Solar-cycle peak threatens Max to the max.

Solar-cycle peak threatens Max to the max

In Tucson, Ariz., this week, scientists installed an instrument in a 60-foot-high tower at Mt. Wilson Observatory to provide some of the most precise images yet to aid in mapping the sun's interior.

At the same time, researchers who had gathered at the NASA Goddard Space Flight Center in Greenbelt, Md., to discuss their work with the Solar Maximum Mission satellite heard NASA's current prediction of Solar Max's fate: Heating and expansion of Earth's upper atmosphere as the sun approaches the maximum activity in its 11-year cycle will make the device impossible to control by late September, so that a few months later it will burn up in the atmosphere.

Even before that, says Joan Schmelz of Applied Research Corp. in Landover, Md., "we expect to hit a period of intense solar activity, possibly causing [Solar Max] to fall kilometers at a time, like hitting a wall. The effects of the drag are already strong enough that we feel the effects on operations, and it often takes several minutes to reacquire the spacecraft [with commands sent from the ground]. The effects are only going to get worse."

Several researchers have hoped NASA would use the space shuttle to rescue Max, either by raising its orbit or by bringing it back to Earth for modifications and later relaunching. The agency, however, has declined, citing the lack of money and an available shuttle mission. "We have no manifest slot," Schmelz says, "and no 5 to 6 million dollars."

On the positive side, however, a group of Solar Max scientists has recently overlaid the images from one of the craft's instruments with those taken by the Soviet Phobos 1 satellite, providing new insights into the sun's energetic surface activities. Phobos 1 went dead in September due to an incorrect computer command from the ground, but its coronagraph made several images of the solar disk in July and August. Now Schmelz and her colleagues have succeeded in aligning the pictures from Phobos 1 with those from Solar Max's X-ray polychromator, which provides such details as studies of the dynamics of solar flares.

In fact, says Schmelz, "the Phobos 1 instrument saw an active region just coming over the east limb of the sun in the last couple of days in August. On Aug. 31, when the X-ray polychromator was turned on for the beginning of International Solar Month [SN: 8/27/88, p.134], it saw the same active region, which flared several times and grew to a huge area." The team plans to make a "movie" of its data, compressing about a week's observations into minutes.

At Mt. Wilson, David M. Rust of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and his colleagues are readying a device called the Stable Solar Analyzer, a small telescope equipped with a "cell" of cesium-133 that allows it to make images of precisely measured emissions coming from the sun's extreme depths. The surface of the sun rotates fastest at its equator and slowest at the poles, says Rust, but it is unclear whether the interior rotates at a constant rate, like a solid planet, or with different speeds at different depths.

The study of the inner sun, known, as helioseismology (SN: 7/2/88, p.8), has measured its rotation rate about 80 percent of the way to the center, Rust says, and the Analyzer might add another 10 percent. "The number of published papers," he says, "has been doubling every three years."