A Mixed-Up Sun

Most of the underground activity in Lead, S. Dak., site of the famous Homestake mine, consists of digging for gold. But in recent years, a group of scientists have also been working a mile beneath the surface at Lead to capture elusive emanations from the sun called neutrinos. Traveling at the speed of light and thought to be capable of passing through trillions of miles of solid lead, the ghostlike neutrinos have no mass or electrical charge. They are produced during violent atomic collisions at the core of the sun, and thus are believed to be a vital index to the activity and energy output of the glowing mass that supports life on earth. What astronomers and physicists have learned so far from the neutrino detector in South Dakota suggests that the sun's output is much less constant than has been believed, and that variations in its output may explain broad climatic changes both on earth and on Mars, including such phenomena as ice ages.

The detector was designed by Chemist Raymond Davis Jr. of Brookhaven National Laboratory. Shielded from all other radiation by the rock above, the detector consists of a 100,000-gal. vat of a cleaning fluid called tetrachloroethylene. A small number of incoming neutrinos collide with chlorine atoms in the fluid. The collisions convert the chlorine to radioactive atoms of the element argon, which can then be counted. Davis calculated a year ago that on the basis of what scientists know and theorize about the sun, less than one-fifth as many neutrinos are radiating from it as would be expected.

Since then, other scientists have speculated that this reduced radiation may mean that the nuclear fires at the sun's core are severely banked. Harvard Astrophysicist A.G.W. Cameron and others suspect that the banking effect is caused by a sudden, unexplained mixing of gases in the sun's core, which leads to a brief expansion of the core and a reduction of nuclear reactions. In all, estimates Cameron, it may take some 6,000,000 years for this cycle to run its course--during which the sun's heat and light would be reduced.

Warm Earth. Geological evidence indicates that over most of its history, the earth was a far warmer place than it has been for the past 2,000,000 years. Humidity and temperatures were higher, there was more cloud cover, and barren zones with little vegetation were more common. If the banked-fires theory is correct, the relatively cooler recent period, including short-term "ice ages," might indicate that the sun's core is now being mixed, and may return to its normal output in about 4,000,000 years. Cameron estimates that such mixing events may be separated by hundreds of millions of years.

If solar mixing does occur, it would also affect other planets of the solar system. In Nature, Carl Sagan of Cornell and Andrew Young of Caltech have suggested that fluctuating solar output could explain such Martian mysteries as the river-bed-like channels recently photographed by the Mariner 9 spacecraft. Martian water, now locked firmly in the frozen poles, presumably would have flowed freely during warmer times. Sagan and Young go further. Suspecting that our sun is not unique in its quirky behavior, they checked other nearby stars. In the cluster Praesepe, they found a number of stars that varied widely from expected energy output. Such variations, they say, broaden the long-term temperature ranges to be expected near these stars, increasing the chances that earthlike climates--and perhaps life--exist.

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