Girdled by Garbage

Discarded rockets, exploded satellites, paint flecks and even human waste contribute to the earth's orbital litter. The U.S. Space Surveillance Network tracks all man-made objects down to baseball-size fragments (10 centimeters wide). They pose a risk of serious collision with future space missions. According to a NASA analysis, even if humans stopped launching satellites now, debris will increase after 2055. That is when the formation of new pieces, resulting when larger ones break up, will exceed the rate of destruction by reentry burn-up.

Percent of orbital objects that are debris: 93

Number of fragments at least 10 centimeters wide: 9,000

Combined mass, in kilograms: 5 million

Number of known orbital collisions, 1991–2005: 3

Number of collisions expected in the next 200 years: 18

Number of collisions expected to be catastrophic: 11

SOURCES: U.S. S trategic Command; Science, January 20, 2006