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Space Forum / Astronomy / August 2008Goldilocks Zone vs. Goldilocks Planet?
Several decades ago, astronomers used to talk about the "Goldilocks Zone" around a star that is exactly the right distance from its star to allow life to exist. It was generally considered to be just outside of the orbit of Venus, and inside of the orbit of Mars. Of course, this was all based on observations of just one solar system, our own. Now that all kinds of unforeseen weird configurations of planets are being discovered in various external star systems, they're not too sure about this anymore. I'm wondering if the ability to bear life isn't actually more due to the planet itself rather than its proximity to its star? What I'm talking about is a planet that is able to regulate its own surface temperature due to its own internal processes, and be able to do it over a wide range of distances from its star. For example, Earth is large enough to retain most of its atmosphere, which gives it an advantage over Mars, which wasn't. Venus was also large enough to retain its atmosphere, but it doesn't have a magnetic field which protects its atmosphere from most radiation damage, therefore you have a runaway greenhouse effect. Earth's magnetic field protects not only the lifeforms on its surface, but also its own atmosphere's gases from damage from external radiation, therefore you don't have runaway greenhouse effects. The lifeforms on the surface also play a part in making sure the greenhouse gases don't go out of control, such as carbon dioxide. Life couldn't develop on Venus due to a lack of magnetic protection, therefore its greenhouse gases went unchecked. Also Earth has active tectonic plates which produce volcanos which produce greenhouse gases to regulate the atmosphere. Mars seems to have nothing but extinct volcanos, while Venus may have active volcanos, but no regulation of the gases is possible. So what I'm postulating here is that Earth would've been successful as a life-bearing planet even if it were as close to the Sun as Venus, or as far away from the Sun as Mars. If it were as close as Venus, then Earth would've produced more lifeforms that siphoned off the carbon dioxide reducing the amount of greenhouse effect. If it were as far away as Mars, then its life would've left more of the carbon dioxide intact. Life would've evolved slightly differently in each position, favouring the removal of greenhouse gases to greater or lesser extent, but life would've evolved no matter what. A self-regulating Goldilocks Planet. I'm sure there are limits to this self-regulating ability, for example, will it work just as well if it were as close as Mercury, or as far as Jupiter? Anybody think this is full of sh.t? Yousuf Khan > Several decades ago, astronomers used to talk about the "Goldilocks > Zone" around a star that is exactly the right distance from its star to > allow life to exist. I've never heard that term, though the meaning is clear enough. "Habitable zone" was and is common. > I'm wondering if the ability to bear life isn't actually more due to the > planet itself rather than its proximity to its star? See "Gaia hypothesis." It's controversial at best, though certainly life can have global effects on a planet. > Venus was also large enough to retain its atmosphere, but it doesn't > have a magnetic field which protects its atmosphere from most radiation > damage, therefore you have a runaway greenhouse effect. I don't see how the magnetic field has anything to do with retaining an atmosphere. All the magnetic field does is deflect some charged particles. Why does that help retain the atmosphere? If you want liquid water, the planet has to be in a limited range of distances from its star. Of course planetary composition can also have an effect. A planet made of, say, pure iron wouldn't be very hospitable.  SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) > See "Gaia hypothesis." It's controversial at best, though certainly > life can have global effects on a planet. Thanks I am looking it up now. > > Venus was also large enough to retain its atmosphere, but it doesn't > > have a magnetic field which protects its atmosphere from most radiation [quoted text clipped - 3 lines] > an atmosphere. All the magnetic field does is deflect some charged > particles. Why does that help retain the atmosphere? I wasn't saying it helps retain the atmosphere (the gravity takes care of that), I was saying that it protects the atmosphere from some forms of radiation damage. For example, cosmic rays are supposed to hit the atmosphere and create clouds. Clouds create a greenhouse effect, and too many clouds create a runaway greenhouse. A magnetic shield would deflect some of the cosmic rays, and other dangerous particles. So you need both gravity (to hold the atmosphere in), and a magnetic field (to protect against radiation). Mars has neither, so it's a dead world. Venus has gravity, but no magnetic field, so it's also a dead world. Also since I wrote the initial hypothesis, I also realized that perhaps part of the Goldilocks potential is also derived from having a substantial moon in orbit around the planet which stabilizes the rotation rate of that planet. And a hot molten core of the planet would be responsible for releasing some additional heat into this atmosphere over time, through volcanos. > If you want liquid water, the planet has to be in a limited range of > distances from its star. Of course planetary composition can also > have an effect. A planet made of, say, pure iron wouldn't be very > hospitable. Actually, I'm saying that the planet itself might be responsible for creating some of the conditions necessary for liquid water. The water might enter the planet as icy comets, but the hot molten nature of a young planet would quickly melt and/or vaporize that ice, even at substantial distances away from the Sun. As long as the planet remains volcanically active the lower atmosphere can remain warm. The rest of the heat will be stored up solar energy from the Sun, through greenhouse effects. So let's say the Earth were further away from the Sun than it is now. Let's say it was at the same distance as Jupiter is now, could it keep itself warm enough through its own volcanism and with additional greenhouse blanket to become nearly as warm as it is at its present location? I'm not saying that Earth needs to be a moon of Jupiter, but just to replace Jupiter in its current orbit. Actually, come to think of it, the Earth could be a moon of Jupiter and this might still work out. Perhaps Jupiter's distance is too extreme, but what if Earth were as far away as Mars or the asteroid belt distances? Would something within the Earth change enough to allow it to retain more solar warmth, even at those greater distances? And life itself would be somewhat responsible for creating this additional warmth retention. Yousuf Khan SW> I don't see how the magnetic field has anything to do with retaining SW> an atmosphere. All the magnetic field does is deflect some charged SW> particles. Why does that help retain the atmosphere? > I wasn't saying it helps retain the atmosphere (the gravity takes care > of that), I was saying that it protects the atmosphere from some forms > of radiation damage. But why would "radiation damage" cause the atmosphere to be lost? > For example, cosmic rays are supposed to hit the > atmosphere and create clouds. Clouds create a greenhouse effect, and > too many clouds create a runaway greenhouse. I think the effect of clouds is to _cool_ the surface by reflecting sunlight. In any case, I doubt cosmic ray irradiation makes any significant difference in cloud cover. > Also since I wrote the initial hypothesis, I also realized that > perhaps part of the Goldilocks potential is also derived from having a > substantial moon in orbit around the planet which stabilizes the > rotation rate of that planet. A moon causes rotation rate to slow down. What it _may_ do, though, is stabilize the "obliquity of the ecliptic," i.e., the planet's tilt with respect to its orbit. People have suggested this is important for life, or at least intelligent life, but I don't see why. > Actually, I'm saying that the planet itself might be responsible for > creating some of the conditions necessary for liquid water. The water > might enter the planet as icy comets, but the hot molten nature of a > young planet would quickly melt and/or vaporize that ice, even at > substantial distances away from the Sun. As long as the planet remains > volcanically active the lower atmosphere can remain warm. This mechanism could presumably extend the habitable zone outwards of where it otherwise would end. I doubt the extension would be very far. > So let's say the Earth were further away from the Sun than it is now. > Let's say it was at the same distance as Jupiter is now, could it keep > itself warm enough through its own volcanism and with additional > greenhouse blanket to become nearly as warm as it is at its present > location? Only with a _huge_ greenhouse blanket. It might be interesting to calculate what temperature Venus would have at this distance. I'm guessing it would get cold enough to freeze out the atmosphere, but maybe you could set things up with enough volcanic heating to avoid that. An example you might want to look at is Titan, though it's farther from the Sun than your idea. Enceladus is another one to check. Both are, of course, far less massive than Earth. > Perhaps Jupiter's distance is too extreme, but what if Earth were as > far away as Mars or the asteroid belt distances? Would something > within the Earth change enough to allow it to retain more solar > warmth, Offhand I don't see anything that would change "automatically." That's not to say one couldn't imagine an atmospheric composition different from Earth's that would have liquid water. After all, there's probably liquid water in Jupiter's atmosphere if you go far enough down. SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) >> I wasn't saying it helps retain the atmosphere (the gravity takes care >> of that), I was saying that it protects the atmosphere from some forms >> of radiation damage. > > But why would "radiation damage" cause the atmosphere to be lost? I wasn't saying that. I was just saying that radiation damage would create properties in the atmosphere that would not be conducive to maintaining life-bearing temperatures. That is it may create properties in the atmosphere that either lead to too much greenhouse effect, or not enough. >> For example, cosmic rays are supposed to hit the >> atmosphere and create clouds. Clouds create a greenhouse effect, and [quoted text clipped - 3 lines] > sunlight. In any case, I doubt cosmic ray irradiation makes any > significant difference in cloud cover. Clouds make the surface warmer in winter in cold climates. >> Also since I wrote the initial hypothesis, I also realized that >> perhaps part of the Goldilocks potential is also derived from having a [quoted text clipped - 5 lines] > with respect to its orbit. People have suggested this is important > for life, or at least intelligent life, but I don't see why. Yeah, can't see a big advantage to having one angle of tilt or another. However, I can see there being a big advantage to having a stable tilt. If the Earth were to tilt all of a sudden to 50° from its current 23°, that would lead to chaos in the global climate. Hell, even a relatively small change in tilt from 23° to 30° will lead to chaos. Life would survive probably on such a wobbly planet, because life would adapt, but there would whole species that go extinct, replaced by new species that are more adapted to the new climate. I doubt that high-intelligence would evolve on such a planet, as all adaptations would be geared towards preparing for the next cataclysmic change in the climate. But then again, intelligence might come in handy on such a world. But I don't think it really matters whether the tilt were 23°, 30°, or 50°. As long as the tilt remained stable for millions of years at one of those angles, it would be enough for intelligent life to emerge. >> Actually, I'm saying that the planet itself might be responsible for >> creating some of the conditions necessary for liquid water. The water [quoted text clipped - 18 lines] > maybe you could set things up with enough volcanic heating to avoid > that. Yes, Venus might actually be a good candidate for life if it were this far away from the Sun. > An example you might want to look at is Titan, though it's farther > from the Sun than your idea. Enceladus is another one to check. > Both are, of course, far less massive than Earth. I think both might be candidates for life once the Sun has turned into a red giant. The Sun would be much radiating more energy at that time than it is now. Actually, speaking of a difference in the Sun's energy. One of the indicators of a planet being a Gaia planet (or Goldilocks, your pick), is that the Sun has increased in brightness by about 20-30% since life first emerged on Earth, but the surface temperature on the planet has remained roughly stable since that time. This is one of conditions that the Gaia Theory says is as a result of the life (the biota) changing the abiotic environment on the planet enough to keep the planet habitable. >> Perhaps Jupiter's distance is too extreme, but what if Earth were as >> far away as Mars or the asteroid belt distances? Would something [quoted text clipped - 6 lines] > there's probably liquid water in Jupiter's atmosphere if you go far > enough down. "Automatic" in the sense that, once life gets started on a properly stable planet, it will then just take control over the atmosphere to keep living on that planet for a long time. Not "automatic" in the sense that if you were to suddenly move a planet from one orbit to another, that life would then be able adjust itself accordingly and fast enough. A planet that shifts its orbit would not be a stable planet, obviously. Yousuf Khan Dear Yousuf Khan: >> In article >> <9980f0ee-7945-4a29-b869-f3f2308b9ddd@k37g2000hsf.googlegroups.com>, [quoted text clipped - 13 lines] > either lead to too much greenhouse effect, or > not enough. In general, ionizing radiation tends to produce additional clouds (if water vapor is present). Witness "cloud chambers". >>> For example, cosmic rays are supposed to >>> hit the atmosphere and create clouds. Clouds [quoted text clipped - 3 lines] >> I think the effect of clouds is to _cool_ the >> surface by reflecting sunlight. Correct. >> In any case, I doubt cosmic ray irradiation >> makes any significant difference in cloud cover. http://www.dsri.dk/~hsv/ ... it seems that it does, actually. Just like in "cloud chambers". > Clouds make the surface warmer in winter > in cold climates. Actually I think it is the increased water vapor (the "front" that comes in with the clouds), and the heat capacity (and heat load) that it carries. The clouds do tend to reflect heat way from the clouds, so if the ground is warm, it will tend to stay warm(er). No response required. David A. Smith > In general, ionizing radiation tends to produce additional clouds > (if water vapor is present). Witness "cloud chambers". Right. The issue is whether the increase can be "significant" in the context of whether a planet is habitable or not. > http://www.dsri.dk/~hsv/ It's hard to tell from a single-author web site whether the claimed increase of clouds with incident radiation is generally accepted or not. Even if so, it doesn't seem the amount of increase would be enough to affect habitability, though it seems to be "significant" in the statistical sense. Incidentally, the effect of clouds seems to be to _decrease_ temperature. > Actually I think it is the increased water vapor (the "front" > that comes in with the clouds), and the heat capacity (and heat > load) that it carries. The clouds do tend to reflect heat way > from the clouds, so if the ground is warm, it will tend to stay > warm(er). The last sentence is correct and is the basis for cloud sensors used at automated observatories. My guess at the cause would be the opacity of the clouds themselves. The heat capacity is almost certainly negligible. SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) Dear Steve Willner: > In article <yq%6k.2177$Y84.1...@newsfe10.phx>, > "N:dlzc D:aol T:com \(dlzc\)" <dl...@cox.net> writes: [quoted text clipped - 6 lines] > "significant" in the context of whether a planet is > habitable or not. Depends on the duration of the ionizing radiation. "A day" no problem. "A month" or more would be an issue. > >http://www.dsri.dk/~hsv/ > [quoted text clipped - 8 lines] > Incidentally, the effect of clouds seems to be > to _decrease_ temperature. It depends on the context. You have agreed that clouds tend to reflect heat back down. Those formed by ionizing radiation will be hot. And the water droplets of which a cloud are formed are now a diffuse grey body radiator, rather than a gas. > > Actually I think it is the increased water vapor > > (the "front" that comes in with the clouds), and [quoted text clipped - 8 lines] > the clouds themselves. The heat capacity is > almost certainly negligible. Little different than the vapor phase, true. But the "latent heat of vaporization", when clouds are formed by ionizing radiation, and the ionization energy itself... only half of that goes *up*. But I was responding to Yousuf's "plain folks" argument of what (frequently) happens when a winter storm blows in... usually the temperature goes up slightly. I was very surprised one day in the Bahamas when a storrm front blew in. I am from the desert, and it always gets cooler when it rains. But, NO! (attempting early Steve Martin here...) The measured temperature actually went up when it started raining. What is wrong with those people? ;>) ("latent heat of vaporization" still present, to some extent, despite the phase change.) David A. Smith SW> ...whether the increase [in clouds caused by ionizing radiation] can be SW> "significant" in the context of whether a planet is SW> habitable or not. > Depends on the duration of the ionizing radiation. "A day" no > problem. "A month" or more would be an issue. In context, I don't think duration is an issue. Suppose Earth had a permanent cloud cover. Are you arguing it would then be uninhabitable? No doubt the temperature would differ from what we are used to, but only at the edge of the habitable zone would that matter very much. > > >http://www.dsri.dk/~hsv/ > > Incidentally, the effect of clouds seems to be > > to _decrease_ temperature. > It depends on the context. You have agreed that clouds tend to > reflect heat back down. Those formed by ionizing radiation will be > hot. I think you might want to work out the energy input from plausible amounts of ionizing radiation compared to the heat capacity of the atmosphere. The point remains that _on Earth_, the observed correlation is that temperature goes down when ionizing radiation goes up. SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) Dear Steve Willner: > In article <8e128194-3b64-4df9-81fe-e3704d33a...@u6g2000prc.googlegroups.com>, dlzc <dl...@cox.net> writes: > [quoted text clipped - 9 lines] > Suppose Earth had a permanent cloud cover. > Are you arguing it would then be uninhabitable? Yes. A frostball. > No doubt the temperature would differ from what > we are used to, but only at the edge of the > habitable zone would that matter very much. I disagree. The clouds from a single volcano can drop global temperatures. Cessation of overflights for a couple of days can raise temperature. Now we really aren't talking about rainclouds, nice fluffy white "reflective" things, but global "cirrus" type clouds, converting the amounts of water vapor at altitude to cloud. So it might be less drastic than I "fear". > > > >http://www.dsri.dk/~hsv/ > > > Incidentally, the effect of clouds seems to be > > > to _decrease_ temperature. > > It depends on the context. You have agreed that > > clouds tend to reflect heat back down. Those [quoted text clipped - 3 lines] > from plausible amounts of ionizing radiation > compared to the heat capacity of the atmosphere. incident radiation + latent heat of vaporization (LHV) = quite a bit. But the LHV should not all be disspated, since these "boosted" clouds evaporate right away again. > The point remains that _on Earth_, the observed > correlation is that temperature goes down when > ionizing radiation goes up. Have you already provided a link? I makes sense that clouds are clouds, and increase reflectivity. David A. Smith > Dear Steve Willner: > [quoted text clipped - 12 lines] > > Yes. A frostball. Already happened, didn't seem to involve any effects due to cloud cover. It was called Snowball Earth. In fact it is assumed that volcanos broke the Earth out of the Snowball period, rather than dropping temperatures down due to covering smoke, as you stated. Snowball Earth - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Snowball_Earth Yousuf Khan Dear Yousuf Khan: > > Dear Steve Willner: > [quoted text clipped - 15 lines] > Already happened, didn't seem to involve any effects > due to cloud cover. "Global dimming". > It was called Snowball Earth. In > fact it is assumed that volcanos broke the Earth out > of the Snowball period, rather than dropping > temperatures down due to covering smoke, as you stated. But, volcanos have been shown to *cool* the Earth globally. > Snowball Earth - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Snowball_Earth David A. Smith > > It was called Snowball Earth. In > > fact it is assumed that volcanos broke the Earth out > > of the Snowball period, rather than dropping > > temperatures down due to covering smoke, as you stated. > > But, volcanos have been shown to *cool* the Earth globally. Probably depends on the situation and timeframe whether volcanos cool or warm the Earth. Same thing for clouds. If the Earth is lacking carbon dioxide, the volcanos add it back into the atmosphere, and warm it up over millions of years. If the Earth like it is now, then the volcanos spew smoke and dust into the atmosphere, and cool it down for a few decades. Yousuf Khan Dear YKhan: >> > It was called Snowball Earth. In >> > fact it is assumed that volcanos broke [quoted text clipped - 7 lines] > > Probably depends on the situation The situation is well known. > and timeframe whether volcanos cool > or warm the Earth. Same thing for clouds. Yes, but that does not help with an explanation, or understanding. > If the Earth is lacking carbon dioxide, the > volcanos add it back into the atmosphere, > and warm it up over millions of years. If > the Earth like it is now, then the volcanos > spew smoke and dust into the atmosphere, > and cool it down for a few decades. ... and condensation helps drop the particulates back to Earth. David A. Smith > ... radiation damage would > create properties in the atmosphere that would not be conducive to > maintaining life-bearing temperatures. You haven't yet given any justification for this. Why should "radiation damage" -- whatever you mean by that -- affect the temperature? > Clouds make the surface warmer in winter in cold climates. Why do you think that? Clouds slow down cooling at night, but they also slow down heating during the day. As far as I know, the net effect is cooling, though there may be something I've missed. I suppose if you could set up circumstances where clouds form only at night, there would be net heating, but I don't see what circumstances those could be. SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) >> ... radiation damage would >> create properties in the atmosphere that would not be conducive to [quoted text clipped - 3 lines] > "radiation damage" -- whatever you mean by that -- affect the > temperature? Well, I'm talking about such things as ozone, as an example. But there may be other compounds in the atmosphere that may also be damaged by radiation. "Geophysicists point to Mars as an example of a planet that likely lost its magnetosphere early in its history, letting the bombardment of radiation from the sun slowly erode its early atmosphere. Theories of Earth's field say it's generated by the convection of our liquid iron core, but scientists have always been curious to know when Earth's solid inner core formed because this process provides an important energy source to power the magnetic field. Scientists are also interested in when Earth's protective magnetic cocoon formed." http://astrobio.net/news/article2294.html >> Clouds make the surface warmer in winter in cold climates. > [quoted text clipped - 4 lines] > night, there would be net heating, but I don't see what circumstances > those could be. You don't live in a cold climate do you? During bright, clear, sunny days, the temperature is much colder than on cloudy days. I don't know how you want to explain that, perhaps the albedo of the snow and ice on the ground reflect more sunlight making it colder? Whatever the case, the clouds have the effect of both cooling and warming depending on the season of year. A place like Venus with so much clouds, is retaining its heat due to its clouds. Clouds don't need to get their heat only from the Sun, they could be retaining the heat from the planet's own volcanism. | >> ... radiation damage would | >> create properties in the atmosphere that would not be conducive to [quoted text clipped - 7 lines] | may be other compounds in the atmosphere that may also be damaged by | radiation. Ozone is created from oxygen by radiation, which it then blocks. Another negative feedback system that is self-regulating. | "Geophysicists point to Mars as an example of a planet that likely lost | its magnetosphere early in its history, letting the bombardment of [quoted text clipped - 5 lines] | when Earth's protective magnetic cocoon formed." | http://astrobio.net/news/article2294.html For "scientists" read "crackpot theoreticians". Only a journalist waves the term around indiscriminately for a lay audience. | >> Clouds make the surface warmer in winter in cold climates. | > [quoted text clipped - 15 lines] | clouds. Clouds don't need to get their heat only from the Sun, they | could be retaining the heat from the planet's own volcanism. To see the daily cloud cycle look to the Amazon rain forest. http://earthobservatory.nasa.gov/Newsroom/NasaNews/2004/2004060917103.html > | Well, I'm talking about such things as ozone, as an example. But there > | may be other compounds in the atmosphere that may also be damaged by > | radiation. > > Ozone is created from oxygen by radiation, which it then blocks. > Another negative feedback system that is self-regulating. Yes, but something must have protected the initial ozone layer as it formed, and allowed it to build up in the high atmosphere on Earth. On Venus there is no ozone layer. Why is there no ozone on Venus? What besides a magnetic field could provide such protection for the ozone? I'm thinking the magnetic field allowed the ozone layer to form, and then the ozone supplements the magnetic field as a form of renewable ablative shielding. Radiation wears away the ozone, but the magnetic field reduces this radiation damage to the ozone down to a manageable-enough rate where newly formed ozone is sufficient to completely replace lost ozone. Here's a quote and a link: "On Earth, the ozone layer is several kilometers above this, and the ozone prevents ultraviolet light from destroying water in our atmosphere. On Venus, there is no ozone layer, and the atmosphere doesn't become opaque to ultraviolet light until a depth is reached below the cold trap. This allows ultraviolet light to destroy water between this height and the cold trap's." http://filer.case.edu/sjr16/advanced/venus.html > | "Geophysicists point to Mars as an example of a planet that likely lost > | its magnetosphere early in its history, letting the bombardment of [quoted text clipped - 8 lines] > For "scientists" read "crackpot theoreticians". Only a journalist > waves the term around indiscriminately for a lay audience. Well, perhaps you have a better (i.e. less "crackpot theoretician") explanation for the atmospheric discrepancies between Earth and its two next-door neighbours, Venus and Mars? Since these three planets formed in nearly the same section of the solar system at around the same time as each other, shouldn't they be chemically similar? The only difference I can see is that Earth had a magnetic field and these other two didn't. Yousuf Khan | > | Well, I'm talking about such things as ozone, No no, I did not write that and I'll thank you not to say I did. If you have to snip, do it at a suitable place and don't be so sloppy and lazy as to mis-attribute what I say. If you have some argument, some debate that is worthy of discussion then at least have the courtesy to attribute what was said to the right person. This discussion cannot continue in it's present form. | > Ozone is created from oxygen by radiation, which it then blocks. | > Another negative feedback system that is self-regulating. | | Yes, but something must have protected the initial ozone layer as it | formed, and allowed it to build up in the high atmosphere on Earth. On | Venus there is no ozone layer. Why is there no ozone on Venus? http://en.wikipedia.org/wiki/Atmosphere_of_Venus Why do you still beat your mother? | What besides a magnetic field could provide such protection for the | ozone? See this building: http://en.wikipedia.org/wiki/U.S._Steel_Tower It's made of steel. Steel rusts and it's not painted. Maybe it's protected from corrosion by a magnetic field? http://en.wikipedia.org/wiki/Cor-ten | I'm thinking the magnetic field allowed the ozone layer to form, | and then the ozone supplements the magnetic field as a form of renewable | ablative shielding. Radiation wears away the ozone, but the magnetic | field reduces this radiation damage to the ozone down to a | manageable-enough rate where newly formed ozone is sufficient to | completely replace lost ozone. "Ozone in the upper atmosphere filters potentially damaging ultraviolet light from reaching the Earth's surface. It is present in low concentrations throughout the Earth's atmosphere. It has many industrial and consumer applications. Ozone, the first allotrope of a chemical element to be recognized by science, was proposed as a distinct chemical compound by Christian Friedrich Schönbein in 1840, who named it after the Greek word for smell (ozein), from the peculiar odor in lightning storms." http://en.wikipedia.org/wiki/Ozone There are fewer and less intense lightning storms in the polar regions of the Arctic and Antarctica than the tropics. There are certainly less in London England than in New Orleans. | Here's a quote and a link: | "On Earth, the ozone layer is several kilometers above this, and the | ozone prevents ultraviolet light from destroying water in our | atmosphere. On Venus, there is no ozone layer, And no free oxygen either, it's all bound up with carbon. and the atmosphere | doesn't become opaque to ultraviolet light until a depth is reached | below the cold trap. This allows ultraviolet light to destroy water [quoted text clipped - 19 lines] | in nearly the same section of the solar system at around the same time | as each other, shouldn't they be chemically similar? They are. Look, I'm not saying the atmosphere in not a by-product of the biosphere because it certainly is, but what I am saying is that you should not jump to conclusions. | The only difference | I can see is that Earth had a magnetic field and these other two didn't. Since these three planets formed in nearly the same section of the solar system at around the same time as each other, shouldn't they be magnetically similar? One of the only differences I can see is that Earth had a biosphere and a Moon and an abundance of water at the right temperature and tidal effects and these other two didn't, and if I thought more about it I'd find even more only differences. For "scientists" read "crackpot theoreticians" who cannot see past the end of their noses. Lightning -> ozone -> UV protection -> life in water - > carbon dioxide broken down -> oxygen atmosphere -> weather circulation -> lightning. Life in water = microbes plus tides plus evolution -> life on sea shores -> life on land -> vertebrates -> mammals - > evolution - > whales = life in water feeding on plankton which feeds on (gets energy from) sunlight. One cannot take a simple sub-system in isolation and then try to explain the big picture. Like a jigsaw puzzle, each piece plays a part of the picture as a whole but they all interlock and they also evolve with the passage of time. Its a jigsaw puzzle of movie, you have to fit the pieces together in the time domain as well as spatially, with chemistry, biology, archaeology, mathematics, geology, physics, astronomy etc. etc., all branches of science playing a part in understanding it. Maybe the Earth's magnetic field does play a significant role, but then so do many other factors. Dear Yousuf Khan: >> | Well, I'm talking about such things as ozone, as >> | an example. But there may be other compounds [quoted text clipped - 8 lines] > initial ozone layer as it formed, and allowed it > to build up in the high atmosphere on Earth. No. Ozone is formed regardless of type or amount of radiation, so it needs no "protection". Water vapor will decay ozone with time, so in a humid or warm environment, you may have to reform the ozone layer near local noon. > On Venus there is no ozone layer. Why is > there no ozone on Venus? Ozone spontaneously decays at 390 degC (734 degF), and its halflife in "normal" air at 20 degC is about 20 minutes. Its halflife is reduced by each 10 degC above this. All you need to do is cool the planet a bit, and get rid of thigs that will catalyze ozone destruction. David A. Smith "N:dlzc D:aol T:com \" (dlzc1@cox.net) writes: > Dear Yousuf Khan: > [quoted text clipped - 25 lines] > All you need to do is cool the planet a bit, and get rid of thigs > that will catalyze ozone destruction. And maybe supply a source of molecular oxygen? --John Park Dear John Park: > "N:dlzcD:aol T:com \" (dl...@cox.net) writes: > >>> | Well, I'm talking about such things as ozone, as [quoted text clipped - 30 lines] > > And maybe supply a source of molecular oxygen? Ozone is formed from molecular oxygen, so you already had that. So a short lived source of singlet oxygen, maybe. A little chainsaw massacre guy, complete with ready chainsaw, waiting for a passing molecule... David A. Smith > Dear John Park: > [quoted text clipped - 18 lines] > massacre guy, complete with ready chainsaw, waiting for a passing > molecule... There's a significant amount of molecular oxygen on Venus? (If you have O2, solar UV will give the atomic oxygen (singlet-D which is converted to triplet-P) which combines with O2 to give ozone . . . as you probably knew anyway.) --John Park Dear John Park: > > Dear John Park: > [quoted text clipped - 26 lines] > to give ozone . . . as you probably knew > anyway.) *If* ozone were produced, it would decay "instantly". *If* ozone were produced, there is plenty of stuff to help it to decay. I was simply pointing out ozone could not long survive in that atmosphere. Venus has "no" free oxygen in its atmosphere. http://www.daviddarling.info/encyclopedia/V/Venusatmos.html So it would have to split off of something that oxygen has affinity for: carbon or sulfur, not reoxidize those compounds, not oxidize carbon monoxide, and attach itself to... a non existent oxygen molecule to make ozone? There is plenty of oxygen there... it is just tied up in compounds that are much more stable than ozone, with lots of available states in between the two. David A. Smith > Dear John Park: > [quoted text clipped - 44 lines] > that are much more stable than ozone, with lots of available states in > between the two. Which is why I suggested you'd need a surce of molecular oxygen, which would in turn act as a continual source of ozone. I get the feeling we've been talking past each other, but I'm not sure how that happened. --John Park Dear John Park: ... > > There is plenty of oxygen there... it is just tied up > > in compounds that are much more stable than [quoted text clipped - 4 lines] > molecular oxygen, which would in turn act as a > continual source of ozone. Not on Venus, at those temperatures, it wouldn't. > I get the feeling we've been talking past each > other, but I'm not sure how that happened. Beats talking to ourselves. ;>) David A. Smith > Dear John Park: > [quoted text clipped - 9 lines] > > Not on Venus, at those temperatures, it wouldn't. I don't think a high-altitude ozone layer is precluded, given a source of O2. --John Park Dear John Park: > > Dear John Park: > [quoted text clipped - 12 lines] > I don't think a high-altitude ozone layer is precluded, > given a source of O2. http://www.datasync.com/~rsf1/vel/1918vpt.htm It is precluded below about 40 km, give or take. Above that, and once all the carbon monoxide had been oxidized, you could be right. David A. Smith > something must have protected the initial ozone layer as it > formed, and allowed it to build up in the high atmosphere on Earth. What do you think it needs protection from? > On Venus there is no ozone layer. Why is there no ozone on Venus? Lack of molecular oxygen, as someone posted. > [Earth], Venus and Mars? Since these three planets formed > in nearly the same section of the solar system at around the same time > as each other, shouldn't they be chemically similar? The only difference > I can see is that Earth had a magnetic field and these other two didn't. Mass and distance from Sun. The latter likely had a strong influence on composition, in particular the fraction of volatiles. Earth also has a large satellite, though that's _probably_ not terribly important for such things as composition and temperature. SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) > http://astrobio.net/news/article2294.html I suggest you read the article again. The key phrase is "the solar wind, which can strip away a planet's atmosphere." That has nothing to do with "radiation damage" in the sense that phrase is normally used. The idea in the article is that high-speed particles from the Sun collide with molecules in a planet's atmosphere and mechanically expel them to space. Venus seems to have retained a massive atmosphere, despite having no global magnetic field, so at first glance this process doesn't seem to have had much effect in our solar system. However, the process isn't ridiculous and could perhaps have been important in other solar systems. Or perhaps a much stronger solar wind in the early solar system did indeed strip away Venus' atmosphere, and the atmosphere we see now was created by later outgassing. > You don't live in a cold climate do you? See my .sig. > During bright, clear, sunny > days, the temperature is much colder than on cloudy days. The sky is often clear after a cold front goes through, but it's the global average temperature we are talking about. Increasing cloudiness has to make that go down because more radiation is reflected to space instead of getting absorbed, and the weather record mentioned in the other article shows that's what is observed. > A place like Venus with so much clouds, is retaining its heat due to its > clouds. The 90 bars of CO2 have a lot more effect than the clouds. Also in the opposite direction: Venus would be much hotter if the clouds (which are sulfuric acid particles high in the atmosphere) didn't exist. > Clouds don't need to get their heat only from the Sun, they > could be retaining the heat from the planet's own volcanism. I suppose this is possible in principle, but volcanic heat is negligible for Earth's surface. I'm not sure how good the measurements are for Venus, but I doubt it's important there either. Rock is a really good insulator, and active volcanoes (and geysers, hot springs, black smokers, etc.) simply don't cover very much of the surface. SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) > > A place like Venus with so much clouds, is retaining its heat due to its > > clouds. [quoted text clipped - 3 lines] > (which are sulfuric acid particles high in the atmosphere) didn't > exist. Wrong. Actually Venus would be cooler with no clouds! Because Venus's lower atmosphere is in convective equilibrium, adding heat to the surface will not raise its temperature. Since the dry adiabatic lapse rate extends to the base of the clouds, the temperature there determines that of the surface. The current base of the cloud layer would cool with no clouds, due to radiating more heat into space, and thus the surface would also cool despite receiving more sunlight. I read that this effect in fact would be about 125 K at the surface, which likely reflects about half that at the clouds. The log ratio of the absolute temperatures equals the log ratio of the pressures divided by the heat capacity, so would actually increase as temperature falls (as the heat capacity of gases is lower at lower temperatures). Andrew Usher > Actually Venus would be cooler with no clouds! I was going to agree with you, but on further thought, I'm not so sure. > Because Venus's lower atmosphere is in convective equilibrium, > adding heat to the surface will not raise its temperature. I agree that the temperature gradient of a convective atmosphere will be fixed (at least to first order). Do we know the atmosphere of Venus is convective? Does convection end at the cloud base? If so, is there a reason for that, or is it just a coincidence? As you can tell, I'm no expert on planetary atmospheres. > Since the dry adiabatic lapse rate extends to the base of the > clouds, the temperature there determines that of the surface. OK. > The current base of the cloud layer would cool with no clouds, due > to radiating more heat into space, This is where I'm having trouble. With no clouds, there would also be more heat input to that layer from the surface. I would think the two effects would balance at the same temperature to first order. While I'm not sure, if there is any radiative cooling at all, I'd expect second order effects to lead to an increase in temperature at the cloud bases and thus also at the surface. As I say, though, I could easily be wrong. All this neglects possible changes in composition of the atmosphere except for magically making the clouds disappear. Composition changes, if there are any, might well be the dominant effect, but I have no idea what they might be. > I read that this effect in fact would be about 125 K at the > surface, which likely reflects about half that at the clouds. The > log ratio of the absolute temperatures equals the log ratio of the > pressures divided by the heat capacity, so would actually increase > as temperature falls (as the heat capacity of gases is lower at > lower temperatures). Agreed about the heat capacity of gases at the end, but I'm afraid you lost me with the rest. SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) > > Actually Venus would be cooler with no clouds! > [quoted text clipped - 7 lines] > be fixed (at least to first order). Do we know the atmosphere of > Venus is convective? Does convection end at the cloud base? I don't have the references at hand right now, but the gradient is essentially adiabatic from the surface to ~55 km (called the tropopause). The cloud base is a bit below that. > If so, > is there a reason for that, or is it just a coincidence? As you can > tell, I'm no expert on planetary atmospheres. I'm no expert either, but I'd conjecture that the remaining atmosphere becomes optically thin at the relevant IR wavelengths, allowing radiation to take up all the heat flow from below. > > The current base of the cloud layer would cool with no clouds, due > > to radiating more heat into space, > > This is where I'm having trouble. With no clouds, there would also > be more heat input to that layer from the surface. I would think the > two effects would balance at the same temperature to first order. Increased heat input to that layer would consist of direct, scattered, and reflected sunlight. These would all increase in the same ratio: the reduction of cloud opacity. So the balance between the two effects would be determined by whether the clouds are more opaque to sunlight or to thermal radiation - and I'm pretty sure water-based clouds are most opaque in the IR, so their removal would result in cooling. > All this neglects possible changes in composition of the atmosphere > except for magically making the clouds disappear. Composition > changes, if there are any, might well be the dominant effect, but I > have no idea what they might be. The likely compositional change causing the disappearance of the clouds is simply the reduction of H in the atmosphere. Getting rid of water vapor would reduce the optical depth of the atmosphere to thermal radiation, causing further cooling. > > I read that this effect in fact would be about 125 K at the > > surface, which likely reflects about half that at the clouds. The [quoted text clipped - 5 lines] > Agreed about the heat capacity of gases at the end, but I'm afraid > you lost me with the rest. That's simply the equation for convective equilibrium, expressed in words. As an equation: d(log T) = d(log P) / Cp where Cp is the constant-pressure heat capacity in dimensionless units. Andrew Usher [In Venus' atmosphere] > I don't have the references at hand right now, but the gradient is > essentially adiabatic from the surface to ~55 km (called the > tropopause). > The cloud base is a bit below that. Thanks. [where convection ends] > I'd conjecture that the remaining atmosphere becomes optically > thin at the relevant IR wavelengths, allowing radiation to take up > all the heat flow from below. This seems plausible, though I can't help wondering whether condensation of water might have a role, too. SW> With no clouds, there would also e more heat input to [top of SW> convection] layer from the surface. I would think the SW> two effects would balance at the same temperature to first order. > Increased heat input to that layer would consist of direct, scattered, > and reflected sunlight. But mainly energy convected from the surface, no? > These would all increase in the same ratio: > the reduction of cloud opacity. So it would seem, unless the convection top is above the (present) cloud tops, as it seems is the case. If that's correct, energy convected from the surface would increase by the reduction of cloud opacity, but the others would be unchanged (to the extent composition doesn't change). One thing that seems likely is that the convective zone would extend higher up. > So the balance between the two effects would be determined by > whether the clouds are more opaque to sunlight or to thermal > radiation - and I'm pretty sure water-based clouds are most opaque > in the IR, so their removal would result in cooling. Not Earth clouds. The opacity is mainly scattering from water droplets, and wavelength dependence depends on particle size. By experiment (on far too many cloudy nights, in my case), it's about the same in the visible and thermal infrared. If anything, you would expect slightly less opacity in the infrared. I don't know of any precise measurements, though. Earth clouds start to become transparent at submillimeter wavelengths, though water _vapor_, which often accompanies clouds, is quite opaque at those wavelengths. In any case, this doesn't seem too relevant. Assume the Venus clouds are grey; what happens if you take them away? Seems to me the surface should heat up because the shallow convective temperature gradient will extend to higher altitude. > The likely compositional change causing the disappearance of the > clouds > is simply the reduction of H in the atmosphere. Getting rid of water > vapor would reduce the optical depth of the atmosphere to thermal > radiation, causing further cooling. I was thinking of results rather than causes, but this is interesting. Compared to the CO2, isn't the water optical depth negligible (though certainly not zero)? Yes, if you get rid of it, I have no doubt the top of the convective zone will cool off. Why would that affect the clouds? Are you simply imagining no H to form H2SO4? > That's simply the equation for convective equilibrium, expressed in > words. As an equation: > d(log T) = d(log P) / Cp Ah, yes, clear now. I don't see the relevance to the present discussion, though. SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) > In article <556dfdd9-bf2b-412b-8737-59234396b...@25g2000hsx.googlegroups.com>, > [In Venus' atmosphere] [quoted text clipped - 14 lines] > This seems plausible, though I can't help wondering whether > condensation of water might have a role, too. No - the mixing ratio of H2O is so low that the effect of condensation should be negligible. > SW> With no clouds, there would also be more heat input to [top of > SW> convection] layer from the surface. I would think the [quoted text clipped - 4 lines] > > But mainly energy convected from the surface, no? Yes, which is also proportional. > > These would all increase in the same ratio: > > the reduction of cloud opacity. [quoted text clipped - 4 lines] > opacity, but the others would be unchanged (to the extent composition > doesn't change). > One thing that seems likely is that the convective zone would extend > higher up. You haven't shown that. > > So the balance between the two effects would be determined by > > whether the clouds are more opaque to sunlight or to thermal [quoted text clipped - 7 lines] > expect slightly less opacity in the infrared. I don't know of any > precise measurements, though. Which wavelengths do you consider 'thermal infrared'? True, if the droplets are smaller than a wavelength, their opacity falls with longer wavelength (Mie scattering). One would think, though, that they still must have some absorption in the IR bands where H2O absorbs. > Earth clouds start to become transparent at submillimeter > wavelengths, though water _vapor_, which often accompanies clouds, is > quite opaque at those wavelengths. Yes, and water vapor exists on Venus too, hence my comments below on composition. > In any case, this doesn't seem too relevant. Assume the Venus clouds > are grey; what happens if you take them away? Seems to me the > surface should heat up because the shallow convective temperature > gradient will extend to higher altitude. How exactly do you figure this? I see that the top would remain about the same. In any case (here's the important part of this post) there's a much larger effect neither of us has mentioned yet. This is that the clouds' existence increases the effective transmission of the atmosphere below. This is true even without Rayleigh scattering, due to the reflections between the surface and clouds, but becomes much stronger in Venus's thick atmosphere as light that would be scattered back into space is reflected by the clouds. In fact, the radiation hitting Venus's surface now is about 20% of that at the cloud base, while it would be about half that without clouds. This means the illumination of the surface drops by _less than_ the cloud opacity, and therefore the convective top is higher than without clouds. To get my estimate of 'half', I used a surface albedo of 0.2 and a cloud albedo of 0.7. The correction increases as either does. Let me give some numbers, just for fun: Venus's normal Rayleigh optical depth is about 2 at 1 micron, 14 at 620nm, 50 at 450nm, and 140 at 350nm, where transmission ends because of SO2 absorption. It's often said that light reaching Venus's surface is orange, but it would actually look white to our eyes: its color temperature is about 3500 K, which is essentially constant throughout the Venusian day, even though the intensity changes. > > The likely compositional change causing the disappearance of the > > clouds [quoted text clipped - 6 lines] > negligible (though certainly not zero)? Yes, if you get rid of it, I > have no doubt the top of the convective zone will cool off. The column density of H2O in Venus's atmosphere is about 10 mm PWV, which is not insignificant. That above the convective zone is about 0.05 mm, which is still significant in the thermal IR (remember, this layer is ~300 K). > Why would that affect the clouds? Are you simply imagining no H to > form H2SO4? Right. Andrew Usher > Let me give some numbers, just for fun: Venus's normal Rayleigh > optical depth is about 2 at 1 micron, 14 at 620nm, 50 at 450nm, > and 140 at 350nm, where transmission ends because of SO2 > absorption. Maybe not. The SO2 column density in Venus's atmosphere is about 3e23/cm2, but scattering effectively increases that by a factor of ~50 at 400nm, so the actual column passed through is about 1.5e25/cm2. This data http://www.atmosphere.mpg.de/spektrum_image3.php?subkat=Inorganic+S-compounds&ka t=Sulfur+compounds&file=SO2_340-405nm_lin.JPG then suggests a cutoff about 405nm. At this wavelength the scattering depth is about 80. The Venus sky spectra on this page: http://www.mentallandscape.com/C_CatalogVenus.htm seem to confirm this cutoff. Note that this data has pretty lousy agreement, but that's typical of these bogus 'compilations'. They're worse than useless: a real compliation is combining data on different things to produce a dataset too large to be obtained by one experiment, whereas these are throwing together disparate, inconsistent data - which can't possibly be any better than the most accurate measurement. Andrew Usher [For those who haven't followed this thread, the discussion is what would happen to the Venus atmospheric temperature gradient if the clouds magically vanished.] > > So it would seem, unless the convection top is above the (present) > > cloud tops, as it seems is the case. If that's correct, energy [quoted text clipped - 6 lines] > > You haven't shown that. Isn't it obvious? The top of the convection zone is where the radiative and convective gradients are equal. If you add heating, primarily to the surface, the heat flux is larger. That doesn't change the convective gradient but does increase the radiative gradient, so the convective zone has to extend higher. Am I missing something here? > > > So the balance between the two effects would be determined by > > > whether the clouds are more opaque to sunlight or to thermal > > > radiation Because the clouds are below the top of the convective zone, removing them doesn't change the outgoing heat flux (to first order) but greatly increases the incoming heat flux to the surface. > > > - and I'm pretty sure water-based clouds are most opaque > > > in the IR, so their removal would result in cooling. I take your point in the other thread that diffuse transmission may differ from specular transmission. (I'm not sure that last is the correct term, but I think it's clear what I mean.) That turns out to be a very complex issue: you have to consider both scattering and absorption and all relevant constitutents, dust as well as gases. However, I don't think it much matters to the main discussion. > > In any case, this doesn't seem too relevant. Assume the Venus clouds > > are grey; what happens if you take them away? Seems to me the > > surface should heat up because the shallow convective temperature > > gradient will extend to higher altitude. > In any case (here's the important part of this post) there's a much > larger effect neither of us has mentioned yet. This is that the [quoted text clipped - 12 lines] > To get my estimate of 'half', I used a surface albedo of 0.2 and > a cloud albedo of 0.7. The correction increases as either does. I am failing to follow this. Do you mean the incoming visible light? Right now, most of that is reflected by clouds. Take the clouds away, and almost all of it reaches (near) the surface. What happens then is complicated, but either with or without clouds, most of that incoming energy has to be convected to the upper atmosphere, it seems to me. > Let me give some numbers, just for fun: Venus's normal Rayleigh > optical depth is about 2 at 1 micron, 14 at 620nm, 50 at 450nm, > and 140 at 350nm, where transmission ends because of SO2 > absorption. This is ignoring the clouds? If so, probably only half or so of the incoming energy reaches Venus' surface, but if the atmosphere has constant composition, nearly all the rest will be deposited in the lowest one or two scale heights. That won't change anything fundamental as far as I can tell. SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) > [For those who haven't followed this thread, the discussion is what > would happen to the Venus atmospheric temperature gradient if the [quoted text clipped - 20 lines] > > Am I missing something here? First, there is an upper cloud layer above the convection top (tropopause). This is about 20-25% of the whole cloud optical depth in the visible. It's interesting that the tropospheric and stratospheric clouds seem to be practically two different systems: the former has pronounced weather, the latter is pretty much static. They even seem to form differently: the upper cloud comes from H2SO4 homogenous nucleation in the mesosphere, and the drops slowly fall and accrete, the visible cloud top being where they become optically thick. The tropospheric clouds presumably form like Earth clouds, around nuclei carried up from the surface (we've detected Fe there spectroscopically). However, the bigger problem is that more convection does not necessarily mean higher convection. Radiation must balance the convective heat flux, but the amount radiated by a layer depends on its temperature, not just its height, and even more importantly, on the opacity above it. If the clouds are removed, the layer at the present cloud base (47.5 km) will be able to radiate IR directly to space, where it can't now. It's likely the tropopause will fall, and even though it will be warmer than at present, the surface would be cooler (adiabatic lapse rate is about 9 K/km). > > > > So the balance between the two effects would be determined by > > > > whether the clouds are more opaque to sunlight or to thermal [quoted text clipped - 3 lines] > them doesn't change the outgoing heat flux (to first order) but > greatly increases the incoming heat flux to the surface. See above. > > > > - and I'm pretty sure water-based clouds are most opaque > > > > in the IR, so their removal would result in cooling. [quoted text clipped - 4 lines] > be a very complex issue: you have to consider both scattering and > absorption and all relevant constitutents, dust as well as gases. Yes, it is. That's why I don't claim quantitative accuracy! > However, I don't think it much matters to the main discussion. It certainly does, their total opacity beyond 2.6 microns is why they produce a greenhouse effect. > > In any case (here's the important part of this post) there's a much > > larger effect neither of us has mentioned yet. This is that the [quoted text clipped - 16 lines] > Right now, most of that is reflected by clouds. Take the clouds > away, and almost all of it reaches (near) the surface. No, most of it is scattered back into space, with or without clouds. The effect I mentioned is real - the net surface flux increases (!) when the cloud depth is less than a few times the Rayleigh depth. I did some more accurate calculations of transmission at 6 relevant wavelengths and for 4 different cloud optical depths: 0 (clear), 10, 30 (Venus's real atmosphere), and 100. I again assumed a surface albedo of 0.2 (is that about right?). Here are the results: Cloud depth 0 10 30 100 1000nm 0.591 0.543 0.304 0.115 760nm 0.316 0.397 0.269 0.111 620nm 0.168 0.237 0.208 0.103 540nm 0.103 0.142 0.149 0.092 450nm 0.050 0.063 0.077 0.067 405nm 0.034 0.041 0.051 0.051 CCT 3300K 3100K 3600K 4700K The transmissions for the first 3 wavelengths are in the right ratio, but too high. This is likely because my geometric scattering model is inaccurate for the upper cloud layer which is composed of very small particles. Nevertheless, the actual transmission at 620nm is nearly equal to the no-cloud value, showing the effect. The last 3 are inaccurate because the 'unknown blue absorber' dramatically reddens the spectrum below 600nm - the actual CCT at Venus's surface is about 2300K, where I computed 3600K. The blue absorber is likely elemental sulphur in the lower atmosphere, plus ferric iron in the entire atmosphere (carried up largely as FeCl3). (Those figures were for 45 deg. incidence, the angle dependency for all is almost exactly what it is in a pure Rayleigh atmosphere - proportional to (1 + 2 sin a) where a is the Sun's altitude.) > If so, probably only half or so of the > incoming energy reaches Venus' surface, It's much less than that. Remember that much sunlight is in the IR where the atmosphere absorbs. > but if the atmosphere has > constant composition, nearly all the rest will be deposited in the > lowest one or two scale heights. Again, most of the light _scattered_ goes back into space and does not contribute to heating at all. Andrew Usher > First, there is an upper cloud layer above the convection top > (tropopause). > This is about 20-25% of the whole cloud optical depth in the visible. Have we been discussing what would happen if this layer magically vanished? I'd expect the lower layer not to matter too much because the upward heat transport is mainly convective. > If the clouds are removed, > the layer at the present cloud base (47.5 km) will be able to > radiate IR directly to space, where it can't now. It's likely the > tropopause will fall, and even though it will be warmer than at > present, the surface would be cooler (adiabatic lapse rate is > about 9 K/km). If you've done a real calculation, I'm in no position to argue with you, but I don't see the physical reason the surface should cool. Yes, it's harder for radiation to get out, but there's also less heat that needs to be radiated, and to first order the two effects should balance. > It certainly does, their total opacity beyond 2.6 microns is why > they produce a greenhouse effect. Are you saying the cloud opacity in the IR is greater than in the visible? That would indeed lead to warming now, hence cooling if the clouds were removed. I don't see any reason why the opacities should be that way round, though. Scattering increases dramatically towards shorter wavelengths, though of course it depends on particle size. But all I know is general principles, nothing at all about the actual Venusian atmosphere. > > First, there is an upper cloud layer above the convection top > > (tropopause). [quoted text clipped - 3 lines] > vanished? I'd expect the lower layer not to matter too much because > the upward heat transport is mainly convective. See next paragraph. > > If the clouds are removed, > > the layer at the present cloud base (47.5 km) will be able to [quoted text clipped - 5 lines] > If you've done a real calculation, I'm in no position to argue with > you, but I don't see the physical reason the surface should cool. Here's an approximate calculation. Without clouds, the temperature of the effective radiating layer needs to be around 282 K to radiate all of the solar absorption. In the window region, the atmosphere has unit optical depth around 40 km (CO2-CO2 continuum). Since the 15-micron window can kill about 10% of the emission, that altitude could be around 295 K. 295 K + 40 km * 9 K/km = 655 K or 90 K cooler than the current surface. This difference is large enough that I do not think its direction could be wrong in spite of the crudeness of this procedure. There's also an effect that makes things even cooler at the surface: latitudinal variation. On present Venus, the tropopause is about 60 K cooler at the poles, and it's the polar tropopause that actually limits the surface temperature. I don't know how this would change with no clouds, though. > > It certainly does, their total opacity beyond 2.6 microns is why > > they produce a greenhouse effect. > > Are you saying the cloud opacity in the IR is greater than in the > visible? Remember I mentioned a few posts ago the difference between 'specular' and diffuse optical depths. The specular depth is not greater in the IR, as it is a function of cross-section only. The diffuse opacity is also a function of absorption, which becomes very high in the thermal IR. Of course, they start to become transparent when the wavelength is much larger than the particles. Andrew Usher > > So the balance between the two effects would be determined by > > whether the clouds are more opaque to sunlight or to thermal [quoted text clipped - 7 lines] > expect slightly less opacity in the infrared. I don't know of any > precise measurements, though. Ah, I see what you're saying. You are apeaking of the opacity in the direct line, which is of interest in astronomy, which is indeed gray (nearly) for large particles. But for radiation balance calculations, we are concerned with the amount that gets through, both direct and scattered. That will be influenced by absorption by the particles; the absorption of liquid water is significant from 2.6 microns to microwaves. This superseded my other reply on this question. Andrew Usher >> http://astrobio.net/news/article2294.html > [quoted text clipped - 4 lines] > Sun collide with molecules in a planet's atmosphere and mechanically > expel them to space. Yes the solar winds strip the atmosphere away, but the solar winds are allowed to enter the atmosphere due to the lack of magnetic field. Secondly, if you read this article on Venus, although it has retained the major bulk of its atmosphere, radiation damage in the form of UV has stripped away most of its water, by dissociating its water into hydrogen and oxygen, and letting the hydrogen escape into space. So Venus seems to have retained most of its atmosphere, yet it has lost components of its atmosphere that would have been desirable by life. "So, as water rises in Venus' atmosphere and reaches this region, UV light dissociates it into two hydrogen atoms and one oxygen atom. The hydrogen is much lighter than the water molecule was, and so it easily escapes Venus' atmosphere. The water will usually quickly recombine with a carbon or carbon monoxide molecule to form carbon monoxide or carbon dioxide. This is probably one reason why there is so much carbon dioxide in Venus' atmosphere today." http://filer.case.edu/sjr16/advanced/venus.html Although ozone is regarded as the major radiation shield on Earth, there must be a reason why ozone does not form on either Venus or Mars. I would say it's probably because the magnetic shield provides enough of a cover for ozone to form in the first place. The ozone then takes over the bulk of the radiation protection duties once it has formed in sufficient quantities. > Venus seems to have retained a massive atmosphere, despite having no > global magnetic field, so at first glance this process doesn't seem [quoted text clipped - 3 lines] > system did indeed strip away Venus' atmosphere, and the atmosphere we > see now was created by later outgassing. I doubt all of Venus atmosphere is due to simply internal outgassing. The mass of atmosphere there is on Venus would indicate it must have been its original atmosphere. Outgassing can only contribute a small amount of additional mass to the atmosphere, although the types of gases it produces would be significant for changing the temperature profiles. >> Clouds don't need to get their heat only from the Sun, they >> could be retaining the heat from the planet's own volcanism. [quoted text clipped - 5 lines] > hot springs, black smokers, etc.) simply don't cover very much of the > surface. Volcanic heat is negligible on Earth because Earth doesn't have the runaway greenhouse effect to retain all of that heat. That comes back to the effect of life on regulating greenhouse gases. That brings up another interesting event, Snowball Earth. That's the period of time between 800 million to 600 million years ago, where the Earth was believed to be completely covered in snow and ice, from the poles down to the equator. That's more severe than any of the Ice Ages. There might have even been more than one Snowball Earth, though the last one seems to be most easily detected. Prior to the last Snowball Earth, most of the life on Earth were photosynthetic bacteria, which were consumers of carbon dioxide and producers of oxygen. That early life stripped the Earth of all of its carbon dioxide, and the lack of enough greenhouse gases led to a complete covering in ice. After awhile the carbon dioxide replenished itself through millions of years of volcanism, recreating the greenhouse effect. After the snowball thawed, life was all of a sudden more complex and included types of life that consumed oxygen and produced carbon dioxide, and we've never had a Snowball Earth ever since then. Snowball Earth - Wikipedia, the free encyclopedia "The carbon dioxide levels necessary to unfreeze the Earth have been estimated as being 350 times what they are today, about thirteen percent of the atmosphere.[40] Since the Earth was almost completely covered with ice, carbon dioxide could not be withdrawn from the atmosphere by the weathering of siliceous rocks. Over 4 to 30 million years, enough CO2 and methane, mainly emitted by volcanoes, would accumulate to finally cause enough greenhouse effect to make surface ice melt in the tropics until a band of permanently ice-free land and water developed;[41] this would be darker than the ice, and thus absorb more energy from the sun — initiating a "positive feedback."" http://en.wikipedia.org/wiki/Snowball_Earth#Breaking_out_of_global_glaciation Yousuf Khan > Yes the solar winds strip the atmosphere away, but the solar winds are > allowed to enter the atmosphere due to the lack of magnetic field. If this process were important, why didn't it remove the bulk of Venus' atmosphere? (Yes, the process occurs at some level and affects the details such as removing some of the hydrogen.) > Although ozone is regarded as the major radiation shield on Earth, there > must be a reason why ozone does not form on either Venus or Mars. I > would say it's probably because the magnetic shield provides enough of a > cover for ozone to form in the first place. I think you need to read up on ozone chemistry. Also on the difference between high-energy particles and electromagnetic radiation. > Volcanic heat is negligible on Earth because Earth doesn't have the > runaway greenhouse effect to retain all of that heat. It's not a question of retention, which would apply equally to incoming solar radiation. In comparison to solar input, volcanic heat is utterly negligible for Earth, and I suspect equally so for Venus. (But I don't know for sure about the latter.) Volcanic eruptions do have short-term climate effects and could have long-term effects as well, but these are because of gases and particles expelled into the atmosphere, not released heat. > Snowball Earth - Wikipedia, the free encyclopedia > http://en.wikipedia.org/wiki/Snowball_Earth Note "hypothesis," "remains controversial," and "contested." SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) > See "Gaia hypothesis." It's controversial at best, though certainly > life can have global effects on a planet. Wow, I've now read about this hypothesis, it's even more ambitious than what I am proposing. Under the Gaia Theory, you could actually consider the Earth itself to be a living organism. One of the arguments against Gaia is that if the Earth were a living organism, then why doesn't it divide and reproduce? Then the counter-argument is that all of these space probes that we've been sending out are the signs of a planet getting ready to reproduce by colonizing other planets! Wow, scientific and philosophical at the same time. Just how I like my theories. :-) Yousuf Khan | > See "Gaia hypothesis." It's controversial at best, though certainly | > life can have global effects on a planet. [quoted text clipped - 4 lines] | Gaia is that if the Earth were a living organism, then why doesn't it | divide and reproduce? It isn't yet mature enough (like you). SignatureAndrocles Why did Einstein say the speed of light from A to B is c-v, the speed of light from B to A is c+v, the "time" each way is the same? 1/2[tau(A)+tau(A')]= tau(B) where A = (0,0,0,t) A' =(0,0,0,t+x'/(c-v) +x'/(c+v)) B = (x',0,0,t+x'/(c-v)) x' = x-vt Ref: http://www.fourmilab.ch/etexts/einstein/specrel/www/figures/img22.gif "Easy: he did NOT say that." - cretin harald.vanlintelButNotThis@epfl.ch According to moron van lintel, Einstein did not write the equation he wrote. Then the counter-argument is that all of these | space probes that we've been sending out are the signs of a planet | getting ready to reproduce by colonizing other planets! Wow, scientific | and philosophical at the same time. Just how I like my theories. :-) | | Yousuf Khan > | > See "Gaia hypothesis." It's controversial at best, though certainly > | > life can have global effects on a planet. [quoted text clipped - 6 lines] > > It isn't yet mature enough (like you). Great come-back, Hollywood is awaiting your talents as a writer. However, some of the concepts of the Gaia model are pretty undeniably consistent with what's actually happened on Earth. Such things as the remarkable global temperature constancy throughout its history, despite the fact that the Sun's energy output has risen 20-30% since life first began on Earth. The near constancy of the elements that make up the atmosphere (nitrogen, oxygen, water, carbon dioxide). The constant salinity level of the Earth's oceans at around 3.4%, despite the fact that the worlds rivers continuously dump more and more salt into the oceans from the land. And most of all, the fact that when life first started on Earth, the Earth's atmosphere was a reducing atmosphere (no oxygen), and after organisms came into effect, it became highly rich with oxygen. Yousuf Khan | > | > See "Gaia hypothesis." It's controversial at best, though certainly | > | > life can have global effects on a planet. [quoted text clipped - 8 lines] | | Great come-back, Hollywood is awaiting your talents as a writer. Thank you, but I'm too good for Hollywood. :-) | However, some of the concepts of the Gaia model are pretty undeniably | consistent with what's actually happened on Earth. Such things as the [quoted text clipped - 11 lines] | | Yousuf Khan Yes, I accept all that, but the "living organism" concept when reduced to chemical reaction or simple physics is strictly analogy only. Sunlight evaporates oceans, the water condenses to cloud, clouds are reflective and hide the ocean from sunlight until they vanish as rainfall. The system regulates itself, but it is not "life". Where a simple lifeform does exist -- such as shellfish for example -- the shell to protect the organism from predators is made of calcium carbonate which is extracted from seawater in which it was dissolved. Birds then attack the shellfish and deposit the shells on land until we have hills of them such as can be seen here: http://cache.eb.com/eb/image?id=74594&rendTypeId=4 By the Gaia analogy the "living organism", Earth, has grown a tumour. Then the sea erodes the tumour by wave and tidal action and dissolves the chalk, keeping the cycle going, so the Moon is also part of the "living organism"; if you want to find evolved life on another world look for one with ALL the right conditions. As to the rivers dumping sodium chloride in the ocean, brine is denser that fresh water and will sink, so the oceans are saltier on the bottom than the top. Perhaps cars are "living organisms" too, they evolve quite rapidly and by now should have divided and reproduced. :-) The danger with analogies is they can be taken too far. SignatureAndrocles, proud to be as British as Baldric. http://www.androcles01.pwp.blueyonder.co.uk/MagnaCarta.wmv |
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