Friday, September 25, 2009

Seas of Luna?

Full Moon
The lunar maria, 'seas,' are the only surface features on another astronomical body that we can easily recognize with the naked eye. But (so far as I know) no one ever thought to name them or map them till the telescope showed that they were indeed surface features on a world. And they had barely been named before it was realized that they were not seas at all, but dry plains.

The Moon has been getting dryer ever since. Until yesterday, when news came out that a research team using data from three spacecraft has shown that the Moon apparently does have water after all, in fact quite a bit of it, though very thinly dispersed as a nano-rime on surface rock grains. Moreover, the water seems to migrate toward the poles, suggesting that it might be in greater concentrations there.

I saw the story in yesterday's LA Times, dead tree edition. It is not up yet at Sky & Telescope, but it is up at the Bad Astronomy blog.

Of course there is already speculation about where the water comes from. Perhaps it is primordial, perhaps deposited by comet impacts over the eons. But coolness points for the theory that the solar wind is constantly breeding the stuff, hydrogen living up to its name by sometimes binding to oxygen atoms in the lunar surface.

But this is also one of those times when the March of Science can be exasperating. There wasn't a whole lot of hope for lunar water even back in the pre-Apollo books I read as a kid, and Apollo ended whatever prospects there were for anything like a subsurface permafrost layer. The possibility of ice hung on in a few perpetually shadowed craters, but my recollection is that even this hope had pretty much - so to speak - evaporated. Just back in May I blew off the Moon, largely for this reason.

Now, if these new findings hold up, lunar science is doing an Emily Latella on us: 'Oh. Never mind.'

But it gets better. Two of the three spacecraft whose data provided this information weren't even exploring the Moon; they just happened to pass through the neighborhood. (The third is Chandrayaan-1. I completely missed the news that India launched a moon probe; what a cool way to find out.) But just to add to the weirdness, one of the passers-by was Cassini, which hasn't been anywhere near the Earth-Moon system since it did a flyby in 1999, two years after it was launched. So that data was pretty much sitting on a hard drive somewhere, until someone decided to pull it up and look at it.

So the whole thing is wonderfully contrary and serendipitous. How much it affects the prospect of Doing Stuff on the Moon, I have no clue. On the one hand, 0.1 to 1 percent is quite a bit; at least a few glasses of water from every ton of moon rubble, and perhaps a couple of jugs of it. And baking it out of the rock, then freezing the vapor, doesn't seem hard to do on the Moon, given a pressure vessel. On the other hand, that is a lot of rock you'd have to bake to get a steady supply of water for, say, rocket fuel.

But in any case, the prospects for recoverable water on the Moon seem a lot better today than they did the day before yesterday. And much more important in the great scheme of things, even the prosaic, touched-already Moon has not lost its ability to surprise and enchant.

21 comments:

Citizen Joe said...

I was wondering when you'd bring this up. I've been seeing recent stories saying how there is ALOT of water on the moon and then others saying there is very little or none. I would say that using moon water for fuel isn't so good an idea, but using it for habitation (where you recycle the water) means less to be transported from earth.

Anonymous said...

Just to add insult to injury - Apparently the Viking lander missed discovering water on Mars by about 3-4 inches.

http://www.wired.com/wiredscience/2009/09/martian-ice/

Water water everywhere. Just not exactly where we were looking.

Ian_M

Rick said...

Citizen Joe - I've heard both ways, but the 'dry moon' side always seemed to have the stronger case, until now.


Ian - Yes, I saw that story as well! And also about the newly formed crater (as in within the last year or so with ice thrown up around it.

Jean Remy said...

I never really doubted the usefulness of the moon, water or no water. I always thought that the combination of relative closeness, sizable real estate while having a low escape velocity, mineral richness, lack of atmosphere and being tidally locked simply was too hard to pass by.

