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

[qraal]

Hi All

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

At first pass I thought it was easy - same as for an isothermal atmosphere, Po/g, where Po is surface pressure and g is surface gravity. Simple. Except Venus doesn't come close to approximating an isothermal atmosphere. From a graph in Mark Bullock's PhD thesis (Hi Mark if you're visiting) I pulled the figures for Po and To as 92 bar and 735 K, while the left-side of the temperature curve was 250 K at 0.1 bar and 63 km. At about 210 K the temperature drop with altitude stops, then slowly rises into the Cytherean stratosphere.

Ok. My atmospheric physics is pretty limited - I 'modelled' that lapse rate pressure curve as a power law:

P/Po = (T/To)^n

and likewise for density, d/do = (T/To)^n.

Temperature, T, as a function of altitude, Z, I computed as T(Z) = To*(1-Z/(n.Zo)).

Zo = (k.T/m.g), where k is Boltzmann's constant and m is the molecular mass of the atmosphere.

These equations I then integrated between 210 K and 0.033 bar, 70 km, and 735 K and 92 bar, zero altitude.

The resulting equation is m = (n/(n+1))*(do.Zo)*(1 - (T/To))^(n+1) - a bit of simple algebra and the Gas equation shows that do.Zo = Po/g.

Thus the mass is lower than for a simple isothermal atmosphere by roughly (n/(n+1)). In this case n = 6.33, higher than the dry adiabat for CO2 which gives n = 4.45.

Now an adiabatic or polytropic atmosphere is an idealisation, but it seems odd to me that whenever Venus' atmospheric mass is discussed people always use the higher isothermal value. Have I missed something important in the physics, or is Venus's atmospheric mass just 86.4% of the usually quoted value?

[Guest_DonPMitchell_*]

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.

[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.