"There is an estimated 40 trillion tons of Uranium and 120 trillion tons of thorium in the Earth’s crust. "
Sure it’s rare, but there’s still a lot of it. Apparently there is Uranium on the moon and mars, but not sure if theres enough of it to save the earth or not.
Except the Earth itself is 5.9 ×10^24 kg. Yes, there’s a lot of Uranium in the Earth in absolute terms. In relative terms it is an extremely rare element.
Although looking at the tables it’s a lot more common than gold or silver, but still much less common than such obscure but relatively abundant elements as lanthanum, dysprosium, or rubidium.
If I was an alien traveling light years across the galaxy to get some salt water I’m not going to stop and extract hydrogen, oxygen, chorine, and sodium from a bunch of different planets, I’m heading right toward that big blue ball that’s got 2/3 of it’s surface covered with salt water. I’m probably gonna be happy about all the other stuff on the planet that’s in ready to use form. Especially edible stuff. Did I mention that we started the obesity crisis you have years before we arrived?
Well I just phrased the question a cute way, but the real question I’m wanting to know of course, is, are all the materials we could possibly need for industry available outside earth in sufficient quantities.
What about making plastics? could we make them from short chain hydrocarbons available on the moons of Jupiter and Saturn?
Given all the planets came from the same primordial cloud, the general range of elements in all the planets is much the same. At least to a good first approximation. The gas giants retain the lighter gasses, but after that there isn’t a lot to pick and choose between one rocky planet and another in terms of gross constituents.
However there is a feature that the Earth has that is close to unique - an active geology, and one that involves the presence of water. It is this pairing that results in the creation of most mineral deposits. It is all well and good to have x trillion tons of rare element y in the crust. It is a very different thing to have had an active geology including mineral transportation mechanisms that have leached and concentrated that element over the millions of years into easily mineable highly concentrated deposits. Ones that don’t require a large fraction of the planet to be put through a blender to extract the one part in a trillion that is the average concentration.
Mars shows some signs of such mineral transport, but it stopped a very very long time ago. Pluto might have some active geology, but it is too cold, and doesn’t involve water. Venus and Mercury seem too geologically quiet - and again, no water on Mercury.
Water is critical as deep down, the water is both very hot, and under high pressure. Much hotter than boiling point at the surface. Water under these condition can dissolve just about anything. Including metals you would never imagine ever dissolving. Geological processes drive a huge engine of mineralisation that delivers streams of mineral laden water to near the surface, where over time it leaves highly concentrated deposits. If our alien friends were in need of most of our favourite industrial elements, they would be calling here first, where the pickings are easy.
It is possible we might solve two problems in one go if we could convince them that the best place to mine is our trash dumps.
Hey, if people said “we don’t know if there are whales on Europa until we send a probe…”
Pearls? Amber?
Trailer parks?
Regards,
Shodan
Hey, maybe there’s a Space DeBeers that’s really, really committed to peddling the stuff.
If girls like snazzy cars, can you imagine what they’d put out for a guy with a spaceship? Try to compete with that male, earth mortals. 
Hah! I was going to suggest that in my post, but decided at the last minute not to.
And yes, it would be odd that interstellar travelers would need coal, but who knows? The OP didn’t specify that it had to be realistic.
If you’ve ever seen the movie you know the aliens have something even more attractive than spaceships. 
:eek:
And if you haven’t seen the movie, you’ve been missing some mighty fine 1980s Grade-B stuff. Highly recommended if you’re into dumb low-brow movies. Art house it ain’t.
Europa would be a much easier place to get salt water from. At worst, you just need to bore a hole through about 10 miles of ice, and then you have access to all the salt water you could ever want (more than Earth has, anyway). There may be places where the crust is much thinner. The big advantage over Earth is escape velocity is only 2 km/s, compared to 11 km/s on Earth.
