Venus Atmosphere Puzzle, one man's struggle with atmospheric physics Options

[qraal]

Hi Don

Hey thanks for the insights - Venus is truly weird. Would be dull if it was easy.

Your webpages on the Russian Venus efforts are amazing too.

What do you think the 'crystals' in the atmosphere might be?

Adam

The U of Arizona books are essential. There are actually two Venus books, and you want them both (Venus and Venus II). Also check out their Mars book.

There have been many descent probes on Venus. The first really detailed information came from Venera-9 and 10 in 1975, which had nephelometers, spetrometers, and various other instruments. The three-layer cloud structure was discovered then, as well as the first photos of the surface.

Venera-11, 12 and the Pioneer probes arrived in 1978. The Venera probes contained more sophisticated spectrometers than the 1975 versions, and also mass spectrometers, gas chromatography and x-ray fluorescence spectrometers. The latter provided the first real data on the composition of the cloud material, including the discovery of Iron Chloride as a component. The PV large probe had a particle-size device which provided unique data. There has been much debate about the PV results, which some believe show a distinct large particle size that may be crystals -- the so-called mode 3 controversy.

Venera descent probes relayed data through the high-gain connection of the main spacecraft, so they were able to send almost 100 times as much data as the Pioneer probes, including large numbers of mass spectra and optical spectra as they descended.

The last word has been from the Vega descent probes. They were particularly geared to study the clouds and try to answer questions raised by the Pioneer particle-size spectrometer. Two different particle analyzers were on the Vega probes, as well as a more sophisticated gas chromatography experiment, which discovered the profile of chlorine, sulphur and phosphorus abundance as a function of altitude. The clouds are a lot more complex than just sulphuric acid droplets, particularly the lower layers.

The big names in Venusian atmospheric chemistry are Vladimir Krasnopolsky, the late Vasily Moroz and Larry Esposito. They have a joint paper in Venus II, and Krasnopolsky has a good book on the chemistry of Mars and Venus.

[Guest_DonPMitchell_*]

That is a mystery. Many believe there are no crystals, just larger sized droplets. Sulphur, Chlorine, Phosphorus and Iron have all been identified as important elements in the cloud material. There are many theories about how these elements might combine.

[qraal]

Hi Don

The exobiological theory is the most exciting, but we know so little about the chemistry of such vapours on such a scale. Maybe some process is making odd carbon allotropes?

Adam

That is a mystery. Many believe there are no crystals, just larger sized droplets. Sulphur, Chlorine, Phosphorus and Iron have all been identified as important elements in the cloud material. There are many theories about how these elements might combine.

[edstrick]

The Pioneer Large Probe Cloud Particle Size Spectrometer took images of the shadows of particles as they flowed through the field-of-view / focal plane of the instrument. These data were processed to count particles and sort them into size-bins, producing particle size "spectra" or more accurately, "size-distribution histograms".

As I vaguely recall, the largest, better resolved particles were analyzed for departures from circuarity or "equi-dimensional" form.. some "length-vs-width" number. In some parts of the clouds, small numbers of particles considerably larger than the approx 1 micrometer sulphuric acid droplets were supposedly detected and these particles were flagged as not round.

There was an extended arguement over the validity of the data, and it (as far as I used to know -- my info's obsolete), was never resolved as there wasn't enough data to go any further. No other missions took comparable data. One Mission, One Instrumet, One descent profile..... "Tiz a Puzzlement".

[Guest_DonPMitchell_*]

Vega-1 and Vega-2 performed similar experiments. The LSA particle-size spectrometer and the ISAV-A optical aerosol analyzer were installed on the last two spacecrafts to land on Venus. The ISAV-A investigators concluded that the large particles were approximately spherical with a refractive index of 1.4 +/- 0.1.

The Vega instruments also measured sub-micron particles in considerable abundance, which were too small for the PV instrument to see.

The Venera-9 and 10 nephelometers measured scattering at several angles, but that data was never as conclusive as the aerosol particle sensors on PV and Vega.

[JRehling]

Venus' Double Vortex Confirmed in New Animation
Scientists think the vortexes are created by a combination of a natural cycling of hot air in the planet's atmosphere and high velocity, westward-blowing winds that take only four days circle the planet. It is still unclear, however, why there are two vortexes at each pole.

I didn't know about the double vortex -- it is odd.

I wonder if it has something to do with a vortex forming on the solar side then rotating into shade in time for a new vortex to form when the first one has moved into night. As for why that would happen in discrete pairs per rotation is bound to be a tricky question, but cyclical patterns do arise in turbulent systems -- the devil is at a level of detail my [non]study of fluid dynamics has never gotten to.

[qraal]

Thanks Don & Ed

More data to cram into my brain.

I'd really like to get my hands on the Venus International Reference Atmosphere, but VIRA isn't available even second hand on all the usual web-shops. I have found journal articles which give some values from VIRA, but they're kind of empty without the underlying rationale - the scale heights vary so much between levels I can't see any pattern except for large poly-nomials. Why? Tighter fit to the data I guess, but the underlying processes seem obscure.

Will have to try and dredge up those Venus books.

Adam

[Guest_DonPMitchell_*]

Planetary circulation is fascinating. Rotating patterns of vortices are not unusual.

