One of the most remarkable chapters in the history of planetary exploration ended Sunday when the American spacecraft Galileo plunged to its demise into the dense atmosphere of Jupiter. The suicide mission was deliberate.
Galileo's dramatic dive brought the curtain down on 14 years of exploration that began with a launch from the U.S. space shuttle Atlantis in October 1989. Shuttle commander Donald Williams bid it farewell. "Galileo is on its way to another world," he said. "It's in the hands of the best flight controllers in this world. Fly safe!"
After a six-year journey, Galileo became the first spacecraft to orbit the solar system's largest planet. For the next several years, it completed the first detailed reconnaissance of the giant gaseous body, despite the failure of its main communications antenna and a data recorder that worked only intermittently.
Among its major accomplishments were the deployment of a probe to measure Jupiter's turbulent atmosphere and the examination of volcanoes on the moon Io. U.S. space agency scientist John Rummel pointed out that the most spectacular findings were ice cover and evidence of salt water beneath the surface of the moon Europa and possibly on Ganymede and Callisto, too. "In the case of Europa, that ocean may be as close as 20 kilometers from the surface. It's an ocean that may imply life elsewhere in this solar system," he explained.
Galileo was also the first spacecraft to fly by an asteroid and discover the moon of an asteroid.
The orbiter's main mission ended six years ago after circling Jupiter for two years. The space agency NASA extended the mission three times to continue taking advantage of its unique vantage point. The flight team finally ended operations last February as fuel became low.
But rather than let the orbiter take a random plunge after the propellant ran out, John Rummel decided that it should be targeted into the planet while it still had fuel and flight directors could still control it. He did not want Galileo to hit one of the planet's moons accidentally and contaminate their oceans with microbes from Earth.
"Galileo was assembled in a clean room and it was done very well, but there was a certain amount of microbial contamination," explained Mr. Rummel. "My intention is to make sure there are no live microbes that get deposited on Europa in particular, or Ganymede and Callisto, so that it doesn't endanger the discoveries that it has made. So that's why Jupiter is the place and Sunday is the time."
The spacecraft will have traveled more than 4.5 billion kilometers by the time it takes its dive. Many scientists and engineers have spent much of their careers on Galileo since its design, construction, and launch in the 1980s, and Eileen Theilig says the end of the mission is an emotional time for them.
"It is a sad time for the flight team to be saying their farewell to a spacecraft that they have been working with daily," she said. "But I think that the sadness is offset by the pride that the team has in its accomplishments."