This seems like the relevant place to post this (could be wrong): http://www.newscientist.com/article/dn24743-first-water-plume-seen-firing-from-jupiter-moon-europa.html#.UqnptUZFCbF? Apologies if it's already been up. The link to the Science article at the bottom doesn't work for me, does anyone have a working link to the original? Cheers.
Here's a link to the paper.
http://hubblesite.org/pubinfo/pdf/2013/55/pdf.pdf
Apparently, Europa joins Enceladus in having active water plumes observable in the present.
http://www.sciencemag.org/content/early/2013/12/11/science.1247051
This might suggest tailoring exploration plans, already in progress, to focus on the study of these plumes, if they are continuous enough to be active when a putative mission could observe them in situ.
The modeled density is comparable to that of plumes at Enceladus. Campaigns to observe plumes over Europa visually failed, which may indicate simply the transience of such activity, although the schedule of the transience becomes extremely interesting. If there is outgassing at some point during every (or nearly every) orbit, then any jovian orbiter with Europa flybys could observe the plume in situ, if the tour is designed appropriately. If the outgassing is rarer, or unpredictable, then that makes in situ observation a challenge.
An extraordinarily interesting possibility here is that the source of Europa's plumes may involve water in contact with a sub-surface ocean floor, which could make the chemistry arbitrarily complex, whereas some models of Enceladus's plumes indicate that the source may be surrounded by more ice on all sides, which limits the possible chemistry.
The lens-melt model of Europa's ice argues that the evidence of surface/melt-through contact occurs between lakes of water which are not in direct contact with the ocean, but exist between the ocean and the top of the ice. This would be of greater interest if the ice that melted to form those lakes had been part of the ocean previously (especially if they were in contact recently).
The proposals for the Europa Clipper mission include a neutral mass spectrometer making flybys of <1000 km to sample the Europa atmosphere. The new discovery, and follow ups, may suggest a different trajectory, but that instrument is already part of the package. The proposals suggest a launch of 2021 or 2022, although that seems tentative.
The possibility of a free-return trajectory sample return bringing some of these plumes to Earth is extremely exciting. A sample return from Europa's surface would be very challenging. The free-return option is much, much more modest in terms of delta-v.
I have now taken a quick look at the article. An enhanced emission was detected near 90° west longitude. Here is a quick and dirty orthographic render of Europa's southern hemisphere:
I think this finding dramatically strengthens the case for what would essentially be Galileo Mk 2. It's quite possible that ALL the major Jovian satellites experience transient activity.
Europa is of particular interest, of course, but a mission with broader objectives would be much more likely to fly.
I think only Europa is the only moon with a thin enough crust to sustain geysers though. But who knows? Maybe Ganymede had geysers billions of years ago.
I can't wait until JUICE is launched. Absolutely one of the most exciting planetary missions of the next decade.
Wouldn't infalling comets deliver carbon to Europa as they do to other places in the solar system?
I wonder about that. Certainly the Jovian system gets more than its share of comet & asteroid impacts...what have we seen, two or three since the early 1990s, now that we know what we look for?
I don't see why Europa could not have obtained abundant carbon from these infalls. We seemingly don't have any way to assess its impact history any further back than 10 million years or so, which is not surprising for what seems to be a dynamic surface environment.
I look forward to any sort of exploration of this moon. There are a LOT of questions to be answered, and doubtless we'll have even more later.
A habitable environment without life would be very useful as a comparison to habitable environments with life. Not as headline and budget friendly perhaps, but scientifically just as good.
Looking at smaller missions than ESA's JUICE or the proposed Europa Clipper, there have been at least two proposals to explore Enceladus with Discovery-class missions. One, JET would image the tiger stripes with a high resolution thermal instrument and sample the plume chemistry with a duplicate of the Rosetta mass spectrometer (much more capable than Cassini's spectrometer). The other would return samples collected in aerogel a la Stardust. I suspect that the concepts could be easily adapted for Europa with the added advantage of being able to use solar power instead of an MMRTG.
Does anyone know whether JUICE would be lucky enough to encounter Europa at its apojove when the plumes (if confirmed and if persistent) are likely to be active?
