Galileo Reaches the End of its Road
News story originally written on September 19, 2003

Artist's depiction of the Galileo spacecraft near Jupiter's moon Io. Click on image for full size (44K JPEG) Image courtesy NASA/JPL.

The Galileo spacecraft, which has been orbiting Jupiter since 1995, has finally reached the end of its road. On September 21, 2003, Galileo will make a fiery plunge into Jupiter's atmosphere and be vaporized. Galileo's demise is not an accident; mission planners have intentionally aimed the robotic spacecraft at the gas giant planet!

Galileo has far outlived the duration of its original mission. Its fuel supplies are dwindling, its power supply is getting low, and its instruments are failing after years of exposure to the intense radiation around Jupiter. Instead of shutting Galileo down and letting it drift in orbit around Jupiter, the Galileo mission team has placed the craft on a collision course with Jupiter. Why? Europa, one of Jupiter's moons, is one of the most likely places in the Solar System to harbor life. If Galileo is left to drift, there is a chance it might someday crash into Europa. Despite long years of exposure to the harsh environment space, there may be living microbes (or their spores) lurking somewhere inside the Galileo spacecraft. A crash into Europa could contaminate the moon with Earthly microbes.

Galileo has been a fabulously successful mission that has helped us learn a great deal about the largest planet in our Solar System, its many moons and complex rings, and the vast magnetic fields and deadly radiation belts that surround Jupiter. It is with a touch of sadness that we bid Galileo a fond farewell. Reflecting back on the long history of the Galileo mission, the scientists and engineers who conducted the mission recently assembled a list of some of Galileo's greatest accomplishments. Here they are:

• The descent probe (which plunged into Jupiter's atmosphere in December 1995) made measurements that furthered our understanding of how Jupiter has evolved. The measurements opened up new questions, however.
• Jupiter has numerous, large thunderstorms with a spatial extent that is different from the Earth. Galileo made a first observation of ammonia clouds in another planet's atmosphere. The atmosphere seems to create ammonia ice particles of material from lower depths, but only in "fresh" clouds.
• Evidence supports a theory that liquid oceans exit under Europa's icy surface.
• Galileo magnetic data provide evidence that not only Europa has a liquid-saltwater layer but Ganymede and Callisto may as well.
• Europa, Io, and Ganymede all have metallic cores. Callisto is more homogeneous (undifferentiated) inside.
• Europa, Ganymede, and Callisto all provide evidence of a thin atmospheric layer - known as a 'surface-bound exosphere'.
• Ganymede generates a magnetic field.
• Galileo took many images showing unique geological phenomenology: Europa faults and "scalloped" shaped cracks, Ganymede's surface that indicates high levels of tectonic activity with faulting and fracturing, Callisto's surface showing evidence of extensive (and mysterious) erosion.
• Io's extensive volcanic activity may be 100 times greater than that found on Earth. The heat and frequency of eruption are reminiscent of early Earth. This means that Io may be a laboratory for the study of the early Earth.
• Galileo studied the complex plasma interactions at Io.
• Jupiter's ring system is formed by dust kicked up as interplanetary meteoroids smash into the planet's four small inner moons. The outermost ring is actually two rings, one embedded within the other.
• Galileo was the first spacecraft to dwell in a giant planet magnetosphere long enough to identify its global structure and to investigate its dynamics.

Artist's depiction of the Galileo spacecraft near Jupiter's moon Io. Click on image for full size (44K JPEG) Image courtesy NASA/JPL.

The Galileo spacecraft has finally reached the end of its road. Galileo has been orbiting Jupiter since 1995. On September 21, 2003, Galileo will dive into Jupiter's atmosphere and burn up. This crash into Jupiter is not an accident; mission planners have aimed the robotic spacecraft at Jupiter!

Galileo has lasted much longer than its original mission plan intended. But now Galileo is running low on fuel and its instruments are failing after years of exposure to radiation. The Galileo mission team could shut Galileo down and letting it drift in orbit around Jupiter. Instead, they have chosen to aim the craft on a collision course with Jupiter. Why? Europa, one of Jupiter's moons, is one of the most likely places in the Solar System to find life. If Galileo is left to drift, there is a chance it might someday crash into Europa. There may be living microbes (or their spores) lurking somewhere inside the Galileo spacecraft. A crash into Europa could infect the moon with Earthly microbes.

Galileo has been a very successful mission that has helped us learn a great deal about the largest planet in our Solar System, its many moons and complex rings, and the vast magnetic fields and deadly radiation belts that surround Jupiter. The Galileo mission crew is sad to see Galileo end. However, they are proud of what Galileo has done in its long mission. They made a list of some of Galileo's greatest accomplishments. Here are some of those:

• There may be an ocean under the icy surface of the moon Europa.
• Two other moons, Ganymede and Callisto, may also have layers of salty water beneath their surfaces.
• Europa, Io, and Ganymede all have metallic cores. Callisto does not; it is a big ball of ice.
• Europa, Ganymede, and Callisto all seem to have thin atmospheres.
• Ganymede has a magnetic field.
• Io has many, many volcanoes. It may be a lot like Earth was when Earth was young. Maybe we can learn about Earth's early history by studying Io.
• Jupiter's ring system is formed by dust kicked up by meteoroids that smash into the planet's four small inner moons. The outermost ring is actually two rings, one inside of the other.

Artist's depiction of the Galileo spacecraft near Jupiter's moon Io. Click on image for full size (44K JPEG) Image courtesy NASA/JPL.

Galileo is a spacecraft that has been orbiting Jupiter for eight years. On September 21, 2003, Galileo will crash into Jupiter. It will burn up in Jupiter's atmosphere. The crash is not an accident! The people who run the Galileo mission are making Galileo crash on purpose!

Why are they doing that? They want to make sure Galileo doesn't crash somewhere else. One of Jupiter's moons, Europa, might have life on it. There are probably microbes inside of Galileo somewhere. If Galileo crashed on Europa, the microbes might get out and start growing there. Scientists don't want that to happen!

The team of scientists and engineers who worked on the Galileo mission are sad to see it end. However, they are proud of all the great things Galileo has done. Here are some of the things Galileo has helped us learn:

• There may be an ocean under the icy surface of the moon Europa.
• The moons Europa, Io, and Ganymede all have cores with metal in them. Callisto does not; it is a big ball of ice.
• Europa, Ganymede, and Callisto all seem to have thin atmospheres.
• Ganymede has a magnetic field.
• Io has many, many volcanoes. It may be a lot like Earth was when Earth was young. Maybe we can learn about Earth's early history by studying Io.
• Jupiter's ring system is formed by dust kicked up by meteoroids that smash into the planet's four small inner moons. The outermost ring is actually two rings, one inside of the other.