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Comment by cl42 | Hacker News Reader

Wow! If anyone is curious as to why Triton is so bright...

> Covered in a frozen sheen of condensed nitrogen, Triton reflects an average of 70 percent of the sunlight that hits it. It far outshines Neptune in this image because the planet’s atmosphere is darkened by methane absorption at these near-infrared wavelengths.

That's pretty neat!

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The fact that methane absorbs infrared/near-infrared frequencies is also the mechanism that causes it to be a greenhouse gas.

https://en.wikipedia.org/wiki/Neptune#Internal_structure

> "At a depth of 7,000 km, the conditions may be such that methane decomposes into diamond crystals that rain downwards like hailstones.... the top of the mantle may be an ocean of liquid carbon with floating solid 'diamonds'."

Thanks for pointing this out, that is truly fascinating to imagine. I'm now short on sleep due to the wikipedia rabbit hole :)

Also explains why the rings are brighter than the planet here, when they were all but invisible to Voyager 2.

> 70 percent of the sunlight that hits it

It looks like that's comparable to fresh snow or a glacier?

Better than a glacier but worse than fresh snow. "More than 80 to 90 percent of the sunlight falling on fresh snow is reflected back into space, compared to 15 to 35 percent of the sunlight reflected by most ice."[1].

[1]https://earthobservatory.nasa.gov/features/DirtySnow/page2.p...

Is there a good chemical / spatial argument for why this is so?

I think it is because a flat surface gets one chance to reflect by refraction and predominantly only at a shallow angles. A bunch of micro surfaces in an aggregate formation mean it could bounce around multiple times and then head out, or pass through the ice medium and then bounce back out when it exits and reflects off more. Absorption wise a greater ratio of air to ice means it will absorb less often too over the same distance through snow.

This is correct, it's why things like solar panels have a surprisingly low albedo despite being mostly black, they are completely flat.

woah

I originally thought it was a star

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