–Mark
On the other hand, getting in and out of Europa orbit takes a pretty significant amount of energy. Even if you grant the aliens the perfect ability to aerobrake on arrival in the Jupiter system, they still need 6 km/s to transfer to Europa, 2 km/s to land, 2 km/s to take off, 6 km/s to leave Europa’s orbit, and 3 km/s to depart the Jupiter system (for a total of 19 km/s if I’m reading this delta v chart correctly).
Compared to Earth, again with perfect aerocapture and landing they only need 12 km/s to take off from the surface of the Earth, and a few more km/s to go back to the outer solar system again. So if the aliens can handle crazy aerocapture maneuvers, re-entry and landing on planets with dense atmospheres, the Earth might be a better option. For anyone capable of interstellar travel, a few dozen km/s of orbital maneuvers might be more trivial than re-entry and landing.
My WAG, however, is that all basic elements will be easiest to gather from a small gas giant with a decent size system of rings and small moons. And if the interstellar travelers are planning to stop for a while before departing, they’re better off staying as far out in the solar system as possible. For that I’d recommend they just visit Uranus or Neptune, whichever has the easiest to collect sources of rocks and metals.
Interesting, I hadn’t thought of the cost to get in and out of Jupiter’s gravity well. But you counted 2 km/s to land on Europa and 2 km/s to take off, but only 12 km/s total for the Earth case. Wouldn’t they need 12 km/s to land and 12 km/s to take off? And they’d be deeper in the Sun’s gravity well if they went to Earth compared to Jupiter, so the cost of leaving the solar system (assuming that’s where they want to take the water) would be higher for Earth. I haven’t fully grokked that delta-v chart yet.
–Mark
Also, if we’re estimating the energy cost, we can’t just add the escape velocity of landing and taking off, because the ship would presumably be landing empty and taking off full of water, so the mass would be higher.
–Mark
I did a delta-V chart just like this for Kerbal Space Program! This one is nicer though…
Not if they use any sensible amount of aerobraking. Rather than using a giant rocket to slow down, just use friction conveniently provided by the atmosphere that surrounds the planet you want to land on. It’s the same reason why the Apollo missions didn’t need an entire Saturn V rocket to return to and land on Earth. (On that chart, opportunities for aerobraking maneuvers are shown with the red arrows.)
Aerobraking from interplanetary (or interstellar!) speeds is a hell of a lot more dramatic, so maybe they still need to use their own propulsion to slow down a few km/s to a reasonable re-entry speed. But if we’re positing an interstellar race we might as well give 'em either unobtanium heat shields or the patience to do smaller, repeated aerobraking maneuvers over the course of months or weeks.
You have a point about payload capacity of any resource gathering lander. A Europa launcher will have a much better payload fraction than an Earth launcher, and will be much easier to design as well. Less delta V, lower thrust requirements, no atmosphere means there’s no need for a fairing or a structure that can withstand significant aerodynamic forces… basically just strap whatever cargo you want to the side of your launcher.
[hijack]Can anyone recommend good scifi about a society that survives almost entirely in deep space? It seems that if you can get the basic resources you need from asteroids, comets, etc., then gravity wells are just a trap. I recall that the Hyperion Cantos had the Ousters, with “orbital forests” of solar panels and “comet farms” but there wasn’t a lot of focus on them.[/hijack]
Yeah, aerobraking a vessel large enough to take off again AND carry a large amount of water seems highly problematic, although the cargo space could perhaps be collapsable. If I really needed to extract a large amount of water from Earth I’d probably build a space elevator. That would presumably be well within the capabilities of an interstellar race.
–Mark
A problem with going to Europa and most other Jovian moons is the tremendous radiation from Jupiter. Interstellar aliens may have a solution, though.
By definition, they’d have to. Going at relativistic speeds through the interstellar hydrogen literally converts it into hard radiation at a disastrous rate, and slowboating it means that the total long term exposure becomes far, far worse than what would be experienced in a few years of extracting water from Europa.
More exotic means might not have the same dangers… but we really don’t know. And would imply far more advanced tech than we can anticipate. Frankly, if you can get a working Alcubierre drive or something which accomplishes the same goals, you probably don’t need to travel for resources in the first place.
