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Europa's Ice May Be Miles Thick
serutan writes "Space.com has an article detailing recent measurements of the shell of ice covering what is believed to be an enormously deep ocean on Europa, which could harbor life. The thickness of the ice -- many times the previous estimate -- poses a major obstacle to sending a lander that would burrow down through it to the water. [Seems like if they could make the probe kinda warm it would eventually sink through any amount of ice.]"
If they run the probe with Intel chips it should generate enough heat...
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If the probe is kept hot enough long enough it will indeed melt its way through. However, keeping it that hot for that long takes a lot of energy which has to be either carted all the way to Europa or has to be found in situ. A sufficiently large chunk of high-level nuclear waste might do it. Although this suggestion would reduce the waste problem here on earth slightly, I can't see the tree-huggers being very enthusiastic.
An alternative approach might be to punch through in one explosive event. Steer an appropriately sized cometary nucleus into Europa, wait for things to settle down a little and then dive into the relatively thin and slushy crater floor.
Paul
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The whole idea is to look for life... You gonna do this by dropping a comet on them??? How they going to take this?
Seriously, you could disrupt things that way even if it's only bacteria mats.
I thought the point of the probe would be to cause as little damage and disruption as possible.
On the other hand there is nothing those wacky Nasa engineers can't do with time.
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and they would do that how? barring a nuclear power source i think they're out of luck - solar won't work once it goes too far into the ice. and most of the space based nuclear power plants don't make a huge amount of energy afaik.
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One of the lines of evidence for liquid water was surface features typical of refreezing, which would mean that at least locally and temporarily there is liquid water close to the surface.
Given an infinite amount of heat energy, sure. But if the probe's just "kinda warm", it will merely create a stable pocket of water around itself. The water will never get significantly above 32 degrees (F) ya know.
Eventually the area of the boundary between the liquid pocket and the surrounding ice will be sufficent that you'll be losing heat faster than you're putting it in - unless you are talking a lot more heat than "kinda warm" - the kind of heat we might refer to as "unbelieveably blazing hot consuming titanic amounts of energy".
Hey, how 'bout this: Leave a solar array on the surface, make the submersible part as small as possible (camera, heat elements, and spool of fine wire). Then you can power the heater electrically from a wire you unwind as your blazing hot ice-melter sinks.
You heard it first on Slashdot! (Of course, I *am* a former rocket scientist, so we might be cheating)....
The problem I see presented is: once you have your bot in place under twelve miles of ice, how do you get your signal back? Through a tether? Then how do you get the tether through all that ice without it freezing in place and jamming the probe during descent?
Use the same technique that wire guided missiles use, the tether is deployed from the probe/tunneler it doesn't matter if it freezes in place then, in fact it would be a good idea, since that would probably support the mass of the tether and reduce risk of it breaking. Of course, if the ice isn't rock solidly imobile, then the slightest shift would slice most practical tethers instantly.
Actually it is rocket science...
An alternative approach might be to punch through in one explosive event. Steer an appropriately sized cometary nucleus into Europa, wait for things to settle down a little and then dive into the relatively thin and slushy crater floor.
I'm pretty sure the Europians will take something like that as an act of war.
Seems like if they could make the probe kinda warm it would eventually sink through any amount of ice.
That's a bit of an understatement. Let's do a quick calculation, shall we?
The article says that the ice is at least 19km (11 miles) thick. Let's assume we can somehow magically make our probe fit into the volume of a square foot or 30cm per side. That means we have about 1700 square meters of ice to melt, which is around 2e6 kilograms.
Europa has no real atmosphere, the pressure at the surface is around 1e-11 bar (1e-6 Pa) -- i.e. almost nothing. So the ice would most certainly vaporize rather than melt, and at a temperature lower than 0C. See this neat phase diagram of water. As we go down farther the pressure will necessarily increase, but I don't feel like calculating it exactly. Based on the phase diagram I'll use 200K as the approximate transistion temperature. It's close enough to be within an order of magnitude of correct.
