Jupiter's Hot Halo

Whatever future space explorers may find, a couple of California scientists have already decided that the big planet Jupiter and the little planet Earth have at least one thing in common: each is girdled by a strong magnetic field, a rare phenomenon anywhere in the solar system. Using the twin, 90-ft. radio telescopes at California Institute of Technology's Owens Valley Observatory. Research Fellow David Morris and Graduate Student G. L. Berge have estimated the strength of Jupiter's mighty magnetism.

Observed by radio waves instead of light waves. Jupiter does not look round. It appears to be an oval object more than three times as long as it is broad. This is the same shape as the doughnut-like Van Allen belt of charged particles that have been trapped by the earth's magnetic field, and Morris and Berge concluded that Jupiter also has a magnetic halo that captures charged particles thrown from the sun. As they whirl around the planet at nearly the speed of light, the particles in Jupiter's halo give off radiation in the form of radio waves.

Moving Core. After keeping a radio watch on Jupiter for months. Morris and Berge calculated that its Van Allen belt is a doughnut 300,000 miles in diameter and 80,000 miles thick. It is several times as radioactive as the earth's and is held in place over the planet's magnetic equator by a magnetic field that must be several times stronger than the earth's. Since the earth's magnetic field is believed to be formed by the motion of its metallic core, and since Jupiter proved to be surrounded by magnetism, it seems likely that it. too. has some sort of moving core.

Every ten hours, Morris and Berge recorded bursts of radio energy that seemed to come from a small area on Jupiter's surface. Other radio astronomers had detected these bursts and developed theories about them. Some thought a giant volcano might be disturbing Jupiter's atmosphere and generating radio waves. Others decided the waves came from the lightning strokes of enormous thunderstorms. But none of these theories is satisfactory to Morris and Berge. Their explanation: the Jovian radio outbursts are caused by Jovian auroras. If Jupiter has a magnetic field, they argue, it must have magnetic poles, just as the earth does. When speeding particles in the Jovian Van Allen belt come near a magnetic pole, some of them plunge too low and hit the outer fringe of Jupiter's atmosphere. One result of the collisions might well be radio waves strong enough to be detected far off on the earth. Bright Target. Another result is probably an extremely bright aurora. No human has seen this spectacle because Jupiter always shows the earth an almost entirely sunlit face. If a spaceship from earth ever cruises behind the dark side of Jupiter (never less than 460 million miles away), the crew may see a ring drawn around its darkened magnetic pole in brilliant auroral light. That bright target will illuminate the safest landing spot, the hole in the doughnut, where the explorers will be able to set down (if Jupiter has any solid surface at all) without passing through the Van Allen belt's hot and dangerous webs of energy.

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