Fifty years ago today humans took their first steps on the Moon. Dr Vincent Eke of Durham University’s Institute for Computational Cosmology, looks at what the Apollo missions taught us and what the future holds for Moon exploration.

WHEN Neil Armstrong and Buzz Aldrin first stepped onto the Moon 50 years ago, the audacity of the astronauts captivated the imaginations of people around the world. Images of the US flag placed next to the lunar module have become iconic, but what did the Apollo lunar adventures teach us about our place in the solar system?

The most important scientific findings from the Apollo lunar missions come from analyses of the returned rocks. Earth is so geologically active that its crust has been recycled many times through the mantle, wiping out evidence about conditions when the planets were forming 4.5 billion years ago.

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In contrast, the geological evolution of the Moon has been much simpler, consisting mainly of pulverisation of the surface by impacting meteorites. Moon rocks provide far better clues to what happened during planet formation. Before Apollo, there were three competing theories for the formation of the Moon:

  • It formed elsewhere and was gravitationally captured by the Earth;
  • The early Earth was spinning so rapidly that a portion was flung off, which became the Moon;
  • The Moon and Earth formed from the same disc of material at the same time as one another.

Thanks to the Apollo rock samples, we can confidently say that all of these theories were wrong!

Crystals of the light grey mineral anorthite were found in the samples returned by Apollo 11, but it was not until the “Genesis Rock” was returned by Apollo 15 that a big chunk of the stuff was found. Apollo16 was the first mission to land in the lunar highlands, the lighter parts of the Moon, and this mission discovered an anorthite-rich rock that was 4.5 billion years old according to radiometric dating techniques, almost as old as the solar system itself.

Anorthite forms during the crystallisation of molten rock, so its discovery implied that the early Moon was over 1,300°C. This led to theory number four for how the Moon formed, our current best guess, involving a Mars-sized object smashing into the early Earth. The hot debris that was flung into orbit around the Earth subsequently built up to form the Moon.

Most Apollo missions to land on the Moon went to the darker parts, known as the maria or seas. These areas are less cratered than the highlands, and provided smoother landing sites. The rocks gathered from the maria were basaltic, similar to dark lavas found on Earth, and represent relatively young surfaces where seas of molten rock filled in depressions in the older anorthite-rich lunar crust. Some of the returned samples contained green and orange volcanic glass beads, which were brought to the surface during eruptions of fire fountain volcanoes a few billion years ago. These glasses tell us about the lunar composition hundreds of kilometres beneath the surface, and led to the surprising discovery that there are traces of water present in the lunar mantle.

Other returned rock samples have yet to be studied, so the gift of the Apollo rock collection keeps on giving.

Apollo’s astronauts also left retroreflectors on the lunar surface, to help measure the distance to the Moon. This was done by timing pulses of laser light sent from and reflected back to Earth. It turns out that the Moon is moving away from us at a rate of almost 4cm every year because of gravitational tides from the Earth. Measurements from the laser retroreflectors also provide a precise test of the Theory of General Relativity; so far, Einstein’s theory is passing this test.

SO what next for the Moon? Our near neighbour could prove to be a useful stopping-off point on the way to Mars as we seek to explore the Red Planet. China, Japan, Russia and the USA all have plans to put humans onto the Moon before 2040. With private companies such as SpaceX developing rockets for spaceflight, exciting times lie ahead.

Indeed, the last ten years has seen a resurgence of lunar science with various robotic orbital and lander missions. Currently, the Chinese Chang’e-4 rover is exploring the largest confirmed impact crater, the South Pole-Aitken basin, which was created by an impactor that punctured through the lunar crust and brought deeper layers of the early Moon to the surface.

This crater is on the far side of the Moon so it can never be seen from Earth and is one of the few places to remain unpolluted by noise from Earth. For this reason, astronomers are keen to build a radio telescope there to look out into space and study the early Universe as it looked about 13 billion years ago, long before the solar system came into existence.

Apollo may not have found any signs of extra-terrestrial life on the Moon half a century ago, but a radio telescope peering out from the far side of the Moon may in future receive a friendly greeting from some “little green men” living outside our solar system.