[attachment=6553:attachment]

This old Tiros-9 photo of the Earth shows a number of large cyclonic and anti-cyclonic weather patterns extending cross the north and south temperate zones. You get a sort of standing-wave pattern like that, with about six of these giant vortices moving around the Earth in the north and south. Called Rossby Waves or planetary waves.

Around the equator, where the change in angular momentum is less, you just have simple hadley-cell circulation, tilted at an angle by coriolis force.

On Jupiter you see many bands of this stuff. A trade-wind band around teh equator like Earth, then some Rossby waves in the temperate bands, and then nearer the poles, the powerful coriolic forces lead to chaotic circulation.

[MichaelT]

Hi All

This might seem like a really dumb question, but what's the mass of the Cytherean atmosphere per unit area?

If I get your question right you don't have to integrate, because you know the surface pressure and the acceleration of gravity of Venus. That makes it much simpler:

pressure = force / area
force = mass * acceleration
=> pressure = mass * acceleration / area

This translates to the following formula:

p = M * a / A

=> M / A = p / a

All you have to know is the (equatorial) acceleration of gravity of Venus, which is a = 8.87 m/s², and the surface pressure p = 9.3 MPa.

Therefore:
M / A = 9,300,000 Pa / 8.87 m/s²
M / A = 1,048,478 kg/m²

The Venusian atmosphere has a mass of more than 1000 tonnes per square meter. It's almost exactly 1/100th of that for Earth (p = 101300 Pa; a = 9.81 m/s²; M/A = 10,326 kg/m²). For Mars it is just 217 kg/m².

Michael

[edstrick]

I'd forgotten the instruments on the Vega probes, remembering the collected particle composition measurements and the like. Ultimately, Venus atmosphere science needs a long-lived balloon system that can make repeated up and down "bobbing" oscillations from under the sub-cloud haze layers to at least the bottom of the upper haze layer.

[Bob Shaw]

Planetary circulation is fascinating. Rotating patterns of vortices are not unusual.

This old Tiros-9 photo of the Earth shows a number of large cyclonic and anti-cyclonic weather patterns extending cross the north and south temperate zones. You get a sort of standing-wave pattern like that, with about six of these giant vortices moving around the Earth in the north and south. Called Rossby Waves or planetary waves.

Around the equator, where the change in angular momentum is less, you just have simple hadley-cell circulation, tilted at an angle by coriolis force.

On Jupiter you see many bands of this stuff. A trade-wind band around teh equator like Earth, then some Rossby waves in the temperate bands, and then nearer the poles, the powerful coriolic forces lead to chaotic circulation.

Don:

Remember the early National Geographic paintings of our world as seen from space, back in the mid 1950s? They tended to show Earth with belts, just like Jupiter!

Bob Shaw

[ngunn]

If I get your question right you don't have to integrate, because you know the surface pressure and the acceleration of gravity of Venus. That makes it much simpler:

pressure = force / area
force = mass * acceleration
=> pressure = mass * acceleration / area

This translates to the following formula:

p = M * a / A

=> M / A = p / a

All you have to know is the (equatorial) acceleration of gravity of Venus, which is a = 8.87 m/s², and the surface pressure p = 9.3 MPa.

Therefore:
M / A = 9,300,000 Pa / 8.87 m/s²
M / A = 1,048,478 kg/m²

Graal and I have been round this a couple of times since his 5th June post which you reply to here.
The expression 'mass times acceleration due to gravity over surface area' is fine, but to calculate the total weight of the atmosphere you have to take account of the variation of gravity with height. How much of the atmosphere is at which height depends in turn on how the integrals of pressure, temperature etc shape up. By measuring the surface pressure we in fact measure the weight of the atmosphere, not it's mass directly. To infer its mass we need to refer to the same model of the atmospheric parameters as we would if reasonong in the opposite direction, from mass to weight, and hence pressure. This is what graal has been doing (I think!)

[MichaelT]

measuring the surface pressure we in fact measure the weight of the atmosphere, not it's mass directly. To infer its mass we need to refer to the same model of the atmospheric parameters as we would if reasonong in the opposite direction, from mass to weight, and hence pressure. This is what graal has been doing (I think!)

Oh, I see
Yes, that is what I forgot. Gravity acceleration is not constant with height and the change is not negligible... So the formula that I gave would just be the lower mass limit wouldn't it?

That's certainly a difficult problem.

Michael

[The Messenger]

Oh, I see
Yes, that is what I forgot. Gravity acceleration is not constant with height and the change is not negligible... So the formula that I gave would just be the lower mass limit wouldn't it?

One would think so, but if I have followed Gaal correctly, the quoted mass of the Venus Atmosphere is less than this 'simple' limit. There are a number of possibilities that could lead to this unintuitive result - including the non-linear thermal capacity CO2.

[ngunn]

Which is what I still don't understand (or believe). In this limiting 'skinny atmosphere' aproximation every air molecule is assumed to be near the surface experiencing the maximum possible g. The atmosphere cannot weigh more in any other configuration than it does in this one and the thermal and other properties of the gas become irrelevant in this approximation. There is one, and only one, way that the air molecules could exert a reaction force on the surface of the planet greater than their own weight and that is if they were being fired off ballistically faster than the escape velocity and leaving the planet altogether.