What will Juice tell us about Europa?

[skydivephil]

Now that ESa have selected Juice as its next main mission it seems dissapointing that the main target is Ganymede rather than Europa.
I guess this is due to the extra cost of extra radiation shielding for Europa and due to the fact that NASa were supposed to do Europa as part of the original Laplace mission.

So given Juice plans only 2 fly bys of Europa what will we really learn?
Will it definitley answer the ocean hypothesis and measure the depth fo the ice sheet?

 

[marcus]

All in all, I've always considered Ganymede a lot more interesting moon to explore than Europa. So I hope the JUICE mission stays funded and goes ahead and stays focused on Ganymede. From what I can see they plan for the craft to ORBIT Ganymede for several months.

I don't think Europa is likely to be unique in having a subsurface saltwater ocean. Do you think there is something special about Europa that makes it extra interesting?

Details about Ganymede:

Largest moon in solar system (bigger than the planet Mercury)
surface gravity about 1/7 of Earth's
has its own internal geomagnetic field
density about twice that of water ( about 2 g/cc)
assumed makeup about half water-ice and half rocky material etc.
likely subsurface saltwater ocean.

Not bathed in deadly radiation, at least not to the extent that Europa is.
Correct me if you think I'm wrong, but it seems obvious that Ganymede is the J-moon best suited for colonization by Earth life.

By comparison, Europa is small and bathed in radiation. Is there some reason to bother with it?
http://en.wikipedia.org/wiki/Ganymede_(moon )

 

[SHISHKABOB]

I think the reason why Europa tickles the fancy of many a person interested in space is because of Mr. Clarke's excellent novels and their depictions of life on that particular moon. As I am no exobiologist, I do not know how realistic his ideas were, and I also have never seen (nor gone looking to find) a person say exactly why it would be unlikely for those creatures to be possible.

But of course you raise good points for why Ganymede would be a possible place to put people in the future.

 

[skydivephil]

I think finding signs of life is the key issue rather than colonisation. As I understand it Europa gets more press due to the higher probability of interaction between the surface and the ocean this increases the odds for life and for us to find signs of that life. Also there's more energy available for life at Europa than Ganymede. Life should be protected from the radiation by the ice sheet. If we are every going to drill to the ocean , it's going to be easier at Europa as it's believed to be closer than Ganymede.
Am I wrong?

 

[Cosmo Novice]

I am very interested in the Juice missions and I sincerely hope it goes ahead as planned and within budget.

If we are ever going to find any non terrestrial life then I think the Jovian moons are the place to start - who knows: it may be that beneath the ice sheets of the J-moons are complex ecosystems. Assuming all the requirements for life!

I am in no way talking about little green men but we shall see - there have been detections of organic compounds by Cassini so the possibility is there!

 

[lpetrich]

If I had to choose, I'd choose Europa. That's because Europa has gotten resurfaced much more recently than either Ganymede or Callisto. That's from counting craters. Hardly any on Europa, but lots of them on Ganymede and Callisto.

 

[PhilDSP]

likely subsurface saltwater ocean.

Interesting comment. On what basis should we suspect that the temperature might be warm enough to melt ice? Is the orbit eccentric enough to develop a sub-surface tidal warming along the lines of Io?

An alternate perspective in support of investigating Europa is that a life form that is not sensitive to the frigid temperatures likely to be prevalent on Europa may neither be sensitive to radiation.

 

[PhilDSP]

I am in no way talking about little green men but we shall see - there have been detections of organic compounds by Cassini so the possibility is there!

I'm with you there buddy! I recently discovered the Cassini-Huygens website. The photographs and descent animations for Titan are just spectacular! Way underbilled. The general public should experience them as they really are a dream to either a science or science fiction fan. It's almost like waking up on a planet not so very far away that is close enough to our own to start feeling at home in a strange way.

 

[lpetrich]

High Tide on Europa - Astrobiology Magazine

The effect is known as tidal flexing, which arises from their resonant orbits, provides heat for volcanism on Io and could result in the presence of liquid water beneath Europa's icy surface. There is good evidence for liquid water on Europa based on geological evidence from images of Europa taken by the Voyager and Galileo spacecraft . This geological evidence is tantalizing, but incomplete - it suggests that liquid water could be present, but also allows for the possibility that the strange features we see on Europa's surface could all have formed through the motion of soft ice, without any liquid water at all.

So from some of the modeling, Europa seems to have enough tidal heating to keep its interior ocean liquid.

Surf's Up on Europa? - NASA Science

As Galileo flew just 351 kilometers (218 miles) above the icy moon on January 3, its magnetometer detected directional changes in Europa's magnetic field. Such changes are consistent with fluctuations that could occur if Europa contains a shell of electrically conducting material, such as a salty, liquid ocean.

It's unlikely to have any other kind, like a liquid-iron core. That's what the Earth has.

But how thick is the surface ice?
The great thickness debate: Ice shell thickness models for Europa and comparisons with estimates based on flexure at ridges
Abstract:

Estimates of the thickness of the ice shell of Europa range from <1 to >30 km. The higher values are generally assumed to be estimates of the entire ice shell thickness, which may include a lower ductile layer of ice, whereas many of the smaller thickness estimates are based on analyses that only consider that portion of the ice layer that behaves elastically at a particular strain rate. One example of the latter is flexure analysis, in which the elastic ice layer is modeled as a plate or sphere that is flexed under the weight of a surface load. We present calculations based on flexure analysis in which we model the elastic ice layer as flexing under a line-load caused by ridges. We use precisely located, parallel flanking cracks as indicators of the location of greatest tensile stress induced by flexure. Our elastic thickness results are spatially variable: ∼500–2200 m (two sites) and ∼200–1000 m (one site). Thorough analysis of Europan flexure studies performed by various researchers shows that the type of model selected causes the greatest variability in the thickness results, followed by the choice of Young’s modulus, which is poorly constrained for the Europan ice shell. Comparing our results to those of previously published flexure analyses for Europa, we infer spatial variability in the elastic ice thickness (at the time of load emplacement), with smooth bands having the thinnest elastic ice thickness of all areas studied. Because analysis of flexure-induced fracturing can only reveal the elastic thickness at the time of load emplacement, calculated thickness variability between features having different ages may also reflect a temporal variability in the thickness of Europa’s ice shell.

The authors note that their colleagues had found a lot of different numbers for the ice-shell thickness, and they themselves think that it can be different at different places on Europa.