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• THE LUNAR EXPLORER ARCHIVES
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A R C H I V E S

Japetus, Saturn's third largest moon, is a serious candidate for being the strangest moon of Saturn. Tidally locked in its orbit around the Ringed Gas Giant, Japetus is sometimes also called the "Yin-Yang Moon" because its Leading Hemisphere is very dark, reflecting only about 5% of the Sunlight, while its Trailing Hemisphere is almost as bright as Snow. During the NASA - Cassini Spacecraft Fly-By occurred in September 2007, we received many close views of this Celestial Body, including several images of an Highly Cratered Region known as the "Transition Zone" (such as that area in between the very Bright Terrain and the extremely Dark one). Japetus itself has a density close to that of Water Ice, but the peculiar Reflective Properties of the Dark Material suggest an organic composition. Honoring the moon's discoverer, the Dark Terrain has been named Cassini Regio.

This frame, instead (whose serial number is N00092009), taken on September 10, 2007, and received on Earth on September 11, 2007, shows us a Mountainous Region informally known as the "Voyager Mountains". The reason of this name is in the fact that these Mountains were originally detected in NASA - Voyager Spacecrafts images and, as far as we know for now, they might compete in height with the tallest mountains on Earth, those located on Jupiter's moon Io and, possibly, even some of tha tallest Mountains (Volcanoes, in fact) of Mars. Further observations will be required, however, to precisely determine their exact heights.

Interestingly, the Line of Peaks drawn by these Mountains is aligned remarkably close to the Equator of Japetus and, in fact, the strangest Surface Feature of this Saturnian moon is to be found in an extremely bizarre, Equatorial Ridge, which extends itself all around Japetus, across and beyond its dark, Leading Hemisphere, and that gives to the two-toned Saturnian Natural Satellite its very distinctive walnut shape. Furthermore, the Ridge's combination of Equatorial Symmetry and Uniform Scale (the Ridge is about 20 Km wide and reaches up to 20 Km above the Surface of Japetus), is not known to be duplicated anywhere else in our Solar System. This, therefore, absolutely unique Surface Feature of Japetus (that we shall show you and analyze, in deeper detail, sometime in the future) was discovered in some Cassini images from the AD 2004.

The Ridge appears to be heavily cratered and so we believe that it should be very ancient; its origin, however (jointly with many other Surface Features visible on Japetus itself and a few other Saturnian moons), is probably doomed to remain an unsolvable mystery. As a curiosity, we like to add to the above the fact that the orbit of Japetus is somewhat unusual too. Although, as we said hereabove, Japetus is Saturn's third-largest moon, it orbits much farther from Saturn than the next closest Major moon, Titan. Japetus has also the most inclined orbital plane of the so-called Saturnian Regular Satellites (such as those Natural Satellites of Saturn which have a round shape); only the irregular Outer Satellites of Saturn (like Phoebe, for instance) have more inclined orbits and the cause of this is also unknown.

Because of this distant, inclined orbit, Japetus is the only large moon of the Saturnian System from which the Rings of Saturn would be clearly visible; from the other inner moons, instead, the Rings would be edge-on and therefore difficult to be seen in all their astonishing beauty. Furthermore, from the Surface of Japetus, Saturn would appear, to a human Astronaut looking at it, to be about 1° and 56' in diameter (such as approx. 4 - four - times the size of the Moon as viewed from Earth).

This frame (taken whan the NASA - Cassini Spacecraft's camera was pointing toward Japetus from a distance of approximately 7.037 Km only) has been colorized in Absolute Natural Colors by (such as the colors that a human eye would actually perceive if someone were onboard the NASA - CASSINI Spacecraft and then looked down, towards the Surface of Japetus), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.