NASA's Galileo spacecraft detected changes in the interplanetary magnetic field as it passed the asteroid Ida on August 28, scientists reported today.
Dr. Margaret Kivelson, principal investigator of the Galileo magnetometer and a physicist at UCLA, reported that the instrument measured several field rotations, as it had two years ago while flying by the asteroid Gaspra.
Magnetic field rotations, in which the direction of the magnetic field swings or shifts, are commonly observed in interplanetary space.
"The team believes these observed rotations were produced by the interaction of the solar wind with Ida," Kivelson said. However, several sorts of interactions could cause the field to rotate, and thus the observations do not necessarily show that the asteroid has a magnetic field.
Kivelson said that in the case of the smaller asteroid Gaspra, the measurements provided indirect evidence of an asteroid magnetic field for the first time.
Before Galileo's Gaspra encounter in October 1991, small asteroids were not generally expected to possess their own magnetic fields, though some meteorites -- believed to be fragments of asteroids -- have measurable fields.
Analysis of data from Galileo's Ida flyby has not progressed far enough for Kivelson's team to speculate on whether this asteroid is also magnetized, she said.
Kivelson presented the results at the annual meeting of the Division of Planetary Sciences of the American Astronomical Society in Boulder, Col.
Galileo's magnetometer and other instruments have been collecting data on the solar wind and the space environment since shortly after the spacecraft's launch in October 1989.
Ida represented the fifth encounter for Galileo, said Project Scientist Dr. Torrence Johnson. The spacecraft flew once by Venus and twice by the Earth and Moon for gravity assists and scientific observation, in addition to encountering the asteroids Gaspra and Ida.
Galileo is now on its way to Jupiter, where in 1995 it will direct its instrumented probe into the atmosphere and then go into orbit to conduct a two-year survey of Jupiter, its satellites and its magnetosphere.
Project Galileo was developed and is managed for NASA's Office of Space Science by the Jet Propulsion Laboratory.
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