Galileo was launched from the space shuttle on October 18, 1989. After a
interplanetary cruise that involved multiple flybys of Venus and Earth to use
those planets’ gravity fields as a velocity boost and two flybys of asteroids
(Gaspra, October, 1991) and (Ida, August, 1993) it entered Jupiter orbit on
December 7th, 1995.
Galileo returned images of the fragments of Comet
Shoemaker-Levy as it plunged into the Jovian atmosphere. Upon approaching
Jupiter, Galileo released a probe that plunged into the Jovian atmosphere on December 7th, 1995 and
returned data for several hours. The probe discovered that Jupiter has thunder
storms, caused by the circulation of water in the upper atmosphere, many times
the size of those on Earth.
Galileo spent eight years in orbit around Jupiter and,
despite the failure of a high gain antenna, returned an enormous amount of
data. Among its discoveries were the existence of volcanoes on the moon Io, an ocean
beneath a layer of ice on Europa, a magnetic field around Ganymede, and another
possible, subsurface ocean on Callisto.
Galileo ended its mission on September 21st, 2003 and was ordered to crash
into Jupiter’s atmosphere to avoid possible contamination of Europa, considered
a prime candidate as an abode of extraterrestrial life.
Cassini
Cassini, a joint project of NASA, the European Space Agency,
and the Italian Space Agency, was launched on October 15th, 1997 and entered Saturn orbit
after a long cruise that included gravity boosts from Venus and Earth on July 1, 2004. Cassini will spend the
next several years studying Saturn, its rings, and its satellites. It has
already made passes of the moons Titan, Iapetus, and Enceladus.
On December 25th, 2004 Cassini release a probe
named Huygens which descended into Titan’s atmosphere twenty one days later and
touched down safely on its surface. For over two hours, Huygens returned data
from the surface of Titan, including haunting images of an alien landscape with
rivers and lakes of liquid methane, and hills made of water ice, shrouded in a
hydrocarbon rich atmosphere.