NASA's Galileo spacecraft serendipitously discovered seven to nine space rocks near Jupiter's inner moon Amalthea when Galileo flew past that moon five months ago.
Galileo detected the objects as bright flashes seen by its star scanner, an onboard telescope used to determine the spacecraft's orientation by sighting stars. Information from the star scanner was recorded onto Galileo's tape recorder during the flyby and transmitted to Earth in subsequent months. Experts at NASA's Jet Propulsion Laboratory, Pasadena, Calif., are analyzing the data to estimate the sizes of the objects, which may be anywhere from gravel to stadium-size rocks.
JPL engineers Paul Fieseler and Shadan Ardalan reported the findings to the International Astronomical Union. The star tracker saw nine flashes during the flyby, but two may be duplicate sightings.
"It is likely that these bodies have either been gravitationally captured into an orbit near Amalthea or have been split off of the moon as a result of past collisions," Fieseler said.
The Amalthea encounter was Galileo's last flyby of a jovian moon. After more than seven years in orbit around Jupiter, the spacecraft has nearly depleted its supply of propellant needed for pointing its antenna toward Earth and controlling its flight path. While still controllable, it has been put on a course for impact into Jupiter next September. The maneuver prevents the risk of Galileo drifting to an unwanted impact with the moon Europa, where it has discovered evidence of a subsurface ocean that is of interest as a possible habitat for extraterrestrial life.
Additional information about Galileo and the discoveries is available at http://galileo.jpl.nasa.gov JPL, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C.