There's certainly some evidence of carbon in/on Europa's icy crust in the form of CO2.
http://onlinelibrary.wiley.com/doi/10.1029/2007GL031748/abstract
Carbon is relatively rare as a bulk constituent of Earth's crust (<1%). It's even rarer in the oceans (0.0028%), but that doesn't prohibit, some (to say the least) interesting organic chemistry in the Earth's oceans.
Understanding of the non-H2O composition of Europa's surface is pretty crude at present, definitely not accurate to earthlike levels of carbon abundance, further complicated by the fact that the immediate surface which is visible in IR spectroscopy may be different than the near-subsurface. Enceladus, for one, shows a difference between surface composition and plume composition with more non-H2O stuff in the plumes than on the surface.
So I'd say on the issue of Europa and carbon, we have reason to believe that at least some is present. As far as larger quantities go, we have more of an absence of evidence than an evidence of absence.
I think the real interest in the plume discovery is not about what it says about the nature of Europa as much as what it says about the explorability of Europa. It's an extremely challenging target for a lander, much more so if it were necessary to work to get into the subsurface, and borderline impossible for a lander + sample return. A sample return from the plume via a free-return trajectory is potentially quite affordable, if there's adequate assurance that it would arrive while a plume is active. If the science from a Jupiter-orbiting mission is promising, I think the free-return sample becomes a very high priority mission.
Thing is, it seems as if the plumes are rapidly chemically decomposing upon emission (I'm gonna guess that this is due to the Jovian radiation environment). If the water's already quickly dissociating into atomic oxygen & hydrogen from same, how likely would it be for more complex compounds to survive long enough to be sampled?
Emily, do you mean that Astypalaea and Thasus Lineae could be still active ?
The duration of exposure to local radiation would be a function of how close to Europa's surface the sample is taken. The material is ejected at about 700 m/s, so it ought to be possible to sample it in less than a minute after it was ejected. How short that duration could be made is a question for the engineers. 10 seconds? 5? The lower the flyby, the tighter the margins of error. As the duration is made shorter, the extent of decomposition would be reduced; that's a question for the (organic) chemists. Certainly some organic molecules are extremely durable. I'd be surprised if 10-30 seconds of radiation would obliterate every interesting molecule, if there are any.
The (very preliminary) proposal for the Europa Ice Clipper mission (not to be confused with the current Europa Clipper mission in development) was for a flyby of 50 km. 20+ years later, we might be able to do a lot better than that. It may be desirable to have a leading element, perhaps on the same launch, to verify the presence and location of plumes right before the collector arrives, and to send back a homing signal as a sort of Jupiter-Europa GPS for the collector.
http://www.planetary.org/blogs/emily-lakdawalla/2011/3266.html That's probably why JUICE is so interested in those spots.
Here is a quick (i.e. seams might be visible somewhere) mosaic of Astypalaea Linea, the strike slip fault that apparently might be one of the suspects here. This is from the 17ESSTRSLP01 observation. North is approximately up.
The cross-cutting relationships through here are just maddening!
Yes, this is interesting terrain. In hindsight it would probably have been more accurate for me in the post above to say that this general area is a suspect, rather than only Astypalaea Linea. There are small craters visible at various locations in most of the mosaic and interestingly, some of these occur in clusters, e.g. near (2150,4650) and (500,1800) in the mosaic. But there's also terrain that seems completely devoid of craters. A good example is in the upper left corner of the mosaic
The area of interest is along 180 lon; the authors say 55 and 75 south lat. This is near the boundary between the Galileo E14 global color imaging and G7 global image. Completely coincidentally, the image that shows the area best in one image is the one released the other day, with the comet crash story:
http://photojournal.jpl.nasa.gov/catalog/PIA17658
That two-frame mosaic is from E17, obtained for global shape.
Ted Stryk has a pretty version here: http://planetimages.blogspot.com/2012/05/europa-from-galileo-another-take.html
The Europa Clipper currently has 10 flybys at high southern latitudes, and the study team is examining what it would take to do a targetted campaign.
One of the tricky factors in our limited Europa coverage is the enormous importance of sun angle. The surface is very rough and low sun angle creates shadows along linear features which appear dark. This is easy to confuse with the albedo differences that pertain to composition (dark -> higher non-H2O constituents).
