On September 21, 2003, nearly 14 years after the Galileo spacecraft set out on its mission, it plunged into Jupiter’s atmosphere in order to deliberately destroy itself. The first mission to enter orbit around Jupiter after four previous spacecraft had flown by the system, Galileo, like the famous astronomer it is named after, had by this time studied Jupiter extensively and in greater detail than was ever possible before.
With an aim to study Jupiter and its mysterious moons, Galileo was first conceived in 1977, though the idea was in the making for years. This was chiefly because the data provided by the four spacecraft that had passed by the giant planet – Pioneer 10 and 11, and Voyager 1 and 2 – had suggested that a long-term mission to Jupiter was indeed possible. It took another 12 years to find financial backing and complete construction, before the launch eventually took place on October 18, 1989.
VEEGA flight path
Galileo was designed to save on fuel, which meant that it didn’t carry enough fuel to fly directly to Jupiter. Instead, the spacecraft was to borrow energy from Venus and Earth using gravitational assists during its long trip to Jupiter.
The mission planners dubbed the flight path they had designed for Galileo as VEEGA, which stands for Venus-Earth-Earth Gravity Assist. Using the Venus flyby of 1990 and the two Earth flybys of 1990 and 1992 as three slingshots, Galileo gathered enough momentum to take it to Jupiter.
Flies by asteroids
Galileo encountered the asteroid Gaspra in 1991 during its first trip through the asteroid belt, thereby becoming the first spacecraft to flyby an asteroid. On its second trip through the asteroid belt in 1993, Galileo discovered the first moon around an asteroid as it spotted Dactyl orbiting asteroid Ida.
In 1994, Galileo provided the only direct observations of a comet colliding with a planet. Its flight path meant that Galileo was stationed ideally to observe fragments of comet Shoemaker-Levy 9 crash into Jupiter.
Enters into orbit
After the Galileo spacecraft and probe had travelled together for six years, the probe was released in July 1995 to begin a solo flight into Jupiter. The probe was able to measure atmospheric elements and discover that Jupiter has thunderstorms many times larger than Earth’s. But it was eventually crushed by overwhelming pressure after it descended deep into Jupiter’s atmosphere on December 7, 1995 and had managed to send data for close to an hour.
On that same day, the spacecraft entered into orbit around the giant planet. With only one chance to get it right, lest it sails past the planet, the mission controllers carried out the manoeuvre precisely and Galileo’s primary mission had finally begun.
Studies Jupiter’s moons
The two-year primary mission of studying the Jovian system was followed by three more missions from 1997 to 2003 as the spacecraft remained in good health. During these years, Galileo further studied Jupiter’s moons.
It found evidence for the possible existence of a salty ocean beneath the icy, cracked, frozen surface of Europa. It observed the volcanic processes in Io, showing that some of Io’s volcanoes are hotter than Earth’s. And in Ganymede, Galileo detected the first magnetic field around a moon.
It was one of these – a possible ocean beneath the icy crust of the moon Europa – that led to Galileo’s end. In order to avoid a future accident wherein Galileo crashes into Europa and disrupts possible life, it forcibly plunged into Jupiter’s crushing atmosphere, bringing an end to its existence.
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Important dates
Oct. 18, 1989: Launched from Kennedy Space Center
Feb. 10, 1990: Flies by Venus at an altitude of about 16,000 kilometres
Dec. 8, 1990: First Earth flyby at an altitude of 960 kilometres
Dec. 8, 1992: Second Earth flyby at an altitude of 303 kilometres
Oct. 29, 1991: Flies by asteroid Gaspra at a distance of 1,600 kilometres
Aug. 28, 1993: Flies by asteroid Ida at 2,400 kilometres and discovers Dactyl – first known moon orbiting an asteroid
July 16-22, 1994: While en route to the planet, observes fragments of comet Shoemaker-Levy 9 impacting Jupiter
Dec. 7, 1995: Jupiter arrival and orbit insertion
Sept. 21, 2003: End of the mission
