Re: Earth at Jupiter's Distance (pls see below for the entire question)

Hydrogen and Helium are LIGHT elements.
They travel at higher velocities than other larger atoms
or molecules.
What gasses a planet can hold is related to its mass,
which in turn dictates its escape velocity 
(e.g. Vesc = SQRT[2GM/R]) for any Mass and Radius.

At the distance of Jupiter and beyond, the types of substances
which could exist as solid material were far greater than
closer to the hot primordial sun.  Therefore, the Jupiter-like
planets were able to grow faster and larger and have large enough
escape velocities to hold onto hydrogen and helium.

If Earth would have been at the distance of Jupiter, it too
would have accumulated from the rocks AND ices that were solids
in the outer solar system and would not be "earth" but would
be another "jupiter".  Simply placing the Earth out there now
would not allow it to hold more hydrogen because of its mass and size.
 http://pls.atu.edu/physci/physics/people/psjr/courses/PHSC3053/SolarSystem/