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I am playing Kerbal Space Program with the Precursors Planet Pack, which starts you on the planet Frontier with a white atmosphere, as viewed both from the surface and from space.

What kind of composition would be needed for a white atmosphere like Frontier?

Let us assume for this question that:

  • The planet is similar to the Earth
  • The sun is similar to the Sun
  • The composition of the planet's atmosphere is the only thing that differs.

Of note that in-game, Frontier's atmosphere is classified as "Exotic" and it is not habitable (neither for humans, nor Kerbals), so this rules out an Earth-like atmosphere entirely.

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    $\begingroup$ I have no clue what a white atmosphere is. Do you mean white when viewed from space? What color is Earth's atmosphere? $\endgroup$
    – Daron
    Oct 21, 2022 at 18:50
  • $\begingroup$ @Daron White when viewed both from the surface and from space. $\endgroup$
    – bigyihsuan
    Oct 21, 2022 at 18:59
  • $\begingroup$ Cool, see my edits. $\endgroup$
    – Daron
    Oct 21, 2022 at 19:02
  • $\begingroup$ @bigyihsuan, I once read a journal article that I failed to keep. I've kicked myself a thousand times for it. Here's the gist of the article: All chemical compounds that can support human life at temperatures that can also support human life experience Rayleigh Scattering in the blue spectrum. In other words, if we could come up with a chemical composition that would create a white atmosphere in the same way Earth's is blue, it would be guaranteed to be toxic to human life. Is that OK? (I read your last paragraph, I'm just being sure.) $\endgroup$
    – JBH
    Oct 22, 2022 at 2:03
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    $\begingroup$ @JBH it's 100% ok to be horrifically toxic to human(/Kerbal) life $\endgroup$
    – bigyihsuan
    Oct 22, 2022 at 14:44

2 Answers 2

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Water Vapour

enter image description here

Your planet looks white from space because there is a permanent layer of water vapour in the atmosphere. The top part is called clouds.

On the surface the atmosphere looks like this:

enter image description here

This is called fog. At least on Earth. The locals don't have a name for it, because it's like this 24-7.

White enough for ya?

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  • $\begingroup$ Yep that's gonna be a great way to achieve the effect for sure, since that kind of diffuse visible white light, Mie scattering, is caused by particles that are large relative to wavelengths yet optically "soft" i.e. way too small for the naked human eye to perceive. $\endgroup$
    – Tmartin
    Oct 21, 2022 at 20:13
  • $\begingroup$ To nitpick, that's water droplets, not vapor. You can't really have droplets without vapor, but it's entirely possible to have vapor without droplets. $\endgroup$ Oct 21, 2022 at 21:11
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    $\begingroup$ It should also be worth mentioning Venus, which is near-featureless white in visible light. $\endgroup$ Oct 21, 2022 at 21:17
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Aluminum and magnesium gas

https://www.reddit.com/r/chemistry/comments/n7n0xl/never_seen_white_flames/

flame color

https://en.wikipedia.org/wiki/Flame_test

A flame test is an analytical procedure used in chemistry to detect the presence of certain elements, primarily metal ions, based on each element's characteristic emission spectrum...

The test involves introducing a sample of the element or compound to a hot, non-luminous flame, and observing the color of the flame that results. The idea of the test is that sample atoms evaporate and since they are hot, they emit light when being in flame.

On reading why magnesium (for example) makes white flames you will find a lot of things that state "because it is very hot". I think the experiment of burning epsom salts (magnesium sulfate) in rubbing alcohol (or a wood fire) puts the lie to this - these flames are not super hot. I found a couple on youtube.

When hot, certain atoms emit white light. Other atoms emit colored light. These are properties intrinsic to the hot atom, not to the temperature.

An atmosphere of hot aluminum and magnesium gas should emit white light. It would look white from space. It would look white from inside it. It would not be habitable for humans or Kerbals.

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