Galileo

Like the famed astronomer for which it was named, Galileo spacecraft logged quite a few firsts during its 14-year mission to Jupiter. Among its discoveries: an intense radiation belt above Jupiter's cloud tops, helium in about the same concentration as the sun, extensive and rapid resurfacing of the moon Io because of volcanism, and evidence for liquid water oceans under the moon Europa's icy surface.

The orbiter carried a small probe that became the first to sample the atmosphere of a gas planet. The probe measured temperature, pressure, chemical composition, cloud characteristics, sunlight and energy internal to the planet, and lightning. During its 58-minute life, the probe penetrated 200 km (124 miles) into Jupiter's violent atmosphere before it was crushed, melted, and/or vaporized by the pressure and temperature of the atmosphere.

Galileo changed the way we look at our solar system. The spacecraft was the first to fly past an asteroid and the first to discover a moon of an asteroid. It provided the only direct observations of a comet colliding with a planet.

Galileo was deliberately crashed into Jupiter in September 2003 to avoid an accidental collision with -- and possible contamination of—one of Jupiter's moons.