Astronomy Science

Strange Phenomenon Of The Invisible Moon

Strange Phenomenon Of The Invisible Moon

In the year 1671, famous astrologist Giovanni Cassini discovered numerous incredible wonders by looking through a telescope at the planet Saturn.  Some of these discoveries were the gap in the rings of Saturn, the atmosphere containing detailed elaborate band structures as well as numerous moons. The second moon of the planet which was discovered, named as Iapetus, was noticed by scientists doing a strange thing. It was only visible for half of its orbit something which no other moon had ever done.

Strange Phenomenon Of The Invisible MoonIapetus is named after the Titan Iapetus from Greek mythology

Rest of the time the moon was completely invisible and undetectable. Three decades later, improvement of the telescope enabled Cassini to see the moon both on the sides of Saturn but he noticed that it was much fainter in eastern side as compared to western side.

Strange Phenomenon Of The Invisible MoonSize comparison of Earth, the Moon, and Iapetus.

Cassini through his research came to a conclusion about the moon named Iapetus. He concluded that one of the reasons should be that, one side of the moon would be significantly lighter as well as brighter than the other darker side, and also the second reason must be the fat that the moon was tidally locked to the planet Saturn to ensure that same side of the moon always faces it. Though it was quite a fascinating idea it was not possible to find whether it was true or not.

Strange Phenomenon Of The Invisible MoonThe extraordinary difference in reflectivity between Iapetus' two hemispheres, as imaged by NASA's Cassini mission. Image credit: NASA / JPL / Space Science Institute.
Strange Phenomenon Of The Invisible MoonClose-up of 10-kilometer-high mountains within the equatorial ridge in Iapetus's dark region

The color of the moon Iapetus is not the only reason which makes it unique among the other moons. The fact is that all of the major moons of Saturn lie in the same plane but not Iapetus whose axis is significantly tilted. There is no explanation to this phenomenon as there is no other moon present in the entire solar system whose axis is tilted with respect to its parent planted, like Iapetus does.

There is also a giant ridge along the equator of the moon Iapetus which is about 10km higher than the rest of the world. Neither the speed of rotation is high enough nor is the surface of the moon young enough to suggest the presence of such ridge in middle of Iapetus. Though many researchers and scientists have come up with several theories regarding the ridge there has been no clear explanation about the cause of the ridge as a whole.

Strange Phenomenon Of The Invisible MoonCloseup of the equatorial ridge

Even on the outer rings of the Iapetus lies the moon Phoebe. It is a much smaller moon which is most likely been captured from the Kuiper belt. Contrast to all of the other moons of Saturn, Phoebe orbits completely in an opposite direction, located at a much larger distance, and also significantly very dark in color. It’s darker as compared to all of the major moons found orbiting Saturn, while it is comparable to the darker side of the moon named Iapetus.

Strange Phenomenon Of The Invisible MoonBy orbiting in the opposite direction to how the particles in the Phoebe ring orbit, Iapetus accrues dark material, preferentially, on one side only. Image credit: NASA / JPL-Caltech / Cassini Science Team.

Phoebe also has its own rings which contain lots of dust particles. Phoebe along with the ring particles is revolving clockwise around the Saturn, but on the other hand Iapetus revolves counterclockwise. With time, the dark particles of the rings of phoebe accumulate on a particular side of the moon Iapetus and not the other. When water of the ice of the Iapetus starts to condense and freeze as well as settle on the lighter regions on Iapetus, it does so freely without any inhibition. But whenever it lands over the darker regions, the heat of the surface of the moon completely sublimates the ice, making it capable of landing properly on the only side which is not totally covered by the debris of moon Phoebe.

These two moons suggest the presence of Yin-Yang world which is unlike anything present in the solar system. After almost 300 years, one of the main mysteries of our Solar System is finally solved.

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