One of the hypotheses for the darker (low albedo, not shadow) linear features is that emission of subsurface liquids which are "dirty" deposit along open fissures, spraying the dark material to the sides. If this is correct, then the active plumes may exist exactly where linear features with low albedo are most prominent. There are so many unknowns in the above, I couldn't begin to estimate how likely this is to be true, but at least if one is beginning to consider possibilities, that seems like the possibility to start with.
We're not going to get better maps of Europa until a spacecraft sends them back. Theoretical work on the location of stresses is a nice start, but they depend on unknown and (given only the data we have) unknowable parameters concerning the structure of the icy shell. I don't see any way to pin down the origin of the plumes until observations can be made in situ. That's assuming, in fact, that the plumes and their sources are even persistent over a period of years. Maybe 2023's plumes (if any) will be different than the ones observed so far.
In these blog comments in a Planetary Society post by Leigh Fletcher, I note that Paul Fieseler comments that he thinks he could have seen something in the Galileo data. Perhaps worth following up on?
http://www.planetary.org/blogs/guest-blogs/2013/1212-fletcher-the-plumes-of-europa.html
I see only two references to Galileo in that article:
And the Galileo spacecraft discovered a weak 'induced' magnetic field, caused by the interaction of Jupiter's magnetosphere with a highly-conductive layer beneath the crust, most likely the liquid ocean.
and
Galileo didn't really cover the poles during its 11 passes of Europa, so it doesn't really help us here.
Nothing about plumes there, so what am I missing? Maybe there is relevant comment in his blog, just not in that particular article?? I'd really like to know if there is indeed something worth following up.
True any plumes aren't mentioned in the blog article, just in a comment by someone who posted they may have seen something in the Galileo data. We might check with Paul Fiesler further about his comment. I would speculate that maybe some more distant high phase SSI images could show something and they may have yet to be examined in sufficient detail. UVS would be another instrument to check.
Below is his quote from the Planetary Society blog comment...
................................................................................
Paul Fieseler: 12/12/2013 08:05 CST
Oh my. I think that I may have seen a plume in Galileo data from one of the later Europa flybys, and I didn't realize what I was seeing until now....
................................................................................
With SSI, this image catalogue mentions some high-phase and plume search observations:
http://lasp.colorado.edu/JUPITER/CH15/EuropaGLLSSITable.pdf
I think plumes are extremely unlikely to be present in the Galileo SSI data. The images aren't that many and I'm sure every image (including the low-res and/or high-phase ones) have been carefully analyzed by lots of people. If there are any possible hints of plumes they would be highly ambiguous.
I looked at Galileo images of Europa and I found only one interesting image.
It's c0484888253 from E19 flyby. It has very low compression and it shows something like haze in the northern polar region of Europa (>70N latitude).
I compared this image with another ones from same flyby and no other images is pointing to the same direction and not surprisingly they show nothing.
One of them is for comparison in this brightness enhanced version.
Fieseler is the one who was behind the star tracker discovery of objects around Amalthea. I wonder if it is in the engineering data from that instrument.
Yes, I think that's the most plausible explanation. But it's interesting that it's only in this image with so short exposition (6.25 ms).
I notice that the putative haze in the haze image is brighter on the left side, where the surface of Europa is also brighter. That reinforces the double exposure hypothesis.
It seems exceptionally unlikely that such a tenuous plume could be visible with the Sun behind Galileo in an image with the contrast set to show detail on the surface of Europa, which has an albedo of 0.7.
I agree, looking closely this looks like a double exposure. In addition to being brighter on the left side it's also parallel to the horizon. The exposure, viewing geometry and lighting geometry also isn't particularly favorable for detecting plumes. Here is a schematic view showing the context for image 484888253 at 30 times Galileo's field of view:
I kinda said this earlier, but it it possible that the radiation environment dissociates plumes into atomic constituents almost immediately (well, at least in too short a time frame to catch the molecular effluent in action using the imaging systems that have been close enough in the Jovian system to date)?
Given the apparent volume of the ground-based plume image & even if the activity is highly sporadic it sure seems like we should have seen something visible long before. Io vents mostly sulfur compounds; lots heavier than hydrogen & oxygen, and with colorful allotropic states to boot.
Not asserting this as a theory, just throwin' it out there for consideration.
I'm curious as to what would be the half-life of an H2O molecule in a plume over Europa, given the dissociation that radiation can cause.
