Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why is Venus's atmosphere so hot?

  1. Jun 28, 2008 #1
    Is the temperature of Venus's atmosphere due solely (or primarily) to its density? What would happen if the sun's light could be blocked from its surface, would the atmosphere eventually freeze? If so, how long would it take?
  2. jcsd
  3. Jun 28, 2008 #2


    User Avatar
    Homework Helper

  4. Jun 28, 2008 #3


    User Avatar

    Staff: Mentor

    With no atmosphere, the surface temperature of the moon is 107C during the day. Venus is 2/3 the distance from the sun, which means the sun is more than twice as bright.

    No, Venus would not get cold if there was no atmosphere.
  5. Jun 28, 2008 #4
    The atmospheres excessive temperature is primarily due to a runaway greenhouse effect. Any atmosphere can heat up excessively depending on how much infrared radiation is re-emitted after a certain amount of sunlight is initially absorbed. In other words, Venus' atmosphere is an excellent insulator. It is so good at insulating that there almost no temperature variation between night and day, whatsoever. And keep in mind that a day on Venus lasts over 240 'Earth days', so the night time has plenty of time to cool, if it could. That give you and idea of how well it insulates.

    The atmospheric pressure is definitely the other contributor, just not the sole reason it's so hot. If were to somehow block all sunlight from reaching the planet, it would cool eventually, but it would take some time. How long i'm not sure. Venus' atmosphere is CO2 concentrated just like Mars. On the order of 96 or 97%. If were to block all light and allow the planet to cool completely, the pressure still wouldn't be enough to keep the heat very high. The CO2 gas would turn into a liquid (or possibly skip this phase completely and sublimate) and then into solid dry ice which would accumulate on the surface.
  6. Jun 28, 2008 #5
    I'm wondering if we could use the Atmospheric Vortex Engine concept on Venus too, to serve as an atmospheric processor there.

    If a sufficiently powerful vortex could be generated, perhaps it could lower the atmospheric pressure in some small local vicinity. Hot gases from near the surface could be sent far up to get cooled. Perhaps the vortex could be used to send up reflective nanoparticles into the upper atmosphwere, which would reflect more solar radiation than they absorb, to help act as a solar shield.

    Perhaps a powerful convection cycle could be created, that would create some kind of precipitation even (not of water, but of something else -- perhaps some heavier organic liquid?)

    Here's more on the atmosphere of Venus:


  7. Jun 28, 2008 #6
    Crackpot ways of transforming the atmosphere was not one of the OP's original questions.
  8. Jun 28, 2008 #7
    While temperature on the surface is above the melting point of lead, what about temperature below the surface? What happens when you go hundreds of meters below the ground? Does it get cooler down there? Is there any possibility of underground water aquifers existing far below the surface?

    What is the coolest location on Venus, that is either on the surface or below?
    (We already know that upper reaches of the atmosphere are quite cool)
  9. Jun 28, 2008 #8
    This was explained very well by jim mcnamara in a previous thread.

  10. Jun 28, 2008 #9


    User Avatar
    Homework Helper

    Perhaps a read of the Wikipedia article in the link I provided under the sub-heading of "Surface Geology" would prove helpful in answering your questions?
  11. Jun 28, 2008 #10
    Here is a more useful Wikipedia link:


    Well, if it's 50km thick, then that means there could be underground locations which are much colder than the surface. They would still be under high pressure of course, just like underground conditions on Earth. But suppose we find some Earthly underground bacteria of our own, which are capable of existing under high pressure deep inside the Earth's crust? Could we not try and transplant some of these bacteria to locations deep inside the Venusian crust?
  12. Jun 28, 2008 #11
    That's far beyond the scope of this thread and in the realm of science fiction. We haven't even managed to drill deeper than 12km below our own planets surface.
  13. Jun 28, 2008 #12
    I didn't say you want to drill 50 km down, since that's where you'd encounter magma for sure. But what about even just a couple of km down below the surface? Couldn't that be enough to insulate from the planet's surface heat, without necessarily encountering its geothermal heat? The planet is geologically dead, anyway, so there's probably better protection against geothermal heat. Maybe at lower temperatures and higher pressures, you could find liquid water in the same state as at the bottom of Earth's oceans. maybe extremophile anaerobic life might be able to exist in that situation. Just a speculation.

  14. Jun 28, 2008 #13


    User Avatar
    Homework Helper

    Thinking there would be cooler regions beneath the surface looks like science speculation of the worst sort.

    Apparently what he failed to absorb was this passage:
    "Without plate tectonics to dissipate heat from its mantle, Venus instead undergoes a cyclical process in which mantle temperatures rise until they reach a critical level that weakens the crust. Then, over a period of about 100 million years, subduction occurs on an enormous scale, completely recycling the crust."

    Let's see. Its hot at the core. It's hot at the surface. There is periodic melting of the crust and evidence of volcanism over the last 500 million years.

    Next reading assignment The Second Law of Thermodynamics.
  15. Jun 29, 2008 #14
    Venus' crust is older than Earth's, and it's more geologically stable. If that mantle is getting hotter, that just means its pressure is building up, and not that it's conducting its heat all the way up through Venus' crust at every location. If there's going to be some massive upheaval in 100 million years from now, I'm not going to worry about it.
  16. Jun 29, 2008 #15


    User Avatar
    Homework Helper

    "that just means its pressure is building up, and not that it's conducting its heat all the way up through Venus' crust at every location."

    This is your last grasp at hoping there are subsurface pockets that are dramatically cooler? Perhaps you can suggest the mechanism that would leave pockets cooler in the sense that temperatures would be dramatically dissimilar to the surface temperatures surrounding the planet on all sides since the last time the mantle melted and the current crust was developed?

    Your hopes for subsurface water in carbon based life sustaining environments beneath the Venusian surface looks a trifle far fetched.

    Never mind the practicality of touching down on a 460C surface at 92 atmospheres to even begin digging?
  17. Jun 29, 2008 #16
    Does anyone know by how much the greenhouse effect has on the planet? Obviously if it was like earths atmosphere it would be a little hotter due to being closer to the sun. But I would be very interested in how much the greenhouse effect effects the temperature. Lets just say it is partially out of curiosity an partially to try to prove to people who don't believe in the greenhouse effect.
  18. Jun 29, 2008 #17
    Maybe we could try to drop reflective aerosol particles into the upper reaches of the atmosphere, to reduce the planet's energy capture and to cool the entire planet over time.

    I was reading about how lasers can manipulate nanoparticles:


    I'm wondering if one day lasers could be used as conduits for transporting nanoparticles through space. That might afford us an easier way to send nanoparticles to Venus.
  19. Jun 30, 2008 #18
    Someone not believing in the greenhouse effect would be akin to someone not believing in magnetism. The greenhouse effect is simply the name given to what happens when a planets atmosphere absorbs and holds energy... which every atmosphere does, to an extent. The differences lie in how much heat is withheld.

    From the Venus Wikipedia link...

  20. Jun 30, 2008 #19
    Thank you very much. I scanned the article but I guess I missed that.
  21. Jun 30, 2008 #20
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook