Venus on acid

By Phil Plait | February 22, 2008 9:35 am

Some people call Venus our sister planet, but if it is, it’s the sister that went very, very bad.

The atmospheric pressure at the surface is a crushing 90 atmospheres. The surface temperature is 470 Celsius (about 900 F). The atmosphere is almost entirely carbon dioxide, and it rains sulphuric acid. To paraphrase Chekov, it’s not exactly a garden spot.*

Through a telescope (and by eye for that matter) Venus is beautiful and bright, but featureless. In visible light, the best you can see are very subtle patches on the disk of the planet. The atmosphere is far too thick to see the surface.

But there’s still a lot to learn from the planet. The European Space Agency’s Venus Express orbiter arrived at the hellish planet in April 2006 and set up shop. It’s equipped with an ultraviolet camera, and when viewed in UV Venus is a whole ‘nuther place. The chemicals in the atmosphere reflect or absorb UV from the Sun ,creating beautiful global weather patterns reminiscent of Earth’s. Here’s a recent UV shot:

As you can see, the story is different in UV than in visible. Things is, scientists aren’t exactly sure what they’re seeing. The bright stripes are due to sulphuric acid droplets in the air (yikes… I mean seriously, yikes). But they’re not sure what’s causing the darker regions; something is absorbing UV, but it’s unknown exactly what it is.

And the weather on Venus is weird, too. The science team was recently amazed to see a bright haze form over the south pole of Venus, then, over the course of several days, grow to cover the southern half of the planet. Then, just as quickly, it receded. What could cause such a thing? No one knows. There are very small amounts of water vapor and sulphur dioxide in Venus’s atmosphere, located deeper down (below 70 km in height). If this wells up, the ultraviolet from the Sun can break the molecules apart, which would reform into sulphuric acid, creating the haze. But why would those two molecules suddenly well up to the top of the atmosphere in the first place? Again, no one knows.

The only thing to do is keep looking. Venus Express has been orbiting the planet for nearly two years now, and that allows the long view, so to speak. By examining the data taken over long periods of time, scientists can investigate global properties of the planet and look for trends, connections, cause and effect. Venus has the same mass, size, and density of Earth, but at some point in its past it took a very different path than we did. Studying it carefully will reveal more about the Earth and why things turned out so well for us.

Sure, when you look into the abyss, sometimes it looks back into you. But that can be pretty helpful when you want to learn more about the abyss as well as yourself.


*What, you thought I meant Anton Chekov?

CATEGORIZED UNDER: Astronomy, Pretty pictures, Science

Comments (37)

  1. SteveT

    Given how hellish the atmosphere and surface are, I have always been mightily impressed by the Soviets for having managed to get functional landers to the surface. I still get a feeling of awe whenever I look at the pictures the Venera landers sent back in 1975.

  2. Gary Ansorge

    According to Wiki, it has a liquid core, mantle, etc, but no plate tectonics or magnetic field. It’s very slow rotation probably explains why it has no appreciable magnetic field, since there is no way to churn the liquid core.
    I note that Mars, with its’ far smaller core and faster rotational velocity, DOES have a mag. field.

    I wonder however, if there is significant volcanic activity??? That could explain the up-welling we’re seeing.

    Gary 7

  3. Gnat

    Can you have volcanic activity without tectonic plates?

  4. Sili

    Yes -yes, I did …

    Question: Why isn’t there an IR spectrophotometer aboard that satellite? That ought to give some idea about the compostion of those clouds, oughtn’t it?

  5. To paraphrase Chekov, it’s not exactly a garden spot.

    Bradbury would have to disagree, of course. ;)

    What I find fascinating about Venus as a setting for exploration is that, given the thickness of the atmosphere, it’s possible to build neutral-buoyancy airships filled with 1 ATM of breathable air. Assuming, you know, that your materials science is good enough to prevent the sulphuric acid rain and 400 mph winds from tearing it apart.

