As long as there have been humans, we’ve known about the Moon. It captivates us, and it would be hard to imagine our world without it. Indeed, if it were’t for the Moon, the Earth might well be a lifeless ball of rock.
There are moons in our Solar System larger than our Moon. But they orbit monstrous worlds like Jupiter and Saturn and are dwarfed by comparison by the planet they orbit. Our moon is so large, that it would be safe to say it and Earth form a double planet. Our moon is about a quarter the size of the Earth. Only one other world sports a moon nearly as large as the primary world it orbits, and that’s Pluto.
We look at the rest of the so called rocky worlds and none of them have anything like it. Mercury and Venus have no moons and Mars has two tiny rocks orbiting it.
Our Earth-Moon system is unique.
So, where did it come from?
There’s several theories, most of which have been disproved by the rocks brought back by Apollo.
One theory was the Co-created Theory. When the Earth was forming so many billions of years ago, the Moon formed right alongside it. Both worlds are about the same age, and so it seemed only natural. For years, this was the dominate theory.
The other was the Capture Theory. According to this, the Moon formed out of the steller dust cloud as did the rest of our solar system form as a world in its own right. However, it was close enough to Earth and moving at just the right speed for our world to capture it and hang onto it as a satellite.
The rocks say it didn’t happen this way.
Enter the Collision Theory. The early Solar System was a wild place. Planets were on the move, being pulled this way and that by gravity. Worlds like giant Jupiter might have formed closer to the sun and, courtesy of gravity, moved out to outer solar system where we find it now. As it moved, it churned things up, changing the courses of whole worlds.
One such world was “another world.” We know almost nothing about this world since it doesn’t exist anymore. We know it was slightly larger than present day Mars. It careened through the inner solar system like a drunk driver speeding down the interstate. And like the drunk driver, it managed to hit something.
That something was the Earth. This rogue crashed into our planet, and all but destroyed it. The planet was reduced to rubble, but the blow was slow enough that the rubble stayed close together. According to the theory, the Earth, along with the remains of the other world, collapsed into the planet we know today.
But not all of the debris fell back together to form the Earth. Some of it had reached orbital velocity and and became our moon. But there’s more. In studying this incident using computer simulations, almost every simulation ended up with a second, smaller moon forming out of the debris. If this happened, then it explains some odd things about the Moon we know. But more on that later. t the same time as the Earth.
When the Moon formed it was very close to our Earth. It made one orbit in hours instead of days. This nearness was a good thing. At the time, a day on earth was about five to six hours. I wonder what it would have been like to stand on the hellish surface of the world we’d one day call ours and watch the sun visibly move across the sky. Sunrise to sunset would have been a mere three hours or so. To make matters worse, the axis of our planet, the north and south pole if you will, wandered in the course of hundreds of years. During one period, our world might have been spinning along with the poles pointed towards the sun. At another time they’d be pointed north. All of this would happen in a few thousand years. Our Earth wasn’t so much spinning through space, as tumbling.
The Moon started doing two things for the primitive Earth almost right away. Like today, the Moon generates tides. The tides are actually slowing the spin of our Earth. It began to make our days longer. The other thing it did was to stabilize our axis. Instead of this wild, hundred to thousand year movement of the axis of rotation, we have the more serene movement of today. The pole still wanders but it’s slow. That’s why every few thousand years, we end up with a new North Star.
Without the influence of our Moon, it’s doubtful life would have gotten far on Earth. Our world was just too chaotic to allow it.
The moon itself wasn’t unaffected. First, it stopped spinning and is now in what we call “Tidal Lock.” It will forever keep the face we know pointed at us. The other effect was even more strange. Since it was slowing the Earth through tidal forces, that energy in the spin had to go someplace, and the Moon soaked up that energy.
Think of it this way. We have two skaters. One is spinning rapidly on her skates while her partner skates nearby. He or she reaches out and gently touches the spinning skater. Her motion is now transmitted to the skater touching her. The result is the touching skater is pushed away.
Soaking up the spin of our planet caused the Moon to maneuver away from the earth. It continues to move away today, in a few billion year, it will be half, maybe even a quarter of the size in the sky as it is now. We know it’s moving. The laser reflectors left by the Apollo astronauts on the surface of the moon have confirmed the Moon is slowly shifting away from us.
The same smash up scenario has been proposed for how Pluto ended up with its moon Charon.
The moons of the giant planets seem to be a combination of Capture and Co-created.
Our early solar system was a really busy place. If there could be such a thing as time travel, going back in time and watching it all happen would have been endlessly fascinating.
The fact that it all settled down to produce a world like ours, and one we’re fitted to so well, is amazing to me. When we look our across the stars, we see few places as unique and ordered as ours. It was like there’s a blueprint for forming our Earth. I’d love to read it.
I know some believe everything we see was the end result of some incredible coincidence (in short, not the kind of odds I’d go to Vegas on), or even an inevitability in our universe. I just can’t look at it that way. I can’t look across billions of light years of creation, and the wonderful splendor of the worlds in our system, the stars in our galaxy, and the billions of island universes beyond our own, and say it just happened. To me, it’s too incredible to think it’s the end result of some incredible accident. To me, it distracts from the wild beauty and jaw dropping wonder of it all.
When I look out there, I’m looking into the face of the One who drew up the blueprints, and who laid the foundations of the world. Looking out across the void to me, is much an act of worship and lifting my hands in church service. I’m fully appreciating what God did when I behold the skies.
And it humbles me.
That said, let me get off my soap box.
But wait one minute. Remember I said that when the Earth-Moon formed out of the debris cloud generated by the crash, that there might have been a second Moon. What happened to it?
Stay tuned, and I’ll tell you.