Sun And Jupiter Trap Earth In Ongoing Particle Bombardment

December 08, 1997

New findings by a University of Colorado at Boulder research team indicate Earth is alternately peppered by extremely high-energy electrons from the two giants of our solar system, the sun and Jupiter.

Daniel Baker, director of CU-Boulder's Laboratory for Atmospheric and Space Physics, said the team has documented the complete sequence of events that produce high-energy electrons near Earth using data collected from an armada of spacecraft. "This work shows that Earth is awash in high-speed, charged-particle flow from the sun that quickly causes electron acceleration to energies thousands of times the typical energies normally observed near Earth."

The extremely high-energy electrons also are known as "killer electrons" because of their adverse effects on spacecraft and satellites, said Baker. Hostile space weather events caused by such energetic electrons have been blamed for the failure of a number of satellites in recent years, he said.

The CU-Boulder team, along with scientists from NASA's Goddard Space Flight Center, have used data from NASA's SAMPEX and ISTP satellites to piece together the sources of these high-energy electrons surrounding Earth.

SAMPEX data indicate highly energetic electrons from Jupiter, the solar system's largest planet, bombard the magnetic poles of Earth every 13 months during relatively quiet solar periods, Baker said.

"All the evidence points to these electrons having been accelerated in Jupiter's giant magnetosphere and then traveling near the speed of light to Earth's vicinity," he said. The electrons from Jupiter arriving at Earth appear to have even more energy than the high-energy electrons caused by solar disturbances.

"These results show that in many ways, Earth is like a cork bobbing up and down on the currents flowing back and forth between the solar system's giants," Baker said. "The sun dominates the energy flow to Earth, but when this flow subsides it is Jupiter that exerts the clear influence. The comparatively tiny Earth is caught in the ebb and flow between these two competing titans of the solar system."

An invited paper on the subject was presented by Baker at the American Geophysical Union's annual fall meeting held in San Francisco Dec. 8 to Dec. 12. Other authors include Shri Kanekal of NASA-Goddard, Tuija Pulkkinen of LASP and NASA's Barbara Thompson.

Disturbances on the sun observed by the NASA/European Space Agency's SOHO satellite and the Japanese Yohkoh spacecraft appear as bright, growing spots on the sun's surface and as bursts of material flying from the solar surface into interplanetary space. Two NASA satellites, WIND and POLAR, have detected the near-Earth effects of solar storms, said Baker, who is an investigator on the POLAR mission.

The solar material bombarding Earth at high speeds causes bright auroral displays and large magnetic disturbances, said Baker, also a professor in CU-Boulder's astrophysical and planetary sciences department. The SAMPEX data has been used by Baker, Kanekal and Pulkkinen to produce daily maps of the Earth's Van Allen radiation belts, zones in Earth's magnetosphere where the highly charged particles are confined by the planet's magnetic field.

The researchers have produced a unique video which shows the dynamic variation of the sun and the dramatic response of killer electrons in the Van Allen radiation belts.

University of Colorado at Boulder

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