Is Ganymede better than mars?

[daniel l.]

Here's What ganymede has that mars doesnt

#1: An oxygen atmosphere (Not breathable but you can compress it to fill your oxygen tanks)

#2: A vast untapped source of water (The planet is practically made of it!)

#3: A stable magnetic field to protect colonists from solar flares

#4:Awesome views of jupiter (Not required)

I just want to know you guys's opinion on this.

[SargeRho]

Mars is much closer, and not orbiting a giant cyclotron. Has a lot of frozen water as well.

[Tommygun]

Ganymede receives about 0.08 Sv of radiation per day from Jupiter.

So people would need to travel by shielded ships and immediately go under the ice.

It's not undo-able for a mining or science station, but I don't think a lot of people are going to want to colonize it.

[Thomas988]

This is definitely an interesting idea, but I still think Mars is better. Getting colonists to Ganymede rather than Mars will take a ridiculous amount of money, technology, and time. Are we even technologically capable of landing on Ganymede yet? Plus we know much more about Mars than Ganymede.

[RAINCRAFTER]

Ultimately, I think Ganymede is cooler, but getting there and Jupiter radiation makes Mars better for colonization in my opinion.

(and probes... and other manned missions)

Edited March 22, 2015 by RAINCRAFTER

[Cirocco]

Mars is a far better prospect for colonization I think.

Mars is a a looooot closer than Jupiter, receives less radiation thanks to its atmosphere, also has a lot of frozen water (and possibly liquid subsurface), has an actual soil which can be used to grow plants in greenhouses (martian soil isn't that different from earth soil. somewhat different pH, but that's mostly it if I recall correctly), is a lot warmer than Ganymede (still really freaking cold but at least we're talking about -50°C or something rather than -100°C on Ganymede), etc.

One big one is as the availability of water as well. Yes, Ganymede has a ton of water, but it's also under a 100km thick crust of ice and rock. Mars has frozen water (and possibly transient liquid water) on its surface. Far easier to get to.

So yeah, Ganymede might be okay for an outpost if ever technology gets to that point, but not much more I think.

[lajoswinkler]

With some 3333.3 µSv/h (0.08 Sv/day), which is like 16666x my hourly dose at my home, and the enormous distance from Earth, and lack of atmospheric pressure, Ganymede is a lot worse place to be than Mars.

As SargeRho said, Ganymede is orbiting a giant cyclotron. No, thanks.

The view would also be a bit scary IMHO. Jupiter would have an angular diameter so large it would appear kind of like a closed fist when you stretch your arm into the sky.

Mars is a far better prospect for colonization I think.

Mars is a a looooot closer than Jupiter, receives less radiation thanks to its atmosphere, also has a lot of frozen water (and possibly liquid subsurface), has an actual soil which can be used to grow plants in greenhouses (martian soil isn't that different from earth soil. somewhat different pH, but that's mostly it if I recall correctly), is a lot warmer than Ganymede (still really freaking cold but at least we're talking about -50°C or something rather than -100°C on Ganymede), etc.

One big one is as the availability of water as well. Yes, Ganymede has a ton of water, but it's also under a 100km thick crust of ice and rock. Mars has frozen water (and possibly transient liquid water) on its surface. Far easier to get to.

So yeah, Ganymede might be okay for an outpost if ever technology gets to that point, but not much more I think.

Martian atmosphere is virtually useless shield against any ionizing radiation. Thing is Mars doesn't have a giant cyclotron nearby like Ganymede does.

Also Mars doesn't have readily available water. There is no evidence of water ice just waiting to be dug out and thawed. No evidence of transient liquid water, either. Those things have been blown out of every proportion by the media. Mars is pretty much a desert drier than Sahara, with barely any atmosphere.

Edited March 22, 2015 by lajoswinkler

[AngelLestat]

none of these has pressure or enoght gravity to reproduction.

Venus is still the best case outside earth.

[HoloYolo]

none of these has pressure or enoght gravity to reproduction.

Venus is still the best case outside earth.

Venus has 93x the pressure of Earth, and is the hottest place in the solar system not counting the Sun. It rains Sulfuric Acid, and has a Co2 atmosphere. As much as Venus has it's pro's, we will not have the technology and money to colonize Venus, yet.

[Airlock]

How about Callisto? Being the outermost of the Galilean Moons, it lies outside of Jupiter's radiation belt, and yet is still protected from solar radiation by Jupiter's magnetosphere. It has a mass-fraction of 25-50% water ice, which may hide a subsurface ocean underneath.

From Nyrath's Atomic Rockets site:

The four major Galilean moons are within Jupiter's lethal radiation belt, except for Callisto. If you want ice that isn't radioactive, you've come to the right place. It is almost 50% ice, and remember this is a moon the size of planet Mercury. That's enough ice to supply propellant to the rest of the solar system for the next million years or so.

Edit: http://www.dailykos.com/story/2013/02/23/1188459/-Getting-to-Know-Your-Solar-System-25-Callisto

Daily unshielded radiation dosage on Callisto is about 0.1 mSv or (0.0001 Sv). This is 800 times lower than the dosage on Ganymede, 54,000 times lower than the dosage on Europa, and a staggering 360,000 times lower than what you would get every single day on Io. The reason is that Callisto is outside the most active parts of Jupiter's magnetic field while still being protected by it from solar and cosmic particles.

Though 0.1 mSv per day is not a trivial amount of radiation, it's actually better than what astronauts orbiting Earth experience - eight times better - and only about 13 times the average daily background radiation dosage on Earth. NASA has standard career radiation exposure limits for its astronauts, limiting how often they can fly: A 55-year-old male astronaut can accumulate a maximum of 4 Sv (4000 mSv) over the course of his career, and a female astronaut of the same age can safely accumulate 3 Sv (3000 mSv). To receive the lower amount (3 Sv) on Callisto, you would have to remain unshielded all day, every day for 82 years straight. In other words, in terms of radiation risk, colonizing Callisto would be safer than what NASA astronauts are doing right now.

[my bolding] Edited March 22, 2015 by Airlock

[YNM]

How about Callisto? Being the outermost of the Galilean Moons, it lies outside of Jupiter's radiation belt, and yet is still protected from solar radiation by Jupiter's magnetosphere. It has a mass-fraction of 25-50% water ice, which may hide a subsurface ocean underneath.

From Nyrath's Atomic Rockets site:

The four major Galilean moons are within Jupiter's lethal radiation belt, except for Callisto. If you want ice that isn't radioactive, you've come to the right place. It is almost 50% ice, and remember this is a moon the size of planet Mercury. That's enough ice to supply propellant to the rest of the solar system for the next million years or so.

Edit: http://www.dailykos.com/story/2013/02/23/1188459/-Getting-to-Know-Your-Solar-System-25-Callisto

Daily unshielded radiation dosage on Callisto is about 0.1 mSv or (0.0001 Sv). This is 800 times lower than the dosage on Ganymede, 54,000 times lower than the dosage on Europa, and a staggering 360,000 times lower than what you would get every single day on Io. The reason is that Callisto is outside the most active parts of Jupiter's magnetic field while still being protected by it from solar and cosmic particles.

Though 0.1 mSv per day is not a trivial amount of radiation, it's actually better than what astronauts orbiting Earth experience - eight times better - and only about 13 times the average daily background radiation dosage on Earth. NASA has standard career radiation exposure limits for its astronauts, limiting how often they can fly: A 55-year-old male astronaut can accumulate a maximum of 4 Sv (4000 mSv) over the course of his career, and a female astronaut of the same age can safely accumulate 3 Sv (3000 mSv). To receive the lower amount (3 Sv) on Callisto, you would have to remain unshielded all day, every day for 82 years straight. In other words, in terms of radiation risk, colonizing Callisto would be safer than what NASA astronauts are doing right now.

