Venus surface temperature and pressure numbers are misleading

Wednesday, February 25, 2009

Maxwell Montes, containing the highest point on the surface of Venus.

I've noticed that the numbers given in articles about the temperature and surface pressure of Venus are often quite misleading. Let me give a few examples before I explain why.

First example:

I know what you're thinking. Venus? Surface temperature of 490 degrees Celsius with about 92 times the atmospheric pressure of Earth's surface? Doesn't sound very hospitable.
Second example:
The prototype Switched Reluctance Motor (SRM) has been operated non-continuously for over 20 hours at Venus-like conditions (460° C temperature, mostly CO2 gas environment) and it remains functional. A drilling system, actuated by two SRMs was tested in Venus-like conditions, 460° C temperature and mostly CO2 gas environment, for more than 15 hours.
Third example:
A mission to the surface of Venus would have high scientific value, but most electronic devices and sensors cannot operate at the 450 °C ambient surface temperature of Venus.
Okay, so what's the problem here? Venus clearly has a surface temperature of about 460° C and an atmospheric pressure 90 times that of Earth, does it not?

Well, in most places, yes. But let's not forget that this area (Ishtar Terra) technically counts as the surface as well:

Ishtar Terra is a highland region with a surface area between Australia and the United States, and as you can see on the map has a large relatively flat area about 5000 m above the surface of the planet. And in the same manner that we see on Earth, the higher up you get on Venus the lower the temperature and pressure. 5000 m above the surface reduces the temperature to 424 °C and the pressure from 92x that of Earth to 66x. At the very highest regions of the planet this falls to 385 °C and 47x the pressure.

This is naturally still extremely hot and the pressure is still immense, but since every degree counts when carrying out a mission, a surface mission to this part of the planet would be that much easier to carry out. That's why when discussing the attributes of a hot planet like Venus I think we should always give the temperature and pressure as a range, not a single number that only shows what conditions are like at "sea level", because there is no sea there in the first place, and Ishtar Terra is no less the surface of Venus than any other part of the planet.

Therefore, change:
Surface temperature: 450 °C
Atmospheric pressure: 92 bars
Surface temperature: 380 ~ 450 °C
Atmospheric pressure: 46 ~ 92 bars
and we finally have a more realistic picture of what Venus is like at the surface.

This could be applied for other colder planets as well like Mars, but since spacecraft we send to planets have already withstood the extreme cold of space on the way over it's not really an issue. With Venus we're often conceiving surface missions using the assumption that surface temperatures and pressures are going to be around 460 °C and 90 bars when simply landing in a different part of the planet will result in numbers lower than this.

Note that this isn't about questioning the knowledge of the people that wrote the three examples I gave above (indeed, I'm a big Geoffrey Landis fan) but rather the fact that always including this one number for surface temperature and pressure is misleading to those that don't know a great deal about the planet.


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