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If a planet like Crait existed and was covered by (mostly) white sand, what would its average albedo be? Crait is a planet from Star Wars that has a thin layer of white salt on its surface.

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Given the pictures of the planet in it's Wookipedia entry I'd estimate it's Albedo to be similar to Ocean Ice, approximately 0.6. So from space it would appear darker than fresh snow but brighter than a lot of clouds appear from space on Earth. White Sands in New Mexico is made of gypsum sand, the individual grains have an albedo of approximately 0.85 but the desert as a whole has a lower value, in the 0.45-0.65 range depending on angle of incidence, so for a world largely covered in similar deposits I'd say 0.6 is about right, if not a little high if the planet has at least some oceans.

Having actually read the Wookipedia entry it turns out the planet is covered in Salt rather than white sand, the salted areas could have an albedo similar to the Bonneville Salt Flats, which depending on the angle the sun hits them can be above 0.9. While my estimate stands the fresh salt areas may be far brighter than the average I've given above would suggest.

Have a look at this article if you want to see where I'm pulling the numbers for the salt-flats and White Sands from but be warned it's not easy reading.

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According to the Wikipedia article on albedo, the value for dry sand varies between around 0.37 and 0.44.

Now, sand should produce an effect similar to that of the moon's regolith: it's called retroflectivity, and makes granulous materials shine a lot more when seen from the same direction as the light source. This makes the full moon more than 10 times as bright as it should be because of the regolith's albedo alone. In the case of sand it may not be 10 times, but, as Ash suggest, could increase the albedo to 0.8-0.9 when the planet is in "full" phase

The idea is that grains of sand cast shadows on each other, producing an overall perceived darkening of the surface. These shadows disappear if you look from a similar angle to the light source, just as nightly photos with flash show little to no shadow

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