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marsbug
2014-Feb-01, 04:48 PM
Hello! I’m going to offer up a slightly outside the box (though maybe not that original) thought. A while back on this thread (http://cosmoquest.org/forum/showthread.php?111131-Making-Moon-habitable/page3)on lunar terraforming quite a bit of evidence - studies, simulations etc – was unearthed by interested parties showing that the Moon could have held onto a substantial atmosphere (http://www.nature.com/nature/journal/v248/n5450/abs/248657a0.html)for meaningful (though geologically very brief) periods of time. Major asteroid impacts could have supplied a short lived atmosphere in the milibars range, which might have persisted for centuries:


a tycho generating impactor occurs of the order of every 10^8 years…which would generate a millibar class transient atmosphere.

Quote from this paper (by Alan Stern) (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.21.9994&rep=rep1&type=pdf) page 47. Such an atmosphere and it’s decay would be a hell of a thing for a scientist to watch, or learn about. As it cooled things would condense out of it, it would carry winds and potentially vaporize subsurface volatiles (it would start out very hot), redistributing them. The Moon has certainly seen impacts of this size, and bigger, throughout its history. It has also seen volcanism, perhaps a recently as a billion years ago (http://www.space.com/12419-moon-side-rare-volcanoes.html). I’m wondering: As we explore the Moon, will we begin to see signs of the effects of these atmospheres, and is it possible that we’ve already seen them without knowing what we’re looking at?

To quote Alan sterns paper again: “the 100 year to 200 year timescale between impacts of sufficient size to temporarily transition the lunar atmosphere… is particularly interesting [here he’s talking about atmospheres that are far thinner than millibar class tycho atmospheres, but still much thicker than the current exosphere]…crudely speaking this implies that the duty cycle for significant lunar atmosphere transients above the current level is 0.1% to 3%, which is surely non trivial. The fact that the Lunar atmosphere routinely exhibits transients of this magnitude is not widely recognised.” It sounds as if the Moon may have a meaningful (but still very thin) atmosphere at some point in the next century or so, or may have had one in the relatively recent past. If this happens regularly, will it have had a measureable effect over billions of years?

Squink
2014-Feb-02, 12:53 AM
Mars typically runs near 6 millibars, and we regularly see dust devil trails formed there (http://apod.nasa.gov/apod/ap091021.html).
Lunar impact gardening would cover trails like those over time, but it'd take a while (http://en.wikipedia.org/wiki/Impact_gardening)
It is estimated that the top centimeter of the lunar surface is overturned every 10 million years. Might still be visible sign of lunar dust devils if the last big impact wasn't too far back.

marsbug
2014-Feb-03, 11:28 AM
I was more considering chemical traces, for example where a hot transient atmosphere had deposied a thin layer of something on the surface as it cooled. But I wonder if physical traces might be preserved somewhere like you suggest? An atmosphere that lasted long enough to move material by wind might leave a layer of windblown regolith in regions regolith should not have otherwise reached?

Or: A lunar atmosphere would even out temperatures between shadowed and light regions, and redistribute volatiles trapped in polar craters more evenly. If there are atmospheres thick enough to transport significant amounts of heat into polar craters forming every few thousand years they might leave behind evidence by smoothing out the concentrations of volatiles across the poles, and driving them into the deeper regolith where temperatures are more stable. So volatile concentration might be one indicator of how often a significant atmosphere is generated.

publiusr
2014-Feb-08, 08:25 PM
I was thinking about atmospheric transport on shell worlds. If you want to blow a lot of dust, opening up a vent on one side would blow some surfaces rather clean. I think the atmosphere on Titan blows its icy crust a bit IIRC.

marsbug
2014-Feb-13, 07:08 PM
Titans atmosphere is even denser than earth's so I imagine the wind carries at least as much force! Following the train of thought on impact produced lunar atmosphere's volcanic activity would produce a more consistent atmosphere. And an impact into a volatile rich area would produce a bullseye effect, where the subsurface volatiles were processed differently at different distances from the impact site. Including, maybe, limited amounts of aqueous processing at the right distances from the impact and below the surface.

Van Rijn
2014-Feb-14, 04:55 AM
There are some nice links up there marsbug, thanks. I remember reading some of that before, but it's been decades.



Or: A lunar atmosphere would even out temperatures between shadowed and light regions, and redistribute volatiles trapped in polar craters more evenly.

And if the cold traps were warmed enough, they might increase the density of a temporary atmosphere more than you'd expect just from the external source alone. Or perhaps the cold traps would freeze out part of a temporary atmosphere faster than you'd expect from other loss mechanisms. Layers of volatiles in the cold traps might have evidence of temporary atmosphere. I wonder if future selenologists might eventually be able to study the past lunar "climate" by taking core samples there, like ice cores form Antarctica that tells us about the past Earth climate?

