What-If 0143: "Europa Water Siphon"

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What-If 0143: "Europa Water Siphon"

Postby cyanyoshi » Wed Jan 27, 2016 3:38 am UTC

Europa Water Siphon

A group of Google Search SREs wrote:What if you built a siphon from the oceans on Europa to Earth? Would it flow once it's set up? (We have an idea for selling bottled Europa water.)

xkcd wrote:No, but I like where you're going with this.

Image

What-Ifs seem to be back on schedule, everyone! Let's party! I'll buy the drinks. Hope you all like salty alien water!

Also, it seems that the dates on the What-If archive have been fixed finally. Huzzah!

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Re: What-If 0143: "Europa Water Siphon"

Postby theactionisgo » Wed Jan 27, 2016 4:19 am UTC

I believe there's a mistake in this What-If. In the sixth footnote it states "Occasionally, in the Earth, layers of dense rock will end up above layers of less-dense oil. That is why—when oil wellheads break—oil can sometimes come spurting out without any help from the pumps." First, this feeds into the misconception that oil is floating freely below layers of rock (because of the phrase "layers of less-dense oil") when its actually trapped inside the pores of rock. Second, and more importantly, that's not why oil will flow freely without pumps. Oil and natural gas flow because the pressure in the wellbore is less than the pressure of the oil and gas trapped in the formation. When this pressure difference is great enough, the oil and gas migrate out of the formation and into the wellbore. The relative density between the formation in which the hydrocarbon is trapped and the layers above it isn't a major factor.

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Re: What-If 0143: "Europa Water Siphon"

Postby Higure » Wed Jan 27, 2016 6:13 am UTC

But you can siphon water past the 34 feet barrier. Just ask any 35 feet-or-taller tree. Technically, they aren't really siphoning, but they are pulling water way further up than 34 feet (almost 400 feet in the case of the tallest redwoods).

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Re: What-If 0143: "Europa Water Siphon"

Postby Pfhorrest » Wed Jan 27, 2016 6:18 am UTC

There are certainly ways to transport water more than 34 feet upward. Siphoning just isn't one of them.

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Re: What-If 0143: "Europa Water Siphon"

Postby Higure » Wed Jan 27, 2016 6:25 am UTC

Pfhorrest wrote:There are certainly ways to transport water more than 34 feet upward. Siphoning just isn't one of them.

But the problem has trees solved is directly applicable to siphoning. If we just do like the trees, then they are living proof that you can siphon water over a 100 meter tall top point. It is just that the mechanism that drives the water in trees isn't "even more water pulling down on the other side", it is low pressure inside every single cell.

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Re: What-If 0143: "Europa Water Siphon"

Postby KarenRei » Wed Jan 27, 2016 12:18 pm UTC

Very much disagree with this. An atmosphere isn't the only thing that can apply pressure. We know for a fact that sometimes there are geysers on Europa when the ocean breaks the surface. And that these geysers eject water upwards of at least 200km (possibly sometimes all the way to escape velocity), in a situation that's far from a nice smooth flow through a large diameter pipe. Europa may well have the internal pressure to eject water to escape in an ideal situation. As for escaping from Jupiter, your siphon "pipe" (which we know already must be a flexible, telescoping, moving structure in its own regard) could be routed so that the water receives gravity assists from other moons. In addition to the geometry, your tube is going to want to freeze from the outside in, so you're going to need to have good insulation and heaters.

Really, I don't think the tube serves a purpose after some point... if you can eject the water at the proper angle in a controlled stream, it'll follow its trajectory regardless of whether there's a tube present - just a continuous stream of ice chunks and snow. Everything that doesn't vaporize en route will eventually make it to Earth. So if you really want it to arrive in a tube you could put a "catcher" tube on the earth side, but otherwise, what's the point of the tube en-route?
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Re: What-If 0143: "Europa Water Siphon"

Postby ocelot2 » Wed Jan 27, 2016 12:34 pm UTC

There are siphons that operate under vacuum; the surface tension of the liquid can bind the two halves of the siphon together; the area labelled 'vacuum' opening up in the middle of the tube also represents more surface for the liquid. There's even a video demonstration of a siphon working under vacuum here ( youtube·com/watch?v=8F4i9M3y0ew ) using a liquid with a low vapour pressure.
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Re: What-If 0143: "Europa Water Siphon"

Postby sevenperforce » Wed Jan 27, 2016 1:44 pm UTC

Higure wrote:
Pfhorrest wrote:There are certainly ways to transport water more than 34 feet upward. Siphoning just isn't one of them.

