Water plumes over Europa Options

[Gerald]

I'd think, that the carbon-nitrogen triple bond should be rather stable.
A paper about CN-photochemistry.

[rlorenz]

I guess I'll be the one who asks -- how much more or less susceptible to degeneration by the radiation environment are carbon-carbon and carbon-nitrogen bonds when compared to carbon-oxygen bonds?
In other words, since the environment rapidly dissociates a lot of molecular bonds, can the lack of more interesting carbon bonds than C-O be attributable to it?

I think the answer is that all bonds are weak compared with the energies of the intense trapped particle environment around Jupiter. Thus
the observed abundances reflect not relative bond strength but the fact that a free carbon atom is most likely to encounter a free oxygen radical rather than another carbon.

[dvandorn]

So, observed species abundances reflect the end result of a process of emission of some carbon species, the dissociation of those species in the radiation environment, and finally the recombination of some species (as allowed by the environment) and the emplacement of these recombined species on the surface?

Just trying to wrap my mind around the most likely process. Seems to me that modern science offers a lot of theoretical concepts that are weak on the actual processes you have to have to get to the current observed conditions, which is why I'm always harping on the process side of things.

-the other Doug

[Gerald]

Some species will escape, and therefore thin out selected chemical elements at the surface.
(Hydrogen (besides helium) is the first element going lost by photolysis of water, leaving oxygen.)

Things will be rather complicated in detail. Here a paper which tries to simplify the processes for the Martian atmosphere, detailed photochemical reactions in Appendix A (p. 22ff).
The more chemical elements and transport processes have to be considered the more complicated.

Comet impacts may replace some of the lost surface material.

[JRehling]

Other Doug,
I think it's useful to consider the relative rates of processes on the surface of a world. We have few visible craters on Earth because erosion and tectonics both work faster than impact cratering.
On Europa, the effects of radiation work fastest, although those obviously alter only the immediate surface.
Recycling of crustal material (faults, occasional melt-through) is next fastest. Then the flux of major impactors comes after that.

I've read enough about Europa to know that there are certainly unknowns and seemingly unknowable unknowns (to paraphrase Donald Rumsfeld), or at least internal parameters that cannot be deduced unless we get hard data about the interior of a kind we don't have, or someone comes up with new and clever ways of interpreting the clues we have. It is generally the case that the interior properties of worlds are hard to pin down without a tremendous amount of in situ seismographic, etc, data of a kind we have only for Earth and to a lesser extent the Moon and a far lesser extent Mars.

[JRehling]

The options for future Europa missions have to highlight a sample return that flies through the plumes, collects material, and returns to Earth. One of the big problems with this architecture is the inconsistent nature of the plumes. A free trajectory return from Earth back to Earth by way of Jupiter has the least possible delta-v, but is also completely inflexible to midcourse adjustment, and it could miss the active period of the plumes.

So an intriguing alternative has to be a mission which enters Jupiter orbit and parks, waiting for the plumes to become active, possibly performing the observations that determine when the plumes are active. To be practical, this would mean something like a Galileo-style elliptical orbit with apojove well outside the orbit of Callisto, and perijove well outside the orbit of Europa. When the determination had been made that the plumes were active and likely to remain so, it could perform a single pass over Europa's surface, perform the collection, and then exit Jupiter orbit for a return to Earth. This would entail more delta-v than the free return trajectory, but avoids the reliance on a single timeframe for sample collection, and still entails vastly less delta-v than a lander-based sample return. It would also offer opportunities for flyby science of Callisto and Ganymede and long-range science of Jupiter, Io, and Europa.

I think something like this has to become a major candidate for a future mission.

[Explorer1]

The issue with parking directly in Europa orbit for any lengthy period is dealing with the high radiation environment and its effect on electronics, correct? Because staying near would take a lot of guesswork out of detecting and intercepting plumes.

[vjkane]

If the plumes are shown to be consistent and persistent (big ifs), then gathering the samples from a hyperbolic solar orbit (i.e., not enter Jovian orbit) would result in a very high speed encounter. That would tend to break apart the molecules of interest. The slowest encounters would come from most closely matching Europa's orbit but that would also break the highest radiation exposures.

