Profits From Asteroid Mining

After the very cool news showing pretty solid evidence that an asteroid breakup and bolide shower was likely responsible for the mid-Ordovician ice age (Schmitz et al 2019), I read about one candidate parent body (or what's left of it) for the L-type chondrites, 433 Eros. This article states that 433 Eros contains "...20 billion tonnes of aluminum and similar amounts of metals that are rare on Earth, such as gold and platinum."

So I set out to calculate the mineral value, based on current prices. For aluminum, I see bauxite cheapest at $50/ton. For gold and platinum, I couldn’t find values per ton of ore so I looked up the current prices (US$1533 and $955/oz resp. as of this writing) then look up average richness of the ores (1 oz/ton and 0.1 oz per ton resp.). Assuming similar richness in asteroid ores to deposits on Earth, would be over thirty-three trillion dollars, which is about 41% of the annual GDP of Earth. And that’s assuming an average 2% growth rate. (The article I linked to calculated twenty trillion, which it may have been closer to in 2014.) Granted, obviously the value will drop when there is suddenly an influx of valuable metals, but I'm assuming you're smart enough to leak the ore slowly and somehow get it to the surface with causing any repeat Chicxulubs.


A question and an observation:

1) How to get down to the surface? Gliders? Can you make gliders out of the (maybe partly processed) material that are disassembled at the surface? There are a number of established concerns that have gathered investors for this enterprise, but that I found, none of them has described how they would get material to the Earth's surface.

2) Most proposals involve mining the asteroids where they are, rather than bringing them nearer to Earth. There's actually a Wikipedia article with a good roundup and list of the companies, but that also points out that Osiris Rex will bring back 60g at a cost of 1 billion dollars.

3) At 2900 cubic kilometers, even if 433 Eros were a perfect sphere (which it's not) it would be just under 9 km to the farthest point from the surface. The deepest operating mine on Earth is South Africa's Ashanti Mponeng at 3.84 km deep. But on Eros, there would not be the same increase in heat and all the attendant problems of real gravity - so the proper comparison is to distance to the pit face. El Teniente in Chile is digging out a single (underground) road that is 17 km, and there are overall in that one mine 3,000 km of tunnels. Compare to Earth, which may have mineral deposits more than 4km below the crust, but we may never got to them - and past the crust, the inside of the planet is a waste because the mantle is molten and mixed. Of course the lay conception of asteroids as solid rocks is usually not correct, as most of them we've interacted with have been rubble piles barely held together by gravity.

4) I selfishly want asteroids to be mined in my lifetime because I believe that's where we'll find evidence of alien life - in the form of small mutant von Neumann probes made from organic chemicals.