What Would Happen If the Moon Was Made of Gold?


What would happen if the entire moon was made of gold, would it be very heavy? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.

Answer by Corey Powell, Book author and science editor at Aeon, on Quora:

What would happen if the entire moon was made of gold?

This is a fun thought problem!

As David Goodman noted here, the high density of gold means that the mass of the new Gold Moon would be about 7 times that of our current moon. There are some interesting implications that come with that.

Lunar tourism might not be the draw you’d think.

First, the Gold Moon’s surface gravity would be much higher. If radius stays the same, surface gravity increases linearly with mass. That means the surface gravity of the Gold Moon would be 7 times that of the current moon, or slightly greater than the surface gravity on Earth (about 11 meters/second^2).

Astronauts visiting the moon would now weigh slightly more than they do on Earth. That would be a notable impediment for gold-loving space tourists who wanted to visit the new Gold Moon. Remember the bulky suits and heavy equipment the Apollo astronauts wore? At full Earth gravity, they would have been pretty much immobilized. We’d have to develop radically lighter suits and life-support systems.

The Gold Moon’s escape velocity would also be higher than it is now. If radius stays the same, escape velocity increases as the square root of mass. That would bring it up to a bit over 6 kilometers per second: still quite a bit lower than Earth’s, but enough that landing and taking off would require a lot more energy than what Apollo needed. No humans have landed on the moon in 45 years because it’s so difficult and expensive. Landing on the Gold Moon would be quite a bit more difficult still.

The moon would be very beautiful in the sky.

I take your question to mean that the moon would be replaced by a physically identical Gold Moon, complete with all the same kinds of craters, boulders, and surface dust (just all made of gold). In that case, there would be scattered sparkling reflections all over the moon over the course of the month, as opposed to a single image of the sun bouncing off a polished gold surface.

Nevertheless, gold is overall about 8 times as reflective as the surface of the (current) moon, so the Gold Moon would be about 8 times as bright in the sky. Scattered reflections of the sun would sparkle like diamonds in the sky, creating sharp point shadows. The Gold Moon would be dramatic even in daytime. It really would be lovely.

The tides would be miserable.

This would be the huge downside of the new Gold Moon. If distance stays the same, the strength of the tidal pool increases linearly with mass. That means the tides from the moon would be 7 times as strong as they are now. Currently, the highest tides come at full and new moon, when the pulls of the sun and moon combine to be about 1.5 that of the moon alone. Under the Gold Moon, the highest tides would be 7.5 times that of the old moon alone.

In other words, tides would be 5 times as strong as the strongest ones we have now, and would stay pretty much the same through the whole month.

Every coastal region of Earth would experience strong daily flooding. Life would adapt, of course, but coastal cities and beaches around the world would be devastated. Low-lying islands and countries with extensive coastal floodplains (like Bangladesh) would be in trouble. Lunar tides already correlate weakly with earthquakes and volcanic activity. Increase the strongest tides by a factor of 5, and those effects would surely become more pronounced, too.

Bottom line: the Gold Moon would look great to look at, but the effects here on Earth would not be pretty.

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