But the problem has trees solved is directly applicable to siphoning. If we just do like the trees, then they are living proof that you can siphon water over a 100 meter tall top point. It is just that the mechanism that drives the water in trees isn't "even more water pulling down on the other side", it is low pressure inside every single cell.

It's not low pressure in cells so much as it's capillary action. Capillary action works very well for this sort of thing.

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Re: What-If 0143: "Europa Water Siphon"

Postby KarenRei » Wed Jan 27, 2016 3:17 pm UTC

ocelot2 wrote:There are siphons that operate under vacuum; the surface tension of the liquid can bind the two halves of the siphon together; the area labelled 'vacuum' opening up in the middle of the tube also represents more surface for the liquid. There's even a video demonstration of a siphon working under vacuum here ( youtube·com/watch?v=8F4i9M3y0ew ) using a liquid with a low vapour pressure.


You mean note 5 in the comic?

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Re: What-If 0143: "Europa Water Siphon"

Postby Higure » Wed Jan 27, 2016 4:49 pm UTC

sevenperforce wrote:
Higure wrote:
Pfhorrest wrote:There are certainly ways to transport water more than 34 feet upward. Siphoning just isn't one of them.

But the problem has trees solved is directly applicable to siphoning. If we just do like the trees, then they are living proof that you can siphon water over a 100 meter tall top point. It is just that the mechanism that drives the water in trees isn't "even more water pulling down on the other side", it is low pressure inside every single cell.

It's not low pressure in cells so much as it's capillary action. Capillary action works very well for this sort of thing.


I beg to differ. At least, Derek Muller begs to differ in this Veritasium video.

https://www.youtube.com/watch?v=BickMFHAZR0

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Re: What-If 0143: "Europa Water Siphon"

Postby rmsgrey » Wed Jan 27, 2016 5:21 pm UTC

KarenRei wrote:Really, I don't think the tube serves a purpose after some point... if you can eject the water at the proper angle in a controlled stream, it'll follow its trajectory regardless of whether there's a tube present - just a continuous stream of ice chunks and snow. Everything that doesn't vaporize en route will eventually make it to Earth. So if you really want it to arrive in a tube you could put a "catcher" tube on the earth side, but otherwise, what's the point of the tube en-route?


If you can eject water in a controlled stream at the proper angle from a high pool, it will land in the low pool without a tube - the point of a siphon is that once you set one up, the water ejects itself rather than needing you to squirt it.

It's probably not a terribly useful effect over the Europa-Earth distance, but it still does provide some assistance in getting the water to Earth...

Of course, the construction and maintenance costs of the tube are going to dwarf any energy savings involved but that's economics rather than physics :P

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Re: What-If 0143: "Europa Water Siphon"

Postby trpmb6 » Wed Jan 27, 2016 5:57 pm UTC

First, Randall has some interesting friends. (Ref. Flagnote 1)

Second, I love any reference to 2010: A Space Odyssey.
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Re: What-If 0143: "Europa Water Siphon"

Postby Sleet » Wed Jan 27, 2016 8:02 pm UTC

Pretty interesting What If. "Pumping water from Europa's surface would take some work" and the talk about oil wells had me thinking Randall was about to propose pumping the water from [however deep water is believed to go on Europa], but the extra pressure is probably negligible anyway?

That final image is the most brilliant ad campaign I've ever seen, though.

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Re: What-If 0143: "Europa Water Siphon"

Postby boutch55555 » Wed Jan 27, 2016 11:33 pm UTC

Honestly I don't get it.

If you filled the tube with water at the start, earth having a 6,379km gravity well should act as a pump to Europa's 2,500km. The gravity pull is the pump. Put the ends of tubes deep underwater, atmosphere irrelevant.