This paper:
http://people.virginia.edu/~rej/papers09/Paranicas4003.pdf
Derives for the surface, an "average integrated column production rate of H2O2 in icy regions" of ~5 × 10^10 H2O2/cm^2/s.
The recent report is of 7 tonnes of H2O per second, which spends about 1200 seconds between ejection and falling back onto the surface. That means 2x10^29 molecules of water being ejected per second, so at any time there should be about 3x10^32 molecules of water in the plume.
The plume has an area of about 2x10^25 cm^2, so radiation hitting that area of surface would radiolyse about 1e^36 molecules of water per second, quite a bit more than what is in the plume. But the final factor to take into account is how much of the radiation would actually hit any molecules in the plume, which would seem to be a slim minority since it's mainly empty space, whereas all charged particles hitting the surface will hit some molecule very soon.
Given 3x10^-10 for the span of a water molecule, the plume has a total cross section of about 2.5x10^13 m^2, which means it's only about 10^-8 of the plume, so the radiolysis rate should be more like 1x10-28 molecules per second. The plume has 30,000 times that number of molecules in the air for 1200 seconds, so it looks like the amount radiolysed should be several percent, but less than half. And, as I noted earlier, the effect would be proportionately less closer to the plume's origin.
This sort of computation merits peer review if anyone's interested.
Coincidentally, I'd already asked for the very nice "Europa" book from Arizona State, edited by vexgizmo and others, as a Christmas present before this discovery (I'd previously read some of it in the form of PDFs available online) and with it now in hand, one of the first things I looked for was information about carbon on Europa.
CO2 is one of the detected components and the estimated abundance is 360 ppm in certain locales. There are many interesting points to make about that:
1) Trace amounts of CO2 should not be stable on Europa's surface for long time scales, and it's obvious that Europa's surface is nearly uncratered, and thus has been reworked through processes much faster than impacts could emplace new exogenous carbon, so whatever is present should be in some sense coming from below, even if its origin was previously through impact.
2) Spectroscopy only tells us about the immediate surface, so we don't have any source of information regarding carbon below the first cm or so, but point (1) gives us some reason to believe that the subsurface abundance would be the same or greater below the immediate surface.
3) IR spectroscopy gives us a potentially incomplete account even of the surface composition, much less the subsurface. The total carbon inventory can be greater than that indicated by CO2.
4) Even given the CO2 figure alone, that implies an abundance of carbon of about 100 ppm by mass.
5) The Earth's oceans have a carbon abundance of 28 ppm. The Earth's crust has a carbon abundance of somewhere between 200 and 1800 ppm (Wikipedia offers many sources).
At the very least, the presence of carbon looks promising.
I wonder about the prospects of using occultations to study the composition of plumes from Earth. The most common kind of occultation study, generally, is to capitalize on circumstances when the body in question (here, Europa's plume, much smaller, unfortunately, than Europa itself) happens to pass in front of a star. A far more common event would be when Europa passes in front of one of the other Galileans, a technique which has been used to study the Galileans for decades, although the signal-to-noise ratio of such work might be lacking given all the light coming from the two moons as opposed to the tiny amount filtered through the plume. Occultations of Io by Europa have been used to pinpoint Io's volcanic activity, and perhaps Io could return the favor in the near future.
Pluto has been observed occulting stars every 5-10 years or so, and Europa's plume (if active) ought to do so a bit more often than that. That could be the next chance to upgrade our information, likely sooner than any in situ measurement.
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?
-the other Doug
I'd think, that the carbon-nitrogen triple bond should be rather stable.
http://people.cas.uab.edu/~gerak/papers/gerakines2004Icarus170.pdf.
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
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. http://yly-mac.gps.caltech.edu/reprintsyly/A_RecentPapers/stock%202012%20mars%20co2%20.pdf 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.
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.
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.
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.
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.
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.
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.
Any chance that the Gemini Planet Finder instrument could detect the plume ?
http://www.gemini.edu/images/pio/News/2014/pr2014_01/Europa.jpg
I'm skeptical since GPI operates in infrared and the plumes are going to be virtually invisible in backward scattered light.
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.
As mentioned earlier, opportunities when Europa occults a background object and its light passes through the plumes (or fails to do so) could give us information about the presence and composition.
