Alien Gold

[coyotesfrontier]

Most of the metals on the periodic table are a boring grey. Gold is one of the few with a different color, making it very valuable along with its rarity. However, gold's coloration only appears unique in the visible spectrum. In other wavelengths it loses its uniqueness, and other metals take the crown of having a unique color.

The eyes of aliens would only be able to see in the wavelength outputted by their star, which would be different then what human eyes see. Therefore, a different metal then gold would have a unique coloration to their eyes, and be valuable.

I'm curious to see what metal would have a special color to aliens that have evolved under the light of a class-M red dwarf, but I'm not sure how to do the calculations.

[NFUN]

It's pretty intuitive to do with without having to do any math

 

Here's a chart of the reflectance of gold:

Higher reflectance means it's more that color, simple enough. Gold has very little reflectance until you get past 500 nanometers

Here's the visible spectrum. Gold has little violet or blue colors. It's a mix of a little green, and mostly yellow, orange and red colors. Pretty much what you'd expect

The Sun's radiation curve (as a blackbody) looks like

In micrometers. I've marked about where the visible light range is, from violet at 380nm, and red at 750nm. The blackbody curve for the star you're talking about, at ~3000K, looks like

Assuming that the min/max wavelengths the alien would see at should have the same proportional intensity to the max as our Sun has (their curve might be wider, because it'd be dimmer), eyeballing this curve, I'd say you'd be looking at a range between 750nm and 1500nm

So, now you need to find data on metal reflectance that indicate a weird curve like gold has, so that some covers show up much more strongly than gold does. I found this

which is a pain to read, but seems to be the most comprehensive thing of this type I can find easily. You're not getting anything nearly as weird. Molybdenum seems to be your best bet here. If it had a curve like that in the visible range, I'd say it'd look something like copper. You can try finding more graphs like this and eyeballing things

[Spacescifi]

41 minutes ago, NFUN said:

It's pretty intuitive to do with without having to do any math

 

Here's a chart of the reflectance of gold:

Higher reflectance means it's more that color, simple enough. Gold has very little reflectance until you get past 500 nanometers

Here's the visible spectrum. Gold has little violet or blue colors. It's a mix of a little green, and mostly yellow, orange and red colors. Pretty much what you'd expect

The Sun's radiation curve (as a blackbody) looks like

In micrometers. I've marked about where the visible light range is, from violet at 380nm, and red at 750nm. The blackbody curve for the star you're talking about, at ~3000K, looks like

Assuming that the min/max wavelengths the alien would see at should have the same proportional intensity to the max as our Sun has (their curve might be wider, because it'd be dimmer), eyeballing this curve, I'd say you'd be looking at a range between 750nm and 1500nm

So, now you need to find data on metal reflectance that indicate a weird curve like gold has, so that some covers show up much more strongly than gold does. I found this

which is a pain to read, but seems to be the most comprehensive thing of this type I can find easily. You're not getting anything nearly as weird. Molybdenum seems to be your best bet here. If it had a curve like that in the visible range, I'd say it'd look something like copper. You can try finding more graphs like this and eyeballing things

 

While I have no need for this, the fact that put yourself out to answer his question...that's impressive to me.

[YNM]

5 hours ago, coyotesfrontier said:

I'm curious to see what metal would have a special color to aliens that have evolved under the light of a class-M red dwarf, but I'm not sure how to do the calculations.

Given your question, I actually wonder whether fool's gold (FeS₂) would look much more convincing to human eyes under the lighting condition. Fool's gold is pretty much just grey under strong sunlight (hence you can tell them apart easily, actually) but in a mine when your source of light is only a torch (so reddish light) back then it's easy to be fooled.

Edited January 11, 2021 by YNM

[Piscator]

I don't know about strong, direct sunlight but (uncorroded) pyrite is pretty golden under regular lighting conditions too, not just by torchlight.

Also as a quick side note, the traditional value of gold doesn't originate from its interesting coloration alone but also from its mechanical and chemical properties, that is, its workability and high resistance to corrosion, as well as its relative rarity. (After all copper looks as interesting as gold color-wise but is less highly regarded because it's a more common element and has a tendency to patinize.)

[JoeSchmuckatelli]

@NFUN - solid answer! I enjoyed reading your response 

@coyotesfrontier-cool question.  Not something I'd ever thought about 

Edited January 11, 2021 by JoeSchmuckatelli

[Nuke]

gold has other properties that make it a desirable currency beyond its color. though i think our assigning value to gold is cultural rather than physical.

[kerbiloid]

It's a chemically stable rarity with highest density between other other ancient/medieval metals,

so:

It can't be (created/found by the side of the road) or easily reproduced, so its amount is limited.

It can be stored for millenia without erosion, in any medium (air, ground, water, bog, sea water, sunlight, etc).

Its alloys are significantly less dense than gold, because of ~20 g/cm³, twice greater than the next neighbors , silver and lead.
So, a counterfeit coin is either of same size and shape but lightweight, or of the same weight but smaller/thinner.

[mikegarrison]

3 hours ago, kerbiloid said:

So, a counterfeit coin is either of same size and shape but lightweight, or of the same weight but smaller/thinner.

You messed that up. If it's the same weight but not gold, the coin is probably larger.

[kerbiloid]

Yes, larger. The original one is smaller.

Edited January 12, 2021 by kerbiloid

[K^2]

11 hours ago, Nuke said:

gold has other properties that make it a desirable currency beyond its color. though i think our assigning value to gold is cultural rather than physical.

