# What would Earth be like without the Moon?

If somehow our moon was destroyed (for example by an asteroid) what would happen to Earth?

Would the Earth be affected by the absence of the moon? Would humans be able to live normal lives without the moon?

• An asteroid big enough to destroy the moon would rain down a lot of debris on the earth. That would be a pretty bad day though the fireworks and seeing the moon blow up would be fun to watch for a little while. A few hours later, however, the sky would be on fire from falling debris. – userLTK Jun 21 '16 at 10:06
• We would be very lucky that the moon shielded us from the initial asteroid impact. The subsequent debris would probably be less bad by a large margin. – gerrit Jun 21 '16 at 10:09
• There is an absolutely outstanding book about this. It is the most recent book (2015) of science-oriented author Neal Stephenson: Seveneves. It has full, total scientific details of the situation included. I can really recommend the book to you without hesitation. It also has one of the best opening sentences of any book :) Enjoy... – Fattie Jun 21 '16 at 12:51

Destroying the moon is not easy. It's pretty big. Has quite a lot of gravity and is sitting in the Earth's gravity well. It gets hit by a lot of asteroids and doesn't get destroyed.

The moon has a binding energy of about $10^{29}$ joules. That is a lot of energy. Even if you got the largest asteroid (ceres) to collide with the moon you would not get close to destroying it.

You would need something like the full power of the sun for about 15 minutes.

If something massive enough to disrupt the moon were to hit it, the energy of that explosion, and the massive amount of moon rocks that would subsequently hit the Earth would probably be enough to melt the surface of the Earth. It would be the end of life on Earth.

There is another way to get rid of the moon. Get a wizard to magic it away. The effect of not having a moon would then be pretty minor in the short term (no tides) and fairly significant in the long term. Human life could continue as normal for a while.

The moon stabilizes the rotational axis of the Earth, without the moon the angle would vary more (over thousands of years) this might mean more extreme ice ages and perhaps ultimately a snowball Earth scenario.

• Raises an interesting related question. Assuming the Giant Impact hypothesis, what if the impact never occurred - "Theia", or whatever, cleanly missed Earth to find its destiny somewhere else, leaving Earth with no exchange of material with the impactor and no hunk of mantle hurled out to condense/coalesce into the Moon as we know it. How that might have affected Earth's geological and biological evolution. – Anthony X Sep 25 '16 at 19:44
• part of the "rare earth" hypothesis is that an unstable rotation would have made life pretty difficult. However until we find some examples of extraterrestrial life, this is mostly speculation. – James K Sep 25 '16 at 21:24
• Apart from the influences of the Moon on Earth's rotation (imparting stability), tides, and so forth, would the chemical composition of Earth's crust be significantly different (taking into account the way material gets recycled through Earth's interior) if the hypothesized Theia collision never happened. – Anthony X Sep 25 '16 at 22:08

Short term: The loss of oceanic tides. Very dark nights.

Long term: Erratic wobble of the earth's axis relative to the sun as it no longer has the moon to keep things stable, massive chaotic weather changes as a result possibly culminating in worldwide mass extinction that may never be recovered from.

• There's some uncertainty on how important the Moon's stabilization actually is. Earth's axis wouldn't wobble all that much. This article suggests 10 degrees, which would be problematic but likely not world-wide mass extinction. astrobio.net/news-exclusive/… – userLTK Jun 21 '16 at 18:44

Adding on to answers how the absence of the moon would affect the Earth's axial tilt (aka 'obliquity'):

If the Moon were to magically vanish, we can speculate that Earth's obliquity would change over time, similar to Mars's in that Mars's obliquity can vary from 14 to as much as 60 degrees.

Mars does have two small satellites, but relative to Mars itself, their masses aren't enough to drastically stabilize Mars. Over time this has affected Mars' seasons and its temperature differences at the poles. If the Moon vanished we can assume that Earth's obliquity would vary in the same way, leading to some wacky seasonal changes. If the Earth were tilted nearly 60 degrees, it's poles would be much more exposed to the Sun possibly leading to the melting of the polar ice caps.