Why is Venus's atmosphere so hot?

[Unbeliever]

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?

 

[LowlyPion]

This wikipedia entry is a good start:

http://en.wikipedia.org/wiki/Venus

 

[russ_watters]

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.

 

[B. Elliott]

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?

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.

 

[sanman]

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:

http://en.wikipedia.org/wiki/Atmosphere_of_Venus

Unlike Earth, Venus lacks a magnetic field. Its ionosphere separates the atmosphere from outer space and the solar wind. This ionized layer excludes the solar magnetic field, giving Venus a distinct magnetic environment. This is considered Venus' induced magnetosphere.

The atmosphere of Venus is composed mainly of carbon dioxide, along with a small amount of nitrogen and other trace elements. The amount of nitrogen in the atmosphere is relatively small compared to the amount of carbon dioxide, but as the atmosphere is so much thicker than that on Earth, its total nitrogen content is roughly four times higher than Earth's, even though on Earth nitrogen makes up about 78% of the atmosphere.

 

[B. Elliott]

Crackpot ways of transforming the atmosphere was not one of the OP's original questions.

 

[sanman]

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)

 

[B. Elliott]

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)

This was explained very well by jim mcnamara in a previous thread.

When I had a soils courses eons ago, the idea about temperature was this: the temperature near the surface (say less than 10') will change with the seasons. As you go down it begins to approximate the yearly average temperature above ground.

The average surface temperature of Venus is 461C. So at 20' down, if there are soils present, then that's the temperature there. Much hotter than your kitchen oven.

https://www.physicsforums.com/showthread.php?t=205432

 

[LowlyPion]

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)

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?

 

[sanman]

Here is a more useful Wikipedia link:

http://en.wikipedia.org/wiki/Geology_of_Venus

Venus's crust appears to be 50 kilometres (31 mi) in thickness, and it is composed of silicious rocks. Venus's mantle is approximately 3,000 kilometres (1860 mi) thick, but its composition is unknown. Since Venus is a terrestrial planet, it is presumed to have a core made of semisolid iron and nickel with a radius of approximately 3,000 kilometres (1860 mi).

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?

 

[B. Elliott]

Here is a more useful Wikipedia link:

http://en.wikipedia.org/wiki/Geology_of_Venus
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?

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.

 

[sanman]

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.

http://www.popsci.com/environment/article/2008-05/deepest-dwelling-life-forms-found

 

[LowlyPion]

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.

 

[sanman]

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.

 

[LowlyPion]

"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?

 

[bassplayer142]

Does anyone know by how much the greenhouse effect has on the planet? Obviously if it was like Earth's 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. Let's just say it is partially out of curiosity an partially to try to prove to people who don't believe in the greenhouse effect.

 

[sanman]

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:

http://focus.aps.org/story/v21/st21

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.

 

[B. Elliott]

Does anyone know by how much the greenhouse effect has on the planet? Obviously if it was like Earth's 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. Let's just say it is partially out of curiosity an partially to try to prove to people who don't believe in the greenhouse effect.

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...

The enormously CO2-rich atmosphere, along with thick clouds of sulfur dioxide, generates the strongest greenhouse effect in the solar system, creating surface temperatures of over 460 °C.[18] This makes Venus's surface much hotter than Mercury's which has a minimum surface temperature of -220 °C and maximum surface temperature of 420 °C, even though Venus is nearly twice Mercury's distance from the Sun and receives only 25% of Mercury's solar irradiance.

 

[bassplayer142]

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...

Thank you very much. I scanned the article but I guess I missed that.

 

[sanman]

Anyway, has anybody seen these pictures from the surface of Venus?

http://wanderingspace.net/2006/11/the-surface-of-venus-revealed/

Pretty cool, if I may say. This is the first time I've seen them.
They were taken from one of the Soviet-launched Venera missions to Mars during the 70s.

 

[LowlyPion]

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.

You might better push a bowling ball from a mile away with a single strand of wet angel hair pasta as sharpshooting a stream of nanoparticles with a laser beam across the vast expanse of solar winds with the intent to inject them in the Venusian stratosphere.

