Galileo’s Last Rendezvous

Amalthea and friends
Galileo's best images of the inner Jovian moons (from left) Thebe, Amalthea, Adrastea, and Metis. All four bodies play a role in maintaining Jupiter's tenuous ring system.
Courtesy Cornell University and NASA/JPL.
In the seven years since reaching Jupiter, NASA's Galileo spacecraft looped around the planet 34 times and made myriad discoveries about the king of planets and its major satellites. However, Galileo's mission is nearing its end: the camera and other imagers aboard have been turned off, and next September the spacecraft will plunge directly into the Jovian atmosphere. But Galileo should provide one more burst of science data before making a final orbit around Jupiter. Next week it will sweep past Amalthea (Jupiter's innermost large satellite), race through the planet's ring, and experience its most intense magnetic and radiation environment to date.

Galileo will glide 160 kilometers above Amalthea's surface on November 5th at 6:19 Universal Time. Despite the blind approach, mission engineers hope to measure how the moon's gravity alters the trajectory of the spacecraft, then use that information to derive Amalthea's mass and overall density. These measurements will help determine whether the evolution of Jupiter's moons paralleled that of the planets around the Sun. Theorists believe close-in satellites such as Amalthea (which, at a distance of 181,000 km, is Jupiter's third-nearest moon) are dense, just like the inner planets of our solar system.

After passing Amalthea, Galileo will fly through Jupiter's thin "gossamer" ring to determine the masses and velocities of dust particles. Later, the spacecraft will measure — and try to survive — the intense charged-particle environment in the inner Jovian magnetosphere. "The spacecraft will be flying closer to Jupiter that it's ever flown before," said Eilene Theilig, project manager at the Jet Propulsion Laboratory, dipping to within roughly 70,000 km of the planet's cloud tops. These radiation data will prove crucial in designing future missions to Io and Europa, which are constantly bombarded by magnetospheric particles. Even though Galileo has endured four times the amount of radiation it was originally designed to withstand, Theilig notes, the spacraft remains in "remarkably good shape."

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