What am I missing ?

Assuming a nanofiber tube that can handle the pressure, flex around the solar system and keep water from freezing.

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Re: What-If 0143: "Europa Water Siphon"

Postby phlip » Thu Jan 28, 2016 3:04 am UTC

boutch55555 wrote:Honestly I don't get it.

If you filled the tube with water at the start, earth having a 6,379km gravity well should act as a pump to Europa's 2,500km. The gravity pull is the pump. Put the ends of tubes deep underwater, atmosphere irrelevant.

What am I missing ?

It doesn't matter how deep underwater the ends of the tube are... the maximum that the water will go up the pipe is [air pressure at surface / (density of water * gravity)]. Plus a very amount for capillary action. If the pipe goes up any further than that, it doesn't matter what's going on at the other end, you're not going to get a siphon.

For a simpler non-planetary analogy: if you have a pool of water at the bottom of a wall, with a pipe leading to a pump at the top of a wall, you can only pump the water up about 10 metres. If the wall is taller than that, it doesn't matter how good your pump is, it can be powerful enough to suck out a complete vacuum in the pipe, it won't be enough. The action of "sucking" is simply unable to make the water level any higher than P/ρg.

If you want the water to go up the pipe for more than that, you need to either increase the air pressure at the bottom (having a pump at the bottom of the wall, instead of only at the top), or have the air pressure inside the pipe be less than zero (which is impossible).

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Re: What-If 0143: "Europa Water Siphon"

Postby rmsgrey » Thu Jan 28, 2016 3:22 am UTC

boutch55555 wrote:Honestly I don't get it.

If you filled the tube with water at the start, earth having a 6,379km gravity well should act as a pump to Europa's 2,500km. The gravity pull is the pump. Put the ends of tubes deep underwater, atmosphere irrelevant.

What am I missing ?

Assuming a nanofiber tube that can handle the pressure, flex around the solar system and keep water from freezing.


You're missing the hump - take an ordinary routine terrestrial siphon, say with a garden hose and an inflatable paddling pool. So long as the hose is laying flat on the ground aside from the short stretch going over the side and into the pool, you can siphon out the water just fine. Lift up part of the hose high enough, leaving the ends where they are, and the water will stop flowing. Of course, not many people are in a position to lift part of a hose the 34 feet needed (equivalent to getting someone on the 3rd/4th floor (depending on whether ground level is "ground floor" or "first floor") to attach it to their balcony railing) and a standard garden hose is only 50 feet anyway, so you'd need some special equipment to make it work (or, rather, stop working).

Getting out of Jupiter's gravity well, rather than keeping a continuous body of liquid water, you'll end up with a near-vacuum (water vapour) filling most of the tube, with a relatively short column of water near the surface of Europa...

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Re: What-If 0143: "Europa Water Siphon"

Postby Mikeski » Thu Jan 28, 2016 7:10 am UTC

It would be a lot more efficient to repurpose that ocean-to-Mars portal to bring Europa's water here.

Just hope there are no Europan Dutch to do what the European Dutch did...

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Re: What-If 0143: "Europa Water Siphon"

Postby Flumble » Thu Jan 28, 2016 7:56 am UTC

Does (maximum) pressure relate to (minimum) gravitational potential in any way? Probably not, since some bodies have jets that fire out of the solar system, but I'm asking nonetheless.

Mikeski wrote:Just hope there are no Europan Dutch to do what the European Dutch did...

Worst thing they can do is conquer the whole of Europa, and we're not allowed there anyway.

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Re: What-If 0143: "Europa Water Siphon"

Postby Mikeski » Thu Jan 28, 2016 7:59 am UTC

Flumble wrote:
Mikeski wrote:Just hope there are no Europan Dutch to do what the European Dutch did...

Worst thing they can do is conquer the whole of Europa, and we're not allowed there anyway.

The last line & last picture in Part 2 imply otherwise.

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Re: What-If 0143: "Europa Water Siphon"

Postby Higure » Thu Jan 28, 2016 8:01 am UTC

phlip wrote:It doesn't matter how deep underwater the ends of the tube are... the maximum that the water will go up the pipe is [air pressure at surface / (density of water * gravity)]. Plus a very amount for capillary action. If the pipe goes up any further than that, it doesn't matter what's going on at the other end, you're not going to get a siphon.(...)