As a side note just how long might you think it would take such particles to make this fantasy trip you envision anyway? Surely you weren't thinking the speed of light as their cruising speed.

 

[B. Elliott]

Thank you very much. I scanned the article but I guess I missed that.

Your welcome. The basic concept is very simple, but naturally as you start to investigate individual contributing factors, it get's complicated.

Since I didn't, Here's a good general site that touches on a few of the specifics...

http://www.ucar.edu/learn/1_3_1.htm

 

[chazzone]

The "greenhouse effect" is a misnomer. A greenhouse works because there is an actual physical barrier to trap warm air. This does not occur in an atmosphere. While water vapor can hold on to some heat for a very short time, it is quickly radiated away from the planet. In fact recent data has shown that heat is escaping Earth at a much faster rate than had been imagined/calculated. CO2, especially in the incredibly small amounts that are contained in Earth's atmosphere, has virtually no impact on our planet's ability to slow heat loss.

 

[Drakkith]

The "greenhouse effect" is a misnomer. A greenhouse works because there is an actual physical barrier to trap warm air. This does not occur in an atmosphere. While water vapor can hold on to some heat for a very short time, it is quickly radiated away from the planet. In fact recent data has shown that heat is escaping Earth at a much faster rate than had been imagined/calculated. CO2, especially in the incredibly small amounts that are contained in Earth's atmosphere, has virtually no impact on our planet's ability to slow heat loss.

You're going to need to provide a reliable reference, as that goes against everything I've ever heard of in regards to the greenhouse effect for Earth and Venus.

 

[chazzone]

You're going to need to provide a reliable reference, as that goes against everything I've ever heard of in regards to the greenhouse effect for Earth and Venus.

I suppose rational thought and basic thermodynamics is too much to ask?

Science is not based on consensus, and no matter how many people get it wrong, it will never be right. There are plenty of people out there who have apparently never really considered what is actually happening here, but if there is something specific that you don't understand, I'll be happy to assist.

 

[Jamie Kern]

I suppose rational thought and basic thermodynamics is too much to ask?

Science is not based on consensus, and no matter how many people get it wrong, it will never be right. There are plenty of people out there who have apparently never really considered what is actually happening here, but if there is something specific that you don't understand, I'll be happy to assist.

When light is absorbed by a particle, it may be re-emitted in any direction. That is the essence of the greenhouse effect: a balance between how much light gets from space to the surface, is then absorbed by the surface and re-emitted as infrared light, and then absorbed and re-emitted by particles in the atmosphere. Individual molecules of CO2 and H2O do not hold on to the heat long at all. But they re-emit a percentage of it back down toward the planet instead of out to space, which results in a higher average temperature than there would be without any greenhouse gas. This is a relatively simple concept. This is why temperatures on Earth do not drop to 100 K at night.

The more particles present in the atmosphere that can absorb and re-emit infrared light, the more times an infrared photon will be absorbed and re-emitted before escaping to space. It just slows the cooling process down.

Conceptually, this is similar to the "random walk" of photons in the radiation zone of the Sun, which is supposed to cause light to take hundreds of thousands of years to escape the Sun's innards. If that layer were less dense, or contained fewer particles capable of absorbing those photons (somehow!), the process would not take as long, and the Sun's interior would release energy faster - therefore cooling it faster as well. (And yes, I realize this would effect energy production as well - just trying to draw a parallel with the concept, not start a discussion on fusion rates vs. inward pressure in the Sun).

 

[6.28318531]

I think maybe you are confused ;

quoting wikipedia

The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere. As a result, the average surface temperature is higher than it would be if direct heating by solar radiation were the only warming mechanism

If we didn't have the "greenhouse effect" It would be nice and cold,

 

[chazzone]

I think maybe you are confused ;

quoting wikipedia


If we didn't have the "greenhouse effect" It would be nice and cold,

The problem is that, as usual, wikipedia isn't really accurate. There is zero direct heating of the Earth from the Sun.

That's ZERO, nadda, zilch.

