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What is Kepler-70b's surface like?

  1. Jul 28, 2014 #1
    The hot side of Kepler-70b is immensely hot. It orbits a star 21.8 times brighter than the sun at a distance of just 0.006 AU. The equilibrium temperature of a blackbody at that distance is about 7770 Kelvins, hotter than the surface of the sun by a substantial margin. The maximum temperature for such a body in the "noon" part of it is 10988 Kelvins.

    The boiling points at 1 Atmosphere of all known forms of matter are substantially lower than either of these numbers.

    And yet, this is classed as a "rocky" planet. Why? Is there something that I'm missing that would allow such a ball of fire to be able to support itself as a ball of rock and not, say, as a ball of lava covered in a multi-thousand-atmosphere glob of metallic vapor?

    For that matter, It has an escape velocity of 8514 m/s. If I remember correctly, anything gaseous over 1/5th that speed will escape within a few thousand to a few million years, and the stellar wind will only accelerate that. This means that any gas less dense than 67g/mol, anything with less than a molecular/atomic weight of 67, will evaporate over a relatively short timescale.

    This means that CO2, for example, would not be stable in the atmosphere. Worse still, I'm not sure it could even hold together at those temperatures.

    So this means that any long-term atmosphere would need to be composed of individual atoms instead of molecules. The lightest individual atom that could be sustained is probably Galium.

    Is there something I'm missing that would allow such a planet to exist without being coated in a thick layer of trace metals as gasses?
  2. jcsd
  3. Jul 28, 2014 #2


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    Kepler-70b is believed to be the rocky core remnant of a gas giant that fell into its star's envelope during its red giant phase. The planet is probably still around in its current form because the star only recently passed through the red giant phase.

  4. Jul 28, 2014 #3
    Yes, but what IS its current form? A ball of rock? A ball of lava? A ball of compressed metallic vapor? Is it likely to have an atmosphere? Is it evaporating? Is it made of plasma?
    Last edited: Jul 28, 2014
  5. Jul 28, 2014 #4


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