“How’d the moon get here? Look, you pinheads who attacked me for this, you guys are just desperate. How’d the moon get here? How’d the sun get there? How’d it get there? Can you explain that to me? How come we have that and Mars doesn’t have it?” –Bill O’Reilly
Once upon a time, humans looked at the tides — going out and coming in — and we had no idea what caused them. At high tides, the sea level would rise, and the coast would get swept up by the oceans, while at low tides, the water would recede, leaving tidepools behind.
Low tides and high tides would each happen twice a day. But we started noticing that the highest high tides and the lowest low tides — spring tides — happened during new Moons and full Moons. On the other hands, the most moderate tides, where high tides were relatively low and low tides were relatively high — neap tides — happened during the first and last quarter Moon phases.
It wasn’t long before we put this picture together.
Sure enough, the Moon is the dominant cause of the tides, with the Sun responsible for about 30% of what we get. And thanks to the laws of gravity we understand how the tides work, even in more extreme cases.
But apparently, this isn’t good enough for Bill O’Reilly. After stating that nobody can explain the tides and this proves the existence of God, many people (rightly) threw the Moon in his face.
But instead of retracting his statement, O’Reilly went one step farther into it, and delivered the rant quoted atop, complete with his five great questions. Some people attacked him, others defended him, but no one’s tried to teach him.
Lucky for you, Bill, I am a patient man.
1.) How’d the Moon get here? I’ve tackled this before, but it’s been years. The Giant Impact Hypothesis is the leading theory, as simulations and measurements of the Moon and Earth’s interior both support it.
Basically, in the young Solar System, you’ve got a star with a thin disk of matter orbiting it. Small gravitational instabilities create the first small objects. They then gravitationally attract larger ones, and the more mass you get, the more mass you pull in towards yourself.
Mercury managed to clear its orbit, as did Venus. But out by us, we had two large objects — one roughly Venus-sized, one roughly Mars-sized — and they finally caught up to each other.
The densest elements, of course, were primarily at the center, so when they collided, only the light elements in the crust and mantle should have gotten ejected to form the Moon, while the heaviest elements migrated down to the Earth’s core. And in fact, our observations confirm that this is, in fact, the case.
The Moon is almost completely devoid of iron, the densest abundant element on Earth. And the rocks the Apollo astronauts have brought back from the Moon have, conversely, demonstrated that the rocks on the Moon’s surface — unlike asteroids, meteorites, and Mars’ rocks — are identical in composition to the rocks on Earth’s surface. So that’s why we’re pretty sure the Moon came from the collision of two proto-planets that collided, forming the Earth and the Moon as we know them today.
2.) How’d the sun get there? Well, there’s the entire scientific field of star formation devoted to the study of it, but here’s the basic story. A molecular gas cloud — many of which exist in our galaxy — collapsed under its own gravity, probably triggered by the explosion of a dying, massive star.
And that gave rise to the Sun, along with a proto-planetary disk of gas and dust that collapsed to form the planets, comets, and asteroids, among other things.
3.) How’d it get there? Well, I assume you mean in context with everything else that’s there. Our Sun lives in this place we call “the galaxy.”
A collection of hundreds of billions of stars, our star formed about 4.6 billion years ago out of a combination of pristine hydrogen gas from the Big Bang and recycled material from at least two previous generations of stars. Gravity holds our star in a stable orbit, about 25,000 light years from the center of our galaxy.
4.) Can you explain that to me? Over time, galaxies grow and evolve through gravitational mergers with other galaxies. The Milky Way was likely a much smaller object in the past, that has since cannibalized other galaxies and grown to its present size. In fact, headed into the future, the Milky Way is likely to merge with the Andromeda galaxy, perhaps headed for an intense gravitational interaction like NGC 4676, above.
But Mars has its own interesting story that we’re just figuring out, and this little guy has truly helped uncover it over the last six years.
Now, you may tell me that science doesn’t have all the answers, and you’d be right. After all, I don’t have a good explanation for what caused inflation, which is the thing that sets up the Big Bang. But everything starting from that point or afterwards, we learn, and science is how we do it.
And if you want an alternate take on Bill O’Reilly’s latest, you can always listen to Stephen Colbert’s extremely informed opinion on it.