Yin/Yang Moon


There is something strange and powerful about black-and-white imagery. ~ Stefan Kanfer.

The greatest science fiction author of all time, Arthur C. Clarke, has been thought by many to have been a modern day prophet. Did he have premonitions? Sometimes when you read his works, you have to wonder if he had some inner knowledge about the cosmos, some link to a higher being. In his Rendezvous with Rama, a great spherical spaceship is found in the solar system. The story and its subsequent sequels follow the exploration of this mysterious craft. Was Clarke just using Rama as a metaphor for an actual spacecraft in our midst, the third largest moon of the ringed planet Saturn, the moon of Iapetus?

Alastair Reynolds, too, saw another Saturnian moon as being an extraterrestrial craft in his novel Pushing Ice. Instead of Iaptetus, Reynolds chose Janus. Another of Saturn’s moons is looked upon as being artificial in the Gaea Trilogy by John Varley.

The original 2001: A Space Odyssey, a novel based on some short stories, notably "The Sentinel," written in 1948 by Clarke, follows the discovery of an alien monolith and true to his visioning he chose Iapetus--written as the alternate spelling Japetus--as the setting. Certainly the moon itself has enough oddities that it truly makes you wonder if Clarke was onto something.

Italian/French astronomer Giovanni Cassini discovered the moon in 1671. He saw through his small telescope a body that appeared to wink in and out of existence. Instead of jumping to a supernatural explanation (much in vogue at that time) he correctly observed that the moon would appear approximately for forty days in the sky to the west of Saturn only to dim and eventually disappear entirely for about another forty days. His conclusion to explain this apparent phenomenon was that the moon was tidally locked with the same face turned towards Saturn as it orbited the planet and that one side must be much darker than the other. Theodore Sturgeon, in 1958, wrote the short story "The Comedian’s Children" about a 2034 unmanned mission to the moon, which results in a craze on Earth for black and white designs.

It was only with the recent Cassini probe, named after the astronomer himself, that scientists were able to verify the explanation offered by the astronomer Cassini. However, it still did not explain why there was the difference between the light and dark hemispheres. The difference could be likened to the difference between coal and snow. 

Clarke eerily displays his visioning further in 2001: A Space Odyssey. In the story, the protagonist Dave Bowman discovers an alien monolith originally observed as a black dot in the exact centre of the white hemisphere. When Voyager 1 arrived thirteen years later, it actually verified Clarke’s fiction. Voyager had photographed a black region within the moon’s brighter hemisphere. Carl Sagan, famous astronomer and a member of Voyager’s imaging team, is said to have sent a message and photo to Clarke upon the discovery of this dark area in the white hemisphere, “Thinking of you…” 

The novel, when it was made into the cinematic masterpiece, was moved to Europa, a moon of Jupiter. Stanley Kubrick, the director of the movie, did not feel he could do visual justice to the ringed planet which would have been a backdrop to the story.

Iapetus is not lost to science fiction authors in their visioning. Author Jack McDevitt wrote in The Engines of God about a strange ice-made icon on Iapetus. This leads to the discovery that all civilized societies could be obliterated by a Dark Force between the galaxy’s spiral arms. Poul Anderson, in his short story "The Saturn Game," describes an expedition to Iapetus whose secrets more than made up for the dullness of the voyage from earth to the Saturn system. In The Armageddon Inheritance David Weber writes about aliens attempting to use the moon as a weapon to destroy the earth.

Scientists were hard pressed for years to explain the yin/yang appearance of the moon. One theory is that Iapetus is sweeping up debris from the more distant moon Phoebe. Another theory is that the colour variation is due to volcanic eruptions on the darker half ejecting hydrocarbons which further reacted with sunlight making the chemical even darker. The problem with these theories is that  they are incomplete. They explain the colour variation; however, they fail to explain the seemingly sharp delineation between the light and dark sides.

Interestingly enough, the delineation between the hemispheres initially appeared very clear cut. However, when the Cassini probe passed by the moon in September 2007 it found that the delineation between the dark and light hemispheres is not as sharp as originally thought but consists of scattered patches of dark and light material giving it a somewhat spectacled appearance.

A more complete explanation of the light and dark sides of Iapetus is thermal migration. Iapetus experienced an influx of material from the past such as meteorite impacts on adjacent moons, which could have started this thermal migration process off. Due to the fact that Iapetus has a slow rotation (a sharp contrast to the other major moons of Saturn) the temperature cycle is very long. That allows the dark material to absorb heat from the Sun and warm up. The heating causes any icy material within the dark material to sublime out and retreat to colder regions of Iapetus. The sublimation of the icy material causes the darker material to become even darker and the colder regions to become lighter. The redistribution of ice is further facilitated by Iapetus’ weak gravity, which means that at ambient temperature +143 degrees Celsius on the warmer dark side and -173 degrees Celsius on the cooler light side, a water molecule can migrate from one hemisphere to the other in a very short time.

We’ve been able to explain one of the mysteries of Iapetus but the moon holds many more, some of which are not so readily explainable. During the Cassini flyby on December 31, 2004, another unusual feature was found--the equatorial ridge that runs the entire length of the moon. It is about thirteen hundred kilometers long, twenty kilometers wide and about thirteen kilometers high. Kim Stanley Robinson in his novel 2312 describes a giant city that is built on this very ridge. Some jump to the conclusion that the ridge is an artificial structure while scientists have been scrambling to come up with a more sedate explanation.

One suggestion is that the ridge is a remnant of icy material that welled to the surface and eventually solidified. Another idea is that Iapetus could have had a ring system during its formation and that the ridge is the remnant of that ring; the ring was possibly formed by the collisional accretion through the electrostatic attraction between microscopic dust and ice particles. However, recent evidence of tectonic lines in the ridge is inconsistent with the collapsed ring or icy remnant hypotheses.

The ridge is a difficult geological feature to explain since it follows the equatorial line almost perfectly. Cassini scientists have suggested that the ridge could be a remnant of a time when the moon rotated more rapidly than it does today. Calculations based on the current height of the ridge have shown that the period of rotation was once as low as seventeen hours as opposed to today’s 79 days. In addition to the ridge, the slowing of the rotation of Iapetus over time would explain the unusual shape of the moon; Iapetus is a very oblate moon in that it has a bulging equator and flattened poles.

Even the orbit of Iapetus is somewhat of an enigma. It has the most inclined orbit of the major satellites of Saturn which makes it the only world to be able to actually see the full splendor of the rings. The other moons are so aligned so that if one were standing on their surface, one would only see the rings head on. Jack McDevitt wrote a short story, "Melville on Iapetus," which is about an alien statue that is discovered on this moon; the human explorers wonder about the motivations of the artist. The story offers some unique descriptions of Saturn as viewed from the moon.

Theories abound as to why Iapetus is the way that it is. Science fiction authors have their own ideas about the strange moon. In addition to science fiction authors, there are some theorists who also believe the possibility that not only is Iapetus an alien landing site, but an artificial world altogether waiting for us to discover.

One such theorist is Richard Hoagland, who wrote a large treatise on the possibility of Iapetus being an actual alien structure. Donald Goldsmith and Tobias Owen in their textbook Search for Life in the Universe even hypothesized that Iapetus is an alien signpost. Tobias was the American team leader for the development of the joint NASA-European Space Agency program that would eventually become the Cassini mission to the Saturn system where Iapetus is located.

We may never know the real truth about Iapetus until we are able to land on the surface and conduct tests there. One can only imagine the first human or even space probe landing on the moon that could put the contentious moon’s secrets to rest. A real-life version of Clarke’s prophetic fiction.

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