October 22, 2011 | David F. Coppedge

Ski Enceladus

Want the ultimate in powder snow?  Ski Enceladus, a little moon of Saturn.  The snow is deep and vast.  Drawbacks: except for occasional craters and steep canyons, the land is flat; there are no ski lifts; there is no air; you would weigh one or two pounds, and transportation will cost you billions of dollars.  Other than that, science news outlets are advertising it as a great place for snow lovers!

Enceladus weather: Snow flurries and perfect powder for skiing.”  That’s PhysOrg’s travel ad (a.k.a. science report) earlier this month. Cassini took two close passes by Enceladus this month, #14 on October 1 at 99 km, and #15 on October 19 at 765 miles.  In the second, the spacecraft was able to watch the light of two stars flicker on and off through the plumes.  The Cassini Imaging Team site Ciclops.org posted a preview of raw images from the latest flyby.  Another one, #16, comes up on November 6 at 496 km.  After a pause, there will be more close passes in March, April and May.

That this little moon should have powder snow is astonishing.  The fine talcum-powder-size ice settles down by gravitational attraction from the particles spewing out of the moon’s south pole geysers. PhysOrg said the snow is not composed of snowflakes like we have on Earth, which require an atmosphere.  Instead, tiny ice particles fall on ballistic paths from the ejection sites (long, deep canyons called “tiger stripes” at the south pole).  Although it’s impossible to know the texture and depth of the deposits directly, scientists can infer the particle composition by comparing visible, ultraviolet and near-infrared measurements of the same regions.  According to Dr. Paul Schenk of the Lunar and Planetary Institute in Houston, the accumulated particles would be ideal for skiing.

How long has this been going on?  The PhysOrg article stated, “Mapping of these deposits indicate that the plumes and their heat source are relatively long-lived features lasting millennia and probably tens of million years or more, and have blanketed areas of the surface in a thick layer of tiny ice particles.”  The error bars on that statement extend four orders of magnitude.  The problem with the higher figure (tens of millions of years) is keeping that amount of power going on this little moon for so long.  In fact, to believe that this moon is the assumed age of Saturn, little Enceladus would be coating itself with powder snow for 4.5 billion years.  Is there that much source water available?  If the geysering started more recently, what turned it on?

Readers should remember that the geyser discovery was a surprise.  “The discovery by instruments aboard the Cassini orbiter that there's a currently active plume of icy dust and vapour from Enceladus has revolutionized planetary science,” Schenk said.  It would seem that billion-year snow-coating of this moon would erase features.  We see some softening of crater edges, but numerous cracks and evidences of tectonic activity are visible.  From photos showing recent exposure of accumulated ice, scientists estimate some of the deposits are as much as a hundred meters thick at a maximum.  Using “models of plume deposition” that result in extremely slow accumulation, scientists did some calculations.  “To accumulate 100 meters of deposits would require a few tens of millions of years or so.” But that leads to a confusing conundrum: “This is important as it suggests that the thermal heat source required to drive the plumes and maintain any liquid water under the icy crust would also have to be similarly long-lived.

Long-lived, but long-lived enough?  Why are there not thousands of meters of deposits?  Can these plumes really have been active that long?  What is the energy source in such a small moon that should have frozen solid, like nearby Mimas, long ago?  So much material is coming out of Enceladus that it creates a giant ring around Saturn (the E-ring), composed of micron-size particles.

Another moon of Saturn got some press this month: Titan, the largest.  Maps of this atmosphere-shrouded giant keep getting better and better (see Space.com).  Was Space.com able to resist the urge to say that Titan sheds light on the origin of life?  Yes! –but only on that first article about the maps.  In “The hazy history of air on Saturn’s moon Titan,” Shaun McCormack (a contributor to Astrobiology Magazine), used the L-word six times in another Space.com article.  (News flash: No life has been found on Titan, and it is almost 300 degrees below zero there.)  McCormack agreed the idea is somewhat incredible; “This is remarkable, because it was thought that Earth and Titan were made from a vastly different recipe of materials in drastically different temperatures,” he said.  But then he gave good press to some Spanish astrobiologists who envision Titan as a laboratory for the origin of life.

Speaking of snow, the idea of a prehistoric “Snowball Earth” has been going in and out of fashion.  Astrobiology Magazine wove a tale about how life might have survived a global freeze, but the French, according to Science Daily, are challenging the very concept.  “Their work, published in the journal Nature, challenges part of the so-called ‘Snowball Earth’ hypothesis and rekindles the debate about the origins of the deglaciation mechanism.”  They could not find evidence for a steep climb in carbon dioxide levels.  That means Earth could never have gotten out of a deep freeze.

Thankfully, we live on a planet with just enough ice and snow to give us fun things to do in the winter without making skiing mandatory 24 x 7 x 52.

“Snowball Earth” is another one of those suggestive phrases that secular scientists come up with to titillate the imagination.  They don’t need evidence for it; in fact, it can contradict common sense – to get out of it requires ad hoc conditions.  But if it feeds the Grand Myth, it is useful.  The Grand Myth requires Earth to be born in fire, then go through trial by ice, then end up just right, as if testing all the options of Goldilocks’ soup.  Then, in some warm little pond, Evolution conjures up the elixir of life, just like it did with liquid methane on Titan.  Storytelling is fun because no evidence is required.

Another observation of interest to psychologists of science (a new discipline emerging, according to Medical Xpress) is how the consensus-huggers deal with anomalies.  The Big Question that should emerge from observations of Enceladus is why these geysers are active today, if Enceladus is billions of years old.  A small sparkler does not burn for a year, and a small moon the diameter of Arizona does not have the heat to last 4.5 billion years.  How do the scientists respond?  They say it might have been going on for a few tens of millions of years.  Not even close.  Ten million is to a billion as one foot to a hundred feet.  Big problem.  Quick; let’s talk about life on Titan instead!

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