No. 112: Jul-Aug 1997
It is rather amazing that we can detect neutrinos at all. Carrying no electric charge and possibly massless, most zip right through the entire earth as if it were not there. A very, very few, however, are captured in huge, fluidfilled tanks built by physicists. These trapped ghostly particles tell tales we do not yet fathom.
We have mentioned the solar-neutrino problem before (SF#46/84, for example). It is one of science's more perplexing and enduring mysteries. Even the most modern, sophisticated neutrino detectors count only about one-third the number of neutrinos that the sun "should" be sending in our direction -- according to our best theories on the nuclear reactions simmering away in the solar core. To this classical neutrino problem has been added the discovery that the solar neutrino flux varies in ways difficult to explain. P. Sturrock and G. Walther, at Stanford University, scrutinized 20 years of data from a detector deep in the Homestead Mine in South Dakota and find that the neutrino flux seems to peak every 21.3 days, varying as much as 30% to 100%. It may be that the sun's fusion "engine," long thought to run steadily and smoothly, sputters in a cyclic fashion? If an automobile engine did this, we would take it to the garage!
(Holden, Constance; "More Neutrino Mystery," Science, 273:1663, 1996.)
The problem deepens: The first 102 days of neutrino data from Japan's new Super-Kamiokande detector suggest that the solar neutrino flux is greater at night than during the day, and that it also varies during the year.
(Anonymous; "First Data from New Neutrino Detector," Science News, 151:279, 1997.)
Once we learn how to measure neutrinos really well, we can start looking for intelligent signals impressed upon them by advanced extraterrestrial civilizations. W. Simmons and colleagues at the University of Hawaii at Manoa point out that neutrinos are much better than electromagnetic waves for galaxy-wide communication. They are not blocked by dust nor are they smeared out by ionized gas. Any civilization clever enough to colonize the entire galaxy would want to send out neutrino signals if only to keep clocks in far-flung star systems synchronized.
Simmons et al calculate that a neutrino detector containing a cubic kilometer of seawater could probably detect neutrino signals from artificial sources located within 3,000 light years of earth. A detector that might be able to do this is being installed in the ocean off the Hawaiian Islands. Naturally, it has an acronym: DUMAND = Deep Underwater Muon and Neutrino Detector.
(Chown, Marcus; "Do ETs Phone Home with Neutrinos?" New Scientist, p. 19, December 3, 1994.)
Reference. The problem of the missing solar neutrinos is discussed at length in Section ASF3 in our Catalog The Sun and Solar System Debris. For ordering information, visit here.