If you want the water to go up the pipe for more than that, you need to either increase the air pressure at the bottom (having a pump at the bottom of the wall, instead of only at the top), or have the air pressure inside the pipe be less than zero (which is impossible).


rmsgrey wrote:Getting out of Jupiter's gravity well, rather than keeping a continuous body of liquid water, you'll end up with a near-vacuum (water vapour) filling most of the tube, with a relatively short column of water near the surface of Europa...


I will link the video again. It is possible to siphon past the 34 feet barrier, you just have to be very careful how you construct the siphon. You can have negative pressure inside a liquid.

https://www.youtube.com/watch?v=BickMFHAZR0

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Re: What-If 0143: "Europa Water Siphon"

Postby sevenperforce » Thu Jan 28, 2016 2:16 pm UTC

Lowering pressure in order to increase the vapor pressure of a liquid and cause transfer across a barrier is not the same as siphoning. Capillary action is not the same as siphoning.

If the gravitational potential difference between Europa and Earth was capable of causing water to flow through a cylindrical hose through space, water would already be flowing here through the middle of space. That's called mass transfer, and it happens when two bodies are close enough that their surfaces stretch out and intersect at their L1 Lagrange point. Putting a hose in between the two bodies won't change a thing.

Also, even though the gravitational potential well at Earth's surface is 30x deeper than at Europa's surface, that's not all you have to deal with; Europa's position within Jupiter's gravity well means that the potential well on Earth's surface isn't even twice as deep as the depth of the well at Europa's surface. But all of this is vastly overshadowed by something else -- the gravitational potential well of the Sun. The Sun's gravity well at the orbit of the Earth is five times deeper than at the orbit of Jupiter, by far the dominant factor.

The reason stuff doesn't fall from Jupiter's orbit to Earth's orbit is because it's all in orbit around the sun. If a hose was stretched from Earth to Europa, I'm pretty sure it would actually end up functioning more like a space elevator, and anything that started to climb up the hose from Earth due to capillary action would be flung outward by centrifugal force.

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Re: What-If 0143: "Europa Water Siphon"

Postby Neil_Boekend » Thu Jan 28, 2016 2:47 pm UTC

That is: unless you have a magical portal connecting the Europa and Earth, with the correct orientation to not have troubles with centrifugal force. But if you have the tech to create magical portals between planets I think you can make more money in different ways than selling Europa's water.
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Re: What-If 0143: "Europa Water Siphon"

Postby KarenRei » Thu Jan 28, 2016 4:45 pm UTC

sevenperforce wrote:The reason stuff doesn't fall from Jupiter's orbit to Earth's orbit is because it's all in orbit around the sun. If a hose was stretched from Earth to Europa, I'm pretty sure it would actually end up functioning more like a space elevator, and anything that started to climb up the hose from Earth due to capillary action would be flung outward by centrifugal force.


Again, people are forgetting about gravity assists. Anywhere that you have two or more bodies influencing a third body to varying significant degrees on your path, they're an option to change the orbit of the third body. So if you can escape Europa enough to get a relevant tug from one or more of the other Jovian moons, you can ultimately get enough velocity to leave Jupiter and enter a near-Jupiter orbit of the sun. From there you can get gravity assists from Jupiter itself, then Mars, and finally reach an Earth-crossing trajectory. It'll take many years, but the water would get there (barring constraints like freezing in the pipe, sublimation, etc).

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Re: What-If 0143: "Europa Water Siphon"

Postby teelo » Thu Jan 28, 2016 5:09 pm UTC

New business idea: selling bottled water that I got from my tap, which I just say is from Europa.

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Re: What-If 0143: "Europa Water Siphon"

Postby MyNameHere » Thu Jan 28, 2016 7:17 pm UTC

Revisiting note #5, I think the video demonstrates that siphoning works just fine in a vacuum, and not "at least a little bit." We don't know the exact viscosity of the ionic liquid, but it seems to be siphoning at a reasonably quick pace, in the same ballpark (or at least the same county) as water.

If a siphon works in a vacuum in practice, and the stated theory says it won't, then we can safely assume that the theory is incorrect in some respect.

Coincidentally, a Straight Dope column on the topic was recently re-posted, and it presents a pretty interesting comparison of the effects of the cohesion of the liquid and atmospheric pressure. The Straight Dope forum discussion also mentions this xkcd What If?, so I thought it appropriate to link them. The xkcd forum software will not permit me to insert the Straight Dope url here (says it's spam), but here is an obfuscated version:
boards [dot] straightdope [dot] com [slash] sdmb [slash] showthread.php?t=781758

Clearly, gravity is the primary factor in siphoning. The only question is why there is a limit to the height of liquid that can be siphoned in our gravity well.

Knowing that siphons work in a vacuum, we know that the effects of cohesion and air pressure would have to be complementary--to the extent that air pressure is actually a factor.

See the discussion at The Straight Dope for more.

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Re: What-If 0143: "Europa Water Siphon"

Postby Soupspoon » Thu Jan 28, 2016 11:40 pm UTC

trpmb6 wrote:Second, I love any reference to 2001: A Space Odyssey.


If that's the "All These Worlds Are Yours, Except Europa..." bit, that's 2010: Odyssey Two1. But they're both good, IMO, so it diminishes not my equivalent love for the reference.


On-topic, something like a litre bottle of water dropping into a hand at terminal velocity for such a mass (low cross-section and 1kg, ignoring the final packaging and any prior (ablative?) covering)... would probably be a difficult catch. And the calculations involved remind me of the same calculations deemed necessary for one particular weapon in the book "2312" by Kim Stanley Robinson, if anybody else has read that.


1 "My god, it's full of stars!" also wasn't in the film version of 2001. It was in the book, but then the book originally had them round Saturn, rather than Jupiter, natch. The 2010 sequel film (and book) probably popularised the phrase.

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Re: What-If 0143: "Europa Water Siphon"

Postby Soupspoon » Thu Jan 28, 2016 11:53 pm UTC

teelo wrote:New business idea: selling bottled water that I got from my tap, which I just say is from Europa.


Some bottled waters advertise something along the lines of 'primordial' water. Often because it is tapping an aquifer that has been apparently filtered through a mountain for so-many-thousand years.

But how much typical water is actually older than the Earth? Barring some chemical transitions back and forth between water and various hydrated/hydrolised forms (and perhaps some mass re-association of O-H bonds in masses of water and water-based solutions), a good proportion of basic H2O molecules have got to be essentially the same molecules as in the early solar system.

"Purified water from the same source as Europa/Enceladus/whatever..." might even pass various lies-as-advertisements rules, if it's a big enough proportion.

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Re: What-If 0143: "Europa Water Siphon"

Postby KarenRei » Fri Jan 29, 2016 1:42 am UTC

MyNameHere wrote:Revisiting note #5, I think the video demonstrates that siphoning works just fine in a vacuum, and not "at least a little bit." We don't know the exact viscosity of the ionic liquid, but it seems to be siphoning at a reasonably quick pace, in the same ballpark (or at least the same county) as water.

If a siphon works in a vacuum in practice, and the stated theory says it won't, then we can safely assume that the theory is incorrect in some respect..


It's about the effective "tensile strength" of the water (low). Sure, you have a low gravity gradient in interplanetary space. But on the rise from Europa's surface you most definitely don't have a low gradient, and so all of that hanging water will easily rip the "cable". Except....

Huh....

I just thought of something. We've seen this problem before. "Tensile strength of known materials is insufficient to withstand a cable of its own weight" - this is the Space Elevator problem. And the solution is taper. You have your "cable" - in this case, the tube of water - grow wider with height.

Still, I expect that the "tensile strength" of the water is so low that your taper factor makes this effectively completely impossible in the real world from Europa. But if I had the actual tensile strength I could figure it out... And I guess we really have two different types of "tensile strength" here, right? The adhesion of water to itself with no walls nearby, and the adhesion of water to the walls (the latter would increase if you used intersecting microchannels for your tube, the former wouldn't).

