Galileo Mission to Jupiter

University of Wisconsin-Madison

Space Science and Engineering Center

Net Flux Radiometer

The Mission: Galileo, a 2.5-ton, $1.5-billion spacecraft, is the most ambitious interplanetary mission in the history of space flight. En route to Jupiter for the past six years, the spacecraft and a recently deployed entry probe will rendezvous with the largest planet in our solar system Dec. 7, 1995. It will enable planetary scientists to study the planet and some of its 15 known moons at close range. Its atmospheric probe, an instrument-packed capsule that will penetrate and sample the Jovian atmosphere, will provide scientists with their first-ever direct measurements of the atmosphere of one of the giant outer planets. The mission will help scientists learn about Jupiter's violent weather and atmosphere and, since Jupiter has changed little since it was formed more than 4 billion years ago, may also provide some insight into the early conditions of our solar system.

The Planet: Jupiter is the largest planet in the solar system and the fifth in distance from the Sun. It has 15 known moons. The planet itself resembles a huge spinning ball of gas and liquid. It has more mass than all of the other planets combined. Its Great Red Spot, a raging storm system in the southern hemisphere, is nearly three times the size of the Earth. The Jovian atmosphere is believed to have at least three cloud levels, each composed of different chemical constituents. The lowest level has clouds consisting of water, the next has clouds of ammonium hydrosulfide, and the highest has clouds of ammonia. The gas planets, such as Jupiter, do not have solid surfaces. Their gaseous material simply gets denser with depth. Jupiter is about 90 percent hydrogen and 10 percent helium and has traces of methane, water and ammonia. This is close to the composition of the primordial Solar Nebula from which our entire solar system was formed.

The Net Flux Radiometer: Aboard Galileo's entry probe is a device called the Net Flux Radiometer. Developed in part by UW-Madison scientists, the Net Flux Radiometer is designed to sample the thermal and solar radiation of the planet as the probe descends through the deep Jovian atmosphere. This device will perform some of the first direct measurements of Jupiter's atmosphere. The UW-Madison device will also measure water vapor and cloud structure.

For More Information: Contact Terry Devitt, (608) 262-8282,; or SSEC's Public Information Officer, (608) 263-3373