Why Jovian Planests Thicker Atmos. Then Terrestial Planets? ?

Question

I need help with this science question. Give two reasons why the jovian planets have much thicker atmospheres than the terrestrial planets

Answer 1

Temperature and composition

Basically the nebula from which the planets formed would have been 75% hydrogen.

But to retain an atmosphere, the gas around a planet must not achieve escape velocity. Since the terrestrial planets are closer to the sun they have higher temperatures, which means atoms move faster. But how fast the atoms moves depends on their mass. Hydrogen (H2) is very low in mass, so at a given temperature it moves much faster than, say N2 or O2 or CO2 (which are much heavier).

Consequently, the temperature on the terrestrial planets and their escape velocities means that they can;t retain H2 as an atmosphere - but the outer planets are cooler, so they can retain H2, and since H is more abundant than O or C or N - there is more for it to hold into and the atmosphere gets big.

ADDED: I want to comment on the last answer - its not mass - the mass of the solid part of the planet does dictate the escape velocity - but the mass of the solid part of Jupiter is not much bigger than that of Earth - the temperature effect and the abundance are much more important. So the asnwer to hot Jupiters must be that the solid core (made of rock-forming elements) must be bigger - more massive. This would give a higher escape velocity and allow a hooter planet to retain smaller molecules. A larger core forming could be explained by the metallicity (abundance of heavy elements).

Answer 2

They have more gravity to hold on to more gases and more gases were available during formation at that distance from the sun, so, more material to work with. I think that's it.

Answer 3

It has to do with mass and temperature. Jovian planets are much more massive than terrestrial planets and can hold on to a much thicker atmosphere. They also have larger orbits consequently they could attract gather mass from a much greater area then the inner planets. Also, tempters in the outer solar system are much cooler than the inner solar system. Considerably lower levels of solar wind, heat and radiation make it easier for the outer planets to retain their atmosphere.

At least that's the traditional model and it works for our solar system. It's doesn't explain Hot-Jupiters which have incredibly tight orbits around their primary star.