On July 20th, 52 years ago, humanity first set foot on the moon- the culmination of the original cold war era space race and the endless hours of work of countless passionate scientists and engineers from across the world. Although the program didn’t blossom into permanent inhabitation of the moon, it inspired so many people to enter the industry and science as a whole, so that in 2021, we are gearing back up to head there once again!
With Artemis 1 (the first of the next series of NASA missions) set to launch in November, let’s take a look at the legacy of the Apollo missions, and what there is left to learn!
The Lunar Surface
It’s strange to think, but before we visited the moon, we had no idea what its surface was like! Previous missions which landed or impacted on the moon found it to be covered in fine dust, but how deep this layer went was unknown, and one potential problem (suggested by Thomas Gold, who was the first to theorise the existence of the regolith layer) was that the lunar module- being over 10x heavier than most previous landers- would sink into this layer. Luckily, the layer was found to be only 5-15m, and the weight-bearing concern was mostly resolved with the (literal) impact of the Surveyor missions. Despite this, it was still considered a risk until the Apollo 11 lander touched down and astronauts found the surface was solid enough that they needed a hammer to take core samples of it!
They also discovered that the regolith was incredibly sharp. This is because there are very few erosive processes on the moon: on the earth, wind and flowing water slowly makes sediment rounder over time, but the moon has too thin an atmosphere and water only exists in ice, trapped in rocks, or sparse molecules spread over the surface. This poses quite a problem, as its abrasiveness means it wears away at spacesuits, spacecraft and electronics. It can also be an irritant to the lungs and eyes, which isn’t ideal when astronauts will probably undertake quite strenuous and intricate jobs whilst on the surface.
One of the biggest scientific benefits of the Apollo program was the huge volumes of samples they returned to earth, where they could be analysed with much higher tech equipment than could be sent to the moon, either with the astronauts or uncrewed crafts. Apollo 11 itself collected 22kg, but each mission brought back more and more, to a total of 382kg!
Before then, scientists had used spectroscopy (analysing the spectra from light reflected by the moon for absorption lines, which can be attributed to different minerals) to analyse the moon’s composition, but as far as I can tell (I spent like 2 hours trying to research the history of the geological study of the moon to little avail, so please contact me if you know more!), not much was known in detail. The Surveyor and Luna missions revealed a little more, as they analysed what elements made up the lunar surface. From this, scientists were able to interpret that the maria were probably made from basalt. But it wasn’t enough to actually tell us exactly what type of rocks they were, and the composition of the highlands was still unknown.
This is a fairly common problem with space missions, as the best of our equipment is often too large, heavy or fragile to launch- which is why the samples returned by Apollo were crucial!
The first moon rocks recovered were basalts from the lunar maria, and were mostly very similar to rocks on earth, except for being pretty much devoid of water, and were incredibly old- formed from cooling lava ~3.6 billion years ago. Apollo 14 was the first to land on the lunar highlands and found that rocks here were even older, up to 4.3 billion years old! These paler rocks are made of anorthosite, which made up the bulk of the original lunar crust, most of which has survived at the surface since!
The Lunar Story
Studying the moon rocks also allowed scientists to discuss the origins of the moon, not just with unsubstantiated ideas, but real data. John A Wood, a planetary scientist at Harvard, was one of the first to suggest that the anorthosite would have formed from the crystallisation of a global magma ocean- a stage of planetary evolution that is now an accepted phase of formation. From this magma ocean, the heavier minerals (pyroxene and olivine) sank to form the mantle, lighter minerals (such as anorthosite) crystallised at the surface, and a layer enriched with ‘KREEP’ elements remained liquid for a short time, flooding the maria and powering volcanism.
Bringing the samples back to earth also allowed them to be dated through radioisotope methods, which measures the proportion of a radioactive element, to elements it decays into, which can be converted to an age using the half life of the radioactive element. This helped to place a timeline on the moon’s formation, but also helped to age the surfaces of other bodies in the solar system!