100% of the heat on the Earth comes from shortwave radiation, also known as visible and UV light, being absorbed by matter on the surface.

The atmospheric gases ad virtually no heating as they allow light to pass through unimpeded.

Water vapor pretty much holds on to the IR/longwave radiation/heat for a very short time, and the photons that release it are bounced back into space in nanoseconds. In fact, a photon leaving Earth is more than 3/4's of its way to the Moon in just one second.

But hey, don't take my word for it. You can easily check out the temperature of space just outside our atmosphere. It's a balmy 14 dregrees Kelvin. Not much heat out there, huh?

Too many people sleeping through science class, and not challenging their profs when they say something ridiculous.

 

[Jamie Kern]

Too many people sleeping through science class, and not challenging their profs when they say something ridiculous.

Or not listening to their professors when they have already explained the part you think is missing.

The Sun's light, much of which does indeed penetrate the Earth's atmosphere without being absorbed, strikes the Earth's surface itself. Some of it is absorbed and re-emitted as infrared light, which we feel as heat. It then travels from the surface of the Earth upward, encountering various greenhouse particles as it goes.

See my previous post, a few above this, for the more complete explanation. I would feel silly quoting my own post for you.

 

[Drakkith]

100% of the heat on the Earth comes from shortwave radiation, also known as visible and UV light, being absorbed by matter on the surface.

I'm sorry this is incorrect. In reality much of the entire solar spectrum makes it to Earth's surface. There are bands where nearly 100% of the incoming radiation is absorbed, but much of it makes it through. See below:

The atmospheric gases ad virtually no heating as they allow light to pass through unimpeded.

From wikipedia on infrared: The Earth's surface and the clouds absorb visible and invisible radiation from the sun and re-emit much of the energy as infrared back to the atmosphere. Certain substances in the atmosphere, chiefly cloud droplets and water vapor, but also carbon dioxide, methane, nitrous oxide, sulfur hexafluoride, and chlorofluorocarbons,[31] absorb this infrared, and re-radiate it in all directions including back to Earth. Thus the greenhouse effect keeps the atmosphere and surface much warmer than if the infrared absorbers were absent from the atmosphere.

As it states, much of the energy absorbed by the Earth and it's atmosphere, whether it is from long or short wavelengths, is emitted back out as infrared radiation. So pretty much all of that big chunk of radiation in the 350-900 nm range that isn't reflected back out into space is absorbed and emitted as infrared. Since certain molecules absorb infrared they act just like a blanket does and the result is an increase in the temperature of the Earth.

As you can see on this graph, the amount of infrared that is actually released into space is only about 15-30% depending on the season. In the "Total Absorption and Scattering" part, the gray areas are what is NOT transmitted.

The curved lines in the top picture are the total blackbody radiation for the appropriate temperatures that are labeled for both the Sun and the Earth. They are approximately the spectrum that each body emits. The red is the solar spectrum reaching us, while the blue is Earth's outgoing thermal spectrum.

Water vapor pretty much holds on to the IR/longwave radiation/heat for a very short time, and the photons that release it are bounced back into space in nanoseconds. In fact, a photon leaving Earth is more than 3/4's of its way to the Moon in just one second.

Except for all that radiation that gets released and almost immediately gets absorbed by those same greenhouse gases.

 

[Drakkith]

Let's take this to an extreme and assume that ALL radiation below the visible part of the spectrum is unable to penetrate the atmosphere. So that radiation is now absorbed by the atmosphere, heating it up just like normal while the visible light makes it through. When the atmosphere and surface emit radiation back out it just gets reabsorbed again! (One key thing is to remember that gases can transmit heat directly by contact, so they don't need to release radiation to heat up their surroundings) Only near the very top of the atmosphere where the air is very very thin can any infrared radiation make it back out, resulting in about 95% of the outgoing radiation simply being absorbed again.

The result of all this is that the atmosphere and the surface just keep heating up until the temperature is high enough to make its black body spectrum emit enough energy in the visible range (since that is the only part that can make it out) to equal the incoming energy from the Sun. That's about...2,000 k?