I mean, it's cultural, but it is an almost inescapable consequence of its properties. Because gold was used in jewelry-making, it had some intrinsic value. It's also very easy to split and relatively easy to combine. More importantly, it will never spoil. So you have something that you know will always have some value, even as just a piece of shiny, and it will never, ever lose that value so long as there are people in the world. That in itself has a lot of additional value. Add to that the fact that it's hard to find, so nobody's going to devalue gold by just coming up with an enormous quantity of it, and you suddenly have something that's perfect for storing value. It can be a currency or backing for one. The only aspect of this that's historical is that we now have far more candidates for such a material, but gold is still the go-to due to being time-tested.

The idea that another metal can be more appealing to aliens on another world, and it would make that metal the currency metal isn't completely invalid. It's just that you need to take other properties into account. Specifically, gold being rare, but reasonably easy to find in small quantities by a developing civilization, while also being the sort of metal that never rusts away. There aren't that many candidates.

We also do have backup currencies. Silver and copper were always valuable, for example, and even used as coin. But they were also metals that were in a lot of demand for practical uses, not just jewelry. But even then, they never quite reached the status of gold.

[starcaptain]

What K^2 said.  Coupled with this, in modernity gold has many practical uses due to its density,  conductivity and very high ductility. This is why gold is valuable even today even through fractional reserve banking (and debt) have diminished its value sonewhat in relation to currency. Even though we use it less than we're used to for minting, it is still highly sought after in industry. Gold is somewhat difficult to compete with in this regard, compared to other elements. Nothing stands out immediately that could rival it unless one's civilization operated on very different bases for production and value.

 

Tungsten perhaps. It's very hard,  a useful additive in many alloys to increase strength (and hardness, duh) and has an incredibly high melting point. Useful if your society exists at very high temperatures. 

Or perhaps your society lives on the surface of a neutron star, and literally anything other than exotic forms of iron are ultra-rare.

Edited January 12, 2021 by starcaptain

[Nuke]

rarity would be dependent on location. say alien life develops on a planet that is very gold rich. it might be regarded as a useful metal, but not exactly rare enough to be used currency.

Edited January 13, 2021 by Nuke

[mikegarrison]

4 hours ago, Nuke said:

a planet that is very gold rich

This seems highly unlikely. Like all heavy elements, gold is created by supernovas. So relative to the lighter elements, there will never be a lot of it in any one place.

And then in the process of planetary formation, the most dense elements will tend to sink to the core of the planet while it is molten. This is why you find (relative to it's distribution on the surface of Earth) lots of iridium in asteroids -- because on Earth all the iridium sunk to the center and is not available in the crust. (AFAIK this is also true of gold.)

[kerbiloid]

Heavy uranium at least tends to chemically cosplay alcali metals and stay on top.

While the inert gold doesn't.

Pathetic.

On another hand, we can say that the Earth has a heart of gold.

[YNM]

16 hours ago, Nuke said:

say alien life develops on a planet that is very gold rich.

Unless they're living on an undifferentiated minor planet, all that gold would've sank into the core of the planet. Same story here.

[Terwin]

according to: https://www.westcoastplacer.com/how-much-gold-is-left-on-earth/

"There is no shortage of gold on earth.  The problem is that it is much deeper than we can mine.   Current scientific theories estimate that there is enough gold in the core to cover the surface of the earth with a 4 meter thick layer of pure gold."

So we have lots of gold, it just sank deep inside the planet long before we had a chance to get at most of it.

[kerbiloid]

So, any asteroid larger than several kilometers is useless because the rare metals are below kilometers of rock as well,
while any asteroid smaller than several kilometers is useless because it's just too small to contain a lot.

This makes to ask: isn't "our" asteroid belt a derelict orbital mine, after the aliens have mined everything from a Pluto-sized Eldorado planet, leaving a whole belt of rocky scrap?

Edited January 13, 2021 by kerbiloid

[magnemoe]

On 1/13/2021 at 8:42 PM, kerbiloid said:

So, any asteroid larger than several kilometers is useless because the rare metals are below kilometers of rock as well,
while any asteroid smaller than several kilometers is useless because it's just too small to contain a lot.

This makes to ask: isn't "our" asteroid belt a derelict orbital mine, after the aliens have mined everything from a Pluto-sized Eldorado planet, leaving a whole belt of rocky scrap?

I say it depend, an small asteroid has to low gravity for this effect. The dwarf planet style ones probably have. 
https://en.wikipedia.org/wiki/16_Psyche
is believed to be an core of an proto planet, now I would expect other smaller fragments around but its hard to get density estimates of small asteroids without visiting unless they have an moon. 
 

[YNM]

On 1/14/2021 at 2:42 AM, kerbiloid said:

This makes to ask: isn't "our" asteroid belt a derelict orbital mine, after the aliens have mined everything from a Pluto-sized Eldorado planet, leaving a whole belt of rocky scrap?

Well, Ceres and Vesta seems to have been differentiated... but that's literally the two largest asteroid / minor planet in the Asteroid belt.

[kerbiloid]

2 hours ago, magnemoe said:

I say it depend, an small asteroid has to low gravity for this effect. The dwarf planet style ones probably have. 
https://en.wikipedia.org/wiki/16_Psyche

The always mentioned Psyche is 111 km in radius.

So, its surface ~150 000 km².
It's 11 times smaller than Alaska.
Does it have Yukon gold everywhere?

Going deeper you face same problems like on the Earth. You can't get deeper than first several kilometers.

And as its average density is not very high, unlikely Psyche deserves any hopes and efforts.
Other asteroids do it even less.

2 hours ago, YNM said:

but that's literally the two largest asteroid / minor planet in the Asteroid belt.

That's literally the whole of the Asteroid Belt.