Sci-Fi: speculation about a desert planet

[JQP]

I'm trying to cook up an interesting desert planet. Dune made me wonder if a tool-using species could turn a planet with plenty of water into a desert planet. Say, one nation starts hoarding water via the "catchments" we saw on Arakis (with some plausible mechanism to prevent evaporation), which kicks off a sort of arms race where everybody's doing it so they don't get left behind. And before they know it, they've sequestered all the liquid water on the planet underground. No more precipitation, no more oceans, seas, or lakes.

But I'm not attached to my explanation. I just want a desert planet, but one with enough water to sustain enough agriculture to support a certain level of civilization, and a population big enough for the planet to be interesting. Something like Tatooine, with its "moisture farmers" and "vaporators" would be okay, too.

Another explanation could be an Earth-like planet, but with one ginormous, roughly-circular continent. The coasts and near-coastal inland regions would be okay, but the interior would be a vast desert.

Or, it could be the liquid water is all trapped far below the surface, but giant cactus-like species evolved to tap into it. And then higher life evolved by exploiting these cactii-wells. Or colonized the planet by exploiting them.

I'm just looking for some ideas here. TIA.

 

[Voleure]

For a start you could get Dune right, you have that world backwards. The sandtrout vector of the adult worms was responsible for locking up all the water on Dune not the Fremen. The leather membrane-like sandtrout were an alien species that considers water a poison and locked the water up by sealing around a small quantity then dying. The sandtrout later metamorphosed into the worms when the habitat was amenable to the adult form.

The Fremen's water caches and plantings on mass were done to transform the planet back to it's original lush origins. Important to get the story right if your going to draw from it for your own writing.

 

[JQP]

Dune the movie then. Not that the point of my post was anywhere within a light year of sucking all possible imagination and creativity out of the subject by adhering to the jots and tittles of fanboy-ism.

 

[Voleure]

Insulting response lol, good luck with your thread ;-)
PS Movie & book the same, personally an alien organism that traps water is a bit more imaginative than people making cisterns.

 

[Ophiolite]

Runaway greenhouse, in the style of Venus, interrupted by late bombardment phase influx of water rich comets which provides some water, but just not a lot.

 

[E=ML^2]

There are various ways of thinking about this concept and a few have been mentioned already.
When you say you want a planet like the one in Dune, a desert planet, I'm sure that is what you want. But I just want you to think about the definition of a desert. You see desert only means a certain amount of precipitation over a defined time-period. This means that to have a desert it doesn't have to be a sandy planet, you could also have a ice planet. I would claim that an ice planet is more plausible than a desert planet mainly because far more likely to have a planet that has a temperature range below that of liquid water than a range that includes liquid water. However, water itself is perhaps quite rare either way, and so precipitation doesn't have to be H2O, you could have methane rain (that is extremely cold) for instance.

Venus has been mentioned as a good candidate, but it's doesn't have to go that far (unless you really want that much desertness (yes, I made that word up)). During the Quaternary (we live in that time-period) there has been several cycles of glacial periods and interglacial periods, but we've still had polar ice caps. and during a ice age, a lot of water gets locked up and temperatures fall globally, which leads to a drier climate (one important factor is to have continents at the polar regions).

I am currently reading a book called, Red Mars that is part of a trilogy. I very much like the ideas in that book, especially when it comes to questions about water. It is also possible for a planet not to have any water per se, but you'd have minerals that contain the elements Hydrogen and Oxygen (together or not) and so water has to be fabricated from those minerals.

I hope this helps you somewhat, good luck and please make the geology plausible! ;)

 

[Andre]

Runaway greenhouse, in the style of Venus, interrupted by late bombardment phase influx of water rich comets which provides some water, but just not a lot.

Runaway greenhouse is only speculation that cannot be tested.

 

[Ophiolite]

Runaway greenhouse is only speculation that cannot be tested.

It can be modeled, which removes it from the realm of speculation.

 

[Andre]

That's not how the scientific method works.

 

[Ryan_m_b]

Runaway greenhouse is only speculation that cannot be tested.

It is unfair to suggest that it is only speculation. It is a hypothesis for Venus's atmosphere that has a valid point a long with several pieces of evidence. Even if it turns out that Venus did not form this way there is nothing to suggest that it could not happen elsewhere. That is more than enough for a science fiction plot.

 

[Ophiolite]

That's not how the scientific method works.

Andre, you are mistaken. That is one of the ways in which the scientific method can work. Are you similarily, then, decrying current theories of planetary formation , which rely extensively upon finite element analysis models? A generation of planetologists may be shocked to learn they are not scientists.

 

[Andre]

A generation of planetologists may be shocked to learn they are not scientists.

Well you know the Rutherford quote All science is either physics or stamp collecting. I think he may have a point.

I cleaned out an appartment today and carried stuff around. :zzz: Sorry, but I'll work on a post tomorrow about the science of Venus. And then we'll see about unfair and mistaken.

