What factors influence a moon's reflectiveness?

Question

I know that moon composition and atmosphere (if it exists) will influence how reflective a moon is, but I was hoping for a fairly exhaustive list of materials that moons are actually made of, how reflective each is, and how it compares to our own moon.

For example, if a moon the size of ours had a surface like Mars, or an atmosphere like Venus, or was made of ice, how reflective would it be compared to the moon? What other things might a moon (not invented material but real ones) be made of and how does this impact brightness?

The goal is to understand how much moonlight there is, or isn't, on a built world if we state that a moon is forested, or ice, or whatever.

I'd like a hard science answer that is also written in laymen's terms so non-science people like me can understand.

Answer 1

Sandy Beach identified Albedo as the key measure - and they were spot on for that providing the most scientific approach to determine how much moonlight a specific moon would give off.

Albedo is rated on a scale from 0 - 1 in decimal points. It also generally refers to radiation in the visible spectrum - An interesting concept COULD be if the Albedo was different for different species - therefore giving humans one amount of moonlight and some non-humans a completely different amount of moonlight - eg if their visible spectrum ran much more towards the Infrared or ultraviolet spectrum...

Here is a list of some materials you could potentially "make" an airless moon out of - with their respective Albedo (in the Human visible spectrum):

• Desert sand (grains of silica), 0.4
• magnesium oxide - 0.96 [D]
• matte aluminum - 0.55-0.6 [D-S]
• matte silver - 0.7 [D-S]
• polished aluminum - 0.65-0.75 (S)
• polished silver - 0.88-0.93 (S)
• yellow clay - 0.16 [D]

And here is a list of things you could potentially "make" a moon with atmosphere out of - with their respective Albedo (in the Human visible spectrum):

• Fresh snow, 0.8 - 0.9
• Ocean ice, 0.5 - 0.7
• melting snow (clean) - 0.6-0.62 [M]
• Ice (Sea) 0.3 - 0.45
• Bare soil, 0.17
• black soil (dry) - 0.07-0.08 [D]
• black soil (wet) - 0.02-0.05 [D-S]
• Conifer Forest, 0.08 - 0.15
• autumn foliage - 0.15-0.3 [D-S]
• Deciduous trees, 0.15 - 0.18
• Green grass, 0.25
• Sand 0.15 - 0.45
• tar & gravel - 0.33
• Tundra 0.2
• white dry sand - 0.24-0.32 [D]
• white wet sand - 0,11-0.2 [D]

The letters in brackets refer to:

• D diffuse
• S specular
• M mixed

I found this list collected in this post here: https://corona-renderer.com/forum/index.php?topic=2359.0

which is in a forum dedicated to the rendering software Corona: https://corona-renderer.com/

Albedo is reasonably important in that kind of software so it would make sense someone there would be interested in collecting lists of Albedo of a wide range of materials.

I might not have got the split between airless and moons with atmosphere materials quite right - I suspect clay would change it's albedo if all moisture bled out of it for example.

This would give you a bit of a start on some reasonable scientific approaches. I don't have ANY idea how you would go about getting a list of Albedo for wavelengths outside the Human visible spectrum though... So my list wouldn't really help on my earlier interesting concept :)

To give an example of a moon that would give off a large (Read insane amount) of reflected sunlight would be if it was made largely out of Magnesium Oxide (Which is listed as having an Albedo of 0.96) This means that 96% of all light hitting it is reflected back out.

Answer 2

Astronomers use the term albedo to describe how bright a planet is in absolute terms. When sunlight strikes a planet, some of the light is absorbed by the planet’s surface or atmosphere – and some is reflected. Albedo is a comparison between how much light strikes an object – and how much is reflected.

Venus has the highest albedo of any major planet in our solar system. Its albedo is close to .7, meaning it reflects about 70 percent of the sunlight striking it. When the moon is close to full in Earth’s sky, it can look a lot brighter than Venus, but the moon reflects only about 10 percent of the light that hits it. The moon’s low albedo is due to the fact that our companion world is made of dark volcanic rock. It appears bright to us only because of its nearness to Earth. It’s only about a light-second away, in contrast for several light-minutes for Venus.

Venus is bright (it has a high albedo) because it’s blanketed by highly reflective clouds. The clouds in the atmosphere of Venus contain droplets of sulfuric acid, as well as acidic crystals suspended in a mixture of gases. Light bounces easily off the smooth surfaces of these spheres and crystals. Sunlight bouncing from these clouds is a big part of the reason that Venus is so bright.

By the way, Venus isn’t the most reflective body in our solar system. That honor goes to Enceladus, a moon of Saturn. Its icy surface reflects some 90% of the sunlight striking it.

The most reflective items i can not in our solar system are like the above example of venus of the cloud cover and water and ice on planets/moons which have no atmosphere, its hard to say but this should get you going in the right direction.

This should help a little:

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