The Prodigal Sun

For several days in November 1960, the earth was under attack. Enormous sheets of red and green light nickered in the night sky. Magnetic storms blacked out long-distance radio communications. Compass needles danced crazily and Teletypes printed page after page of utter nonsense. These phenomena were not caused by an alien invader but by the familiar and normally benign sun. In an outburst equal to the energy of a billion hydrogen bombs, it was bombarding the earth with exceptionally intense electromagnetic radiation and a dense hail of high-velocity particles.

The barrage of rays and particles was largely deflected by the Van Allen belts or absorbed by earth's protective blanket of atmosphere, and life on the planet was not endangered. But the magnitude of that solar storm still haunts space scientists. What if an equally severe onslaught were to occur this week, catching the Apollo 10 astronauts within their thin-walled lunar module--or in July, when the Apollo 11 astronauts are on the surface of the moon? If that happened, high-velocity particles would riddle the men, causing serious illness or possibly even death. The odds against such an occurrence are not prohibitive; just as in 1960, the sun is again near the peak of its eleven year cycle of activity, when violent outbursts frequently occur.

State of Turbulence. Astronomers are slowly solving some of the mysteries of the sun, but they have only a vague understanding of the processes that cause its dangerous outbursts. Although the sun is an ordinary, average-sized star, its dimensions and characteristics are staggering by earthly standards. It has a diameter of 864,000 miles (v. earth's 8,000 miles) and consists of 2.2 octillion tons of gaseous matter, most of it hydrogen and helium. In the 27 million-degree F. temperatures in the solar core, 564 million tons of hydrogen are converted by nuclear fusion into 560 million tons of helium every second. Thus, in a single second, 4,000,000 tons of solar matter are converted into energy --more energy than man has used since the beginning of civilization--and hurled into space in the form of heat, light and other radiation.

The surface of the sun, or photosphere, has an average temperature of 10,000 degrees F. Its most prominent features are sunspots--dark areas as large as 80,000 miles across. These spots usually occur in pairs and move from left to right, one spot leading the other, across the visible solar face as the sun rotates. They are probably caused by powerful magnetic fields generated by the flow of tremendous electrical currents (as high as 10 million million amperes) within the sun. Like the tips of a horseshoe magnet, the paired spots have opposite polarity--one positive, the other negative--and are joined together by powerful magnetic lines of force that loop above the solar surface. The lines confine the gases in the spots, so that they cannot circulate and bring heat up from the solar interior. As a result, gases within the spots are cooler--and thus appear darker--than gases in the surrounding areas.

Strange Behavior. At the beginning of a solar cycle, which averages eleven years, a few sunspots materialize about 35 degrees away from the solar equator in both the northern and southern hemispheres. Some last for a few days or weeks, others for months. As the cycle progresses, the spots occur with greater frequency and appear ever closer to the equator. About five years after the cycle begins, the sunspots increase to a maximum number, and appear around 15 degrees from the equator. During the next six years, the number of sunspots gradually decreases. Before the last of the old spots disappear, about five degrees from the equator, the first of the new spots appear once more near the 35 degree latitudes.

Another puzzling change heralds the new cycle: the polarity of the sunspot pairs reverses. Thus, if the leading spots of pairs are negative in the northern hemisphere during one eleven-year cycle, they are positive during the next. Even more remarkable, the overall solar magnetic field reverses near the peak of each cycle, the north and south magnetic poles trading places. This strange behavior may result from distortions in the magnetic fields caused by the sun's uneven rate of rotation; for still-unknown reasons, the equatorial regions rotate around the solar axis every 25 days, regions at higher latitudes every 33 days. This strange phenomenon is possible because the sun is a gaseous rather than a solid body.

It has been evident to astronomers for some time that solar disturbances occur in rather close harmony with the appearance of the sunspots. Thus there were fierce solar storms during and shortly after the record numerical peak in sunspots during 1957-58 and a long lull during the sunspot minimum in 1963-64. There is an even closer connection. Most of the violent solar eruptions occur near clusters of sunspots on the solar surface and seem to derive their energy from the magnetic fields that cause the spots. Suddenly flaring into extreme brilliance, a region hundreds of millions of square miles in area can erupt, shooting a stream of electromagnetic radiation and particles into space. Within 15 minutes after the appearance of some flares, bursts of electromagnetic radiation and some high-energy particles begin to buffet the earth and moon. These are the vanguard of the main and most dangerous body of particles--mostly protons--that arrive about ten hours later.

Constant Vigil. This time lag has enabled NASA to set up a reasonably reliable Solar Particle Alert Network (SPAN) to protect astronauts from the vagaries of the sun. SPAN consists of six observatories that monitor the sun 24 hours a day. During this week's Apollo flight, they will feed information into a space environment console in Houston's Manned Spacecraft Center, where physicists and medical men will keep a constant vigil. In addition, Pioneer, Vela and other patrolling satellites will report any changes in solar radiation. Should SPAN report a suspicious-looking flare during the Apollo mission at the same time the satellites signal a corresponding increase in high-energy proton radiation, the astronauts in the vulnerable lunar module would be ordered back to the command module forthwith. They should need no more than four hours--well before the deadly mainstream of protons arrives--to dock with the orbiting command module (whose walls provide protection equal to one-fifth of an inch of lead, more than enough to withstand any anticipated solar outburst). The art of solar forecasting is still so primitive, however, that many flare alerts could turn out to be false alarms.

Although astronomers admit that they are still novices at short-range solar prediction, they can issue one long-range forecast with some certainty. About 5 billion years from now, they calculate, the sun will have used up the hydrogen fuel in its core. It will then begin burning hydrogen in its outer layers and gradually expand--perhaps to 100 times its present size--turning into a giant red globe that will fill most of the sky when seen from earth. Unfortunately, man will not be around to see this spectacular view. The expanding sun will boil away the oceans, melt rock and heat the earth's surface to 4,000 degrees F. It will leave man's dwelling place a lifeless inferno.

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