[meteorite-list] OT: SATURN'S MOON ENCELADUS HAS "HOT" WATERVOLCANO

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Sep 1 00:19:17 2005
Message-ID: <4316811C.C87211DB_at_bhil.com>

Hi, Mark,

    It's been years since I worked all of this out, but here's some of the salient points.
    Since U235 has a short halflife, that means the present "natural" abundance of U235 of 1:140, or 0.7%, is the relict of much greater abundances in the past. Parley the halflifes backwards and you find that the "natural" abundance of U235 at the time of planet formation was about 27%-28%!
    This is pretty much the same as the best weapons grade enriched uranium (30%) and would make for one lively fast breeder! The natural reactor discovered in the Oklo (or sometimes Aklo) mine in Gabon remained active for several billion years with no better moderator than an underground stream of water running through it.
    The radioactive cores of icy-rocky bodies (Enceladus has a density of 1.6) would not lose all their ice when heated. High pressure ice polymorphs have much higher melting points. Enceladus has been proposed as having a partial under-ice ocean like Europa. Perhaps Enceladus's South Pole is where it is.
    The long-term stability of an icy planet core as a nuclear reactor is more or less impossibile to calculate as an engineering concept, of course. But a core that starts out with a 27% U235 component ought to have a very long life. In general, the determining factor in achieving a steady state is the sufficiency of a neutron moderating material.
    We don't actually know the neuron moderation properties of the high pressure ice polymorphs (never been measured), but they should be good, because of their denser crystal structure.
    Heck, we don't know how much of the Earth's core heat is still produced by radioactive decay, or if any fission takes place there, either.
    If one of the neutrons from the fission of one U235 atom is captured by one U238 atom, it will convert that U238 atom into Plutonium 239, which is itself fissionable, and Pu239 will replace the U235 as the fissionable material, but the amount of fissionable material will remain the same. (We "like" U235 because it produces more neutrons per fission than U238; I think the figure is 2.6 or 2.7 per fission.)
    Depending on the capture rate of neutrons by U238, the total amount of fissionable material could decline, remain stable, or increase. That capture rate is a function of a horrendous number of factors in a "natural" setting, presently beyond calculation, but the process of natural, sustained nuclear reactions is at the heart of how the universe is put together. The Sun and all those other stars keep going rather
nicely, you know...

Sterling K. Webb
------------------------------------------------------------
mark ford wrote:

> Hi Stirling,
>
> Interesting theory, not sure if the fast breeder reactor effect, would be moderated that successfully in a planet situation though.
>
> Since the lighter 'ice' (i.e water/steam when hot) would tend move to the 'outside shell' of the active nuclear core, it would only moderate neutrons on the very outer surface of the core rather than neutrons from the whole core. (Since neutrons deep inside the core would be self absorbed and cause further fission). It would certainly extend the lifetime of the heat slightly but not I suspect by billions of years.
>
> One other thing, could it be that the tidal forces assume the planet is made of certain materials anmd certain desities, if the planet where more elastic than we think, then you could be looking at factors many times what was originally thought.
>
> >> Like Tunguska, maybe?
>
> Trouble with that is, where are all the fission decay products?
>
> Best
> Mark Ford
>
> -----Original Message-----
> From: Sterling K. Webb [mailto:kelly_at_bhil.com]
> Sent: Wednesday, August 31, 2005 9:55 AM
> To: Meteorite List
> Subject: [meteorite-list] OT: SATURN'S MOON ENCELADUS HAS "HOT" WATER VOLCANO
>
> Hi, All
>
> British newspapers and the BBC are making much
> of recently released Cassini photos and data from
> the earlier flyby of Saturn's moon Enceladus.
>
> Enceladus, against expectation, has a water
> vapor atmosphere, eruptive plumes of "hot" water
> vapor from "volcanic" fissures at its South Pole,
> "hundreds of miles high," which raises questions
> about what the source of its internal heat may be.
>
> Most of these articles point out that
> gravitational "tidal" heating is inadequate (less
> than 1% of the energy required) and assert that
> radioactive decay is also inadequate.
>
> While tidal heating is easily calculated, the
> amount of radioactive decay heat depends entirely
> on how much radioactive materials you believe the
> moon to contain, and that is anybody's guess!
>
> How about: wrong guess? If there are only two possible
> explanations and we know one (tidal) is wrong, there don't
> seem to be too many choices
> left...
>
> Both water and uranic oxides condense at the same
> temperature at low pressures (~160 K) and it is logical to
> assume that icy bodies would have a lot of radioactives.
>
> Uranium and ice make a pretty good natural "reactor" (ice
> is a good neutron moderator) and such a reactor would act as a
> "breeder" reactor that would produce a natural fuel cycle that
> would allow the reaction to be maintained for billions of
> years.
>
> Even good-sized comets could contain their own internal
> heat sources from natural reactors, which might explain the
> fact that their "outgassing" has proved impossible to predict
> as a thermal effect.
>
> Comets like comet P/Schwassmann-Wachmann 1, which has an
> almost circular solar orbit without thermal variation, go
> through wild swings of activity and inactivity that are
> impossible to explain otherwise.
>
> If natural reactors sounds weird to you, the Earth had one
> in Gabon that perked along for billions of years until it
> "perked out." No ice for a moderator, you see.
>
> All of which finally and vaguely connects this topic to
> the Meteorite List. An impact from a comet with a natural
> reactor inside would produce an impact event all out of
> proportion to the size of the body, because re-entry would
> cause it to be forced together, whereupon it would go critical
> and explode.
>
> Like Tunguska, maybe?
>
> Sterling K. Webb
> -------------------------
> Text of article follows:
>
> Scientists baffled by mystery heat source on Saturn's moon
> Enceladus
>
> <http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2005/08/31/wmoon31.xml&sSheet=/news/2005/08/31/ixnewstop.html>
>
> Space scientists said yesterday that they were
> baffled and excited at the discovery of a mysterious
> heat source beneath the surface of Enceladus, one of
> Saturn's moons.
>
> Readings taken by the Cassini spacecraft and unveiled
> yesterday unexpectedly showed the 311 mile-wide moon had an
> atmosphere composed mostly of water vapour.
>
> The most detailed images yet of the moon show a series of
> long and intriguing fault lines around Enceladus's south pole.
>
> Cassini's instruments identified an unexplained source of heat
> below the moon's surface in this region that appears to be
> shooting out jets of gas, ice and dust particles.
>
> Scientists are intrigued because neither radioactive decay nor
> gravitational tidal forces, thought to be the only two
> potential sources of internal heating of planetary bodies,
> should be able to generate the effects measured by Cassini.
>
> Prof Michele Dougherty, of Imperial College London, and
> principal investigator for Cassini's magnetic field measuring
> equipment, said: "It was a complete surprise to find these
> signals at Enceladus.
>
> "These new results from Cassini may be the first evidence of
> gases originating either from the surface or possibly from the
> interior of Enceladus."
>
> Dr Torrence Johnson, from Nasa's Jet Propulsion Laboratory in
> Pasadena, California, said at a news conference in London
> yesterday: "We've been here before. These are early days in
> understanding the data. In a sense, it's nice to be baffled at
> this point.
>
> "At the moment the maths does not add up. We did not expect
> what we know to be the available power sources here to be able
> to produce this kind of heat.
>
> "I think we can expect some of our clever colleagues with
> models of evolutionary history of orbits and interior
> structure to come up with ways to explain this." Mission
> scientists made their first surprising discoveries about the
> moon after examining data collected by Cassini during two
> flybys, at 725 miles and 310 miles above the moon, on Feb 17
> and March 9.
>
> The spacecraft's magnetometer showed Saturn's magnetic field
> was being bent around Enceladus, suggesting it had an
> atmosphere, or layer of gas bound to it.
>
> That an atmosphere is able to persist around a body with such
> low gravity indicated a level of geological activity
> sufficient to produce a constant supply of gas and water
> vapour. On July 14 the spacecraft got down to 108 miles above
> the moon's surface.
>
> This time magnetometer readings showed the atmosphere was
> concentrated at the south pole. Cameras captured detailed
> images, showing the variability of its surface.
>
> While the area to the north of the equator is pockmarked with
> impact craters, indicating geological inactivity, large areas
> around the south pole have a smooth surface, suggesting the
> terrain is much younger.
>
> Of interest was a series of large cracks, dubbed "tiger
> stripes", centred around the south pole.
>
> Also unexpected was the detection of frozen methane and other
> simple organic chemicals on the moon and in its atmosphere.
>
> Infrared measurements showed an unexpected temperature
> distribution with a patch of "warm" temperatures, around -188C
> (-307F), near the southern fault lines.
>
> Enceladus is believed to be losing material from its interior
> at the rate of around half a ton a second, probably settling
> an old debate about whether it is the source of material for
> Saturn's "E-ring", the outermost of the planet's famous rings.
>
> Scientists do not know what is creating the heat source but
> believe is has to be a combination of radioactive decay of
> rock and tidal heating - frictional heating of the moon's
> interior caused by the gravitational pull of Saturn.
>
> Cassini, a ?2 billion joint European Space Agency and Nasa
> mission, has been exploring Saturn and its large family of
> moons since July last year.
>
> See also the New Scientist article:
> <http://www.newscientist.com/article.ns?id=dn7924>
> with photos of the fissures at the South Pole
> and flow features
>
> A similar article:
> <http://www.space.com/scienceastronomy/050815_enceladus.html>
>
> Basic facts about Enceladus:
> <http://www.nineplanets.org/enceladus.html>
>
> Even better is the Wikipedia:
> <http://en.wikipedia.org/wiki/Enceladus_(moon)>
>
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Received on Thu 01 Sep 2005 12:18:36 AM PDT