Why Europa and not Ganymede

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steve01

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I have always thought Europa was our best chance for finding liquid water in the solar system, but when I saw some models of Ganymede, it appears to be much larger-with a metallic core and a larger cross-section of possible liquid water. Wouldn't the denser core and tectonic activity not be better indications of internal heat? what are your thoughts?
 
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g_riff

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I believe Ganymede is too far way from Jupiter to generate enough internal heat to melt the ice into a subsurface ocean. Also, I was under the impression that there was less tectonic activity on the surface of Ganymede. I could be wrong though.
 
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robnissen

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Also the liquid water on Europa is under ice, not rock like Gannymede. It will be much easier to get to (and, if current theories are correct, we still will have to go through miles of ice to get to any liquid water).
 
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nopatience

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I have always read that Europa has more surface radiation. Personally when I look at the pictures of the two moons I find myself staring at Europa. The colors and surface cracks are just amazing. Europa looks like no other planet. Ganymede resembles other moons and would have to agree that to get to a subsurface ocean would prove more difficult. <br /><br />But I think that my main goal for Europa is to see those cracks and surface features up close would be amazing. <br /><br />You know what I would like to see on Europa..... a seismograph. I would like to know how much activity the surface is actually undergoing.
 
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thalion

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^<br />Ditto for the seismograph! Many a night have I dreamed of setting three of those bad boys on the surface, and finally figuring out its subsurface structure. Seismometers for Io come a close second, in my wish book. <img src="/images/icons/laugh.gif" /><br /><br />Back to the original topic: <br />I think the consensus is that Ganymede's liquid water would be considerably more difficult to reach than Europa's; indeed, it's probably more of a mantle than a true subsurface ocean. A stickler for life on Europa has been the fact that a Europan ocean would be less favorable for life if there were no influx of materials from the surface, like peroxides created by radiolysis, though this is probably controversial. Ganymede's ocean has probably been completely cut off from the surface for billions of years.<br /><br />That said, I think Ganymede may actually become more favorable for life than Europa, due to its higher gravity, once our Sun swells into a giant and gives the outer Solar System a few million years of hothouse conditions. <img src="/images/icons/wink.gif" />
 
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CalliArcale

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Well, then we'll just have to live on Triton, won't we? <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>
 
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nopatience

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I know that Europa is inside the magnetic influences,if you will, of Jupiter. but does the planet have a magnetosphere by itself?
 
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projectorion

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I believe Ganymede might be within a radiation belt and therefore not ideally suited to exploration.
 
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qzzq

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Ganymede is further away from Jupiter than Europa, so the tidal forces Jupiter's immense gravity causes are less strong on Ganymede than Europa, making Europa a more likely candidate to have a liquid water ocean beneath it's icy crust. For example, Io is too close to Jupiter, making it the most volcanically active body in the solar system. Proximity to Jupiter is key here I believe. <br /><br />Get JIMO up there! <div class="Discussion_UserSignature"> <p> </p><p>***</p> </div>
 
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nopatience

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would radiation be filtered and eliminated (to some extent) as it passes through Europa's surface ice just as water stops radiation?<br /><br />basically, does Ice and water filer radiation the same? <br /><br />oh! Speaking of life on either Europa or Ganymede----<br />would Ganymede be more suitable for human life than Europa? or vice versa?
 
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mikejz

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The ice would serve as a shield, its its effects on the electionics on the probe that make it more difficult. Same story with humans--the feather out, the better.
 
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yurkin

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The problem I see with Ganymede is the pressure. Just like the mantle of earth the mantle of Ganymede should be under incredible pressure. I don’t think the complex chemicals necessary for life can form under those conditions. Jimo’s 100kW sounding radar could really come in handy to answer this.<br /><br />Here's a picture so we all know what it is we are talking about.
 
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qzzq

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NoPatience:<br /><br /><i>would radiation be filtered and eliminated (to some extent) as it passes through Europa's surface ice just as water stops radiation?</i> <br /><br />Yeah, hydrogen absorbs radiation, so an icy mantle is ideal for cover. For radiation blocking in space travel scientists are developping hydrogen rich polymeres, so I don't think it really matters in what substance or state the hydrogen exists. <br /><br /><i>would Ganymede be more suitable for human life than Europa? or vice versa?</i><br /><br />I'd say Europa. It's more likely to sustain life, because it's closer to Jupiter, thus tidal friction will be more significant than on Ganymede, making Europa's interior warmer. It (probably) has salt, minerals and liquid water. Actually, this article suggests we already can see remnants of life on Europa; the odd color of its surface may be caused by bacteria ( extremophile bacteria ): http://nai.arc.nasa.gov/news_stories/news_detail.cfm?article=europa_bacteria.cfm<br /> <div class="Discussion_UserSignature"> <p> </p><p>***</p> </div>
 
