[Boerseun]

So - what's the deal with Venus?

The common perception is that it is Hell incarnate, what with a surface temperature of more than 500C, and pressure like a kilometre under Earth's ocean.

But - Venus has incredibly long days, which means that when the sun sets, it sets for about 90 days (I'm talking under correction here, but that's roughly how long it is). In which period there'll be zero solar input. Will Venus's night side be heated by ground radiation? Will enough energy be radiated to space to cool it down? Will the CO2 atmosphere trap enough heat to perpetuate the hellish condition throughout the night, or, seeing as it's about three-four Earth months before the sun comes up, would the atmosphere start snowing out as dry ice? Does any data exist on the night side of Venus?

Keep in mind how quickly the temperature drops when the sun sets on Earth. If the sun were to dissappear and not come up for another three months, I guess Earth's atmosphere will start snowing out in less than a week. Wild guess, I know - and we have a hell of a lot less atmosphere than Venus, but still - in the lack of solar input for such a long time *something* funny is bound to happen...

[pgrmdave]

I believe that Venus's atmosphere contains a lot of greenhouse gasses, which allows it to retain heat much better for much longer.

[pgrmdave]

Here's Wikipedia's take on it:

Owing to the thermal inertia and convection of its dense atmosphere, the temperature does not vary significantly between the night and day sides of Venus despite its extremely slow rotation

A common conceptual misunderstanding regarding Venus is the mistaken belief that its thick cloud cover traps heat, as the opposite is actually true. The cloud cover keeps the planet much cooler than it would be otherwise. The immense quantity of CO2 in the atmosphere is what traps the heat by the greenhouse mechanism.

[TheBigDog]

This is a venus question for the chemists out there. Are there the right combination of chemicals in the atmosphere of venus, that they could be used as a fuel source for machines that landed there? If so, would it be an atmosphere condusive to a race of self propogating machines, since there would be a virtually limitless supply of fuel?

Bill

[UncleAl]

Venus is 0.72333 the distance to the sun as the Earth. Being about the same size it then intercepts 38% more solar energy, and it cooks. The very large CO2 content of its atmosphere - cooked out of its carbonates and from oxidation if its primordial carbon - makes it cook harder. Positive feedback.

[Tormod]

UA is right. The probes which have vistied Venus have measured about 90% CO2. There is some oxygen (about 4 percent) and some nitrogen, but basically the killer greenhouse effects warms the entire planet, regardless of which side is facing the sun.

Since the cloud cover is so extremely thick, not only does it let heat in, but it also blocks light out. I suspect that the actual difference between day and night is not that huge on Venus as seens from a visible light viewpoint.

It's only going to get hotter for Venus.
A new sattelite/probe , ESA's Venus Express will be arriving april, 11

Want to go? see bottom of link,
http://www.esa.int/esaCP/SEME02NFGLE_index_0.html

[ingannilo]

First things first: The temperature is the same on both the "dark side" and the "light side", perhaps due to it's ultra-dense atmosphere.

I was able to turn up some info on the Venus that satisfied most of my curiosities :

Surface Pressure: 92 bars
Average temperature: 737 K
Diurnal temperature range: ~0
Wind speeds: 0.3 to 1.0 m/s (surface)
Atmospheric composition (near surface, by volume):
Major: 96.5% Carbon Dioxide (CO2), 3.5% Nitrogen (N2)
Minor (ppm): Sulfur Dioxide (SO2) - 150; Argon (Ar) - 70; Water (H2O) - 20; Carbon Monoxide (CO) - 17; Helium (He) - 12; Neon (Ne) - 7

(source: http://nssdc.gsfc.nasa.gov/planetary...venusfact.html )

[Boerseun]

Thanks for the reply guys - UncleAl, great to see you in the land of the living again! What's it like on the other side?

I read the Wiki articles on Venus last night, and they reckon that Venus's upper-air atmosphere makes a circuit of the planet every 4 to 5 days, which transfers energy from the day side to the night side. That's all fair and well, and the upper atmosphere movement have been calculated at about 300Mph.

Good so far. But here's another gripe:

Venus has an equatorial rotation speed of about 5Mph, or slightly faster than the average human's strolling speed. Which means it won't have an ordered atmospheric design like Earth, where the atmopsheric characteristics are relatively steady and predictable depending on lattitude. There are observable bands, like the doldrums at certain lattitudes, etc. A much clearer example of this is Jupiter's atmosphere, where the high rotational speed (spins once every 10 hours) causes a Coriolis force of such magnitude that the atmosphere is split into clearly discernable clear-cut bands that seems to be seperated so efficiently that some bands even have higher rotational speeds than others. Obviously, the border zone between the bands will be zones of incredible turbulence and chaos, causing some sort of diffusion amongst the bands, but from a distance it seems very well ordered.

Venus, on the other hand, should have a chaotic atmosphere where hot cells will rise and stream to the nearest zone of low pressure, regardless of lattitude. There shouldn't be any rotating weather patterns forming like we have on Earth, and this seems to be the case - there's a photo on Wiki which was taken of Venus in the Infrared spectrum which seems to indicate just this. But what would the interface between the night and day zones look like in terms of atmospheric movement? I haven't seen such a photo, but if I were to speculate, I guess that windspeeds should accelerate from the dusk side to the night side at one hell of a speed as the pressure gradient rises.
But what would these winds do as a low-pressure zone approaches in the absence of Coriolis? Or would the curvature of the planetary surface have the same effect as Coriolis, for instance a cell of high pressure moving towards a zone of low pressure in a lower lattitude will have to 'spread out' to follow the curvature towards the equator? Or, alternatively, would a cell of HP increase in pressure if the LP zone lies closer to the pole, seeing as the circumference at the specific lattitude decreases polewards?

How would an atmosphere on a spherical body react in the absence of the Coriolis Force, and with solar thermal input from only one side?

[Racoon]

Originally Posted by Boerseun

like the doldrums at certain lattitudes,

How would an atmosphere on a spherical body react in the absence of the Coriolis Force, and with solar thermal input from only one side?

I had a giant Fart just a bit ago Boerseun, Let me tell you, Its thermal output warmed the Planet a bit!

I did direct it to one side for protection though, and more Coriolis Force!