The surface temperature of Europa is approx -260 dF (111 Kelvin), so to raise it to 200K results in a temperature difference of 89K. The specific heat of ice is around 2e3 J/(kg*K). That means our task will require about 3.5e11 Joules of energy. Let's say we let this process take 100 years at a steady rate. This comes to about 111 Watts. Suddenly "kinda warm" really doesn't cut it.
When you have a self contained source of power that can supply 111 W constantly for 100 years and fit into a square foot of volume, please let me know. Surely, you would have solved our energy crisis by now.
PS - Solar panels are pretty much useless after you get farther from the sun than Mars. That's why probes like Cassini needs radio-isotope thermo-electric generators.
Good idea, but not necessarily. Ice packs tend to be dynamic flows with upwelling, downwelling and lateral movement. Metling say a few meters a day, would still take year or even more to reach the ocean below. In addition, the pressures below the ice pack will be immense once the liquid ocean is reached. Not to mention the giant pod eating monsters that probably lurk there.
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Unfortunately, I believe they didn't have too much luck. Their cylindrical probe would only melt the ice right under it. The walls would freeze back into place and hold it with friction (since ice expands, and as such would create pressure on the hull). I wonder if they would have been more successful with a raindrop-shaped design, where the pressure from the refreezing ice would actually help propel it downward. In any case, the high pressures involved would probably crush any payload.
The other problem was how to relay any information it harvested back to the surface, so it could be retransmitted to Earth. H2O blocks most radio waves pretty well, and stringing a wire all that distance suffers similar problems as the probe itself -- you'd have to keep it hot to keep moving.
Until then, we'll just have to rely on remote sensing...
The recent American Scientist article on this described how the constant flexing of the moon in its orbit around Jupiter may produce tides that rise through the myriad cracks on the surface, bringing water close to the surface.. The cracks are plentiful and it shouldn't be too hard to find the more recent ones. Actually, the article describes in some detail crack formation and propogation. The overall impression is that this is a constant process and that it may be an easy way of getting to the sub-europan ocean.
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[Seems like if they could make the probe kinda warm it would eventually sink through any amount of ice.]
uptake heat = given heat.
dont want to start about that second Law again but, hasnt any done some of these experiments on highschool ?
You have many tons of very very cold ice and you want to melt trough it with a hot space probe???
How hot do you want to have it? Water has also one of the highest heat capacities known unless to can keep on generating a lot of heat and the probe has a substancial mass and heat capacity forget about it.
Besides that the water melted before would freeze again and that leaves one with the problem of getting the prove out of the ice again.
At the "bottom" or tunneling end of the probe put a mass of heat-producing nuclear material. Make certain the probe is designed to orient itself with the heated end down.
Unless the tunnel collapsed or filled with frost you wouldn't have liquid water surrounding the probe until it gets to an ocean. As I recall in vaccuum there is no liquid phase of water. It would flash to gaseous form and spew out the end of the tunnel.
The problem I foresee with this approach is the probe hitting a pocket of liquid water deeper into the ice. If there is no seal behind the probe the pressure difference might be sufficient to blow the probe out of the tunnel. It would need to constantly anchor itself against the tunnel walls -- it would probably have to be a fairly hefty piece of machinery.
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He would have no problem going through all that ice.
Maybe I'll stop eating bugs.
Instead of a spool of wire, would an orbital laser or microwave generator work? The energy beamed down could have 2 uses, one, to heat and power the probe and two, to keep the tunnel from refreezing. Seems I've read about lasers hitting a spinning disc from the ground, or microwaves comming down from above, as a possible launch vehicle here on earth; maybe they could 'backward' the process...I've also read about a remote control airplane with no on-board power sources - it was just beamed microwave juice from a distance (sorry, no links).
Perhaps a powerfull enough low-orbit source could do it as long as it had a constant clear line of sight - it doesn't have much of an atmosphere, does it? Would a really big solar array in orbit be able to collect enough juice from the sun to power something like this?
Interesting technical problem. Makes me wonder if it might be more efficient to cut, rather than melt. Take advantage of the entropy in the situation. Cutter up front that moves ice into a melting/boiling chamber, use the boiling to drive a turbine that will chew up more ice for boiling. Of course, salts and other minerals may complicate the process. Perhaps reserve some of the meltwater to contunually flush out accumulated deposits.