What keeps Jupiter spherical?

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Suzi Maggard

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What keeps Jupiter spherical?
« on: 25/02/2010 22:30:02 »
Suzi Maggard  asked the Naked Scientists:
Hello Chris and all! You have the best podcast!

I have a question, "If Jupiter is made up of gas, why is it round and what keeps the gases from just floating away?"


Idaho, USA

What do you think?
« Last Edit: 25/02/2010 22:30:02 by _system »


Offline stereologist

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What keeps Jupiter spherical?
« Reply #1 on: 26/02/2010 05:23:30 »
Gravity. Jupiter is the largest planet in the solar system. It is substantially larger than the earth. Even our atmosphere does not "float away". We do lose some hydrogen from the upper atmosphere. That loss is small.

Anything that escapes from a planet does so when it exceeds the escape velocity. In our atmosphere temperature is a measure of the average energy of a particle. Light particles such as H2 move faster to have the same energy as a heavier particle say O2 or CO2. Not all particles in the air have the energy. Some move faster and some slower. Evaporation of water has some of the water molecules moving fast enough to boil off. The gas giants have a much higher escape velocity than the earth. That is due to their stronger gravitational field. The hydrogen and helium do not reach escape velocity and thus stay on the gas giants.