We already know that the moon's mineral composition is very similar to Earth's, a fact that surprised geologists (selenologists) when Apollo started bringing back rocks, and which has been since explained by the big impact theory. It always seemed to me that this was an ideal shipyard. Cost to orbit would be ridiculously low compared to an Earth launch: the LEM was able to reach lunar orbit on one piddling little engine and laughable remass tankage. Granted the initial investment will be nothing short of titanic, but over a period of centuries, the savings will probably be felt. The fact that is is a vacuum will allow for very clean "clean rooms" for computer manufacturing. Because of all those reasons, the Moon makes an interesting platform to launch expeditions into deep space.

The tidal lock, on the other hand makes the construction of very large telescopic arrays on the "dark side" rather interesting: nights 15 days long with no Earth to spoil the view and no atmosphere would provide ideal conditions. Sure, telescopes in orbit have their advantages, but with new optical interferometry telescopes and large mirrors, you could build observatories on a scale simply impossible for orbital telescopes. Just as an idea, the ESO completed construction of an array of four 8.2m and four 1.8m telescopes that, like the VLA, can be used as one larger "virtual mirror" and has already returned images at 3 times the resolution of Hubble. The greatest challenge in telescopes now are no mirror size (a 30m and a 40m mirror are planned) but in the complex adaptive optics needed to compensate for atmospheric distortion. This would not be a problem on the moon. Neither would clouds, pollution, or light pollution. Already the big telescope construction sites are in the Andes, showing already the increasingly limited usable locations. It also proves we're willing to go to extreme, hostile places to build them.

If there really is water in the concentrations speculated on by this article, well so much the better. We shouldn't be too surprised at the presence of water, however. After all, we've pretty much accepted now that water is *very* common. Entire moons the size of our moon are made of water, the Oort cloud is basically water. We knew Mars had water before since one of its poles is covered in it (too bad the other one is dry ice). Far more interesting than the presence of water is actually the theory that water is constantly generated by the action of solar wind onto oxygen locked in lunar rock. If we know how that works, can we exploit it? Can we bombard certain areas with hydrogen and actually create more water? I think it is that part of the news, more than the presence of water itself, that could revolutionize plans for lunar colonies.

Anonymous said...

I have to agree with Jean on this one...Luna has, in one day, gone way up in usability. Water, even in tiny amounts, is so useful that its presence could easily tip the scales in favore of setting up a permanant base on our moon. This is so cool; new findings revive old ideas.

Ferrell

Carla said...

I agree with your last comment! Always something new to discover - and just when we think we have all the answers, something will come along and show us that we haven't :-)

Anonymous said...

Speaking of finding odd things out there:

http://www.cnn.com/2009/TECH/space/09/16/new.rocky.planet/index.html

Ian_M

Rick said...

Someone may have been wrong on the Internet last May, namely me.

My problem with the Moon, in practical terms, hasn't been lack of water for drinking or even a full ecosystem, but volatiles for rocket fuel. The Moon is not hard to get on and off of, but if you have to haul all the fuel up from Earth or ship it in from Phobos or Ceres, the pump price will be nasty. (Mass drivers will get stuff OFF the Moon, but 'carrier landings' at 1 km/s are ... iffy.)

My guess is that the first large space mining industry, by far, will be fuel production. If the Moon has recoverable water it has a big, big impact on transportation everywhere beyond LEO. Water is more common than dirt in the Solar System, but most of it is nowhere near Earth.


Ian - I read about that planet at Sky & Telescope. Yikes - it makes Venus seem hospitable!

Jean Remy said...

"I read about that planet at Sky & Telescope. Yikes - it makes Venus seem hospitable!"

Actually if it really is tidally locked, the dark side is going to be as or more (in)hospitable than the moon. The absence of atmosphere removes convection, the entire planet serves as a radiation shield against the stellar wind. Compare it to Venus were the thick acid-laden, corroding, high-pressure, electrically charged atmosphere makes no hemisphere safe.

Now, the DAY side, on the other hand, on the other hand, makes a molten sulfur bath cool and inviting.

Rick said...

True - the night side could be like the old rocketpunk era Mercury, when they thought Mercury was tidally locked, not in a funky resonance.