[my bolding]

... and a very thick ice, with only a very shallow possible liquid. I mean, do you see just how many craters it had contracted ? How'd shallow ice hold those things ? Also it has a very low albedo - 0.22 geometric - which is quite low for an ice object...

Enceladus could be a good option, but it totally lost in terms of distance. Or Titan. Or Mars itself, while doesn't seriously gives anything too surreal, it's better to practice first, then continue on... small steps, one by one.

[AngelLestat]

Venus has 93x the pressure of Earth, and is the hottest place in the solar system not counting the Sun. It rains Sulfuric Acid, and has a Co2 atmosphere. As much as Venus has it's pro's, we will not have the technology and money to colonize Venus, yet.

http://forum.kerbalspaceprogram.com/threads/104177-Nasa-is-considering-a-Manned-Mission-to-Venus-before-Mars!

[Armchair Rocket Scientist]

http://upload.wikimedia.org/wikipedia/commons/thumb/4/43/Ganymede_diagram.svg/1024px-Ganymede_diagram.svg.png

Here's What ganymede has that mars doesnt

#1: An oxygen atmosphere (Not breathable but you can compress it to fill your oxygen tanks)

#2: A vast untapped source of water (The planet is practically made of it!)

#3: A stable magnetic field to protect colonists from solar flares

#4:Awesome views of jupiter (Not required)

I just want to know you guys's opinion on this.

1. Ganymede's atmosphere has a surface pressure of around a micropascal. Mars's atmosphere is 600 Pa and 0.145% oxygen according to Wikipedia. This means that the partial pressure of oxygen is close to a MILLION times higher on Mars than on Ganymede. Trying to compress Ganymede's atmosphere would be absurd. It would probably take many orders of magnitude less energy to electrolyze the water ice of Ganymede's regolith to produce oxygen, or to synthesize oxygen from Martian CO2.

2. Ganymede's ice is FAR more water than a colony would have any use for. Mars should have enough buried ice to support a colony. Also, for the record, Ganymede's ocean is below 150 km of ice/URL]. We can't drill through that with anything remotely resembling current technology. If you want to explore an ocean, going to Europa is a better bet.

3. As everyone else has pointed out, Ganymede's magnetic field isn't enough to protect it from Jupiter's much stronger one. Sure, you could shield a colony by placing it under a couple tens of meters of ice, but why bother?

Aside from that, there are a couple of other important points to consider:

First, travel to/from Ganymede will take much longer than travel to/from Mars. With a hohmann transfer, I believe it's 3-5 years vs. a few months. This means that a ship would need extremely thick radiation shielding, and use an very high dV transfer.

Second, Ganymede takes a LOT of delta-V to reach compared to Mars. Assuming this delta-V map of our solar system is anywhere near accurate, it takes about 4500 m/s to reach the Martian surface from LEO, but 9500 m/s to reach Ganymede's surface. This is assuming you Aerocapture for both Mars and Jupiter. The actual dV needs will be even higher, because again you won't be using a Hohmann transfer. Ganymede has no atmosphere for aerobraking, and is about as hard to land on as the moon. Returning will be even harder; that dV map says that you'd need 6700 m/s to escape Jupiter's immense gravity well from a Ganymede transfer orbit. This is a huge requirement even for nuclear-powered spacecraft.

[lajoswinkler]

Venus has 93x the pressure of Earth, and is the hottest place in the solar system not counting the Sun. It rains Sulfuric Acid, and has a Co2 atmosphere. As much as Venus has it's pro's, we will not have the technology and money to colonize Venus, yet.

That rain never reaches the ground but ground is not colonizable so yeah... clouds. Acid mist. Venus is ok for colonizing the clouds. You float there, experiencing normal gravity and you're cool.

[kStrout]

just because when unshielded you experience more radiation an Ganymede than Mars does not mean it is harder to shield against. The worst radiation is not from the sun as many people believe, but from cosmic rays, they come from every direction and have heavy particles moving extremely fast. Jupiter's magnetic field does have a lot of radiation, but it is slow moving radiation which is easy to stop and the field stops most cosmic rays. But Mars does not have a magnetic field, so you need more shielding.

