The planet Jupiter is surrounded by a blanket of charged particles that may be the hottest things in this solar system, scientists at Johns Hopkins University said yesterday.
Dr. S. M. Krimigis, principal investigator for one of the experiments aboard the Voyager I spacecraft, said the particles regisered 300 million to 400 million degress centigrade, or 15 to 20 times hotter than the interior of the sun. He called the finding "absolutely astounding."
Voyager recorded the blanket of particles, or plasma, when it wheeled past Jupiter in March on its way to the outer planets. But since the plasma, substantial by the standards of space, consists of less than one molecule per cubic foot, the spacecraft was undamaged by the intense heat, Krimigis said.
The particles consist of hydrogen, sulfur and oxygen molecules apparently torn loose from Io, one of Jupiter's 13 moons, by Jupiter's massive magnetic field. This composition is unique, Krimigis said, since denser plasmas around the sun and the other planets, including Earth, consist almost exclusively of hydrogen and helium molecules. "We know why the sulfur is there, but we didn't expect it," Krimigis said.
The plasma rotates with Jupiter, and is believed to reach its high temperatures from a sort of friction with the solar wind, the steady stream of charged particles flowing from the sun.
"As soon as Voyager crossed the boundary between Jupiter's magnetic field and the solar wind at some 3 million miles [from Jupiter's surface], we detected the plasma envelope," Krimigis said.
It was constant all the way to the 173,000-mile altitude that was Voyager's closest approach to the planet, he said. Calculations are continuing to see how far inward the plasma continues.
"We don't have any models at this point to explain fully why the particles are heated," Krimigis said. The massive gravity of Jupiter whirls the particles through space at speeds that increase the farther the particles are from the planet, like a rock at the end of a long string. But the solar wind is distorted as it blows past Jupiter, and the interaction between it and the plasma is only remotely understood, Krimigis said.
Along with co-workers Dr. George Gloeckler of the University of Maryland and Dr. T. P. Armstrong of the University of Kansas, Krimigis will be watching for further information on the mysterious hot plasma from Voyager II, which is due to approach Jupiter next month.