Why does earth have only one moon??

Question

Why does earth have only one moon??

Answer 1

Current accepted theory is that our moon formed by the collision of the still-forming Earth with a large planetesimal.  The debris of that impact went into orbit and eventually coalesced into the moon.

The Earth is relatively small - it doesn't have enough gravity to capture asteroids as moons the way Jupiter and the other gas giants have done.

Mars' 2 moons are captured asteroids, but Mars is much closer to the asteroid belt than Earth so the possibility of Mars capturing moons is greater than for Earth.

The inner solar system is relatively empty of moon-sized objects.  Most either became part of the forming planets or their orbits were perturbed by Venus and Earth so that these small objects ended up in the asteroid belt or further out to be captured by one of the gas giants.

Answer 2

One word.....chance. Everything is a chance. We could of had no moon, or 2, or 3...It is all chance.

Answer 3

THERE USED TO BE 3 MOONS AROUND EARTH.

ONE FELL INTO THE OCEAN, AND THE OTHER WAS TAKEN BY ALIENS BECAUSE IT WAS A GOOD SOURCE OF CHEESE

Answer 4

Go with LINDAJUNE's answer. She da "man"!

Answer 5

The moon doesn't "belong" to earth, there is only one moon (that we know of so far) which is in the same solar system as earth.

Answer 6

There is an explanation how we got our moon.  That it was in orbit somewhere else, and it changed it's orbit twice, finally being captured by the Earth.  You should note that cataclycsms have happened in our solar system.  Look at the asteroid belt - it could be the remains of a planet (it even has a name - Malona).

You can see it is not natural to us (not torn from the Earth at some early stage, etc etc) because Mercury and Venus have no Moon.  And note how large our Moon is - and compare that to the Moons of Jupiter and Saturn  - noting how massive they are.

Here are more details...

http://plain2.tripod.com/251stContactNot...

Answer 7

bcuz it does. earth is close enough to teh sun that any moon orbits would be heavily influenced by teh sun. lindajune  is right.

Answer 8

The Earth has only one moon because moons are made of craters and other materials and we only have one moon.

Answer 9

Ok the only reason for earth only having one moon is that that is the only object that is caught in earth's gravity. And for the people who said that earth is too small, i have news for you Mars has two satellites (for you who don't know thats what an object that orbits a planet is called) and Mars is the size of the Earth's core.

Answer 10

Because that's the way God made it

Answer 11

It is in fact surprising that we do have one, that it is so large and that it orbits outside our zone of gravitational domination.

Do the force calculation:

F_e = G*Mm*Me/(De)^2

F_s = G*Mm*Ms/(Ds)^2

where

F_e is the gravitational force between Earth and Moon

F_s is the gravitational force between Sun and Moon

G is the gravitational constant (so that units come out right)

Mm is the mass of the Moon

Me is the mass of Earth

Ms is the mass of the Sun (332946 times the mass of Earth)

(De) is the average distance from Moon to Earth

(DS) is the average distance from Moon to Sun ((390.22 times further than Earth)

Is the force from Earth greater than the force from the Sun?

If yes, then the fraction F_e / F_s will be greater than 1:

F_e/F_s = [G*Mm*Me/(De)^2] / [G*Mm*Ms/(Ds)^2]

G and Mm cancel out, leaving:

= (Me/Ms)*[(Ds)/(De)]^2 = (1/332946)*(390.22/1)^2 = 152270/332936 = 0.46

clearly less than 1.

The Moon could not have formed as a satellite of Earth where it is now.

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If you do this calculation for the other planets, it is easy to see why Mercury and Venus have no satellites (too close to the Sun), why Jupiter and Saturn have the most, and why even puny Pluto (one sixth the mass of our Moon) can still hold on to 4 (so far from the Sun).

By this determination, Earth could have zero or one, and it should be a small one.

The surprise is not that we have only one, but that it should be so big and so far from us.