[SargeRho]

Jupiter's magnetic field is a giant synchrotron, bombarding not just things the relativistic electrons hit, but everything around them with synchrotron radiation as well, which I think is mostly X- and Gamma rays.

[Technical Ben]

Ganymede receives about 0.08 Sv of radiation per day from Jupiter.

So people would need to travel by shielded ships and immediately go under the ice.

It's not undo-able for a mining or science station, but I don't think a lot of people are going to want to colonize it.

Ah... I don't have a solution to the radiation problem... which means I'll have to "lampshade" it in any scifi... (though it might be ok if radiation levels within the atmosphere of a gas giant are ok... Is Neptune safe, why?)

[lajoswinkler]

just because when unshielded you experience more radiation an Ganymede than Mars does not mean it is harder to shield against. The worst radiation is not from the sun as many people believe, but from cosmic rays, they come from every direction and have heavy particles moving extremely fast. Jupiter's magnetic field does have a lot of radiation, but it is slow moving radiation which is easy to stop and the field stops most cosmic rays. But Mars does not have a magnetic field, so you need more shielding.

Planetary magnetic fields don't do a lot when it comes to cosmic rays. What protects you is mass. The heavier the nuclei and the more of them in your shield, the better. 10 m deep cave is a decent one. Earth's atmosphere is also a good one because it's so thick.

Cosmic radiation levels in Martian orbit and Ganymede surface should be very similar. It's neighbourhood compared to the universe around us.

What magnetic shields can protect you from is solar wind. Unfortunately Ganymede has a pathetic field which doesn't stop much of the incoming and Jupiter-accelerated particle flux. It's being bombarded by protons, electrons and other stuff. You'd get radiation poisoning on its surface rather fast. Each day more than one yearly dose of ionizing rays which, received in one year, will measurably increase your chance of getting some type of cancer. Imagine that. Every day 80 mSv. You'd probably die in a few weeks from acute radiation poisoning.

Ah... I don't have a solution to the radiation problem... which means I'll have to "lampshade" it in any scifi... (though it might be ok if radiation levels within the atmosphere of a gas giant are ok... Is Neptune safe, why?)

Unless you're at gas giant's magnetic poles where the flux is enormous, you should be fine. For example right at the equator where the magnetospheric bulge is the thickest. Gas giants themselves aren't radioactive.

[GigaG]

^I wonder why, too, but doesn't Jupiter just generate a bigger radiation belt from its magnetic field than Neptune and the other giants?

Could somebody answer this? What about Saturn - does it have big radiation belts?

[lajoswinkler]

Jupiter has by far the largest and the most powerful magnetosphere. Saturn's is smaller and weaker because the quantity of metallic hydrogen inside is smaller.

Uranus and Neptune have much weaker fields. Uranus has, on average, stronger magnetic field than Neptune, but it's is highly asymmetrical. Their fields are produced by degenerated semimetallic mixture of ices (ice = water, ammonia, methane, ...) at enormous pressure and temperature when there's significant electron orbital overlapping.

The more powerful the magnetosphere, the more trapped energetic particles are inside. Nevertheless, in proximity of all gas giants ionizing radiation is so intense it would kill a human shortly. That's why manned landing on most of their satellites is out of the question.

[Tommygun]

Ah... I don't have a solution to the radiation problem... which means I'll have to "lampshade" it in any scifi... (though it might be ok if radiation levels within the atmosphere of a gas giant are ok... Is Neptune safe, why?)

I don't know what Neptune's atmospheric radiation levels are, but keep in mind it's still an "Ice Giant" (related to gas giants), so it is basically a failed star that didn't acquire enough mass to go fully nuclear.

It still has a good amount of fission going on in its interior and maybe some fusion too, so I can't imagine it's too safe that close to the core.

