The moon shines bright in the night sky, its monthly phases waxing and waning in a comforting and steady rhythm. Its gravity gently tugs on Earth, creating our tides. And it is drifting slightly farther away with every orbit it makes around the planet. The moon may seem calm and quiet – and it is, geologically speaking – but its birth was not so tranquil.
According to the “giant impact” theory, a Mars-sized boulder known as Theia slammed into Earth almost 4.5 billion years ago, flinging out chunks of rocks that coalesced into the moon. Just after it formed, the moon was so hot it may have had an ocean of magma on its surface.
Another theory says the Earth may have been vaporised in that giant collision, and the moon formed out of gas and dust that glommed together at the outer edge of the donut-shaped cloud that was once our planet. Either way, understanding the make-up of the moon can tell us more about when it formed and help us understand the timeline of early Earth. The best way to do that is to go there.
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The moon is 384,402 kilometres away, so getting there is no easy feat. The Soviet Union first sent an uncrewed spacecraft there in 1959, and the United States followed with the only crewed moon missions. NASA’s Apollo space programme included six missions that landed on the moon, and the ill-fated Apollo 13 that orbited the moon but couldn’t touch down on the surface due to an explosion that crippled the spacecraft.
Six of the 12 Apollo astronauts that walked on the moon also drove lunar vehicles on the surface. They explored the craters that mark the moon’s surface from billions of years of being hit by meteorites, and brought back samples from the lunar surface. No person has been back to the moon since 1972, though a few rovers have trundled over the dusty landscape. In 2019, China sent the first lunar rover to the far side of the moon.
A synchronous rotation keeps one side of the moon shrouded in mystery from our perspective. It takes about as long for the moon to turn on its axis as it does to orbit Earth, so it keeps the same face towards us – the one known in folk tales as the Man In The Moon, a vaguely face-shaped pattern seen in the dark and light of lunar craters.
Moon rocks are nearly identical to Earth rocks, but in almost every other way it is a very alien place. The moon doesn’t have a thick atmosphere, its gravity is about 17 per cent that of Earth’s, and its temperatures swing from a blistering 127°C in the sunlight to a frigid 173°C in the dark.
Once thought to be a dry rock, recent discoveries have shown that the moon has deposits of icy water at its poles. That could come in handy if we are ever to set up a base on the moon – an idea that has taken hold in recent years.
Robotic mining outposts have been suggested by private spaceflight company Moon Express. The firm was founded in order to win the Google Lunar XPRIZE, a competition launched in 2010 to land a privately funded vehicle on the moon. The contest ended without a winner, but it renewed interest in the moon among new spaceflight companies.
Elon Musk, the CEO of SpaceX, says setting up a lunar base may be the first step towards sending astronauts to Mars. That’s because the moon’s lower gravity could make it easier and cheaper to fuel a spacecraft meant for long-distance travel. Whether it’s through government-funded or private spaceflight, with crewed missions or robotic rovers, it seems that we’re likely to keep visiting the moon. Chelsea Whyte