 

[Andre]

Okay here we go, the remark...

Runaway greenhouse, in the style of Venus,..

suggested to me that the condition of Venus atmosphere is a done deal.

We can tentativily accept the usual paradigm that in the current condition, radiative equilibrium exists on Venus, somewhere in the top of the atmosphere of Venus, where the energy of the incoming sunlight is in (dynamic) equilibrium with the outwelling long wave radiation. Down from that level to the surface, the temperature is rising in an adiabatic lapse rate. Since the atmosphere is extreme dense, the adiabat reaches extreme heats. No problem there.

Another totally different item though, is, how did all that energy got 'trapped' there, what is the source of the energy? One possible idea (hypothesis) could be the runaway greenhouse and you can model that, using your suppositions like http://boulder.swri.edu/~bullock/vclime.pdf. Obviously there is a lot of discussion in the blogosphere about this, but notoriously absent in those heated debates is the geology of Venus.

How about a bit of scientific method, predicting things based on your hypothesis? If the runaway greenhouse of Venus was about evaporation oceans and the like, you 'could' predict that the surface of Venus would show signs of old water basins and running water. Also, if the surface was heating up due to extreme greenhouse effect, you would expect a to see that reflected in a somewhat less positive or negative lithospheric thermal gradient (geothermal gradient).

So what do we know of the geology of Venus? Obviously no surprise that reality is totally different http://www.gps.caltech.edu/classes/ge151/references/phillips_and_hansen_1998.pdf , suggesting that the surface temperature could have reached 1000K in the past. Note that they tie that to a runaway greenhouse reference (Bullock and Grinspoon 1996), however their previously linked 2001 study appears to give a limit of 900K.

So if that's greenhouse effect, again you'd expect to see that reflected in the lithospheric gradient in that time. However http://www.sciencedirect.com/science/article/pii/S0012821X97000071

Geodynamic modeling of tessera deformation at the ancient Venusian plateau highlands implies lithospheric thermal gradients exceeding 17 K km⁻¹...Higher strain rates — consequently higher thermalgradients — are more probable. We rule out the possibility that the plateau highlands were locally anomalously hot at the time ridges formed in the tessera, that the highlands are dominantly composed of rock more felsic than diabase, or that the crust was weak because it was hydrated. Therefore, the average global lithospheric heat flux when the highlands tesserae were deforming was considerably higher than it has been since.

Obviously the suggestion here is that was the lithospheric heat flux that caused the thermal deformation, not the greenhouse effect.

So if the atmosphere of Venus trapped the heat, (nearly) all the heat, would it also not have trapped the Geo-erm-Veno-thermal heat? Sure, this would be more than neglectable on Earth, but given the heat in combination with the thermal gradient, it seems less neglectable on Venus.

So what causes the interior heat on Venus, I don't know, and ideas about that are not welcome here. But that heat may have played some role in heating up the atmosphere of Venus. How much I don't know, but I think that it is unethical (in a Feynmanian way) to consider the runaway greenhouse effect a done deal, dismissing the considerable internal heat of the planet. After all science is about attempts to refute hypotheses, not to support them with all kinds of modeling. If they are right, they don't need support and refutation attemps would fail.

 

[billiards]

How about a bit of scientific method...

This should be interesting.

So what do we know of the geology of Venus? Obviously no surprise that reality is totally different http://www.gps.caltech.edu/classes/ge151/references/phillips_and_hansen_1998.pdf , suggesting that the surface temperature could have reached 1000K in the past. Note that they tie that to a runaway greenhouse reference (Bullock and Grinspoon 1996), however their previously linked 2001 study appears to give a limit of 900K.

The fact that they tie it to a runaway greenhouse is incidental, the important point is the constraints they placed on past surface temperature.

So if that's greenhouse effect, again you'd expect to see that reflected in the lithospheric gradient in that time. However http://www.sciencedirect.com/science/article/pii/S0012821X97000071

Geodynamic modeling of tessera deformation at the ancient Venusian plateau highlands implies lithospheric thermal gradients exceeding 17 K km−1...Higher strain rates — consequently higher thermalgradients — are more probable. We rule out the possibility that the plateau highlands were locally anomalously hot at the time ridges formed in the tessera, that the highlands are dominantly composed of rock more felsic than diabase, or that the crust was weak because it was hydrated. Therefore, the average global lithospheric heat flux when the highlands tesserae were deforming was considerably higher than it has been since.

Obviously the suggestion here is that was the lithospheric heat flux that caused the thermal deformation, not the greenhouse effect.

1) This work was based on MODELING. What makes this modeling ok but other modeling not ok?

2) Why is the lithospheric heat flux completely decoupled from the greenhouse effect? Surely a cold atmosphere would increase the heat flux out of the earth.

