Pioneer 5 as seen on the Enterprise viewscreen.
Pioneer 5 was an early Earth space probe, flown by the United States' NASA program in 1960. Pioneer 5 was used to investigate interplanetary space between the orbits of Earth and Venus.
A record of Pioneer 5 was available in the Enterprise library computer. This data was flashed on a viewscreen when the Talosians scanned the Enterprise computer in 2254. (TOS: "The Cage")