Pluto has occulted stars every few years, and Europa moves against the background of stars much faster (about 20x) than Pluto does, which should provide a lot more opportunities. The downside is: Europa provides a lot more background light than Pluto does, and Jupiter is likely a factor for some observations, so a favorable signal-to-noise ratio might requires a brighter star being occulted.
As I also mentioned, Io could possibly serve as the occulted body, although that doubles the background noise of the observation.
Clearly, we will need to characterize the frequency and perhaps periodicity of the plumes before committing to any exploration. They may be very cooperative, like the Old Faithful geyser, or extremely unpredictable, like most terrestrial volcanoes.
I am too lazy to go through the references, so I ask: would the plumes be detectable by the Japanese SPRINT-A UV space telescope?
I am probably very naive, but I thought, if we cannot detect the plume itself, may be it could be possible to detect the hotspot where it originates from (like for Enceladus).
Do we have instruments able to detect this ?
(Again I'm thinking about GPI, since I'm so amazed by the resolution of its pictures).
Regards,
Marc.
According to https://www-n.oca.eu/tanga/GaiaEarthBased/occultations.pdf among others, Gaia will drastically increase the number of stars available for predictable occultations of solar system objects, as well as the precision resulting from those measurements. Perhaps in addition to small bodies (where if I'm reading it right, at 20-50km size the number of opportunities could go from 0.1 to 20+ events/object/year and the orbit precision could improve 100x), this will help for things like this plume study... but of course the useful occultation frequency will very much depend on how bright the star needs to be, and I suppose its spectral type, too, for this work.
Thanks for the answer Ugordan. So we will have to wait 2 decades to know for sure.
Marc.
We will know long before two decades whether or not the Hubble observations can be repeated. I suspect that we'll also get more sensitive stellar occulations as outlined above.
Then in the late 2020s...
Before the plume announcement, one of the goals for the JUICE mission was to use the UVS and cameras to look for plumes using long distance remote observations. (I.e, watch Europa throughout its orbit.) If plume sources have been discovered through any means, then the spacecraft instruments will be nearly ideal. The mass spectrometer is sensitive to AMUs near a thousand (recalling from memory). The radar unit could measure the subsurface structure around the vents. The only key instrument missing would be a thermal imager to image whatever the equivalent of Enceladus' tiger stripes turn out to be at Europa.
One other limitation of the JUICE mission is that its Europa flybys are planned for a single position in Europa's orbit. The plumes may not be active or have reduced activity at this location and the sources might be in darkness.
One note on the geometry of the plumes: They, like Enceladus's plumes, seem to be associated with the south pole. Unlike the saturnian system, the jovian system has essentially no seasons, so it's conceivable that the plume source, if its sunken into the terrain, might never (or rarely) have a line of sight to Earth and/or the Sun.
On the other hand, most of the plumes themselves would never (or rarely) be in Europa's shadow.
If the sources have hotspots, it is not inconceivable that they could be observed and pinpointed from Earth, but the devil's in the details: While any IR thermal analysis would of course lack the spatial resolution to pinpoint the plumes, a temperature sufficiently higher than the background could radiate IR at wavelengths that should be at nearly zero emission from Europa's baseline. This works just fine with Io's hotspots. Moreover, occultation of Europa by Io or Ganymede could allow some extremely precise pinpointing of the source, when the hotspot passes behind the other moon.
However, it seems unlikely to me that Europa's hotspots, if any, would be nearly hot enough to allow this observation to work. The temperature difference between Europa's ambient surface and any hotspots is probably less than 300K°, probably far less than that, as well as being very limited in scale.
Back in December, there was discussion of the available imaging data for the reported plumes region. A blog entry has just been published by Lorenz Roth describing the discovery, along with a nice orthographic view of the identified source region. http://solarsystem.nasa.gov/europa/blogs_lorenz_roth_plumes.cfm
I had a vague recollection that Voyager images of possible Europa plumes were published long ago, but most people didn't really accept them.
I managed to find the references, and now they make very interesting reading.
Sky & Telescope, Jan. 1983, p. 15: Allan Cook (Harvard-Smithsonian) - in a post-flyby Voyager 1 image looking back at a crescent Europa, a bright patch at the southern cusp and a faint plume 100-150 km high. Not seen in other images.
JGR Oct. 1982, Intriligator and Miller: Pioneer 10 may have encountered a plasma cloud emanating from Europa in 1973.
