As we all know, the moon landings started 50 years ago this July, and over the course of six subsequent visits, astronauts brought back 842 pounds of lunar rocks, pebbles, and soil.
Believe it or not, that little collection changed our understanding of where we came from.
How? Well, around 4.5 billion years ago, when the solar system was still in its infancy, it was a much more chaotic place. The sun had burst into being, and it was still surrounded by bits of cosmic debris, all smashing into one another and clumping together to form the planets.
Around this time, it is believed, the proto-Earth is thought to have been hit by a Mars sized planet. The resulting cataclysm fused the two worlds together, forming our Earth. (see pic sequence below).
The power of that collision ejected material from both bodies, which eventually accreted together to establish the Earth/Moon system. It goes without saying the early moon was covered in an ocean of magma, which settled and cooled into the form we know today.
Scientists are still debating the details of this hypothesis. However, because the Earth and moon are made out of similar base materials – suggesting they were created from the same source material – and because that material was molten at the time they formed, it seems reasonable to assume this is due to the power of the theorized impact.
Even so, that’s only the beginning of the story.
A huge part of the history of the lunar crust is its craters. And scientists have been able to use the Apollo samples to accurately date those craters.
The moon has changed far less than the Earth, but that doesn’t mean it hasn’t changed at all. Asteroids have hit it over and over again, leading to the pockmarked surface we can see in the night sky. Those craters tell the story of what happened in the solar system after the Earth and the moon were formed.
By age-dating the moon’s craters, we can age-date craters elsewhere. The bigger the craters, the longer ago they were made – basically, because bigger chunks of debris were much more common further back in time – meaning we have an accurate impact history of the solar system right on our doorstep.
And it doesn’t stop there.
Learning how old the moon’s craters are led to another stunning hypothesis: that the outermost planets — Jupiter, Saturn, Uranus, Neptune — have changed their orbits over their lifetimes.
The craters show that around 600 million years after the planets formed, there was a second period of heavy bombardment, meaning that the moon got pounded by a lot of asteroids. This was odd, as the frantic pace of asteroid collisions were thought to have settled down by then.
So what explains the additional pummeling during this time?
Although scientists aren’t sure, one possible idea is that those big gas giant planets moved closer to the sun to begin with and then spun farther away, disturbing the “settled” field we see around us today.
The White House is currently pushing NASA to send humans to the moon again by 2024. For now, the plan is for those astronauts to visit the lunar south pole at a crater called the South Pole–Aitken Basin — one of the biggest, deepest, and therefore oldest of the moon’s craters. It’s possible the impact that created the basin was so powerful that it exposed the mantle, or interior, of the moon.
Take a look at the color picture of the size of the basis to get an idea why scientists are so excited. It’s over 1,300 miles across. And, because we can’t directly study the Earth’s mantle in the way scientists would like, this is the next best thing. After all, it’s thought to have originated from the same base material at the same time. Even better, it should help us understand why the Earth has such active geology while the moon doesn’t.
And that knowledge could have a lot of practical implications. For instance, in the future, if humans want to start mining asteroids for metals and minerals, it will be enormously helpful to know the exact geologic makeup of a particular asteroid before we arrive. Practicing on the Moon first will help us refine the skills we need to get it right when we’re further from home.
Yes, there are a lot of reasons for us to return to the moon and establish a more permanent presence there. The moon would be an excellent crucible laboratory to teach astronauts how to better survive long, lonely missions in deep space; it would serve as a launching ground for missions to Mars, or beyond; and it could even serve as a new source for the mining of natural resources as we run ever shorter here.
We’ve got a lot to look forward to. . . I just wonder what the next 50 years will bring?