Noclevername
2014-Feb-14, 06:28 AM
Might still be visible sign of lunar dust devils if the last big impact wasn't too far back.

Would the Lunar day/night electrostatic rise and fall of dust obscure those traces?

marsbug
2014-Feb-14, 03:30 PM
There are some nice links up there marsbug, thanks. I remember reading some of that before, but it's been decades.



And if the cold traps were warmed enough, they might increase the density of a temporary atmosphere more than you'd expect just from the external source alone. Or perhaps the cold traps would freeze out part of a temporary atmosphere faster than you'd expect from other loss mechanisms. Layers of volatiles in the cold traps might have evidence of temporary atmosphere. I wonder if future selenologists might eventually be able to study the past lunar "climate" by taking core samples there, like ice cores form Antarctica that tells us about the past Earth climate?

Thank you Van Rijn, it's a thought that's interested me for a while. Re coring in the lunar cold traps: We know (95% sure)that the lunar surface generates water at a constant rate as the solar wind interacts chemically with the solar wind, and that this water seems to be more concentrated towards the poles. It makes sense that the grains in the cold traps are developing a mantle of water ice, and that the depth of ice accumulation will vary with depth below the surface (http://www.ifa.hawaii.edu/~norb1/Papers/2007-coldtrap.pdf).

This ice will likely be fairly amorphous - as the water molecules hit the cold grain surface they will stick at the point the landed due to the cold - and will build at a steady rate. A volcanic eruption or impact causing a transient atmosphere will interrupt the grains icy mantle with a layer of something else, depending on the composition of the impactor/impact zone and resulting atmosphere. We could characterise the transient atmosphere from the depth and composition of its deposit, the degree of crystalinity it has, and how much it has affected the underlying icy mantle.

In this way we could probably build up an impression of lunar history, solar system history (this link goes into some depth on exactly how) (http://www.lpi.usra.edu/meetings/LEA/presentations/wed_pm/3_Crider_History_of_Solar_Syste.pdf), and the history of the solar wind.

There is also the possibility of organic chemistry taking place in the ice over time (due to energy from cosmic rays) or due to episodic impact heating. It all seems like a good piece of science, just sitting in our cosmic back garden! And it could give us glimpse into times when the moon was a totally different world.

marsbug
2014-Feb-14, 03:33 PM
Would the Lunar day/night electrostatic rise and fall of dust obscure those traces?

I imagine that impact gardening wouldn't help either. But we might just need to pick the right spot to look.

marsbug
2014-Mar-11, 02:41 PM
Apologies for the thread necromancy, but this seemed like the logical place to post this abstract on simulations of a transient lunar atmosphere and its effect on water distribution (http://www.hou.usra.edu/meetings/lpsc2014/pdf/2742.pdf) from the upcoming LPSC 2014. There's also one on the amount of water and volatiles in various lunar volcanic deposits (http://www.hou.usra.edu/meetings/lpsc2014/pdf/2012.pdf) ( another transient atmosphere source).

There's a whole section on LADEE and the current lunar exosphere - here's the link to all the abstracts (http://www.hou.usra.edu/meetings/lpsc2014/pdf/program.pdf)

From my quick scan through it seems that large amounts of surface ice in the permanently shadowed craters is looking much less likely (http://www.hou.usra.edu/meetings/lpsc2014/pdf/2811.pdf) - IMHO that makes sense WRT micrometeorite impact gardening. However the evidence for hydrogen (which is generally taken as implying volatiles including water ice) in the upper meter of the lunar soil now extends to poleward facing slopes at high lunar latitudes (http://www.hou.usra.edu/meetings/lpsc2014/pdf/2931.pdf)

And, just to throw the cat amongst the pigeons, Vesta stands accused of having water carved gullies! (http://www.hou.usra.edu/meetings/lpsc2014/pdf/1796.pdf). Not sure what to make of that one (a paper hat with a pinch of salt in it maybe), but in theory if enough water gushed onto the surface fast enough.......

Overall it seems the potential for a transient volatile-composed atmosphere on an airless body like the moon is quiet high, and that thinsg like winds in the short lived atmosphere would indeed leave behind measureable effects in things like volatile distribution.

Squink
2014-Mar-14, 11:10 PM
Apologies for the thread necromancyNone needed. I've brought em back after years sometimes. If it fits, it fits.

marsbug
2014-Mar-20, 01:46 PM
Somehow that reads kinda creepy Squink ;)
WRT lunar volatiles and potential non impact sources for a lunar atmosphere; There are serious, if speculative (by their own admission, and very honestly so) suggestions that the moon might have hosted cryovolcanoes. I'd need to see a lot more proof than the paper has, but it is an intriguing suggestion. The paper is attached. The author is a member of this forum I think!