Whenever a satellite or space mission goes into space, it has the potential to leave behind space junk, which is the term used to describe any object floating in space that no longer has any usefulness. Space junk can include obsolete satellites, dropped payloads, deployed rocket boosters and external fuel tanks. The exact number of junk items floating in space depends on the agency doing the counting, but some counts have estimated numbers around 23,000.
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How does a targeted SETI search work?
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