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

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Wed Aug 31 04:55:39 2005
Message-ID: <43157066.F7C4C2D6_at_bhil.com>

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)>
Received on Wed 31 Aug 2005 04:55:02 AM PDT