April 27, 2009 | David F. Coppedge

Mooning the Public: Life Sells

Advertisers have known for a long time that sex sells.  That’s why ads often include a scantily-clad woman standing next to the pickup truck for sale.  It seems that in planetary science, life sells.  An icy moon can be a pretty dull thing, but announce that there might be life there, and eye appeal jumps.  The latest Sky and Telescope (June 2009) is a case in point.  The feature story is about the moons of Saturn, but the cover accompanies a curvaceous picture of Enceladus with the eye-grabbing title in big, bold letters, “Does this WORLD Harbor LIFE?”
    It doesn’t appear that author Emily Lakdawalla, blogger for The Planetary Society, had life on her mind very much when describing Cassini’s findings at Enceladus, Rhea, Dione and Tethys in “Ice Worlds of the Ringed Planet.”  Sure, she teased occasionally with the L-word, describing Enceladus as having “potential for liquid water and perhaps even life,” and thought it a possible target for a future mission “because of its potential habitability for life.”  Well into the article, she elaborated on the possibility that catalytic chemistry could be occurring in a subsurface ocean under Enceladus: “there was probably liquid water, heat, organic chemicals, and active chemistry – the stuff of life,” she speculated.  “As a possible abode for past and present life, Enceladus has catapulted from being moderately interesting to brief consideration as the prime target of NASA’s next flagship mission to the outer solar system.”  That was the extent of her references to life in the 9-page article, but that is what Sky and Telescope chose to emphasize on the cover: “Saturn’s moon Enceladus has the stuff of life.
    What did not receive emphasis, but is potentially more provocative, are findings Emily relayed about the age of Saturn’s moons.  Noting that Voyager scientists found Enceladus to be wiped free of craters, she said, “It seemed ridiculous that a body as small as Enceladus – only 500 km across — could be geologically active today, and could provide the necessary input of particles to sustain the E ring.”  When Cassini scientists found plumes emanating from the south pole ( 07/14/2005, 11/28/2005), jetting water vapor at “many hundreds of meters per second” (02/09/2008) into space along with ice particles, scientists had found the source for the E-ring and the fresh coat of white on the moon’s surface.  What they also found was a serious age problem (03/01/2006, 12/03/2007, 06/19/2008): “If Enceladus has been venting at its current rate over the age of the solar system, it would have lost 20% of its mass,” Lakdawalla said.  Then there’s Iapetus (07/17/2007).  Scientists now believe the yin-yang appearance of the moon is due to thermal segregation (10/16/2007): “It’s a runaway process that rapidly blackens dusted regions in a matter of a few to a few tens of million years – just a blink of an eye in geologic terms” (05/05/2008).  Taking an upper limit of 50 million years as “a few tens” shows how fast a blink that is.  The entire process would have taken just one percent the assumed age of the solar system (4.5 billion years) – one yard on a timeline the length of a football field.

What Emily didn’t mention is that a significant quantity of ice escapes Iapetus during each 30-year orbit.  There should not be any left after billions of years: in fact, even with generous estimates of the original ice, scientists can only make it last for 1/3 of the solar system’s assumed age (05/05/2008).  The article also mentioned the possibility of rings around Rhea (which shouldn’t exist, 03/10/2008), and the possible detection of plasma around Dione and Tethys, which also should not exist (04/18/2007, 06/16/2007).  These are much more significant actual findings and should have been more newsworthy than tantalizing speculations about life under Enceladus.  For a catalog of age problems throughout the solar system, see the “Resource of the Week” described below.
    To call water, nitrogen, ammonia, propane and acetylene “the stuff of life” is so lame, it’s downright comatose (see online book).  One might as well say that protons and electrons are the stuff of life.  If so, the sun has the stuff of life, too.  Let’s see if Sky and Telescope will add this caption to its next cover story on the sun: “Does this star harbor sunbathers?”  One can only hope that in the next issue’s letters to the editor, astute readers will give editor Robert Naeye a lecture for stooping to titillation to sell copy.

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