  6. Irishman

    Yea! Somebody else who uses the phrase, “a whole ‘nuther”. ‘Course I spell it “nother”, but that’s a whole nother issue. ;-)

  7. “The only thing to do is keep looking.”

    Yes, and it’s sooo beautiful. Who’d have thought sulphuric acid particles could be so gorgeous?

  8. tim

    I keep waiting for (Boulder’s own) David Grinspoon to update his excellent book Venus Revealed to include what’s been learned from Venus Express.

  9. Gary Ansorge says: “I note that Mars, with its’ far smaller core and faster rotational velocity, DOES have a mag. field.”

    But Mars does not have a global magnetic field. It seems to be concentrated in spots over its surface.

    – Jack

  10. Irishman says:”Yea! Somebody else who uses the phrase, ‘a whole ‘nuther’. ‘Course I spell it ‘nother’, but that’s a whole nother issue. ”

    He also spells the brimstone element “sulphur” instead of the American (thank you Noah Webster) “sulfur.”

    Anyone else appreciate the irony of having a “hellish” planet’s atmosphere full of the gas given off by burning brimstone?

    – Jack

  11. Can you have volcanic activity without tectonic plates?

    I’m pretty sure they’ve seen lots of evidence for volcanic activity on Venus. Why wouldn’t it be able to have volcanic activity?

  12. Chip

    Just for fun over in the BABB Forum I launched a poll and a thread within the “Life in Space” category titled “Making Venus Livable”.

    People have posted lots of interesting ideas. We touch on Carl Sagan’s suggestion of cloud seeding the upper atmosphere of Venus with algae, which now, with a better understanding of the atmosphere has been shown to not work. There are however some very interesting ideas from various posters before the thread was taken over several times by the “Floating Cities” folks. (Which to me is a dead end idea.)

    However, by trying to solve the staggering problem of how to hypothetically transform Venus into another Earth through a long series of baby steps, we can learn an awful lot about the nature of Venus known and unknown so far. The new findings Phil writes about could add even more questions and ideas.

    http://www.bautforum.com/life-space/59971-making-venus-livable.html

  13. andy

    Earth and Venus actually have pretty similar atmospheres (if we ignore the oxygen pollution), except that on Earth most of the carbon dioxide is locked up in rocks in the crust rather than being in the skies causing a monster greenhouse effect. On Venus the temperatures are high enough to drive the carbon dioxide out of the rocks and into the atmosphere, causing the generally unpleasant conditions observed at the surface.

  14. Changcho

    To ‘tim’ above – yes, I wish D. Grinspoon would update his excellent book (Venus Revealed), which I just recently finished. Therein, I learned of the weird UV absorber, and I saw that the Bad Astronomer mentioned that its composition is still unknown…a nice mystery to solve.

  15. Tom Marking

    I once remember reading that Venus and Earth have the same amount of CO2, it’s just that on Earth it’s locked up in limestone (calcium carbonate). Let’s see if I can do a little back-of-the-envelope calculation to see if I believe that.

    ********************************************************
    Venus calculation:

    http://en.wikipedia.org/wiki/Venus
    Venusian atmosphere: surface pressure = 9.3 million pascals
    surface temperature = 735 deg K

    Modified ideal gas law: rho = M*P / (R*T)
    rho is density (kg/m^3), M is molecular weight (0.044 kg per mole), and R is ideal gas constant (8.314 joules per deg K per mole).

    So surface density = 66.96 kg per m^3
    96.5 percent of atmosphere is CO2 so CO2 surface density = 64.6
    kg per m^3

    http://en.wikipedia.org/wiki/Atmosphere_of_Venus
    atmospheric scale height of Venus is height at which density falls to factor of exp(-1) = 36.8% of surface density. Using table for pressure as a substitute the approximate scale height is 15 km.

    Total CO2 on Venus in a vertical column = scale height * surface density = 969,000 kg per m^2

    ********************************************************
    Earth calculation:

    Calcium carbonate: molecular weight = 0.100 kg per mole
    (multiply by 0.44 to get equivalent mass in CO2)

    http://www.chem1.com/acad/webtext/geochem/04txt.html
    5 percent of sedimentary rock is limestone

    http://www.ufrsd.net/staffwww/stefanl/Geology/sedrock/index.htm
    5 percent of earth’s crust is sedimentary rock

    http://www.utdallas.edu/~msweet/oc-unit2.html
    Earth’s crust is 0.4% of its total mass

    Using a mass for the earth of 5.97E24 kg and surface area of 5.10E14 square meters:
    Mass of earth’s crust = 2.39E22 kg
    Mass of sedimentary rock = 1.2E21 kg
    Mass of limestone = 6.0E19 kg
    Equivalent CO2 mass of limestone = 2.6E19 kg

    Equivalent CO2 mass of limestone per square meter =
    51000 kg per m^2

    The value for Venus is 19 times higher than this amount. So even though there are uncertainties in some of these percentages it still seems like Venus has much more CO2 than Earth even if you account for the CO2 on Earth tied up as calcium carbonate.

  16. tjm220

    “Venus has the same mass, size, and density of Earth, but at some point in its past it took a very different path than we did.”

    BA, you forgot to include ‘nearly’ in your description.

  17. Tom Marking

    “Can you have volcanic activity without tectonic plates?”

    Yes, you can. Jupiter’s moon Io is a perfect example. It’s the most volcanically active body in the solar system but it lacks plate tectonics. Mars is another example. It has the solar system’s highest volcano, Olympus Mons, with an altitude of 27 km but there is no evidence of plate tectonics.

    Venus is somewhat ambiguous. There is evidence of a massive resurfacing event which took place 300 – 500 million years ago but no evidence of gradual plate tectonics operating currently. But Venus is chock full of volcanoes. There are 167 giant volcanoes on Venus with bases over 100 km across. There is just 1 such feature on Earth (Hawaii).

  18. Actually, Anton Chekhov’s name is spelled with an “h,” unlike the Star Trek character.

  19. Kaptain K

    Good thing you call yourself “The Bad Astronomer”, because a chemist you ain’t! Sulfur dioxide (SO2) plus water (H2O) => sulfurous acid (H2SO3), NOT Sulfuric acid (H2SO4)!

  20. Dualist

    “Venus has the same mass, size, and density of Earth, but at some point in its past it took a very different path than we did.”

    That’s the point I got interested in.

  21. tussock

    Tom: Mass of the Venusian atmosphere is 4.8e20kg, with CO2@96.5% or 4.6e20kg.

    Here there’s also Carbon dissolved in seawater, about 1.4e19kg CO2 equivalent, total that plus limestone is ~4e19kg, or 8.7% of the Venusian atmospheric total. Still a nice warm blanky, I guess.

    Hmm. I’d heard the same with comparative atmospheres. Wonder why we’d start with so much less atmospheric CO2, and so much more H2O?
    A quick read suggests to me more impacts after Neptune moved out and scattered the iceballs. That would’ve made for a pretty sky full of very large, young, disintegrating comets, at least up until one of them killed you.

  22. Michael Lonergan

    I remember reading Bradbury’s short story, “All Summer In A Day” in High School and it had a profound effect on me. Of course, knowing what we know about Venus now, it is totally impossible. I also watched a gem of a movie the other night, “First Spaceship on Venus.” It was an East German film from the 1950’s or ’60’s. It was basically a propaganda film, but had been extensively redubbed in English to present a more positive view of America. Considering when and where it was made, it wasn’t bad.

  23. Tom Marking

    “Hmm. I’d heard the same with comparative atmospheres. Wonder why we’d start with so much less atmospheric CO2, and so much more H2O?”

    Even including the CO2 dissolved in the Earth’s oceans Venus still has a factor of ten more CO2 than Earth does. The reason might have to do with the varying chemical composition in the original solar nebula based on distance.

  24. Michael Lonergan says: “I watched a gem of a movie the other night, “First Spaceship on Venus.” It was an East German film from the 1950’s or ’60’s. It was basically a propaganda film, but had been extensively re-dubbed in English to present a more positive view of America. Considering when and where it was made, it wasn’t bad.”

