Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: The Scientist on 23/12/2010 12:47:03

Title: Why does the Earth only have one moon?
Post by: The Scientist on 23/12/2010 12:47:03

Please share your views with us. Thanks all!  [;D]

Title: Why does the Earth only have one moon?
Post by: syhprum on 23/12/2010 15:53:27

The surprising thing is as a rather small planet it should have any at all it is the large planets like Jupiter or Saturn that have moons while Mars (two tiny captured ones) Venus and Mercury are Moonless.
I seems that Earth had a collision with a Mars sized planet early in its life that split off 1.25% of its mass to form its moon but moons are not usually generated in this manner.

Title: Why does the Earth only have one moon?
Post by: CliffordK on 24/12/2010 00:02:49

Quote from: syhprum on 23/12/2010 15:53:27

The surprising thing is as a rather small planet it should have any at all

Yet, Pluto, which is merely a Plutoid (by definition)...  also has a moon.

Actually, Pluto has 1 large moon, and 2 small moons.

Earth does actually have 1 other co-orbital object called Cruithne, as well as a couple of other smaller co-orbital asteroids.

http://en.wikipedia.org/wiki/3753_Cruithnehttp://en.wikipedia.org/wiki/3753_Cruithne

I wonder if there are a few reasons for the single moon around Earth.  First of all, the Moon is relatively large, orbiting a relatively small planet.  This might tend to destabilize the orbits of any other satellites, although then one would have troubles explaining Nix & Hydra around Pluto.  Except, of course, even Pluto itself is smaller than our moon.

Perhaps the impact and secondary accretion hypothesis of the moon would also tend to cause all orbiting material to either form the moon, fall back to earth, or get ejected from orbit, although I'm having troubles envisioning why it didn't form many smaller moonlets like the rings around Saturn.

Title: Why does the Earth only have one moon?
Post by: Geezer on 24/12/2010 04:48:30

It's probably a bit off topic, but is there something about the Moon being an important factor in stabilizing the Earth's orbit, or is my memory playing tricks on me (again)?

Title: Why does the Earth only have one moon?
Post by: syhprum on 24/12/2010 05:32:10

I don't think our moon is important in stabilising the Earths orbit but what is important is that it stabilises the inclination of the Earths axis.
Although the rings of Saturn are a spectacular sight the amount of materiel in them is nowhere near the mass of our moon.

Title: Why does the Earth only have one moon?
Post by: Geezer on 24/12/2010 05:45:14

Quote from: syhprum on 24/12/2010 05:32:10

I don't think our moon is important in stabilising the Earths orbit but what is important is that it stabilises the inclination of the Earths axis.

Thanks! That makes a lot more sense.