# What would happen if a little less than half of the moon crashed into the Atlantic ocean? [duplicate]

Let's say an asteroid hit the moon and broke it in half. One half remains where the moon usually is relative to Earth, and the other half is flung at Earth near the equator, in the Atlantic ocean. Would Earth's tilt be affected in any way or would there be any catastrophic events that could kill a significant amount of people? What would happen?

• At roughly what speed are you thinking this impact would take place? Commented Sep 23, 2018 at 19:04
• the end on life on earth, whether it hits land or ocean is meaningless, there will be no ocean or land afterwards, it is reaching all the way to the mantle and reliquifying the planet. I think you underestimate how big the moon is.
– John
Commented Sep 23, 2018 at 19:06
• There aren’t any asteroids that are both big enough to break the Moon in half and in orbits that mean they could potentially collide with the Moon. Commented Sep 23, 2018 at 19:39
• Physics would not allow one half to remain in place while the other half is thrown out of position. If an impact is big enough to throw one half of the moon into the planet then it will also send the other half flying off into space. Commented Sep 23, 2018 at 21:18
• VTC as a duplicate as stated, but if it weren't it would be closed for the same reason the duplicate was closed: too broad. Moons affect everything from orbital mechanics to oceanography to ecology to time keeping and a bazzillion things in between. SE's Q&A model is one-specific-question/one-best-answer.
– JBH
Commented Sep 23, 2018 at 22:23

The mass of the Moon is $$7.3 \times 10^{22}$$ kg. Half of it would be then $$3.6 \times 10^{22}$$ kg.

That mass would impact Earth at about 11 km/s, releasing an energy of about $$217 \times 10^{28}$$ J, or, in other words, 100 times the energy emitted by the Sun in 1 second.

That would turn the entire Earth into a molten ball of rock, vaporizing all the water in the oceans.

It would be a drastic way to sterilize the planet.

• Of course this should also tell you that wouldn't get an impact on the Moon that would neatly break it in half. You could have an impact big enough to melt the entire Moon and it would still not take it out of orbit or break it apart. (Not in the short term anyway. In the long term, an impact that big would add a significant amount to the overall mass of the moon, which would affect its orbit, and could cause it to spiral into the Earth over the course of a few hundred million years or so) Commented Sep 23, 2018 at 21:33
• In other words, Everyone Dies™. Commented Sep 24, 2018 at 0:06

It Would Kill approximately all of Everything

All life on earth is wiped out completely. The last time something that big hit the earth was about 4.5 billion years ago. When that happened it essentially liquefied the planet into a ball of magma that remained red hot for a few thousand years and ejected enough debris into orbit to form a new moon. Under these conditions not even primitive life like prions could hope to survive. In the face of such a catastrophic impact any secondary effects like altering the earth's orbit or its axis are pretty much a moot point.

• Hey, TCAT, you think anyone would read a book about a destroyed Earth with no life and no action Commented Sep 23, 2018 at 22:03
• @RobertPaul maybe... Could be focused around the remaining humans in the ISS, if they survive the impact in orbit. Commented Sep 23, 2018 at 22:11
• That story already has a pretty predictable ending "and then they all starved to death." Commented Sep 23, 2018 at 22:19
• I don't think prions are considered alive. Commented Sep 23, 2018 at 23:16
• They are organic protein chains that reproduce. Close enough. Commented Sep 23, 2018 at 23:48