[JRehling]

A craft would have limited lifetime in Europa orbit. Moreover, that is extremely expensive in terms of delta-v to get into Europa orbit, then back out of it, then out of Jupiter's gravity well and back to Earth. Jupiter' gravity is the great obstacle here, not Europa's. What would make a mission like this work is only diving through Jupiter's gravity well, and getting that energy back on the way out.

The cheapest option would be to avoid Jupiter orbit at all, but that requires that the plumes are active at the time of a rendezvous predetermined years in advance. If we had the notion of the plumes performing on schedule regularly, that would be the best option. Otherwise, Jupiter orbit is essential. Europa orbit would kill the craft with radiation if it had to wait a long time for the plumes. So a high Jupiter orbit is the most flexible.

[vjkane]

A craft would have limited lifetime in Europa orbit. Moreover, that is extremely expensive in terms of delta-v to get into Europa orbit, then back out of it, then out of Jupiter's gravity well and back to Earth.

I wasn't suggesting being in Europa orbit, just that as the orbit around Jupiter becomes closer to one that matches Europa's orbit, the encounter speed goes down. What the best tradeoff would be between a slow enough encounter to preserve complex molecules and getting out of Jovian orbit, I don't know. The proposed Enceladus LIFE mission, which would perform an Enceladus sample return a la Stardust (and many of the principals were part of the Stardust team), planned for a ~6 km/sec encounter. This would preserve large molecules but destroy any intact organisms.

Being in Jovian orbit allows multiple encounters to build up the sample. However, if the plumes (if they persist) occur only at a certain point in Europa's orbit, it may be difficult to match the Jovian orbit to encounter Europa at that point within a reasonable time.

[JRehling]

For a mission that sits in a circular parking orbit around Jupiter and then shifts to a Hohmann transfer orbit that intersects Europa's orbit, the relative speeds at the encounter are a function of the initial orbital radius. Here are the relative encounter speeds for three different parking orbital radii:

Ganymede-to-Europa: 1.9 km/s
Callisto-to-Europa: 5.2 km/s
2*Callisto-to-Europa: 11.2 km/s

I'm not including the additional acceleration which would take place due to Europa's gravity. This would be about 2.0 km/s added in each case.

So in the Ganymede case, we could have collection take place at about 3.9 km/s. Stardust, for comparison's sake, encountered Wild 2 at 6.1 km/s.

The penalties of having the parking orbit closer are to increase delta-v on arrival/departure to/from the jovian system and to increase radiation exposure.

The radiation at Ganymede is very roughly 2% that at Europa (depends on which spectrum of charged particle energy we're talking about), so a survival time for craft systems on the order of years should be possible at that distance. This would also allow for Ganymede gravity assists that could be provide some of the delta-v for, e.g., departing the Jupiter system.

[MarcF]

Any chance that the Gemini Planet Finder instrument could detect the plume ?

http://www.gemini.edu/images/pio/News/2014...4_01/Europa.jpg

[ugordan]

I'm skeptical since GPI operates in infrared and the plumes are going to be virtually invisible in backward scattered light.

[Bjorn Jonsson]

Before a sample return mission (possibly somewhat Stardust-like) to sample the plumes is flown it is absolutely necessary to know whether the plumes are continuously active or not. If they are not it needs to be determined whether they are always active when Europa is at a specific point in its orbit. This information is necessary for deciding the mission architecture. A spacecraft like JUICE or Europa Clipper should be able to determine this. Waiting for almost 20 years until this is resolved isn't very fun though so maybe this could be determined sooner from ground based observations.

[vjkane]

For a mission that sits in a circular parking orbit around Jupiter and then shifts to a Hohmann transfer orbit that intersects Europa's orbit, the relative speeds at the encounter are a function of the initial orbital radius...

John - Thanks for doing the calculations. The good news is that after the capture, Ganymede flybys can be used to crank the orbit back up to lessen the delta V of the burn to return to Earth.

Do you know how that compares to the flyby speeds from a Jovian flyby?