SPACE: The Galileo satellite mission to Jupiter comes to a fiery close tomorrow after 14 years in space.
The ageing probe, which spent the last eight years orbiting the solar system's largest planet, is running low on fuel and will be crashed intentionally into the very planet it was sent to inspect.
Few satellite missions have provided as much hard new information about our local part of the universe as has Galileo. Launched from space after being piggy-backed into orbit in 1989 by the space shuttle Atlantis, it delivered a string of discoveries, identified new Jovian moons and took up-close images of the fiery moon Io and the frozen moon Europa.
From launch to impact, the satellite will have traversed 4,631,778,000 kilometres, about 2,800 million miles. It orbited Jupiter 34 times but on the way also became the first spacecraft to fly by an asteroid and the first to discover a moon circling an asteroid.
"Galileo was definitely one of the important ones," says Prof Tom Ray, astrophysicist at the Dublin Institute for Advanced Studies. "It was one of the best we have ever had. We got lots and lots of information about the moons of Jupiter and its weather system. The images from it were fantastic."
The California Institute of Technology's Jet Propulsion Lab managed the Galileo mission for NASA's Washington-based Office of Space Science. There were early hiccups, particularly when a vital antenna failed to operate properly, posing an early threat to the mission.
There was also much public dissent before its launch because of the probe's electrical power system, delivered by two radioactive thermoelectric generators. Galileo did two gravitational fly-bys of the earth to gather the tremendous speed it would need to reach Jupiter, and there were fears it might crash, scattering radioactive material into our atmosphere.
All this was quickly forgotten, however, once Galileo was installed in orbit and began sending back thousands of dramatic images from the Jovian neighbourhood. It provided the first direct measurements of Jupiter's atmosphere after the release of a smaller probe that parachuted into the giant gas ball.
It provided close-ups of the largest volcano in the solar system on the moon Io, permanently convulsed into activity by Jupiter's enormous gravitational pull.
The probe also provided tantalising views of what scientists are now convinced is water ice on Europa, massive frozen floes that have all the signs of floating on liquid water. This has sparked efforts to develop ways to get a new satellite onto Europa in a search for signs of bacterial life lurking in this frozen soup.
Its end will be a dramatic finale suited to such a successful mission. Galileo will plummet into the smothering Jovian atmosphere tomorrow at a staggering 48.2km per second, about 108,000 miles per hour. That speed would get a fast moving commuter from Los Angeles to New York in about 82 seconds.
As ever Galileo will be expected to deliver yet more data. Mission controllers in California are uncertain how long it will be able to transmit because of the extreme radiation levels close to Jupiter.
Further information about the Galileo project may be had from http://galileo.jpl.nasa.gov/