IAU Colloquium 77 (Natural Satellites), Brown U. Preprint #A546 (July 1983, p. 22): A. F. Cook (Hertzberg Inst. and Harvard-Smithsonian) plus Paul Helfenstein (then at Brown): six Voyager 2 images taken during approach show a diffuse plume, not seen in similar Ganymede images. Best view is image 0391J2-002.
Phil
Not so fast! I was summarizing. The version of that image printed in the reference shows the plume area, much bigger than a reseau removal artifact (and we can see where the reseaux are, it's not there) - I'm not saying the Voyager observations are correct, but they are not disproven by this quick look.
Phil
I'm glad to hear that Phil. Makes me wonder how they managed to tease out a putative plume out of this dataset.
Tempting, but I've been trying to search a plume out, and I've been tempted to try to see something centered around the 8 o'clock point in this six-image stack. The result looks a lot like yours but is not in the same place.
Bob Pappalardo and an assembled cast of the usual suspects addressed this directly in JGR in 1999. http://www.planetary.brown.edu/pdfs/2234.pdf (Circa Page 31):
Despite the result from the Hubble telescope, a http://www.sciencedaily.com/releases/2014/12/141218194755.htm failed to reveal any plumes at Europa.
I've reviewed virtually every image from Galileo, Voyager, Pioneer, Cassini, and New Horizons. Nothing except for a Voyager image that depends on one pixel, and that is almost certainly noise.
I wouldn't characterize Enceladus' plumes as 'completely unexpected', though; the moon's association with the E-ring was strongly inferred prior to Cassini, and in hindsight it's about as robust an emission torus as anyone could hope for. Something was clearly going on there but the mechanism was not known.
By analogy, any eruptive activity on Europa must be both extremely transient and volumetrically small given the absence of anything remotely comparable to the E-ring. I wonder if the isolated Hubble observation could be best explained as the aftermath of an impact?
If it was an impact that caused the plumes, would JUICE or Europa Clipper see any evidence? Considering that its effects were visible from Earth, there would have to be a rather large crater, right? Obviously only speculation at this point...
According to its Yellow Book (page 26), JUICE will have a resolution of 500-1000 m/pixel for regional features and under 50 m/pixel for selected local features during the flybys.
Might not have been a particularly large impactor; I'd guess something like a 10m rock. Depending on the inbound trajectory the relative velocity might've been quite high that close to Jupiter so a lot of water vapor could result from a hit & probably the impactor would vaporize as well. Has the data been examined for spectroscopic peaks in typical meteoritic elements like carbon, silicon, iron, etc. in addition to water?
Nobody's keeping score, man.
If I could pick one theme for exploration of the Solar System to date it would be "expect the unexpected".
Not plumes, but another matter about Europa, signs of http://www.nasa.gov/press/2014/september/scientists-find-evidence-of-diving-tectonic-plates-on-jupiter-s-moon-europa/#.VKACfP8AD though the word that comes to my mind is ice shear. Regardless of what term to use, this explains surface features of Europa.
No confirmation for plumes yet:
http://www.scientificamerican.com/article/jupiter-moon-europa-s-giant-geysers-are-missing/
NASA to Hold Media Call on Evidence of Surprising Activity on Europa
http://www.nasa.gov/press-release/nasa-to-hold-media-call-on-evidence-of-surprising-activity-on-europa/
Water plumes detected by Hubble: http://www.nasa.gov/press-release/nasa-s-hubble-spots-possible-water-plumes-erupting-on-jupiters-moon-europa
Hot from Twitter:
" Emily Lakdawalla Retweeted
Tanya Harrison @tanyaofmars · 26m26 minutes ago
Britney Schmidt notes that the idea of plumes from #Europa was proposed during Galileo, but none found at the time. (1/2)"
Actually the first suggestion was based on a Voyager image of Europa - not widely believed at the time, but it was suggested.
----------------
Title: Active Venting of Europa?: Analysis of a Transient Bright Surface Feature
Authors: Helfenstein, S.-P. & Cook, A. F.
Journal: LUNAR AND PLANETARY SCIENCE XV, P. 354-355. Abstract.
Phil
(Hi Tanya!)
grabbed the image "c2076737.imq"
http://imgbox.com/ioJBuBae
false color image
BUT the maybe spot is also aligned with the BRIGHT spot
i would call that optic scatter
Hmm, interesting. The paper also compared the same region with an image taken 6 days prior, and found that the bright spot might have been new...