This exciting prospect was discovered after the Apollo missions proved that the craters on the moon were in fact impact craters, not from volcanoes. This may seem pretty obvious, but for centuries they were thought to be volcanic in origin- after all, the earth does a pretty good job of wiping away evidence of past impact events through erosion, plate tectonics or being covered by trees/water, so in the past the only known location of craters was atop volcanoes!
But on the moon, craters just build up over time, so the older a surface is, the more craters there are. And if we assume that impact events occur at roughly the same rate everywhere in the solar system, we can cross reference the age of rocks sampled from different areas of the moon with the density of craters there, and say that anywhere with a similar crater density will be roughly the same age!
As well as collecting samples, the astronauts also left many experiments in place on the moon, including the Lunar Ranging Retroreflector- basically just mirrors pointed back at earth, that we can point lasers at from down here on earth to measure the distance more precisely than by just reflecting it off the lunar surface.
They are still in operation today (the only Apollo experiment to still work!) and it’s revealed that the moon is moving away from the earth at 1.5 inches a year- which isn’t a lot when you consider how far away the moon is, but that adds up to 6.5 feet since the experiment began! This adds to our knowledge of the lunar story, as it means it must have been closer to the earth when it formed. It’s moving away due to the transfer of energy, which we see daily as the tides on earth, but over longer periods of time, the energy is transferred from the earth to the moon- causing the earth to slow down (making our day longer) and the moon to speed up (increasing its orbital distance)!
But one mystery that remains is exactly how the moon formed- the predominant theory involves a mars-sized body called Theia which collided with proto-earth, releasing large amounts of material into orbit… but a lot is still unknown!
The Lunar Interior
They also left seismometers, and found that the moon has moonquakes! Like on earth, moonquakes are the result of a release of energy in the form of seismic waves, which travel through the interior in all directions and are refracted, reflected or absorbed at boundaries. This has revealed the moon has a partially differentiated structure, with an iron core at the centre, surrounded by a rocky mantle and crust!
In more recent history:
Since Apollo, we’ve been able to send orbiters back to the moon with ever more modern instruments to take further measurements, as well as continuing the research back here on earth, with telescopes and in labs. The Apollo missions initially concluded the moon was entirely barren of water, as the trace amounts of water found in samples returned to earth were assumed to be contaminated… until re-analysis in 2008 using modern equipment found water contained within volcanic glass beads in the samples. And recent missions such as experiments on the ISRO Chandrayaan-1 spacecraft, and the SOFIA telescope (which is mounted on a plane!) have found more exciting evidence of both water ice hidden in shadowy craters at the poles and molecular water even on the sunlit surface!
Why we’re returning
If we know so much from the samples we have and our remote sensing technology has improved so drastically, why do we even need to go back to the moon?
Well first of all, we can go back to the surface with our modern equipment and get even higher resolution data, and collect samples from more locations- the samples we have are still from incredibly limited areas of the moon, there is so much more wacky science and geology to discover. The moon may look like a boring, monotonous grey world by eye, but just looking down a telescope reveals varied landscapes and so many interesting features. Additionally, our satellites and spacecraft have shown that some of the most intriguing places (such as the polar craters) are ones we haven’t yet visited!
If science alone isn’t enough to convince you, the innovation required to send crewed missions out of our protective atmosphere and magnetosphere will undoubtedly result in new technologies to be used back on earth.
Some cool inventions from the Apollo missions included :
- fire resistant material and cooling systems developed for flight suits used in fire fighters clothing
- More efficient solar panels and air/water purification systems
- Cordless devices (like hoovers, but also items used in the medical field)
- Better earthquake-proof construction (as the structures around the launch site- and the Saturn V itself- had to withstand huge vibrations during take off!)
- Digital and automatic flight controls
- Freeze-dried food
The next decade is going to be so exciting in terms of lunar exploration, I am so grateful to be alive at a time where going to the moon is something not just possible, but probable!
Good luck to everyone part of the Artemis program and those run by other space agencies- ad lunam et ad astra!
- images via NASA or myself unless specified