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NASA'S aging Galileo spacecraft plunged into Jupiter's turbulent atmosphere, bringing a deliberately fiery conclusion to a 14-year exploration of the solar system's largest planet and its moons.

The unmanned spacecraft, traveling at nearly 173,770 kph, was torn apart and vaporized by the heat and friction of its fall through the clouds after it dove into the atmosphere at 1957 GMT Sunday as planned.

At NASA's Jet Propulsion Laboratory, hundreds of scientists, engineers and their families counted down the last seconds before the spacecraft ended its 4.5-billion-kilometer journey from Earth.

"We haven't lost a spacecraft, we've gained a new stepping stone in exploration," said Torrence Johnson, the mission's project scientist.

Rosaly Lopes, another scientist on the mission, called Galileo's descent "a spectacular end to a spectacular mission."

"Personally, I am a little sad. I had the time of my life on Galileo and I'm a little sad to say goodbye to an old friend," Lopes added.

Despite the glitches that plagued Galileo since its 1989 launch aboard the space shuttle Atlantis, it was one of the National Aeronautics and Space Administration's most fruitful missions, at a cost of US$1.5 billion.

During its thrice-extended mission, Galileo discovered the first moon of an asteroid, witnessed the impact of a comet into Jupiter and provided firm evidence of salty oceans on three of the planet's moons. Scientists consider one of the three, Europa, the most likely place in the solar system to harbor extraterrestrial life.

Among the most stunning of the 14,000 images returned by Galileo were those of the moon Io. Galileo caught some of the moon's more than 150 volcanoes actively spewing lava and plumes of dust and gas.

"It had more surprises, better stuff waiting to be discovered than we ever could have imagined," said Andy Ingersol, a scientist at the California Institute of Technology.

The last of Galileo's science measurements arrived on Earth after the spacecraft was destroyed on Sunday, taking 52 minutes to cross space at the speed of light.

NASA initially considered leaving Galileo in orbit after it depleted its onboard store of fuel, which was used to trim its course on each of its 35 spins around Jupiter.

Instead, it opted to crash the 1,350-kilogram Galileo to eliminate the possibility it could smack into the watery moon Europa and contaminate it with any microbes aboard. Were Earth bugs to survive on Europa, they could compromise future attempts to probe the moon for indigenous life.

NASA intends to return to Jupiter in a decade with another unmanned spacecraft called the Jupiter Icy Moons Orbiter.

Galileo is the first planetary spacecraft NASA has intentionally destroyed since it steered the Lunar Prospector into the Earth's moon in 1999.

NASA says Galileo met 70 percent of its science objectives, including an analysis of the composition of Jupiter's atmosphere and a probing of the faint rings that circle the planet. Galileo also investigated the dynamics of the magnetic environment surrounding the solar system's largest planet and made a reconnaissance of its planet-sized moons.

The spacecraft was named after Galileo Galilei, the Italian astronomer who discovered Jupiter.

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