[Bill Phil]

I don't know what Neptune's atmospheric radiation levels are, but keep in mind it's still an "Ice Giant" (related to gas giants), so it is basically a failed star that didn't acquire enough mass to go fully nuclear.

It still has a good amount of fission going on in its interior and maybe some fusion too, so I can't imagine it's too safe that close to the core.

Jupiter is no where near a star. It's a tenth of a percent of the Sun's mass.

Saturn is around 1/3 of Jupiter's mass, and Neptune is more like 1/6 of Saturn.

No, giant planets are nowhere near to stars. Unless they're dozens of Jupiter Masses...

[Cirocco]

Martian atmosphere is virtually useless shield against any ionizing radiation. Thing is Mars doesn't have a giant cyclotron nearby like Ganymede does.

Also Mars doesn't have readily available water. There is no evidence of water ice just waiting to be dug out and thawed. No evidence of transient liquid water, either. Those things have been blown out of every proportion by the media. Mars is pretty much a desert drier than Sahara, with barely any atmosphere.

Martian atmosphere indeed doesn't do much against harmful radiation. I think I must have been half asleep when I was writing that post, radiation difference is indeed due to absence of Jupiter. Water on Mars is very much a thing though, but I was referring mostly to the poles. There's a lot of water ice on the north and south pole (it's under a layer of carbondioxide ice on the south pole, but pretty exposed on the north pole) and in craters and other (permanently) shaded areas in more temperate regions.

Transient liquid and subsurface water is indeed unproven, that's why I added the "possibly". And of course "transient" doesn't mean you'll have lakes or rives, but rather you'll have a very, very small stream which will last for a minute or two tops before it evaporates. But there's more water on Mars than you might suspect. Just not liquid.

[peadar1987]

I don't know what Neptune's atmospheric radiation levels are, but keep in mind it's still an "Ice Giant" (related to gas giants), so it is basically a failed star that didn't acquire enough mass to go fully nuclear.

It still has a good amount of fission going on in its interior and maybe some fusion too, so I can't imagine it's too safe that close to the core.

Nope, no appreciable amounts of fission will be going on in Neptune, you need fissile material and a moderator, neither of which it is going to have in large amounts. Perhaps there is some radioactive decay of unstable isotopes in the core, remaining from its formation, but this will have zero effect except right next to them.

There won't be any fusion either, you need a huge amount of temperature and pressure to cause any fusion, and the mass to cause that to happen through gravity alone is far greater than Neptune can manage.

The radiation at Jupiter is caused primarily by energetic particles trapped in its powerful magnetic field (itself caused by the quickly-rotating core of metallic hydrogen). These particles themselves, and electromagnetic waves caused by their interactions with other matter, are what makes the environment around Jupiter so high-dose. Neptune has a far weaker magnetic field, and therefore far weaker radiation belts.

You're right that it won't be safe close to the core though, the pressure would kill you instantly, it is in excess of two million atmospheres at the point where the hydrogen transitions to its metallic phase. It will also be very hot due to the residual energy from the planet's formation.

[lajoswinkler]

There certainly is radioactive decay in all planets and all satellites; that's what gives their cores a great deal of heat, probably most of it in some cases, but for any seemingly controlled fission you can't have all the contents mixed and in fluid state. They will spontaneously separate.

Those atoms are ancient surviving remnants of some old supernova. Uranium and thorium isotopes.

The actual rays coming from such cores are not a threat because the overall power density is very low. It's the sheer huge mass of the material that is responsible for the energy levels. Compare with Sun's fusion - its energy generation is lower than in a gekko, yet it is a scary ball of gas and plasma because it's so huge. Our fission reactors are ungodly powerful compared to stars. Lump of uranium the size of our Sun can't even exist. Hell, lump the size of a TV can't.

Also, satellites and planets are so large that the distance from the radioactive parts and shielding combined gives supreme protection. There simply isn't any such danger from any planet/satellite.

The only threat comes from their magnetospheres catching and concentrating solar wind. You don't need a radioactive source to get ionizing radiation.