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http://news.yahoo.com/jupiter-moons-clu … 53664.html
I wonder what the pressures would be like in this ocean. Ganymede has a low gravity for a Moon that is bigger than Mercury! it has less gravity than our own Moon! Seems to me that pressures would increase slowly with depth because of this. What do you think?
http://gizmodo.com/a-map-of-jupiters-mo … 1521679445
Last edited by Tom Kalbfus (2014-05-01 18:25:43)
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The surface is airless, so far as I know. There's a lot more radiation in the vicinity of Jupiter, too. Any settlements would have to be heavily buried or far underground. One never knows what there might be that could interest us, so I cannot comment on the desirability of going there.
But because of the cold, the vacuum, and radiation, plus being in a massive planetary gravity well, going there would be quite difficult. The water is inside, not on the surface, so far as I know.
Other than simply exploring, at this point in time I don't see that much point to going there.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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That's my feeling, too. The Jovian system is in general not too interesting. But then maybe we just haven't explored it well enough; Who knows what we'll want to do once we've got some good outposts going on the Moon and Mars and Ceres and Venus
-Josh
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Callisto is better: water rich like Ganymede, but outside the radiation belt and still inside Jupiter magnetosphere, that protect it from cosmic ray, so surface radiation dose is very low, almost 1 REM/yr.
Callisto is also at the border of Juppiter gravity well, so departure burn will be not too much delta-V expensive.
Last edited by Quaoar (2014-05-02 16:11:58)
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Actually, departure isn't that much of a problem, because you can use the gravity well to give you a significant boost. If you're departing Callisto, a 6km/s burn deep in Jupiter's gravity well will give you a 24km/s velocity away from the system. Though, if you're heading inwards, you might want to pack a magsail to decelerate...
Use what is abundant and build to last
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Water whether frozen or liquid, makes a good radiation shield, and burrowing under the ice isn't that hard, you just have to melt your way through. Its much easier to tunnel through ice than dirt and rock, it is a less dense medium, and also the temperatures at which you might melt rock might also melt your spaceship.
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I think the answer to the question that is the title of this thread (Could we colonize Ganymede?) is "yes".
The other question is, of course, "should we?". That answer is probably "not until there's something identified there that we need".
That's quite separate from "should we explore Ganymede?", for which the answer is "yes". Always, and as soon as we are ready to take on the difficulties.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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We need water, can't live without it.
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We need water, can't live without it.
Radietion levels on Jovian satellites:
Io 3600 REM/day
Europa 540 REM/day
Ganymede 8 REM/day
Callisto 1 REM/year
Why do you choose Ganymede?
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Ganymede isn't so terrible. Should be possible to land on it and burrow under the ice. The 8/rem a day is only if your sitting on top of the ice. There is also the fact that Ganymede is the largest moon in the Solar System.
Discovered By
Galileo Galilei
Date of Discovery
1610
Orbit Size Around Jupiter (semi-major axis) Metric: 1,070,400 km
Periapsis (closest) Metric: 1,069,008 km
Apoapsis (farthest) Metric: 1,071,792 km
Orbit Circumference Metric: 6,725,518.71 km
Average Orbit Velocity Metric: 39,165.6 km/h
Orbit Eccentricity 0.0013
Orbit Inclination 0.177 degree
Mean Radius Metric: 2,631.2 km
Equatorial Circumference Metric: 16,532.3 km
Volume Metric: 76,304,506,998 km3
Mass Metric: 148,185,846,875,052,000,000,000 kg
Scientific Notation: 1.4819 x 10^23 kg
Density Metric: 1.942 g/cm3
Surface Area Metric: 86,999,665.93 km2
Surface Gravity Metric: 1.428 m/s^2
Escape Velocity Metric: 9,869 km/h English: 6,133 mph Scientific Notation: 2742 m/s
Sidereal Rotation Period (Length of Day) 7.155 Earth days
By Comparison: Synchronous with orbital period
Atmospheric Constituents Oxygen
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Apparently Gamymede is the only moon in the system with it's own magnetosphere, limited to the equatorial zones. More research is probably required to tell if that results in a bubble of protection from Jovian radiation, or a mini Van Allen belt right on the surface.
Ultimately, the cause for colonization is pretty simple, cheap real estate, the ultimate freedom that comes from living off the the land, and the challenge that comes from creating pleasant ecosystems in a hostile environment.
Last edited by Excelsior (2014-05-03 14:09:25)
The Former Commodore
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But then, why not do that on Callisto? The gravity difference isn't that bad; Callisto is about 13% of a g, while Ganymede is 15%. There is a difference in surface area, but when we're talking whole planets that's hardly significant, or at least it won't be for a good long time.
It would sure be nice to not have that much surface radiation. It would simplify everything a lot.
I do find that 1 rem per year surprising, though. Is Callisto protected by Jupiter's magnetic field?
-Josh
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But then, why not do that on Callisto? The gravity difference isn't that bad; Callisto is about 13% of a g, while Ganymede is 15%. There is a difference in surface area, but when we're talking whole planets that's hardly significant, or at least it won't be for a good long time.
It would sure be nice to not have that much surface radiation. It would simplify everything a lot.
I do find that 1 rem per year surprising, though. Is Callisto protected by Jupiter's magnetic field?
Yes. Callisto it's outside radiation belt, but Jupiter magnetic field is still strong enough to deflect galactic and solar cosmic ray.
I think the safest way to expore Jupiter System, is landing astronauts on Callisto and tele-robotically explore Ganymede, Europa and Io.
Last edited by Quaoar (2014-05-03 15:00:46)
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I would say so. An astronaut on Ganymede, unshielded, would surpass yearly radiation exposure limits in less than a week, and career limits in about three weeks. On Io, you could get your annual radiation dose in 20 minutes (and this is ignoring the effects of acute dose, which you can't do at such high radiation rates!) There's an argument to be made about light speed delay, etc., but I don't think that we'll find the three inner galilean moons very useful with those radiation rates.
Do you have a source for that, by the way?
-Josh
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You are of course assuming they would live on top of the surface of Ganymede not inside its icy crust. 60 meters of ice will hold in a 1 bar atmosphere under an icy dome, a second dome within the ice dome can hold in a room temperature environment, and if the ice dome is significantly larger than the inner dome and the inner dome is well insulated, the environment within the ice dome can stay just below freezing. Ice can make for some permanent structures on Ganymede. Convex ice lenses can even act as solar concentrators for solar panels and for the growth of food crops.
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Why would you inhabit a planet where you need sixty meters of regolith over your head to prevent fatal cancer when a neighboring world would require much less and would have enough space for millions of people?
-Josh
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Well actually he 60 meters is to hold in the 1 Bar atmosphere. ! bar of atmospheric pressure equals 10 tons per square meter, on Earth you need 10 meters of water above your head to produce an additional bar of water pressure, that is if you dive into a pool at seal level and dive down to 10 meters your body is experiencing 2 bars of pressure, 1 bar from the atmosphere above you head and an additional bar of water pressure from the weight of the water above your head. Water after all is defined as weighing 1 metric ton per cubic meter which is also 1000 liters. The kilogram is defined as the mass of one liter of water, so I reckon 1 cubic meter weighs 1 ton, so ten of those cubes of water stacked on top of each other would weigh 10 tons. On Ganymede a cubic meter of water doesn't weigh 1 ton, but rather one sixth of a ton, that is why you need 60 meters of ice to equal the pressure of one bar of atmosphere, because even on Ganymede, one bar of atmosphere still equals 10 tons per square meter. With ice you may not need 60 meters of it, as ice has some structural integrity, much as glass does when it holds the internal pressure of a space craft against the hard vacuum of space, so if this was loose ice rather than a solid sheet of it, you would require 60 meters of it to hold down the upward pressure of 1 bar of atmosphere underneath. This is a conservative estimate of what would be needed based alone on the weight of ice under Ganymede's gravity, you can probably get by with less. Also there is no shortage of ice on Ganymede, you can easily find 60 meters of ice a Ganymede is 40% water by composition, this amount of water would be much harder to find on Mars. Water as I said before is much easier to work with, its melting point is only 0 degrees centigrade, I bet you a chemical rocket engine can easily exceed this temperature and melt a hold in Ganymede's ice as it lands. Imagine using a blow torch on a block of ice and you get an idea of what can be achieved. As a matter of fact not melting the icy surface upon which your spaceship lands presents its own unique challenge. Ice tunnels have been created in Antarctica, there is no reason why it can't be done on Ganymede as well. Frozen water also has made uses as structural material, it can also be used as a lens to focus light rays. I remember on Mythbusters, they made an ice lens which focused the Sun's light on a piece of paper to start a fire.
