[twawaaay]

Venus has plenty of atmosphere above the surface, but not above the point where there is 1 ATM of pressure.

In case of Earth most of protection comes from our magnetic field. The reason is that magnetic field sweeps ALL charged particles coming from the sun while atmosphere only stops some.

When a particle drops into atmosphere it has a chance to collide with an air molecule, the deeper the higher the chance. But there is always some number of particles that were fortunate enough to reach far enough. Whereas magnetic field is constantly acting on every charged particle and deflects every single one of them.

Only very highly energetic particles can cross magnetic field and these tend to come from outside our solar system and are very low in numbers.

One thing we rely on atmosphere to take care is UV radiation which is photons which is not charged which means our magnetic field does nothing to it. Up to some energies UV is easily caught even by very thing protective layers (for example sunscreen!). It is not like you are going to be showing skin on Venus anyway -- you are going to be always enclosed with material that can stop UV, so this is not an issue. Over certain energies we land in X-ray territory and here our solutions are pretty limited but I do not see a reason why Venerian atmosphere at 1atm should be any more transparent to X-ray than ours.

[marcosdumay]

It has about as much atmosphere above the point where the pressure is 1ATM as we have on Earth. And no, we don't know if Earth's magnetosphere ever filters most of the incoming radiation (we don't such good measurement of the incoming radiation), what we know is that at sea-level, our atmosphere alone is enough.

AFAIK, every time we measure it better, the effectiveness of our magnetosphere decreases. But it can only stop charged particles anyway, and air is very good at stopping those.

[schiffern]

>And no, we don't know if Earth's magnetosphere ever filters most of the incoming radiation (we don't [have] such good measurement of the incoming radiation)

Where did you hear that?

The space station (and presumably other satellites) is perfectly capable of measuring this.

https://www.jpl.nasa.gov/images/pia04258-comparison-of-marti...

https://ntrs.nasa.gov/api/citations/20070018244/downloads/20...

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016...

[simonh]

The space station is in low Earth orbit, so quite low inside the earth’s magnetic field. That’s why the radiation flux shown in the first chart you linked is so low relative to Mars, even though the earth is much closer to the sun. However we have sent out multiple probes able to measure the radiation environment away from earth. There’s lots more to learn, but we already know a fair bit.

[foobarian]

There is also probably a range of viable pressures so going down to multiple ATM would still work and provide more shielding.

[Retric]

1 ATM of air is the same amount of material as 33 feet of water which provides a great deal of protection from charged particles. I doubt enough charged particles can penetrate to the surface that it’s a meaningful issue.

I’ve seen many books etc suggest the earths magnetic field is required, but I haven’t found direct evidence for it doing anything beyond protecting the ozone layer.

[schiffern]

>1 ATM of air is the same amount of material as 33 feet of water which provides a great deal of protection

"Amount of material" isn't what's relevant. It's closer to "number of atomic nuclei."

A certain mass of air is less shielding then the same mass of water. By number density, air is mostly nitrogen atoms, whereas water is mostly hydrogen atoms. Overall this means that per kilogram, water contains 2.4x as many atomic nuclei as air.

--

Of course there are bigger problems with Venus cloud cities. At the 50 km height where the pressure is 1 atmosphere, the temperature is 75 °C (167 °F). At the 55 km altitude where the temperature is 27 °C (81 °F), the pressure is 0.5 atmospheres.[0]

As a bonus, both these altitudes lie deep within the layer of sulfuric acid clouds (50-80 km).

[0] https://en.wikipedia.org/wiki/Atmosphere_of_Venus

[Retric]

Don’t stop there. Charged particles in the solar wind is mostly alpha and Beta particles. 33feet / 2.5 should stop what 99.9999% ish of them?

https://sciencedemonstrations.fas.harvard.edu/presentations/...

Absorbing materials and their alpha particle penetration depths.

5.5 MeV alphas: AIR(STP) 3.7 cm

2.3 MeV Beta: air 8.8 m

Solar wind is even less energetic.

Edit: “Auroral emissions typically occur at altitudes of about 100 km (60 miles); however, they may occur anywhere between 80 and 250 km (about 50 to 155 miles) above Earth's surface.” it really doesn’t take much atmosphere to stop it.

[schiffern]

That's not really relevant.

Charged particles from the Sun (SEPs) aren't what determine the design envelope for radiation shielding. Your overall dose will almost entirely come from galactic cosmic radiation (GCR) at much higher energy levels, which is significantly harder to shield against.

Those particles are what ultimately determine your shielding thickness requirements. That's true whether you're on Venus, or Mars, or a space colony.

[Retric]

https://ntrs.nasa.gov/api/citations/20205008318/downloads/20...

NASA’s direct comparisons between New Mexico (55) and Antarctica (160) only showing a relatively modest decrease from earths magnetic field when measured by high altitude balloons, but again very little GCR reaches the surface.

To be clear a very small fraction of GCR is extreme high energy particles which penetrate just fine.

[schiffern]

Hard to say, since that's in grays instead of sieverts. The two can give very different curves.

>again very little GCR reaches the surface

On Venus there would be less shielding than on the surface of the Earth.

The minimum acceptable altitude is ultimately limited by temperature, not pressure or radiation.

[zopa]

0.5 atmospheres isn’t a problem: that’s about what Everest Base Camp is. The sulphuric acid might be a bit unpleasant though.

[Ankaios]

The mass of atmosphere above Venus' one-bar pressure line is significant—it's similar to the atmosphere mass above sea level on Earth.

Also, our atmosphere is much more important for protecting us from energetic particles than Earth's magnetic field. The atmosphere can stop everything the magnetic field can, and more.