On Sept. 3, 2002, amateur astronomer Bill Yeung found an asteroid. Initially named J002E3, astronomers tracked it and found that it was in Earth orbit, which was surprising. Objects within the Earth-moon system are quickly ejected, meaning this asteroid must have been a recent capture. Spectroscopic observations revealed the "asteroid" had a signature consistent with white titanium dioxide paint NASA used to paint the Saturn V rockets. Asteroid J002E3 turned out not to be an asteroid at all but the upper S-IVB stage of Apollo 12's Saturn V from 1969.
So what happened to the rest of the spent Saturn V rocket stages?
ANALYSIS: When (Part of) Apollo 13 Reached the Moon
The Saturn V was a three-stage rocket. The first stage, the S-IC, and the second stage, the S-II, both fell away once they were spent and landed in the ocean downrange from the launch site at Cape Canaveral. On lunar missions, the third S-IVB stage stayed with the spacecraft.
After a brief stay in Earth orbit, the S-IVB fired a second time to propel the spacecraft to near escape velocity on its path to the moon. Then came the transposition, docking, and extraction phase: the command-service module separated from the S-IVB then turned around to dock with the lunar module encased within it. Once the two spacecraft were docked, they would separate from the S-IVB entirely.
What happened next varied from mission to mission. On Apollo 8, the first mission to fly to the Moon in December of 1968, the S-IVB was put on a trajectory that had it fly by the moon before entering solar orbit. The S-IVB stages from the Saturn Vs that launched Apollo 10, the second mission that flew to the moon in May of 1969, and Apollo 11, the first lunar landing two months later in July, also ended up in a heliocentric orbit. Apollo 12's, as we now know, is currently orbiting the Earth.
ANALYSIS: Saturn V Also Suffered Engine Launch Anomalies
Beginning with Apollo 13, the afterlives of the spent S-IVB stages became a lot more interesting.
On April 14, 1970, Apollo 13's S-IVB became the first to be deliberately crashed into the moon; the impact and subsequent ground motions were recorded on the seismometer that the Apollo 12 crew had left on the lunar surface five months earlier as part of their Apollo Lunar Surface Experiment Package or ALSEP.
On Feb. 4, 1971, Apollo 14's S-IVB became the second upper stage to be deliberately crashed into the moon's surface. The impact and ground movements were again recorded by the seismometer left by the Apollo 12 crew.
ANALYSIS: NASA's Gutsy First Launch of the Saturn V
The Apollo 14 crew also left an ALSEP on the surface, which meant that when Apollo 15's S-IVB impacted the lunar surface on July 29, 1971, the associated ground movements were recorded by two separate seismometers at two different locations on the moon. This trend continued. Apollo 15 left an ALSEP on the Moon so when Apollo 16's S-IVB impacted on April 19, 1972 it was recorded by three seismometers. The crew also left an ALSEP on the surface, so when Apollo 17's S-IVB impacted on Dec. 10, 1972, the associated ground movements were recorded by four separate seismometers.
All five ALSEPs lasted longer than the single years they were designed to. They were all turned off on Sept. 30, 1977, primarily for budgetary reasons. For more detailed information on the crash sites of the Apollo S-IVB stages, including size and location of the created craters, check out this handy table.