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quasar2

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i wonder if there wouldn`t be a Langrange Point in the vicinity of Jupiter`s moons, there must be @ least 50 of them. it would seem this would easier to deal with than actually landing on a high gee surface. <div class="Discussion_UserSignature"> </div>
 
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spacechump

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I don't think any of the moons are a "high-gee" surface.
 
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nopatience

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qzzq-<br />what about humans? Is the radiation on the surface of Europa way to high for human exploration?
 
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qzzq

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Hey, I think the vacuum 'd kill you before the radiation would. <img src="/images/icons/crazy.gif" /><br /><br />You could dig a hole in the icy crust and go underground. Let the ice protect you. Of course there is always that risk of contaminating Europa's biosphere. O well... <div class="Discussion_UserSignature"> <p> </p><p>***</p> </div>
 
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quasar2

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is there a list of their gravities? <div class="Discussion_UserSignature"> </div>
 
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spacechump

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<blockquote><font class="small">In reply to:</font><hr /><p>is there a list of their gravities?<p><hr /></p></p></blockquote><br /><br />Well here is a list of their size, mass and density:<br /><br />http://curriculum.calstatela.edu/courses/builders/lessons/less/les1/planetstats.html<br /><br />Given that most moons in the solar system are smaller than earth's moon or about the same size(a few exceptions being titan, ganymede, Europa and Io that are closer to Mercury's size) and not as dense they'd have pretty weak gravity. Remember that earth's moons is only 1/6th that of earth's gravity and mars is only 1/3rd that of earth's gravity.<br /><br />So no moon has a "significant" gravity that near rivals earth's.
 
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yurkin

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Hi Steve<br />There are far too many unknowns to resolve this thread.<br /><br />I think if Europa doesn’t have life then its very unlikely Ganymede does. The problem isn’t a lack of water but a lack of energy. If Europa is found to be very volcanically active with just a thin ice crust then there’s a good chance life will be found there. If it’s not then Ganymede won’t either. Ganymede is going to be even less active since it is further out. Europa might be active and Ganymede not, but not the other way around.<br /><br />Jimo is going to try to detect a liquid region, the organic composition, and signs of life on Callisto, Ganymede as well as Europa.<br /><br />I couldn’t find data for radiation level at the surface of the Gallian moons. Perhaps Alex or someone might have that information. What I gathered though from reading the articles is that it’s not low. You’d definitely want to be living with some strong shielding overhead or underground.<br /><br />Callisto is probably the best candidate for human habitation. It’s the furthest from Jupiter so the radiation levels will be the lowest. It requires less deltaV to get to then the other three moons. Its rock/ice surface should be easy to tunnel through, and provide good radiation protection. The rock would also make it more stable then a tunnel on Europa, and it has more gravity then that world. If it weren’t for the distance maybe even better then mars.<br />
 
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quasar2

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callisto`s gravity is? <div class="Discussion_UserSignature"> </div>
 
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spacechump

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Callisto's surface gravity is 1.25 m/s^2...less then that of earth's moon.
 
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quasar2

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forgive me for sounding stupid, but what would that be percentagewise? i guess we`re just going to hafta convert to a new system rather than 1/6 & 1/3 especially when mars isn`t exactly 1/3. precrash i`d asked about gravities of other destinations & got too nebulous of an answer. it may actually be "good" these bodies are essentially less than Luna. precrash i don`t think i was alone in assuming Europa was higher gee than Mars. many folks including myself have advocated launching missions from The Moon. so i`m almost seeing where missions could be launched from Mars. & i`d assumed Europa would be next. i guess until now i never checked the gee factor. i made the mistake of letting others do my thinking, i should know better. i made the same mistake of thinking GEO would be safe for humans. <div class="Discussion_UserSignature"> </div>
 
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thalion

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Callisto's gravity is only 77% that of the Moon, even though it's much more massive; this is a result of Callisto's lower density.<br /><br />Unfortunatley, the low gravity on the Galileans would be of little help in escaping the Jovian system, as the moons are all deep in Jupiter's gravity well. After escaping from the surface, a spacecraft would still have to expend considerable energy to get away from Jupiter itself.
 
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