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Did you Know?
In Did You Know? the National Geographic magazine team shares extra information we gathered to expand your knowledge of our featured subjects.
According to NASA, each day presents a one-in-a-trillion chance of a person getting hit by a falling piece of space junk. In 1968, the Baltimore Sun reported that a piece of U.S. space debris landed in a Cuban pasture, killing two Guernsey cows. Since 1957, human-made space junk has been falling back to Earth on a regular basis. Everything humankind has ever thrown into orbit, haphazardly or otherwise, will eventually make its way back to Earth. The only question is, when.

For Lottie Williams, the cosmic lottery hit a jackpot on a cool Tulsa, Oklahoma, morning in 1997. Soon after witnessing a satellite breaking up in the atmosphere during her early morning walk, Williams entered the history books as the first, and only, person on record to be hit by falling space junk. The feather-light piece of scalded shielding from what is believed to be a Delta rocket booster lightly tapped her shoulder with no ill effect.

Nearly all the clutter of space travel now hangs above us at distances as far as 22,500 miles (36,200 kilometers) and as near as 150 miles (240 kilometers) from Earth, and some of it has long outlived its usefulness. The oldest known object is the 1958 Vanguard I research satellite, which ceased all functions in 1964 and has since orbited the globe nearly 194,000 times. Orbital debris, the technical term for nonfunctional and human-made space junk, includes not only whole, abandoned satellites, but also pieces of broken satellites, deployed rocket bodies, human waste, and other random objects, like the glove lost by astronaut Ed White during his historic 1965 spacewalk. The newest jettisoned junk is a fridge-size ammonia reservoir released into its own orbit on July 23, following a NASA decision that no other disposal options were feasible.

The United States Space Surveillance Network catalogs about 12,000 pieces of debris larger than about four inches (ten centimeters) in diameter, and tracks their speedy march around the globe to help protect larger satellites, shuttles, and the International Space Station. (Small, undetectable pieces number in the millions, and pose a potentially lethal and largely unpredictable threat to human operations in space.) So, how often does orbital debris make its way back home? NASA estimates that, on average, one piece of cataloged debris reenters the lower atmosphere and falls to Earth every day.

—Gabrielle E. Montanez