Shop Windows to the Universe

Earth Science Rocks! Select one of our four cool NESTA t-shirts from our online store, and express your love of Earth and space science!
Artist's rendition of Galileo orbiter (right) and descent probe (left).
Image courtesty NASA/JPL.


The Galileo spacecraft was launched on October 19, 1989. Galileo had two parts: an orbiter and a descent probe that parachuted into Jupiter's atmosphere. Galileo's primary mission was to explore the Jovian system (Jupiter and its moons and rings) more thoroughly than was done by the Voyager missions of 1979 and 1980. The Galileo mission ended on September 21, 2003, when mission controllers sent the orbiter on a fiery plunge into Jupiter's atmosphere.

The Galileo mission was a huge success! Originally, the Galileo orbiter was expected to last about two years in orbit around Jupiter. Despite constant bombardment by intense radiation in the magnetosphere of Jupiter, Galileo continued to function for eight years. It returned hundreds of stunning pictures of the four large Galilean moons of Jupiter (Io, Europa, Ganymede, and Callisto) over the course of more than thirty swoops through the inner parts of the Jovian system.

Galileo arrived at Jupiter in December 1995. On December 7, 1995, Galileo's probe made a dangerous descent into Jupiter's atmosphere, encountering 400 mph winds and deceleration forces 250 times stronger than Earth's gravity. The friction the probe encountered as it went screaming into Jupiter's atmosphere heated it to temperatures twice as high as those at our Sun's surface. Although it did not carry a camera, the probe's instruments measured atmospheric pressure, density, and composition, and explored the planet's radiation belts. Low oxygen content and little lightning indicated a surprisingly low concentration of water, which has caused scientists to change their hypotheses about the planet's original formation.

The orbiter made many discoveries during its eight years looping around Jupiter. It gathered evidence for subsurface liquid layers of salt water on Europa, Ganymede, and Callisto. It documented high levels of volcanic activity on Io. When Shoemaker-Levy slammed into Jupiter in 1994, Galileo had the only direct view of the comet striking Jupiter's atmosphere. Galileo determined that Jupiter's rings are formed from dust hurled up by meteor impacts on planet's the inner moons. Measurements by the orbiter's magnetometer revealed that Io, Europa, and Ganymede have metallic cores, while Callisto does not. Also, Galileo discovered that Ganymede generates its own magnetic field; it is the first moon know to do so. The orbiter also found that Europa, Ganymede, and Callisto all have thin, 'surface bound' atmospheres.

During it's trip from Earth to Jupiter, Galileo passed by and studied two asteroids. Galileo was the first spacecraft to fly by an asteroid when it passed Gaspra in 1991. In 1993, Galileo flew past the asteroid Ida and made the first discovery of a moon orbiting an asteroid - the tiny rock Dactyl.

Last modified September 21, 2003 by Randy Russell.

Shop Windows to the Universe Science Store!

Our online store includes fun classroom activities for you and your students. Issues of NESTA's quarterly journal, The Earth Scientist are also full of classroom activities on different topics in Earth and space science!

Windows to the Universe Community



You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more


The rare geometric arrangement of planets Jupiter, Saturn, Uranus, and Neptune in the 1980's made it possible for the Voyager spacecrafts to visit them over a 12 year span instead of the normal 30. They...more

Galileo Reaches the End of its Road

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....more

An Overview of Jupiter's Magnetosphere

Jupiter's magnetosphere is a unique object in the solar system. It is the biggest object in the entire solar system. Not only is it big enough to contain all of Jupiter's moons, but the sun itself could...more

Galilean Satellites

The Galilean satellites are the 4 major moons of Jupiter, Io, Europa, Ganymede, and Callisto. In this picture, Io, and Ios surface, are shown on the left-most end, then Europa, and its surface, then Ganymede,...more


Europa was first discovered by Galileo Galilei in 1610, making it one of the Galilean Satellites. Europa is Jupiter's 4th largest moon, 670,900 km from Jupiter. With a diameter that is about half the distance...more


Callisto was first discovered by Galileo in 1610, making it one of the Galilean Satellites. Of the 60 moons it is the 8th closest to Jupiter, with a standoff distance of 1,070,000 km. It is the 2nd largest...more

Does Europa Have an Ocean?

The surface of Europa shows many signs of that there may be an ocean under the surface: * flooded terrain * 'freckles' * rafting * 'mushy' craters, and * spreading centers. Taken together, these pieces...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA