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ESA to Send Spacecraft to Venus
teeto writes to tell us The International Herald Tribune is reporting that the European Space Agency is planning to send a spacecraft to peer at Venus." From the article: "If the robot craft pulls off the complex maneuver of slowing down enough to swing into orbit, scientists hope it will help solve the mystery of how the shrouded, churning atmosphere of Venus formed and how it maintains the planet's broiler-like temperatures."
I just think that'd be incredible. Until everything melted.
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This AC comment seems to have been made in jest, but it got me thinking.
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Do we have any way of knowing how long Venus has been a runaway greenhouse? (That phrase, by the way, invokes a really bizarre mental image
Is it conceivable that the climate there went haywire within human history? Given the current pressure, temperature, and chemical composition of the atmosphere on Venus, is there any chance that any indications at all could have survived of a possible former ecosystem there?
Mars is fascinating for what it might have become. Venus is fascinating for what it might have been.
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Do we have any way of knowing how long Venus has been a runaway greenhouse? (That phrase, by the way, invokes a really bizarre mental image ... )
Almost from the get go. From what I've read, Venus has simply way, way too much Carbon Dioxide. Carl Sagan's romantic plan of seeding Venus with bacteria to eat up the CO2 simply fails because there is way too much CO2. To get Venus straightened out for human habitation, you would have flat out get rid of something like 89 parts out of 90 in the Venutian atmosphere, and there's really no place to put that much air. There've been some proposals to freeze it into giant CO2 chunks and launch them into space, or, slam some kind of an asteroid or even planet into Venus to jack the air into space, but both are so far beyond our technology as to be unimaginable. There's also not enough of other gasses in Venus's atmosphere - you really need a lot of nitrogen or something like it, like, well, the Earth has.
Then again, the Earth has an aweful of lot of Carbon Dioxide in the oceans and the limestone.... maybe we could all be doomed.
Is it conceivable that the climate there went haywire within human history? Given the current pressure, temperature, and chemical composition of the atmosphere on Venus, is there any chance that any indications at all could have survived of a possible former ecosystem there?
Well, there's one famous Internet crackpot that swears he sees Zeppelins on Venus and there are people there...and NASA is covering it up. But, outside of that, I think Venus has always been dead. Venus has a lot of problems even besides the grueling atmosphere. It has a long rotational period and lacks a magnetosphere.
As far as the earth goes, the most spectacular environment catastrophe posited is Snowball Earth. Basically, the entire Earth was frozen over with a sheet of ice two miles thick, everything died and there was no oxygen in the atmosphere, for a period of a few hundred million years. It was a rough time, but, ironically, the Earth was saved by an accumulation of 350 times our present level of CO2.
What's really interesting about Earth's past is that the atmospheric composition has varied rather wildly. It is not at all automatic that we have 78% nitrogen, 20% oxygen and then some other gasses. I have no idea how they infer atmosphere, but it must have something to do with chemicals found in rocks and knowledge of how those chemicals must have been made, coupled with radioactive dating. Incidentally, the overall portion of CO2 in the air is rather small, something like 0.04% (and going up). For all the talk about whether the CO2 is manmade or not, or whether it causes global warming, some facts are most certainly known. First, the CO2 level has doubled in a 100 years, and when a planet wide change happens that fast, you really do have to have cause for concern. All sorts of questions need to be asked, but the big one is, is the rate of doubling changing? Like, will we double it again in 50 years, then 25 again, and so on? I think we only need to double the atmosphere not too many times before we all die.
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You make a good argument, but I'd like to add a qualification. I'm not sure the availability of energy itself is a problem with Venus. More than enough energy for any conceivable terraforming rains down on Venus from the Sun. And it's quite usable energy, since its temperature is close to that of the solar photosphere (5500K). Thermodynamically speaking, you can run some very efficient heat engines between a hot reservoir at 5500K and a cold reservoir at even the high temperatures of Venus (300-700K, depending on altitude).
So the energy is there. But it isn't necessarily easy to use. The only plausible scenario probably remains some kind of biological seeding, i.e. designing some kind of photosynthesizing microbial life that can suck up all that CO2 and convert it to carbonate rock, as such life is thought to have done in the early history of the Earth, which is where our CO2 went and why we have great beds of limestone in the crust.
But I believe the problem with this is that there is very little water in the Venusian atmosphere, and all the microbial life we know about needs water. Furthermore, such a seeding process would not be quick -- at a minimum, millions of years are necessary -- and it might be hard to put the brakes on at the end.
The reason for needing this kind of effort to cool the Space Station, even thought it's in the "very cold" environment of space, is that while the temperature of space is very low, the thermal capacity of space is also very low. That is, there's just very, very little of any cold matter around to which you can transfer heat, the way your body transfers heat to winter air when you step outside in December. You can radiate heat as infrared radiation, of course, but to be efficient this requires a lot of surface area for the volume being cooled. And yet, of course, when you build spaceships you tend to want to minimize the surface area for a given volume -- i.e. build compact shapes.
Furthermore, in space the wretched Sun is radiating huge gobs of light and heat at you 24 hours a day. Got to get rid of that, too.