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Re: What-If 0143: "Europa Water Siphon"

Postby KittenKaboodle » Fri Jan 29, 2016 2:21 am UTC

MyNameHere wrote:Revisiting note #5, I think the video demonstrates that siphoning works just fine in a vacuum, and not "at least a little bit." We don't know the exact viscosity of the ionic liquid, but it seems to be siphoning at a reasonably quick pace, in the same ballpark (or at least the same county) as water.


Nah, I'd go with Randal's "little bit", with emphasis on "little". The what if was about bottling and selling Europaean water, not some weird (likely toxic) ionic liquid which is not likely to occur naturally anyway. And even if a weird liquid did allow one to increase the siphon height from, say, 10m to 10.5m one is still well short of 2500Km (even Higure's link with its 100m trees is well short of 2500m). While Europa is smaller than earth, just for an example, if you read anything about space elevators you will find that even flawless carbon nanotubes don't have the "cohesion" to make it very far from Earth. To even reach geosynchronous orbit altitude requires a tapering structure. At least I think it does, perhaps if one nanotubes where indeed flawless a constant thickness cable could work, but then flawless is as impossible as siphoning water 2500Km high in a vacuum. Actually I'm not sure what 2500Km gets you anyway, aren't you still in orbit around Jupiter?, not to mention the Sun. Sure if you have water with near infinite* tensile strength, then I suppose Earth's gravity helps by pulling on the "downhill" end.

* I mean figuratively, compared to normal stuff like Adamantium , not literally infinite, a concept that makes my head hurt, and would be hard on your bottling equipment, not to mention your customers.

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Re: What-If 0143: "Europa Water Siphon"

Postby ps.02 » Fri Jan 29, 2016 7:05 am UTC

Soupspoon wrote:But how much typical water is actually older than the Earth? Barring some chemical transitions back and forth between water and various hydrated/hydrolised forms (and perhaps some mass re-association of O-H bonds in masses of water and water-based solutions), a good proportion of basic H2O molecules have got to be essentially the same molecules as in the early solar system.

Barring the very things that define a molecule as distinct from individual atoms? That's Grandfather's Axe, then. "This is my grandfather's water molecule. It's had the O replaced a couple billion times, and each of the H's replaced a couple billion times. And those electrons, they've each been replaced a billion times too. But we like to think it's still the same molecule."

(Then again, quantum mechanics apparently teaches us that all atoms of a given composition are identical. There's no way to tell them apart. So if what you mean is that a particular instance of two 1H and one 16O bonded together is indistinguishable from molecules that existed prior to the formation of the Earth, that would be correct. But in that sense, it doesn't matter at all where the atoms came from or where they are now.)

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Re: What-If 0143: "Europa Water Siphon"

Postby Pfhorrest » Fri Jan 29, 2016 7:23 am UTC

Since particles-antiparticle pair production and annihilation can be seen as the same particle moving back and forth through time, it's entirely possible that all water molecules are made up of different time-slices of the same, numerically identical electron, up quark, and down quark, recombining with each other and themselves in different ways on different passes through the timeline.
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Re: What-If 0143: "Europa Water Siphon"

Postby cellocgw » Fri Jan 29, 2016 12:33 pm UTC

teelo wrote:New business idea: selling bottled water that I got from my tap, which I just say is from Europa.


At least you'll sell more than if you advertise it as coming from Uranus.

Ok, Ok, but it had to be coming sooner or later.
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Re: What-If 0143: "Europa Water Siphon"

Postby Soupspoon » Fri Jan 29, 2016 12:38 pm UTC

ps.02 wrote:Barring the very things that define a molecule as distinct from individual atoms?
Yes, I didn't say things the way I wanted to. I'm a bit rusty, and maybe outdated anyway.

Chemical hydration (e.g. an -O converting to -(OH)2) would not guarantee the same O pops back off when later de'hydrated', even assuming the two Hs remaind the same protons, leading to what I always knew as the "Irishman's Broom" situation (but Grandfather's Axe is a better term, perhaps even more so than the "Ship of Theseus" classical allusion). But matrix hydration (e.g. wet clays) theoretically could be considered to preserve the water molecules in the X·nH2O matrix for the duration between the soaking and the drying (depending on how it dried!). Promiscuous hydrogens are probably the biggest danger to the provenance. If my ancient lessons in the subject aren't being misremembered, or perhaps are now overturned in the light of newer understandings.