    The American market re-cut of that film turned it into a cartoon. It has since been released in its original form as “Der Schweigende Stern” (The Silent Star) which is based on Stanislaw Lem’s first novel “The Astronauts.” For those who have only seen the butchered King Features release, the original movie is a revelation. It was shot in full 16:9 format 70mm Commie-color (I forget what the eastern bloc’s version of Technicolor was called, probably Agfacolor). The opening credits are completely different with some very avant-garde music. The whole thing feels like a grownup’s version of the film. It comes only in German with English subtitles.

    It was made in 1959 as a response to films like “Forbidden Planet” to showcase the production abilities of the Soviet countries and their Communist states (it was a joint East German/Polish production).

    I have a chapter on it in “Spaceship Handbook” that I’m going to have to re-write for the second edition and base it on the real film. All I had available at the time I wrote it originally was the US version. The “Cosmostrator” (Kosmocrator) is one of the coolest looking spaceships ever to grace the silver screen. Really difficult to model, though.

    – Jack

    PS – It was also given the MST3K treatment in their second season.

  25. andy

    Well, an order of magnitude difference in mass… in astrophysics that’s practically the same number ;-)

    Bear in mind that limestone is only one of the two main carbonate rocks, the other being dolomite… from here, we have that carbonates (not just limestones) make up to 10-15% of sedimentary rocks, which is a factor of 2-3 more than Tom Marking used…

  26. Tom Marking

    So the latest revised numbers are:

    Venus:
    http://en.wikipedia.org/wiki/Atmosphere_of_Venus
    Total mass = 4.8E20 kg
    Mass of CO2 = 4.63E20 kg

    Earth:
    Carbonaceous rocks (limestone, dolomite):
    Total mass = 1.8E20 kg (max)
    Equivalent CO2 mass = 7.9E19 kg (max)

    CO2 dissolved in seawater:
    http://www.eoearth.org/article/Carbon_cycle
    Total amount of carbon = 40,000 billion metric tons = 4.0E16 kg
    CO2 mass equivalent = 1.5E17 kg
    (This is a factor of 90 less than the value of 1.4E19 kg which was cited by someone earlier – a URL for that number would be much appreciated)

    Total CO2 on Earth: 7.9E19 kg (or 9.3E19 kg if the 1.4E19 kg for dissolved CO2 is correct)

    This is still a factor of 5.8 (or perhaps as little as 5.0) less than the number for Venus. So I’m not sure the premise that Earth and Venus started out identical is valid.

    Some other interesting stuff on the Wikipedia entry for Venus is as follows:

    “Another intriguing piece of evidence comes from measurements of sulfur dioxide concentrations in the atmosphere, which were found to drop by a factor of 10 between 1978 and 1986. This may imply that the levels had earlier been boosted by a large volcanic eruption.”

    “The atmosphere of Venus is in state of a vigorous circulation and super-rotation. The whole atmosphere circles the planet in just four days (super-rotation), which is a short time compared with the sideral rotational period of 243 days. The winds supporting super-rotation blow as fast as 100 m/s.”

    I don’t know how the atmosphere can travel around the planet in just 4 days when the rotation period is 243 days. That makes no sense to me at all.

  27. andy

    Well, what this analysis suggests is that the Venusian atmosphere is not anomalously massive – from the link Tom Marking provided in the last post, the total mass of carbon in the various sinks is 6.6E19 – 1.0E20 kg (taking the high and low masses in table 1) – a factor of 5-7 is actually a pretty good match when we consider how much uncertainty is involved in the various quantities. I’d suspect that the global resurfacing event that is supposed to have occurred on Venus would have dramatically altered the atmosphere – I’d suspect it could have degassed a large portion of the planet and increased the atmosphere mass accordingly, but I’m not a geologist (or whatever the Venusian equivalent of the term is).