It just so happens that 60 meters of ice also makes great radiation shielding, those 60 meters aren't required to shield you from the radiation, but only as weight to hold in the air pressure under your dome. the air pressure under the dome holds the ice up quite well, and getting that aount of ice on Ganymede does not present a problem as a large part of that satellite is made of water ice, might as well use it. Digging down ab burying a similar dome on Earth's Moon would require only 20 meters of lunar regolith, as Moon rock weighs about 3 times as much as water. Lunar rock doesn't melt as easily as water ice however!
Last edited by Tom Kalbfus (2014-05-03 22:05:19)
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Equatorial surface gravity (m/sec^2)
Earth: 9.780327
Luna (Earth's Moon): 1.622 (16.5843% Earth, roughly 1/6)
Ganymede: 1.428 (14.60% Earth, roughly 1/7)
Callisto: 1.235 (12.627% Earth, roughly 1/8)
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So about 70 meters of ice, probably you could live with less than a full bar of atmosphere under the dome too. I always heard that Earth gravity was 9.81 meters per second squared.
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Not on the equator (a combination of being further from the core and the centrifugal force of Terra's rotation).
Sure, we *could* colonise Ganymede. But it's further down the list than Callisto, because of the radiation issue. Maybe if it can be warmed up enough for water to sublimate, giving it a thin water atmosphere which may provide some shielding... it might be able to maintain a substantial enough atmosphere to cut the radiation dose down. But we might be able to do that anyway by scattering dust (though I can't find the reference...).
Use what is abundant and build to last
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First study how Ganymede is able to generate a magnetosphere. That will help us undertand how to build an artificial planetary/moon magnetosphere. We really want Ganymede to have an atmosphere thick enough for humans to walk outdoors without a pressure suit. That means retaining atmosphere. And the knowledge would help us build a megnetosphere on Mars and Venus.
While you're at it, prospect Ganymede for sulphur and fluorine.
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I think Ganymede can't be terraformed in the traditional way, its atmosphere will need a roof, perhaps one made of ice.
There are some things to think about. Remember the Earth's atmosphere above a certain altitude remains below freezing, an ice roof on top of such an atmosphere will remain stable, as one descends in altitude, provided an artificial heat and light source, the temperature can get towards a more balmy 72 degrees F/15 degrees C. So what do you think, would water ice make a good roof at the temperatures prevalent around Jupiter?
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I think Ganymede can't be terraformed in the traditional way, its atmosphere will need a roof, perhaps one made of ice.
There are some things to think about. Remember the Earth's atmosphere above a certain altitude remains below freezing, an ice roof on top of such an atmosphere will remain stable, as one descends in altitude, provided an artificial heat and light source, the temperature can get towards a more balmy 72 degrees F/15 degrees C. So what do you think, would water ice make a good roof at the temperatures prevalent around Jupiter?
the ice roof plus atmosphere beneath would also make a fairly effective radiation shield. Then their is the problem of Ganymede ending up as a global ocean, there are worse environments to live under. For this scale of engineering, artificial floating islands would be "small potatoes".
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So about 70 meters of ice, probably you could live with less than a full bar of atmosphere under the dome too. I always heard that Earth gravity was 9.81 meters per second squared.
Yes, but before going in your 70 meters deep in the ice habitat, you have to build it. You have to explore surface to find the right location and this is very very difficoult in a high radiation environment: you have to travel in a heavly screened 30-40 tons rover and you cannot walk outside.
On Callisto there are not such issues: you can explore surface on a 5-6 ton rover, you can go out in spacesuit and you are free to choose to build a surface dome or a subglacial habitat.
Last edited by Quaoar (2014-05-05 02:16:14)
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