(I'd consider electrons as 'free' to jump around, without taking the 'cherry' of the original water molecule. And ignore everything below the level of the baryon, because it's probably all Strings (or wierder!) down there, anyway...)

I was really wondering how much of the post-Hadean oceans was from outgassed water, from arguably 'broken' and dissosociated molecules that may not count, and how much from comet/ice-asteroid impacts of 'original ice', which we could perhaps freely market as Europa-equivalent. But the origin of Earth's waters is a question that is some way from being fully answered, so maybe I should have marked that as rhetorical.

But, whichever, I know you also need to run the early-Earth water through various biologies, fixing and unfixing complex molecules. Perhaps every molecule has (statistically speaking) been broken and recreated as it is collectively absorbed and passed back out of every living creature in the biosphere (even if it avoided chemical bastardisation), mediating in its energy-extracting reactions?


Yeah, a few billion years of biology has probably done-to-death the idea of 'original water', thinking about it. There might be some 'lucky' lumps of ice. Perhaps surviving ice-cores of late-falling water-rich meterorites that landed in polar zones? Either alighting there since the last big defrost, or else sitting beyond the 'ice-line' of all defrosts that happened since their impact. However so originated, they'd be indistinguishable from the surrounding non-original ice, except perhaps for an isotopic skew. Making for an interesting scientific resource, if not grievously used for commercial purposes, but difficult to discover by either camp except by labour-intensive means...

But it was just a side-thought. I wasn't intending to overthink things. (Immediately forgetting both who I was and where I was, of course!)

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Re: What-If 0143: "Europa Water Siphon"

Postby ps.02 » Fri Jan 29, 2016 2:36 pm UTC

Soupspoon wrote:But matrix hydration (e.g. wet clays) theoretically could be considered to preserve the water molecules in the X·nH2O matrix for the duration between the soaking and the drying (depending on how it dried!).

Ah, if that's what you were thinking of, I can see why you would say "barring these reactions" and still consider it the same water. And I would agree.
Yeah, a few billion years of biology has probably done-to-death the idea of 'original water', thinking about it.

This has come up a couple years ago (I was too lazy to linkylink last night), in which Randall apparently believed in a Law of Conservation of Molecular Structure, at least since the Age of Non-Avian Dinosaurs. I was a bit doubtful of this (I even used the term "Molecule of Theseus"), and Skeptical Scientist ran the numbers convincingly.

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Re: What-If 0143: "Europa Water Siphon"

Postby ealloc » Sat Jan 30, 2016 4:47 am UTC

I think the siphon in a vacuum question hinges on what the liquid does when the pressure drops to zero. Let's say there is an intermolecular force f between molecules in the liquid. Then (barring mistakes!) the formula for the maximum siphon height is

h = (f/a + P) / (rho*g)

where a is the area of interaction between two molecules, P is pressure, rho is density and g is 9.81 m/s. If the pressure drops to zero this implies there is still a nonzero maximum height as long as the molecules attract.

This somehow depends on the surface tension of the liquid, gamma. The energy cost to break two molecules apart is roughly "2*a*gamma", and gamma is also related to the size and frequency of cavitation bubbles in the liquid. If the force drops off with distance, I can imagine more cavitation bubbles would mean lower average attractive force. So, I think that a liquid with high surface tension (mercury?) could have a large siphon height even in vacuum. I would also believe that liquids that boil readily at low pressure (eg water) can't be siphoned in a vacuum. You'd have trouble doing anything with such a liquid in vacuum, anyway.

By the way, just last month a paper was published: "The height limit of a siphon" http://www.nature.com/articles/srep04741. The abstract says: "Here we report an experiment of a siphon operating at sea level at a height of 15 m, well above 10 m. Prior degassing of the water prevented cavitation. This experiment provides conclusive evidence that siphons operate through gravity and molecular cohesion." [rather than through atmospheric pressure]

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Re: What-If 0143: "Europa Water Siphon"

Postby teelo » Sat Jan 30, 2016 11:20 am UTC

cellocgw wrote:
teelo wrote:New business idea: selling bottled water that I got from my tap, which I just say is from Europa.


