Earth-based experiments. However, high-energy neutrinos from cosmic sources are much rarer, so enormous detectors are needed to see them.
Neutrinos only interact very weakly with matter, which is both an advantage and a disadvantage in astrophysics. It means that neutrinos can travel enormous distances across the universe and through matter without losing the information they carry about their sources. However, the extreme weakness of their interactions also makes them very difficult to detect.
When neutrinos travel through large blocks of ice, they produce flashes of Cerenkov radiation when they collide with protons and neutrons in the ice. These flashes can then be detected and analysed to reveal information about the neutrino and its source. One such detector, AMANDA, is already operating in the Antarctic and can capture neutrinos with energies of up to 1015 eV. Future detectors – including IceCube and ANITA – may be able to capture neutrinos up to 1018 eV.
Gorham suggests that the large volumes of ice that exist in various parts of the solar system would be capable of detecting neutrinos at even higher energies, possibly up to 1021 eV. The neutrino-induced events in the ice would be monitored by an orbiting spacecraft.
“The best candidate so far is Europa, one of Jupiter’s moons, because it may have a thick covering of ice that is much larger than that found on Earth,” Gorham told PhysicsWeb. “More importantly, Europa’s ice is at about 90 Kelvin, so its thermal noise is much lower than that of Antarctic ice, which is at about 240 Kelvin.”