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Comment by ionwake | Hacker News Reader

Ive always loved this photo

http://www.esa.int/var/esa/storage/images/esa_multimedia/ima...

Beautiful! I guess it's mostly CO2

Edit: holy shit someone else commented that it's water ice. Amazing. I didn't know there was actual water on the surface!

TIL as well. That's pretty cool.

Wouldn't it sublime away within months or weeks in the low-pressure atmosphere?

It won't sublimate if it is always in the shade/in a cold region. See https://en.m.wikipedia.org/wiki/File:Phase_diagram_of_water..... At martian surface pressures (close to 0) it needs to be warmer than ~ -60C to sublimate. Interestingly that's roughly the average temperature measured by rovers. https://en.m.wikipedia.org/wiki/Climate_of_Mars#Temperature

Any idea of the scale of that image? What is the diameter of the crater?

2000 km, so I guess somewhere around the size of India.

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

@edit - 2000km is the size of the whole region, crater is 35 km wide. See below.

2000km is the size of the whole Vastitas Borealis region. The photo depicts only a single unnamed crater inside it.

Indeed, my bad.

Seems to be easy to confuse since the crater seems to have the same name "Vastitas Borealis Crater" [0].

Do you know if it's actually called "Vastitas Borealis Crater" or is it just simply a crater in the region Vastitas Borealis?

> The 35-kilometre-wide crater sits 70° north of the martian equator, in a low-lying region known as Vastitas Borealis. Previous orbiters have spotted ice deposits in craters, but the High Resolution Stereo Camera on board the European probe is the first to return a three-dimensional colour image of an icy spot. The ice may be up to 200 metres thick, and lies over a dune field that has formed in the sediment on the crater's floor. The data were collected on 2 February, and this image was created for Nature last week. [1]

[0] http://www.esa.int/ESA_Multimedia/Images/2006/10/Residual_wa...

[1] https://www.nature.com/articles/435723b

I don't think this one has a specific name. There are a lot of unnamed craters on Mars, even much bigger than this one. [0]

[0] https://en.wikipedia.org/wiki/List_of_craters_on_Mars

Very cool! What's the story there?

Residual water ice in Vastitas Borealis Crater pillars :)

That's going to make SpaceX's eventual ISRU methalox production massively easier. This is great news.

Unfortunately it's at far too high of a latitude - in addition to the solar power problem, it's also far too cold to send affordable hardware.

There's lots of water ice elsewhere on Mars in much more friendly latitudes (Arcadia Planitia is the region I've seen bandied about most often).

At lower latitudes you pick a site where the ice is either not too far underground, or exposed through some exotic action like a calving cliff face (though the latter are usually less convenient for landing).

I wonder how the affordability equation would change with a nuclear power plant. It could be pretty light weight, there is no need for shielding, and the water could possibly be used to cool it.

Unclear - NASA is currently working on the Kilopower reactor, which is probably lower-power than the enormous solar arrays SpaceX is considering. However, if they're expanded into the megawatt range they could be usable.

Shielding is still required, as humans are not the only thing that's vulnerable - electronic and chemical systems are also vulnerable. Burying the reactor in Martian regolith is probably a more risky project than unrolling a massive solar array.

The other problem is the cold. At low latitudes, the temperatures are at a relatively warm Antarctica-like level, sometimes getting to room temperature at the equator at noon. At high latitudes, though, we're talking cryogenics - lows of -150C, averages of perhaps -100C. Making machinery work at those temps is expensive.

I don't understand any of this. On Mars there's a lot of radiation anyway, and humans shouldn't go near the reactor after it's going critical. I don't know what you mean by chemical systems. The point is the reactor doesn't have to be buried, just put it so it's in a crater or behind a ridge (as seen from any settlement) and the radiation is not a problem.

As for cryogenics, either make sure it never drops to cryogenic temperatures in the first place, or make something which can be stored at these temperatures. Once it's operational, the temperature should never drop ever again until it's decommisioned.

The cold is a problem not for the reactor itself (it'll heat itself up quite nicely) but for the other gear involved with a settlement. Chemical plants, mining bulldozers, habitat seals - all of these things get seriously weird when you bring them down to ~125K. (For example: IIRC sabatier plants need to run in the high hundreds of K; if you're going to keep that going in a cryogenic environment you need either an enormous amount of insulation or to be willing to lose a lot of energy to the environment.)

The obvious solution would be to use waste heat from the reactor in a combined heat and power installation, but then you run into the radiation problem. Coolant tubes or heat pipes that run a significant distance are heavy and bulky, but if you want to move your gear closer to keep that weight down you get in trouble from radiation. Note that it's not just people that are sensitive to radiation - the chemical beds required for fuel and oxygen production, electronics on any moving rovers. If you just want power, that's fine, bury it a few km away; but if you also need heat you're out of luck.

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