Business Insider has a good view of the recent plumes -
Hubble/NASA/STScI/Business Insider
From http://www.businessinsider.my/europa-water-jet-hubble-telescope-photos-2016-9
Has a area on europa been narrowed down to the possible activity? I saw no mention of exact area that is thought to be active.
also see post #75 in this thread
http://www.unmannedspaceflight.com/index.php?s=&showtopic=7755&view=findpost&p=207918
and the other image mentioned in the old paper you linked to "c2058143.imq "
there is a little something there but it dose look like tracking motion
-- false color
http://imgbox.com/71ciAXeT http://imgbox.com/fXllU4R3 http://imgbox.com/RoObRrye
by the way, the full paper of Hubble's observations is here: http://hubblesite.org/pubinfo/pdf/2016/33/pdf.pdf
On the arxiv:
Probing for Evidence of Plumes on Europa with HST/STIS
W. B. Sparks, K. P. Hand, M. A. McGrath, E. Bergeron, M. Cracraft, S. E. Deustua
http://arxiv.org/pdf/1609.08215
P
Is there any chance of further study with JunoCam? How does JunoCam's untargeted flyby resolution compare with Hubble?
This NASA press conference was done as a telecon, with reporters calling in and looking at graphics online, and NASA does not archive those telecons. Sometimes they briefly mention a phone number at the end (not the same number ...) you can call to hear a replay of the telecon, but you have to ... listen to the telecon to hear that number! So infuriating.
However, in recent years I've found that SOMEONE will inevitably record the call and then put it online. I just have to keep searching for it, or monitoring the threads here at UMSF and at NSF and see if someone posts it. Lo and behold, yesterday I came across this upload. The guy has taken the audio and synced it to the graphics, so in one video you have everything you need to enjoy a full hour discussion. FAR more information than is covered in the print press releases, or any news story you'll find.
As public thanks to the guy who did this, I'll mention him here:
Matthew Travis / Zero-G News / http://www.zerognews.com / https://www.facebook.com/ZeroGnews
Thank you dude! Click below for the full press conference.
https://www.youtube.com/watch?v=DoUDxseG8xw
briv1016:
"How does JunoCam's untargeted flyby resolution compare with Hubble?" (for Europa)
This helps to answer your question:
http://www.planetary.org/blogs/guest-blogs/2016/0830-will-junos-instruments-observe-jupiters-moons.html
Phil
This eluded me till now, but an interesting consequence of the methodology is that it's blind to plumes that might erupt near the sub-jovian or anti-jovian point – perhaps to far over half of the surface of Europa. So, if the distribution of plume sources is random, detection of plumes on three of ten observations may imply that the number of plumes active at any given instant is far in excess of unity. On the other hand, the distribution of plumes is, of course, unknown, so the number of active plumes may average closer to 30%. If plumes occurred only near the poles, then the lower number would be more accurate, but the observation of one non-polar plume dispels that restriction.
That is, overall, the best news out of all of this. It seems like a multiple mission can expect probably to have a chance to observe sample plumes during its operations, although we're still beholden to unknown variability on longer timescales. But I think we're getting closer to being able to gamble on a mission architecture that is counting on plumes to occur during its operations. The downside is, we don't know where the active plumes will be, so any such mission would need to have a flexible timeline.
Some strong new evidences for water plumes on Europa:
http://iopscience.iop.org/article/10.3847/2041-8213/aa67f8
links to pictures;
Hubble Sees Recurring Plume Erupting From Europa:
https://photojournal.jpl.nasa.gov/catalog/PIA21443
Europa's Plumes Located near 'Warm Spot' on Europa:
https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA21444
Mike Brown with some words on searching for hot spots with terrestrial telescopes:
http://www.mikebrownsplanets.com/2017/04/europa-is-hot.html
Plume activity on Europa would indicate a link between an underlying ocean and the surface. That would perhaps favour the thin ice model versus the thick ice model for Europa which I believe has been an ongoing controversy in Europa science for the past 30 years or so.
Could we imagin a relationship between this unusual warm region (and its potential plume activity) and the very close Pwyll crater (cracks or very thin ice due to the recent impact that formed Pwyll) ?
