Exploring the Moon
A history of lunar discovery from the first
space probes to recent times
The waning crescent Moon.
Meeting the challenge
“Tranquillity Base here. The Eagle has landed.” With these words Apollo 11 commander Neil Armstrong announced the success of
the first manned lunar landing. The time was 20.18 UT on 1969 July 20. (For a
video of the final approach and landing, with the view out of the LM window
compared with surface features on a Lunar Orbiter photograph, click here. It’s a 10MB .wmv file, and plays for four and a half minutes.)
Around them at their landing site in
southwestern Mare Tranquillitatis was a flat, rock-strewn landscape pitted with small craters – in fact, Armstrong had to take over control of the landing from the onboard
computer to prevent the LM from descending into such a crater, called West Crater.
On the surface – one of the Apollo 11 Lunar Module’s legs
Armstrong was the first to climb down the ladder outside the LM, activating a
small camera that monitored his movements. As he stepped off the LM, he spoke
the now-famous words: “That’s one small step for [a] man – one giant leap for mankind.” (For a video of the “first footing”, click here.) Aldrin then joined him on the surface. For the next two hours they set up
equipment including a seismometer for measuring Moonquakes and a panel to
reflect laser beams back to Earth to measure the changing distance of the Moon
with high precision.
Moving around in the low lunar gravity, one-sixth that on Earth, proved
surprisingly easy, even with bulky spacesuits. Armstrong’s Moon walk lasted two and a quarter hours, Aldrin’s half an hour less. During that time, the two men collected over 20 kg of rocks
and soil. On the airless, waterless Moon, their footprints will remain visible
in the soil for millions of years, unless disturbed by careless tourists.
Less than 22 hours after touching down on the
Moon, Armstrong and Aldrin took off in the upper half of the LM to rejoin
Michael Collins orbiting in the Command Module above. (For a video clip of LM
takeoff from the final mission of the series, Apollo 17, see here. It’s a 4.7 MB .mpg file and plays for 36 seconds.) Jettisoning Eagle’s ascent stage, Apollo 11 set course back to Earth, splashing down in the
Pacific Ocean on July 24.
Still there – Eagle’s descent stage seen in 2009 by Lunar Reconnaissance Orbiter
On their return, the astronauts had to spend over a fortnight in quarantine in
case they had brought back any microorganisms from the Moon. But the Moon
samples turned out to be completely sterile, and the quarantine procedures were
abolished for later missions.
Most astounding of the findings from the Apollo 11 samples was their extreme
age, ranging from 3.6 to 3.9 billion years. This is similar to the age of the
oldest known rocks on Earth, yet the lunar mare are among the youngest parts of
the Moon’s surface, demonstrating how ancient the face of the Moon really is. As
expected, the rocks were like basalt lava, indicating that they had once been
molten and had flowed out onto the surface from the Moon’s interior. Chemical differences between various samples implied that they had
come from at least two different magma sources.