September 7, 2005 | David F. Coppedge

Comet Theories Vanish in Puff of Powder

They were supposed to be dirty snowballs, those comets, pristine relics from the primordial solar system.  They were supposed to be blasting volatile ices from their interiors as they approached the sun.  What are they doing with aromatic hydrocarbons, olivine, iron, clays and carbonates?  When the Deep Impact probe hit its target July 4, it made a big impression not only on Comet Tempel 1 but on Earth scientists wondering at the bright plume of powdery material that came out.  A JPL press release announced the “rather surprising” deduction that the comet “has a very fluffy structure that is weaker than a bank of powder snow.”  Since the low-density, fluffy surface cannot conduct heat to the interior efficiently, the coma must not be produced from volatiles deep inside.  Also, some of the materials detected, such as clays, were thought to require water for their formation.
    Nevertheless, though these findings are shaking the conventional wisdom about comets, some news sources are spinning the angle about hydrocarbons to suggest a link with the origin of life.  BBC News, for instance, said this might support the idea of panspermia, that comets delivered life’s ingredients to our planet.  “Some experts,” it claims, “say such molecules could have kick-started life on Earth” (emphasis added).  Another JPL press release highlighting cooperative observations by Deep Impact and the Spitzer Space Telescope tried to describe the “primordial soup” from which comets form.  Then New Scientist titled its report, “Deep Impact collision ejected the stuff of life.”

For goodness’ sake, comets have nothing to do with life.  They are not storks delivering little replicating biomolecules to the Earth, unless you consider “aromatic hydrocarbons, found in barbecue pits and automobile exhaust” the kind of ingredients you find promising.  Using the L word (life) is a distraction from the very real problems planetary scientists now face explaining the origin of comets.
    “How did clay and carbonates form in frozen comets?” is one such problem asked by Dr. Carey Lisse (Johns Hopkins U).  “We don’t know, but their presence may imply that the primordial solar system was thoroughly mixed together, allowing material formed near the Sun where water is liquid, and frozen material from out by Uranus and Neptune, to be included in the same body.”  That suggestion represents a big change in what was taught as fact about comets just a few years ago.  It’s an act of desperation to need distant materials to mix in the same body for a model of comet formation to work.  The gap between “don’t know” and “may imply” is about 30 AU, or 2.8 billion miles.  It’s a little presumptuous to use Deep Impact’s puzzling data to be talking about how life formed (see 08/23/2005) entry), wouldn’t you say?
    The BBC wins Stupid Evolution Quote of the Week for its entries, “Some experts say such molecules could have kick-started life on Earth” and “Under the ‘pan-spermia’ idea, comets pounded the early Earth billions of years ago, bringing organic molecules that reacted with the Sun’s light and heat, creating a rich chemical soup within which life began.”  If you like your soup diluted to a few parts per quintillion, you might as well just be drinking water; shall we call this the homeopathic theory of the origin of life?  And if life can be kick-started, it’s a machine, not a chance assemblage of molecules.  Kick implies a kicker.  Start implies a program.

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