The Cassini spacecraft during processing.
Click on image for full size
Courtesy of NASA

Cassini Flyby Dangerous for Earth
News story originally written on August 16, 1999

The Cassini space probe will use the Earth's gravity to increase its speed while zooming towards Saturn. NASA's most expensive unmanned spacecraft has already made a flyby of Venus during its two-year venture in space. After passing Earth, it has one more flyby of Jupiter in 2000 before reaching Saturn in 2004. NASA probes have completed several successful flybys of Earth since 1973, but this one attracts more attention than usual because the probe carries plutonium.

Plutonium is used in Cassini to power all of its instruments. Solar energy, which is the usual source of power, cannot be used because Cassini is going to Saturn. It would need solar panels the size of tennis courts in order to absorb enough energy. The satellite will come within 725 miles of Earth, which could possibly endanger lives if something happens to the spacecraft.

Plutonium is a radioactive chemical which can cause lung cancer if inhaled. The plutonium is stored as pellets in special cartons aboard Cassini, but if a malfunction occurs, the satellite could burn up in the atmosphere and disperse the harmful chemicals. Scientists say the chance of a problem occurring is less than 1 in a million. Still, the chance of disaster upsets many around the world.

I'm very much in favor of the space program, but I think the use of plutonium in space is a manifestation of organized insanity," said John Gofman, a physicist on the team that developed the atomic bomb for the United States during World War II. "All I can say is that I'll be praying for the success of the flyby."

If a pellet breaks up into powder high in Earth's atmosphere, it will be dispersed all over the globe. Such a small amount will not be harmful. However, if a cannister makes it to Earth and crashes, the chemicals would be concentrated in one area.

"If you hit a hard surface like rock or concrete, there is a potential for the release of some plutonium," said Rich Furlong, a program manager at the DOE, which oversees the manufacture of NASA's plutonium canisters. "But there would not be a release if they landed in water. It just depends on the surface at impact."

Still, NASA believes the rewards are much greater than the risks. There is no way to do space exploration without some risk," said Jim Longuski, a professor of aeronautics and astronautics at Purdue University in Indiana. "The question is what is the balance between the risk and the potential payoff? In this case, I think the benefit far outweighs the miniscule risk involved."

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

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


The Cassini probe began its journey to Saturn on October 15, 1997. It flew by Earth in August, 1999, before heading towards the distant planet. Cassini passed Jupiter in 2000 and then burned towards its...more

1999--A Year in Review...

It was another exciting and frustrating year for the space science program. It seemed that every step forward led to one backwards. Either way, NASA led the way to a great century of discovery. Unfortunately,...more

STS-95 Launch: "Let the wings of Discovery lift us on to the future."

The Space Shuttle Discovery lifted off from Kennedy Space Center at 2:19 p.m. EST, October 29th. The sky was clear and the weather was great as Discovery took 8 1/2 minutes to reach orbit for the Unitied...more

Moon Found Orbiting Asteroid

A moon was discovered orbiting the asteroid, Eugenia. This is only the second time in history that a satellite has been seen circling an asteroid. A special mirror allowed scientists to find the moon...more

U.S. is Fed Up with Russia

Will Russia ever put the service module for the International Space Station in space? NASA officials are demanding an answer from the Russian government. The necessary service module is currently waiting...more

More on Recent Coronal Mass Ejection

During a period of about two days in early May, 1998, the ACE spacecraft was immersed in plasma associated with a coronal mass ejection (CME). The SWICS instrument on ACE, which determines unambiguously...more

Mother Nature's Air Conditioning

J.S. Maini of the Canadian Forest Service has referred to forests as the "heart and lungs of the world." Forests reduce soil erosion, maintain water quality, contribute to atmospheric humidity and cloud...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