3) They are saying that the heat flux was higher then (when the tessera deformed) than it is today.
-- That is consistent with (a) a higher internal temperature for Venus, or (b) a colder atmosphere in venus. (Or indeed other possible scenarios in which the main thing is the temperature difference between the inside and the outside of venus was greater than it is today.) -- Scenario (b) is entirely consistent (indeed expected) with runaway greenhouse. However, we still need some constraint on when the runaway greenhouse actually happened at least in relation to other geologic events.

So if the atmosphere of Venus trapped the heat, (nearly) all the heat, would it also not have trapped the Geo-erm-Veno-thermal heat? Sure, this would be more than neglectable on Earth, but given the heat in combination with the thermal gradient, it seems less neglectable on Venus.

Sure. If it trapped this heat, that would still be the greenhouse effect. Right?

So what causes the interior heat on Venus, I don't know, and ideas about that are not welcome here.

Most likely the same things that cause interior heat in Earth. Predominantly the decay of radiogenic isotopes. Why is that a banned topic now?

But that heat may have played some role in heating up the atmosphere of Venus. How much I don't know, but I think that it is unethical (in a Feynmanian way) to consider the runaway greenhouse effect a done deal, dismissing the considerable internal heat of the planet.

Wow. The science is by no means "a done deal". I believe it is unethical for someone who clearly doesn't fully grasp the science to be throwing their weight around in scientific forums trying to knock down real scientists work by accusing them of being unethical.

 

[Andre]

If you agree that the science is by no means "a done deal", why is it unethical to challenge the notion that the conditions on Venus are the result of a runwaway greenhouse effect?

The essential thing is the "runaway" in the greenhouse effect part. Essentially this means that solar energy alone would be able to generate this end effect with a positive feedback loop, if we accept the definition in wiki:

A runaway greenhouse effect is a process in which a net positive feedback between surface temperature and atmospheric opacity increases the strength of the greenhouse effect on a planet until its oceans boil away.http://pubs.giss.nasa.gov/docs/1970/1970_Rasool_DeBergh.pdf , Uni of Tennessee

On the other hand we could visualize a scorching hot planet with a dense but radiative inert atmosphere. That too would heat up the atmosphere, without the need of greenhouse effect.

If we accept that Venus underwent a catastrophic resurfacing under tremendous heat as suggested by the surface features, how can we see the difference between heating of the atmosphere by runaway greenhouse effect rather than the transfer of the internal generated heat to the atmosphere? Yet that's what you see, the runaway greenhouse effect being taken for granted. Is that ethical then? (in the sense of http://www.lhup.edu/~DSIMANEK/cargocul.htm)

Radiogenic heat? Regardless of all the ideas http://www.sciencedirect.com/science/article/pii/S0019103599960827 the presence of substantial radiogenic heat sources appears not to be supported here.

The 3.3 ppb of radiogenic argon in the atmosphere sets an upper limit on the potassium in the crust, and hence the crustal thickness: 22±10 km; assuming a 10-km decay depth, it also implies 1.0% average surface density of K2O. The present heat delivery from the mantle of this model is 24 mW/m2, about 20% higher than the upper limit for stagnant lid convection ...Reductions of the mantle U and K/U and increase of the atmospheric argon by one standard deviation each would reduce the heat delivery to 16 mW/m2 (http://dev.nsta.org/ssc/moreinfo.asp?id=947).

 

[Ophiolite]

If you agree that the science is by no means "a done deal", why is it unethical to challenge the notion that the conditions on Venus are the result of a runwaway greenhouse effect?

The challenge, Andre, seems to be not to your right to challenge current consensus views, but to the manner of that challenge which included accusations of unethical behaviour on the part of the scientists who form that consensus. Let's stick to the facts and leave the politics out of it.

 

[Andre]

The challenge, Andre, seems to be not to your right to challenge current consensus views, but to the manner of that challenge which included accusations of unethical behaviour on the part of the scientists who form that consensus. Let's stick to the facts and leave the politics out of it.

The reason that the ethics sneaked in was this remark:

but I think that it is unethical (in a Feynmanian way) to consider the runaway greenhouse effect a done deal, dismissing the considerable internal heat of the planet. ...

And I stand by that, if anybody is arguing that, prof, phd anybody, without the caveat that there is evidence that Venus interior could have released plenty enough heat for the same end result somehow, Feynman would have frowned, http://www.lhup.edu/~DSIMANEK/cargocul.htm:

... It's a kind of scientific integrity, a principle of scientific thought that corresponds to a kind of utter honesty--a kind of leaning over backwards. For example, if you're doing an experiment, you should report everything that you think might make it invalid--not only what you think is right about it: other causes that could possibly explain your results; and things you thought of that you've eliminated by some other experiment, and how they worked--to make sure the other fellow can tell they have been eliminated.

Details that could throw doubt on your interpretation must be given, if you know them. You must do the best you can--if you know anything at all wrong, or possibly wrong--to explain it...

Now, that is Feynman ethics.