Why are some planets rocky and some gassy?

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Offline thedoc

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Why are some planets rocky and some gassy?
« on: 11/06/2014 17:01:52 »
A massive planet twice the size and 17 times the mass of Earth has been announced by scientists at NASA.

Read the whole story on our website by clicking here

  
« Last Edit: 11/06/2014 17:01:52 by _system »

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Offline CliffordK

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Re: Why are some planets rocky and some gassy?
« Reply #1 on: 05/06/2014 19:13:24 »
With an orbit of 0.24 AU, that puts Kepler-10c inside of Mercury's orbit.  Perhaps the close interaction with the host star strips the planet's atmosphere, especially for a  relatively old planet.

However, there are  a number of planets considered "hot jupiters" which are even closer to their stars.

Kepler-10c is relatively small, about 1/20th the mass of Jupiter. 

A planet's temperature would be related to the distance from the sun, and thus the atmospheric density would also be related to the distance from the sun.  The lower atmosphere density would mean the upper atmosphere would be further from the planet, and thus experience less gravity, potentially allowing the lighter elements (hydrogen/helium) to be lost.

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Offline evan_au

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Re: Why are some planets rocky and some gassy?
« Reply #2 on: 08/06/2014 04:50:19 »
Planets this close to their parent star are likely to be tidally locked.
  • This means that one side is searing hot, and gas at this temperature is likely to be rapidly lost to space, or carried away by stellar winds.
  • It also means that the other side is exposed to space, and incredibly cold, and gas at this temperature is likely to be frozen - or at least liquid near the day/night boundary.
  • Heat from the planet's interior, or conducted through the planet from the sunny side would continually boil off gasses from the cold side, where they are heated on the hot side, and lost. This mechanism could degas a gassy world, leaving only a rocky core.