Lessons from later missions
Following Apollo 11 in 1969, NASA landed another five crewed craft on the Moon: Apollo 12, 14, 15, 16 and 17. In total, 12 Apollo astronauts explored the Moon’s surface. The last mission, Apollo 17, was in 1972.
No human has set foot on the Moon since then. But spacecraft have continued to visit, with the USA, the then Soviet Union, China, India, Japan, Israel and the European Space Agency all sending uncrewed landers and orbiters there, some gathering more evidence about the Moon.
The Apollo missions showed us that the Moon is closely related to the Earth, their rocks are similar in many ways. Like Earth, the Moon is billions of years old; unlike Earth, its meteorite craters are preserved, untouched by weather. Rock samples can establish the ages of these craters. Using this method, the Moon helps us date the craters of Mars, Venus and Mercury and understand the histories of those planets.
The Moon also contains a record of the Sun’s activity for the last four billion years, as solar radiation has enriched the small rocks and dust on its surface (the lunar regolith) in certain chemical elements or particular isotopes of elements.
What’s missing from Moon rocks is evidence of life, past or present. Whether the Moon can be home to life in the future rests on another finding, one that took time to emerge.
Water on the Moon
Liquid water can’t exist on the Moon’s sunlit surface, but since the ‘60s scientists have thought that water ice might hide in dark craters at the poles.
In 1971 an experiment carried on Apollo 14, the Suprathermal Ion Detector, obtained the first evidence of water vapour on the Moon’s surface. Exciting but inconclusive results followed from other missions over the next three decades.
Firmer evidence started to emerge in November 2008. India’s Chandrayaan-1 spacecraft, in orbit around the Moon, released a probe: as this fell, it recorded evidence of water vapour above the Moon’s surface. In September 2009 a NASA instrument on Chandrayaan-1, the Moon Mineralogy Mapper, detected water molecules in the Moon’s polar regions.
The next month this was followed by positive observations by NASA’s Lunar Crater Observation and Sensing Satellite (LCROSS). The spacecraft jettisoned a booster rocket, impacting a permanently shadowed region on the Moon. This created a plume of debris in which signs of water were found.
NASA is working towards sending humans back to the Moon. Any plans for a human settlement depend on water being available. Does the Moon have enough? We don’t yet know: more exploration is needed.