Water plumes over Europa |
Water plumes over Europa |
Dec 12 2013, 04:55 PM
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#1
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Member Group: Members Posts: 401 Joined: 5-January 07 From: Manchester England Member No.: 1563 |
This seems like the relevant place to post this (could be wrong): Water plumes from Europa? 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.
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Dec 12 2013, 08:32 PM
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#2
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Member Group: Members Posts: 401 Joined: 5-January 07 From: Manchester England Member No.: 1563 |
Here's a link to the paper. http://hubblesite.org/pubinfo/pdf/2013/55/pdf.pdf Thank you! Moderator note: Two topics merged. Quote added at the top of this post to make its context clear. -------------------- |
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Dec 12 2013, 09:27 PM
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#3
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
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. |
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Dec 12 2013, 11:38 PM
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#4
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Member Group: Members Posts: 613 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
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. But for the chemistry to be interesting, there must be available carbon. There is little evidence of any on Europa, and models of the protojovian nebula have it too hot to incorporate much. So yeah, if sulphates are your thing, then Europa is demonstrably great. Prebiotic chemistry may be a very different matter. |
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Dec 13 2013, 06:09 PM
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#5
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
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...031748/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. |
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Dec 30 2013, 07:10 PM
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#6
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
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. |
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Dec 31 2013, 05:47 PM
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#7
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Member Group: Members Posts: 613 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
CO2 is one of the detected components and the estimated abundance is 360 ppm in certain locales. It is an interesting coincidence that the abundance in Europa's ice - a pretty secure detection, judging from the literature -is the same as in the Earth's atmosphere when the observation was made. But this is the only carbon species detected - no carbon-carbon or carbon-nitrogen bonds, despite all the garish red Europa pictures one sees in the popular literature. My point was just because Europa might have water vapor plumes like Enceladus, doesnt mean they are 'rich' plumes like Enceladus' ones. QUOTE using occultations to study the composition of plumes from Earth. Indeed, I'd immediately had the same thought (UV stellar occultations seen by Cassini were among the first probes of Enceladus' plumes). I think it should be possible for Europa from the ground I expect the possibilities from JUICE are being looked at, IIRC it has a UV instrument involving investigators on the HST Europa plume paper. |
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