    In any case, even a factor of 5-7 less atmosphere than Venus would result in a pretty unpleasant atmosphere…

  28. Tom Marking

    “In any case, even a factor of 5-7 less atmosphere than Venus would result in a pretty unpleasant atmosphere…”

    I think the key difference is the slow rotation. If you took the Earth and slowed it down so that the rotation period is 243 days retrograde then the sun would rise in the west and set in the east. The time between consecutive sunrises would be 146 days (3,504 hours) which means that typically the sun would be above the horizon for 73 days (1,752 hours). When exposed to the sun for 73 days straight the oceans of the earth would boil emitting huge quantities of water vapor into the atmosphere. Since water vapor is a greenhouse gas it would cause a run-away greenhouse effect with all the water in the oceans boiling away eventually. The final surface temperature would probably be at least 300 deg C if not more so all life would be extinguished. I don’t know if climatologists have actually run this model or not, but it would be interesting to see what the final results are for it.

  29. andy

    Tom Marking – simulations of synchronously rotating planets have shown they can retain liquid water at the surface (despite one hemisphere being under permanent sunlight), so I doubt slow rotation would be the main problem.

  30. The comparison to Venus’s CO2 using Earth’s dissolved-ocean CO2 misses the huge amount of carbonates in sedimentary rocks. When you do the comparison that way, Venus has about 90 bars of CO2 and Earth has about 60. I believe the comparison was first done that way in the 1950s, by Harold C. Urey (of Urey-Miller experiment and Urey Reaction fame).

  31. Tom Marking

    “Tom Marking – simulations of synchronously rotating planets have shown they can retain liquid water at the surface (despite one hemisphere being under permanent sunlight), so I doubt slow rotation would be the main problem.”

    It all depends on the insolation which in turn depends primarily on the distance from the star, albedo of the planet, and luminosity of the star. In the case of Earth with a 243-day retrograde rotation the sun would appear to move in the sky 2.47 degrees per 24 hours (west to east). If you consider the subsolar point the sun will be within 20 degrees of zenith for 389 hours (16.2 days). The area near the subsolar point is going to get very hot with no chance to cool off at night.

    Let’s compute how much energy that point receives. Assume the solar constant is 1366 watts/m^2 and the albedo is 30%. Assume the average elevation angle is 80 degrees. Then average solar power received over 389 hours is 1366 * 0.7 * sin(80) = 924 watts/m^2. Assume that the same energy is re-radiated back into space assuming a blackbody emitter. Then temperature of emission is (924 / 5.67E-8)^0.25 = 357 deg K = 84 deg C. This is only 16 deg C less than the boiling point of water. The evaporation of water will be tremendous causing huge quantities of water vapor to be released into the atmosphere. The temperature only has to rise 16 deg C before the oceans really start to boil in earnest. So a slow rotation is not a good thing for a terrestrial planet.

  32. Tom Marking

    “Venus has about 90 bars of CO2 and Earth has about 60″

    I’m attempting to do that very calculation including sedimentary rocks on Earth and I’m only getting a value of 18 bar for Earth, not 60. The estimates for the amount of limestone/dolomite in sedimentary rocks seems to vary widely depending upon the source of the information so it’s almost impossible to get an accurate number.

  33. andy

    Tom Marking – you are neglecting heat transfer by ocean currents or wind in the atmosphere in your analysis of the slowly rotating planet, thus you are coming up with a worst-case scenario for the temperature.

  34. Buzz Parsec

    BPL, I think Tom started with the sedimentary rocks, and then someone else added in the dissolved-ocean CO2.

    I’m wondering if Venus could have lost carbon in the form of methane evaporating into space from the upper atmosphere. methane CH4 has a molecular weight of just 16, half O2’s 32 and about 1/3 of CO2’s 44. Lighter molecules travel faster at the same temperature and thus are more likely to reach escape velocity. CO2+2(H2O) -> CH4 + 2O2. If this is the case, wonder what happened to the oxygen?

  35. Buzz Parsec

    Oops! Venus has too much carbon, not too little… “Never mind!”

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