What if moon hit earth

Yes, in the illustration it looks like they collide—but remember that I made Earth and the moon bigger than they should be so that you could see them. In reality, it would be more of a near miss. The best way to make Earth and the moon crash would be to just completely freeze its orbit, or in physics terms, to decrease the velocity of the moon to zero with respect to Earth. Once the moon stops orbiting, it would just fall right into the planet, because the gravitational force from Earth will pull on it and cause it to increase in speed as it heads toward the planet.

If there are any aliens out there reading this, please don't use this as a blueprint for destroying Earth. Could that really happen? Let's start with the simplest case, where the moon and Earth are stationary and almost touching. It would look like this:. Since that water has mass, it has a gravitational interaction with Earth, pulling the water toward the center of Earth.

But there is also a gravitational force from the moon pulling in the opposite direction. Which force would be larger? We can calculate both using the same universal gravitational force for the orbit of the moon. For the interaction with Earth, we will use the mass of Earth and the mass of the water. I picked 1 kg to make it simpler. The distance r will be from the center of Earth to the surface—that's just the radius of Earth.

For the interaction with the moon, I will use the moon's mass and the radius of the moon plus a little extra since they aren't quite touching.

Of course, I used Python, which is the best calculator. Here is the code in case you want to change anything. That gives the following output:.

You can see that the gravitational force from Earth is much larger than the force from the moon. If this was a "tug-of-water," the planet would win. The ocean wouldn't leave. But what if the Earth-moon system isn't stationary, but in a very close orbit both moving on a circular path around a common center of mass? Our tides on Earth are primarily due to the Moon, with the Sun contributing only a small fraction of the tides we see today.

During full moons and new moons, when the Sun, Earth and Moon are aligned, we have spring tides: the largest differences between high and low tide possible.

When they're at right angles, during a half Moon, we have neap tides: the smallest such differences. Spring tides are twice as large as neap tides, but without our Moon, the tides would always be the same paltry size, and only a quarter as big as today's spring tides.

The obliquity of Earth's axial tilt, currently This is a very small variation compared to, say, Mars. Our axial tilt would be unstable. This is an unfortunate one. Earth spins on its axis, tilted at This is known as our obliquity.

You might not think the Moon has much to do with that, but over tens of thousands of years, that tilt changes: from as little as The Moon is a stabilizing force, as worlds without big moons -- like Mars -- see their axial tilt change by ten times as much over time.

Poles wouldn't always be cold; the equator might not always be warm. Without our Moon to stabilize us, ice ages would preferentially hit different parts of our world every few thousand years.

The Apollo mission trajectories, made possible by the Moon's close proximity to us. Image credit We would no longer have our stepping stone to the rest of the Universe. As far as we can tell, humanity is the only species ever to willfully put ourselves on the surface of another world.

Part of why we were able to do that, from to , is because of how close the Moon is to Earth. At only , km away, a conventional rocket can make the journey in approximately 3 days, and a round-trip signal at the speed of light takes only 2.

The moon also has a tidal effect on Earth's land , Comins said. If the moon were suddenly twice as close to Earth, the effect would be like hitting a gong with a mallet, Comins said: Waves of energy would reverberate through the planet due to the sudden increased strength of the moon's gravitational pull. And that sudden whack of gravity "would actually impact the Earth's crust, which means it might trigger more earthquakes , might trigger more volcanic eruptions," said Jazmin Scarlett, a historical and social volcanologist at the Queen Mary University of London.

Take, for example, Jupiter's moon Io , the most volcanically active world in the solar system, Scarlett said. Io's volcanism results from the push and pull from the gravity of Jupiter and two of its other moons. Earth might see a similar fate if the moon were suddenly half as close.

Along with all the sudden buckling of the planet's crust, Earth's spin would slow over time. This is because, as the moon's gravity pulls the oceans, the resulting friction between the ocean floor and water slows Earth's spin. Today, Earth's rotation is slowing by about one-thousandth of a second per century, Comins said. Let's say that for some reason which science cannot explain at the moment, this starts to happen much sooner than that — like in a few years. This would not be fun for anybody, including nocturnal animals or coral, who would suddenly be confused by the super bright thing up in the sky.

But it'll be even worse for us because of the gravitational exertion of the moon on tides. Simply put, any coastal city — think New York and London — would be swallowed by monstrous tides via Space Answers. This would not be one-time thing either. According to Slate , the miles-high tides would repeat around the world many times a day, destroying absolutely everything and then pushing the debris inland over and over again.

If that doesn't sound bad enough, then there will also be massive earthquakes, volcanic reactions, and an increase in the core temperature of the planet. If the melted magma ended up released into the oceans, we could see the water simply boil away, according to Slate.