I hope someone requested new auroral time-lapse images for Jupiter as well. Be interesting to see how quickly the Europa hot spot in the aurora varies vs potential plume activity.
https://www.newscientist.com/article/dn8994-jupiters-aurora-feels-europas-light-touch/
The hot spot's *not* hot.
http://www.mikebrownsplanets.com/2017/08/europa-is-hot.html
It has higher thermal inertia.
https://eos.org/articles/how-hot-is-europa-now-theres-a-map-for-that of the surface of Jupiter's ocean moon Europa by ALMA highlights one spot on the moon that is inexplicably cold. The spot is localized at 90°W and 23°N, in the northern part of Europa’s leading hemisphere. These coordinates are close the Murias Chaos, the Mitten !
“We don’t yet have a good explanation of what the cold spot means,” Trumbo said. “But, since we see the same anomaly twice, at two different times of the Europa day, we think it must be a region that is distinct in its thermal properties, and that could be interesting.”
The team noted that the location does have Europa’s highest water ice concentration and is also almost directly opposite Pwyll. However, neither of those facts can explain that spot’s strange thermal properties, they say.
“We should be able to learn more about this spot with more ALMA [data] and perhaps spectroscopic observations,” Trumbo said, “but we will probably not know if it correlates with unique geology until the Europa Clipper mission.”
A second thermal anomaly seems to correspond to the warm spot localized at the Pwyll crater previously detected and discussed in this topic.
Regards
Marc.
First bright stellar occultation for Europa:
http://sci.esa.int/gaia/61491-astronomers-spy-europa-blocking-distant-star-thanks-to-gaia/
Relevant to this thread because the Hubble data was, I think, derived from Europa occulting Jupiter.
Surprised it's the first!
Today's announcement:
https://www.nasa.gov/feature/goddard/2019/nasa-scientists-confirm-water-vapor-on-europa
This is an exciting result. The intermittent nature of the plumes may create a challenge for Europa Clipper to sample them without some flexibility to alter the mission in response to unpredictable events.
I still cannot come to terms with the idea that Europa has moved from tectonics (ridge formation) onto chaos as the ice crust has thickened over its 4 billion year history. I guess radar should tell us a lot about what is actually happening.
From Nimmo and Manga (2009):
"The manner in which Europa’s shell and interior evolved to their present-day states represents a major unsolved problem for at least three reasons. First, the present-day state, especially of the silicate interior, is poorly known. Second, Europa’s surface may only record the last 1% of its existence, so there are few constraints on its earlier history. Third, the thermal and orbital evolution of Europa are intimately coupled in a manner that is nontrivial to model."
https://websites.pmc.ucsc.edu/~fnimmo/website/draft5.pdf
One significant work since then was the melt-lens model of Schmidt, et al (2011):
https://www.nature.com/articles/nature10608?proof=trueNov
In a nut [ice] shell, the internal dynamics and certainly the history of Europa's ice shell are far from determined, although the tidal forces that create the most visible linea have probably been modeled well.
Even after one or several more missions, I doubt if we will have good information about the history of Europa's ice shell pre-dating that "last 1%" but finding out what's going on there now is something I'm very much looking forward to.
This is just a teaser for now, but JWST will attempt to detect and characterize any Europa plumes, which were detected, but at low signal, by HST, and were detectible only sometimes. JWST has the capability to detect spectral features that HST is simply not capable of, those above 2.5 microns. That corresponds to CO2, among other possible components. Of course, what it actually detects will depend on what, if anything, is actually there when it observes.
^ I was unable to find observation dates on this.
Has this already occurred?
This indicates that the first observations are planned for November and December, 2022.
https://www.stsci.edu/jwst/science-execution/program-information.html?id=1250
Jupiter is just past opposition now, so it will be a bit farther than is optimal when the observations are made; I guess the competition for observing time led to the later dates. Also, there are constraints on the observations as they will want Europa to appear far from Jupiter's disk. Also note that this same observation program, 1250, includes observations of Enceladus.
I recall that JWST cannot be pointed directly away from the Sun, so it cannot never take opposition period images of any outer planet (though at such distances its not a major issue, I think).
See here: https://jwst-docs.stsci.edu/jwst-observatory-characteristics/jwst-observatory-coordinate-system-and-field-of-regard/jwst-target-viewing-constraints
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