What determines the Earth's orbit? What makes the Earth's interior hot?

Hello Jeff,

By Keplers laws, the sum of the mass of the star and the mass of
the planet, together with the separation between the star and
the planet determine the orbit. However, the moon certainly
has some affect on the Earth and is responsible for a precession
in the earth's spin. Other planets also have a small effect.

The gravitational force is certainly responsible for the tremendous
pressures that build up inside the earth, and make the core of
the earth hot.

I have also read that the relative thickness of the earth is
comparable to the relative thickness of the skin of an apple.
Astronomers often quip that the study of astronomy is the study
of everything in the universe with one small exception - earth.
But your question is a good one, and I was curious myself, so
I dug through a geology book in the library and found that the
earth's crust is variable, but of order 10 km. The radius of
the earth is of order 6740 km. So the crust is only 1 part in
674 of the earth's radius. The apple analogy is probably
a reasonable one!

Because teh earth and moon are both spherical, it seems likely
that they formed together in a disk of material around the sun.

Best Wishes,
Debra Fischer

On Thu, 15 Jan 1998, SgtSparkey wrote:

> Does the mass of the earth determin it's orbit, or the sum of the earth and
> moon?
> Also is it the force of gravity that makes the earth's interior hot? What is
> the relative
> thickness of the earth's crust? I read some where that if the earth were an
> apple the
> crust would be as thick as the skin. Is that a correct relation?
> Was the earth and moon formed together , or did the moon seperate from the
> earth to form.
> Thankyou,
> Jeff
>

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