 

[chazzone]

Or not listening to their professors when they have already explained the part you think is missing.

The Sun's light, much of which does indeed penetrate the Earth's atmosphere without being absorbed, strikes the Earth's surface itself. Some of it is absorbed and re-emitted as infrared light, which we feel as heat. It then travels from the surface of the Earth upward, encountering various greenhouse particles as it goes.

See my previous post, a few above this, for the more complete explanation. I would feel silly quoting my own post for you.

I read your post, and I completely understand the process.

 

[chazzone]

Let's take this to an extreme and assume that ALL radiation below the visible part of the spectrum is unable to penetrate the atmosphere. So that radiation is now absorbed by the atmosphere, heating it up just like normal while the visible light makes it through. When the atmosphere and surface emit radiation back out it just gets reabsorbed again! (One key thing is to remember that gases can transmit heat directly by contact, so they don't need to release radiation to heat up their surroundings) Only near the very top of the atmosphere where the air is very very thin can any infrared radiation make it back out, resulting in about 95% of the outgoing radiation simply being absorbed again.

The result of all this is that the atmosphere and the surface just keep heating up until the temperature is high enough to make its black body spectrum emit enough energy in the visible range (since that is the only part that can make it out) to equal the incoming energy from the Sun. That's about...2,000 k?

I'm not sure of why you are using an example that doesn't exist in reality.

100% of all IR is eventually re-radiated back into space, and most of it within a very short time frame.

The IR from one molecule does not just bounce around and heat up another, since it is always re-emitted at a lower energy/longer wavelenght, and gasses only resonate in a very narrow frequency band.
This is why the idea of CO2 as a major greenhouse gas on Earth, is so ridiculous. Water already covers the same wavelength as CO2, and is a thousand time more prevalent in Earth's atmosphere. So, it relegates CO2 to an irrellevant status. It's like heating a BB to red hot, and throwing it into an olympic sized swimming pool. The effect is so negligible as to be nonexistant.

I'm willing to accept that it has a greater role to play on Venus, but Venus' albedo is .9 (where Earth's is between .3 and .36. There simply isn't enough light getting to Venus' surface to create the kind of heat observed.

 

[Drakkith]

I'm not sure of why you are using an example that doesn't exist in reality.

The same reason we simplify things in basic physics to perfect machines and frictionless surfaces, to help people understand the basics.

100% of all IR is eventually re-radiated back into space, and most of it within a very short time frame.

Eventually sure, not within a very short time frame though.

The IR from one molecule does not just bounce around and heat up another, since it is always re-emitted at a lower energy/longer wavelenght, and gasses only resonate in a very narrow frequency band.

You are forgetting that gases bounce around and transfer energy and are able to emit thermal radiation in a broad band because of this.

This is why the idea of CO2 as a major greenhouse gas on Earth, is so ridiculous. Water already covers the same wavelength as CO2, and is a thousand time more prevalent in Earth's atmosphere. So, it relegates CO2 to an irrellevant status. It's like heating a BB to red hot, and throwing it into an olympic sized swimming pool. The effect is so negligible as to be nonexistant.

You must be looking at a different chart than I am. CO2 absorbs wavelengths from 15-20 μm at nearly 100%. Water vapor fall off in the 15-18 μm range. In addition it absorbs wavelengths of 4-5 μm where water vapor absorbs almost none of that.

I'm willing to accept that it has a greater role to play on Venus, but Venus' albedo is .9 (where Earth's is between .3 and .36. There simply isn't enough light getting to Venus' surface to create the kind of heat observed.

The greenhouse effect on Venus is substantially stronger than here on Earth and Venus receives double the irradiance that Earth does. That's how it is able to accumulate so much heat even though it's albedo is so high. Note that Venus relies strongly on the sulfur dioxide, water vapor, and sulfuric acid in it's clouds for it's greenhouse effect. (Ref: http://www.imcce.fr/vt2004/en/fiches/fiche_n13_eng.html )

 

[D H]

Locked pending moderation.