Or the whole surface might be molten - the planet is big for a rocky planet, and it can only shed its internal heat from the night side.

Jean Remy said...

Good point! I hadn't thought about that. It can't really radiate out "into" the star now, can it?

It could be only a strip of it past the terminus. However it's very possible it was never able to actually cool down.

Either way, I sort of forgot the part about gravity probably being several times that of Earth, so in any case this isn't going to be a comfortable holiday resort.

Rick said...

Reaching the night side would also be a challenge - it means getting up close and personal to the parent star.

Of course, if you can get 500 light years to CoRoT-7, the last part should be a snap.

Mark said...

I wonder if this makes it more or less likely that there is ice in the shadows of craters near the poles? on the one hand the hydrogen they detected there could be this stuff, water locked up in the rocks instead of ice, on the other hand i wonder if it's possible for water like this to accumulate. I guess we'll find out next month when LCROSS hits.

Rick said...

If water migrates to the poles, it ought to be in some greater accumulation there. How much greater, as you say, we may soon find out.

Citizen Joe said...

Couldn't you then drag ice asteroids to the moon and drop them at some of the mid latitudes and then just put your pumping stations at the poles. I think I saw plans for a lunar pole based space elevator to the Earth-Luna L1 point. Meanwhile, the equatorial belt would remain clear for orbits.

Jean Remy said...

I have trouble envisioning an elevator going from the lunar pole to the Earth-Moon L1, to be honest. First of all I don't see the point, since an elevator is going to cost a LOT of money. On Earth that might be (somewhat) justified by the high individual cost of each launch, but if it possible to synthesize fuels on the moon (since there is water, I'd assume LH2-LOX chemical rockets become feasible) the cost per launch would be so small the number of launches necessary to recoup your investment will be consequently "astronomical". That's without even taking into account the instability of L1 points and the complexities inherent in trying to build a tangential cable rather than a perpendicular one: the L1 point is not aligned to the Moon's polar axis, so "dropping" the cable down is going to present some very interesting challenges. The L1 point will be interesting because of the ease of transfer between earth and lunar orbits. However an elevator is highly unlikely.

As to the question of lobbing asteroids down at the moon, that's not for the near future, and to even reach said asteroids, never mind to actually move them, will already require an intensive space program, and therefore most likely the moon would already be an industrial powerhouse by that time. Not only that, but I would assume it would be FAR more efficient and far less wasteful to process the ice in space and ship it down, since the impact will certainly vaporize a lot of that water right back into space. The only reason you'd drop an ice comet on a world is if you're trying to terraform it and introduce water vapor in an existing atmosphere.

Rick said...

If you can move asteroids, I would move them into a convenient orbit to work on them, not crash them onto the Moon.

But if asteroids are mostly big rubble piles, they will be harder to move around.

Citizen Joe said...

There's existing designs for the polar lunar elevator. It has to do with the ability to put solar panels there and always have power. Anywhere else and you have weeks of night.

The idea of crashing ice into the moon is to replenish the supply being used. Sort of like rain and an aquifer.

Jean Remy said...

Once again, we crash it into the moon. The only reason to replenish the aquifer is so you can extract it and process it? And then send it to orbit as fuel? Just leave the ice in orbit. Far more efficient.

Jim Baerg said...

Jean:
Regarding the lunar space elevator & the lunar pole: The elevator wouldn't be attached to the ground right at the pole, see this, http://en.wikipedia.org/wiki/Lunar_space_elevator

Though if you have to build a tramway anyway I wonder if it wouldn't be better to make it all the way from the equator to the pole & create easy access to a long strip of lunar territory.

Rick said...

If you can build a railroad (not to mention the elevator) you can probably build a mass driver. The only hitch is that you can't just launch cargo; you need carrier vehicles with an OMS, expensive enough to want it back for re-use.

In principle you could catch things with the mass driver, but making a 'carrier landing' at 1.6 km/s seems to be looking for trouble.