The solar system’s greatest explorer will perish in a kamikaze dive into the solar system’s biggest planet late tomorrow. The spacecraft Galileo — with nearly 3-billion miles on the clock and years of pioneering research behind it — will smash into the upper atmosphere of Jupiter at 108 000mph in one last bid to gather data before its power runs out.
Other craft, launched earlier, have survived longer. But the 2,5-ton, $1,5-billion spacecraft was the first to visit an asteroid, the first to identify a tiny moon orbiting another asteroid, and the only spacecraft so far to monitor a comet crashing into Jupiter. It circled Jupiter 35 times, making close encounters on the way with 10 of the gas giant’s mysterious moons.
It detected a salt water ocean under the ice of Europa, the solar system’s biggest volcanic eruption – a huge plume of sulphur from the moon Io – and an unexpected magnetic field around the largest, Ganymede. The mission was meant to last a couple of years. Altogether, Galileo spent 14 years away from Earth. It was designed to survive only so much of the fierce radiation from Jupiter before it failed: it absorbed four times the planned amount and kept on sending photographs and data back to mission control at Pasadena, California.
The spacecraft was named after the Italian scientist who first observed the moons of Jupiter in 1610. British scientists worked on three of its 11 instruments. It should have been launched from the space shuttle in 1986: the loss of the Challenger, with its seven astronauts, meant a three-year delay.
In 1989 the shuttle Atlantis finally lifted Galileo into low orbit. Its Nasa managers then fired a thruster that sent the explorer first around Venus, then around Earth twice, each time gathering speed through a gravity slingshot effect, until it had the push needed to get to Jupiter. Altogether, the voyage took six years.
Everything about Galileo was a challenge. The flight path took it nearer the sun than first planned, so engineers had to devise sunshades to protect it, and keep its high gain antenna folded away from damage. When the moment came to unfurl equipment that would pump epic quantities of data back to Earth, the antenna jammed. So Nasa engineers cooked up new software, and beefed up ground stations to make use of the much slower low gain antennae intended just to receive commands.
Its spotted the asteroid Gaspra in 1991. Two years later it swept past another asteroid called Ida, and discovered that it was orbited by its own little moon, less than a mile in diameter. Galileo neared Jupiter in 1994 in time for a grandstand view as the comet Shoemaker-Levy 9 broke up and fell in a series of glowing pieces into the Jovian atmosphere.
In 1995 Galileo dropped a little probe on a slow, five-month freefall into the giant planet’s atmosphere to detect clouds of ammonia, 250mph windspeeds, and lightning 1 000 times more powerful than any on Earth. Acting on commands from Nasa scientists, the mothership began a series of sweeps around Jupiter and its moons.
The most dramatic was a pass over Europa, so close that it could detect features the size of a school bus. This revealed that the moon’s icy surface was fissured and rafted like the Earth’s polar icecap, as if there were a huge ocean of liquid water underneath it. Europa is now the strongest candidate as a home for extraterrestrial life. It sped past Io as a giant fountain of fire erupted from its volcanic surface, and it detected liquid salt water on Ganymede and Callisto. And it did all this with a temperamental tape recorder, a main communications antenna that failed to deploy, an onboard computer of the kind used to play Pac-man games, and the spare power to light up a 60 watt bulb.
Three times, Nasa chiefs extended the spacecraft’s life. By this morning, it had send back 14 000 photos and 30 gigabytes of data, and travelled 2,8-billion miles on 246 gallons of propellant and used up every drop. Rather than risk an accidental crash that might pollute Europa Nasa chiefs decided on one last plunge into a planet 1 400 times the size of Earth. Galileo will stream in to Jupiter at 30 miles a second at a point just south of the Jovian equator, and vaporise in a planet with an interior pressure 100 million times that on Earth.
”It has been a fabulous mission,” said the project manager, Claudia Alexander, at the Jet Propulsion Laboratory in Pasadena. ”We are keeping our fingers crossed that, even in its final hour, Galileo will give us new information about Jupiter’s environment.” – Guardian Unlimited Â