At least you'll sell more than if you advertise it as coming from Uranus.

Ok, Ok, but it had to be coming sooner or later.

:lol: :lol: :lol: Brb, making kickstarter.

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Re: What-If 0143: "Europa Water Siphon"

Postby KarenRei » Sun Jan 31, 2016 2:19 am UTC

ealloc wrote:I think the siphon in a vacuum question hinges on what the liquid does when the pressure drops to zero. Let's say there is an intermolecular force f between molecules in the liquid.


Randall mentioned this in comment 5, and I and others have commented extensively on this above. It's as if the water has some tensile strength, like a liquid. The problem is that this tensile strength is very low. So a column isn't going to hold itself up over great gravitational gradients without a totally impractical taper factor.

By the way, just last month a paper was published: "The height limit of a siphon" http://www.nature.com/articles/srep04741. The abstract says: "Here we report an experiment of a siphon operating at sea level at a height of 15 m, well above 10 m. Prior degassing of the water prevented cavitation. This experiment provides conclusive evidence that siphons operate through gravity and molecular cohesion." [rather than through atmospheric pressure]


Did you link the wrong paper? That quote isn't there. Furthermore, if you're adding in that "rather than through atmospheric pressure", you're misinterpreting that. Intramolecular forces are in addition to pressure, not instead of it.

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Re: What-If 0143: "Europa Water Siphon"

Postby ealloc » Sun Jan 31, 2016 8:21 pm UTC

Oops sorry, you're right I linked an older paper of theirs (with the same theme). The Dec 2015 paper is at http://www.nature.com/articles/srep16790 .

And by adding "rather than through atmospheric pressure" I am summarizing their argument in the introduction. As they explain, there are two competing theories for how siphon works (gravity + liquid cohesion, or gravity + atmospheric pressure), and the question has been controversial even recently. They argue the gravity + liquid cohesion is more correct. The other paper I accidentally linked makes the same argument.

Like I said before, I would believe that siphoning water doesn't work in vacuum because it cavitates/boils at 0 pressure, but I would also believe that mercury would be siphonable.

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Re: What-If 0143: "Europa Water Siphon"

Postby ealloc » Sun Jan 31, 2016 8:53 pm UTC

A possible test: Take a u-shaped glass tube greater than 76cm in height, submerge it in mercury to fill it, and then slowly pull it bent-end up out of the mercury, keeping the open ends submerged.

If you can pull it up (in eath's atmoshpere) higher than 76cm without a cavity forming at the top, then a siphon would work in vacuum. The vacuum siphon height would be equal to the height you can pull it past 76cm before cavitation.

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Re: What-If 0143: "Europa Water Siphon"

Postby sevenperforce » Mon Feb 01, 2016 2:06 pm UTC

ealloc wrote:By adding "rather than through atmospheric pressure" I am summarizing their argument in the introduction. As they explain, there are two competing theories for how siphon works (gravity + liquid cohesion, or gravity + atmospheric pressure), and the question has been controversial even recently. They argue the gravity + liquid cohesion is more correct.

Not really. Rather, they're arguing that liquid cohesion can allow a siphon system to exhibit flow in excess of the barometric limits under which siphoning primarily operates. Which, as we've pointed out repeatedly, is something Randall expressly mentioned in the What-If to begin with.

A fluid with a lower surface tension (e.g., oil) will flow across an atmospheric pressure differential in exactly the same way that a fluid with a higher surface tension (e.g., water) will. Thus, atmospheric pressure differentials are the reason why siphons work; the possibility of additional flow from cohesive force does not replace the mechanism of atmospheric pressure differential.

Framing this as a "controversy" between "two competing theories" is not correct. It would be like saying that there's a "controversy" concerning whether tides are caused by the sun or by the moon. Tides are primarily caused by the moon; the fact that the sun affects the duration and height of certain tides doesn't make it a controversy or a competing theory.


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