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Have you seen photos of Venus?  When the planet is observed in visible light it looks like a big bland ecru ball (see above).  Put a whiteboard and some plastic rolling chairs on that puppy and you would have a corporate conference room in some awful suburban office-park.  Yet ultraviolet imaging of Venus paints a somewhat more interesting picture of swirling bands or darkness in the heady acid atmosphere of our sister planet.  But what does that mean?

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The dark bands turn out to be the result of sulfur compounds (carbonyl sulfide, hydrogen sulfide and sulfur dioxide) and other yet unknown chemical compounds in the upper atmosphere of Venus.  On Earth these sulfur compounds are hallmarks of life…or of volcanic activity.  Some scientists are provocatively asking whether extremophile bacteria could have a place in the temperate upper atmosphere of Earth’ closest planetary neighbor.  The bacteria could use the rich sulfur and carbon clouds as building blocks and the UV (and other EM radiation!) bombardment of the sun for energy.  Perhaps, they muse, these dark bands are something akin to algal blooms in Earth’s oceans.

More than a billion years ago, Venus enjoyed a period of prolonged earthlike climate with surface water and an atmosphere which was not so hellishly heavy and hot.  But something went hideously awry and runaway greenhouse effect created a terrible feedback loop which changed the planet’s surface into the monstrous place it is today.  Apparently the igneous/volcanic processes of Venus are rather different than those of Earth, so it was probably not all treeferns, friendly dinosaurs, and bikini-clad aliens even before the runaway greenhouse phase melted away the old surface of Venus, but perhaps bacteria (or analogous lifeforms) could have evolved and escaped the catastrophe by moving into the upper clouds (which, as previously noted here, have temperatures not unlike those of Earth’s surface).

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My guess is that Venus is lifeless as a jackhammer (though, like a jackhammer it can give the alarming appearance of life), yet even if this is the case, we should know more about all of this! What happened to Venus’ original surface? Was there ever life there?  What is going on with its volcanoes and internal geology?  What is the composition of the clouds of Venus? Is there anything there other than strange sufur compounds and esoteric hydrocarbons formed from the mixture of sulfur, carbon dioxide, and UV radiation?   Once again, our nearest neighbor is beckoning.  We need to move forward with sophisticated atmospheric probes (like VAMP) and NASA should collaborate with Russia on their next Venus mission (it looks like our governments are closer than ever anyway).  For some reason, popular imagination disdains Venus, yet the questions there seem salient, and the possibilities for a nearby Earth-sized world of unlimited energy and resources seem, well, unlimited.

A Chiton (Tonicella lokii) off the coast of California

Italo Calvino’s existential classic, Il cavaliere inesistente (“The Nonexistent Knight”) is a novel about Sir Agilulf, a medieval knight who follows the rules of chivalry with complete devotion. Unfortunately, Sir Agilulf is only an empty suit of armor: although the knight trains and stands vigils and fights in the manner of a person, there is actually nobody inside the shell. Calvino’s perplexing fable evocatively captures the workaday world where many (maybe most) people are empty “suits” who exist merely to keep a seat warm, however this predicament is nothing when compared to that of the chiton, a primitive marine mollusk covered by a row of aragonitic shells. Not only are the chiton’s rocky eyes a constituent part of its armor, the chiton itself is part of its armor!  Bands of dense muscles are interwoven through the plates and sensory cells are embedded within. When the chiton dies, the shell phalanx falls apart into perplexingly shaped hunks of calcium carbonate.   The remarkable segmented shells are composed of 8 plates and they afford substantial protection to the chitons which are capable of rolling themselves into armored balls. Chitons are classed as the Polyplacophora.  They take their common name “chiton” from the Latin word chitōn, which means “mollusc”. The Romans derived this word from the Greek word “khitōn”, meaning tunic.

Another Chiton (Tonicella marmoreal)

Cryptoconchus porosus

 

For locomotion the chiton relies on its rubbery “foot”, a large band of adhesive muscles with which it crawls along the sand and rocks of the ocean bed. A chiton’s foot can produce substantial adhesion, and the creatures are able to cling to rocks with amazing tenacity.  Most chitons are herbivorous grazers and eat algae, bryozoans, diatoms, and other microbes, all of which they scrape up with their sharp radula tongue–however, a few species of chiton have left the gentle lifestyle of herbivore behind and become predators. These hunting chitons trap their prey (usually small shrimp and fish) by making a box trap out of their enlarged, hood-like front end.  They hold this segment of their girdle above the ocean bottom and then clamp down on unsuspecting prey which thinks they are small cavern-like rocks.

The Gumboot Chiton (Cryptochiton stelleri), the world's largest chiton!

 

Chitons are ancient.  Fossils of stem-group chitons date back to the beginning of the Ordovician over 488 million years ago (and these lineages probably stretch back earlier into the Cambrian). Yet the Chiton’s rocky aragonite eye is comparatively recent, having evolved only ten million years ago. Chitons are hundreds of millions of years older than mammals but their eyes are much more contemporary than our own.

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