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Iapetus moon of Saturn

 Automatic translation  Automatic translation Category: moons
Updated June 01, 2013

Iapetus is the third moon of Saturn by the size. During its flying by the probe Cassini, the passed on images revealed the existence of an equatorial crest stretching on approximately 1 300 km long, reaching by places the exceptional height about 20 000 m.
This crest is not without arousing the interest of the planetologists who advance several hypotheses as for its formation: she could notably result from the accretion of former rings or still the progressive collapse, by effect of tide, from an equatorial sausage due to a massive centrifugation during the formation of the satellite.
So, we waited for many of the second flying over its ground by the same probe on September 10th, 2007 at a height lower than 1 700 km.

Image: Image Cassini, Credit: NASA/JPL/Space Science Institute.

IapetusMoon of Saturn
Mean diameter1 469 ±2.8 km
Masse2,0 x 1021 kg
Density1,27 x 103 kg/m2
Semi-major axis 3 560 820 km
Eccentricity 0.0286125
Orbital period 79.3215 d 
(to Saturn's equator)

Discovered dateOctober 25th 1671
Discovered byJean-Dominique Cassini
Rotation periodsynchronal to Saturn
Gravity0,26 m/s2
Albedo0.04 to 0.6

The chain of mountain of Iapetus


The density of Iapetus, close to that of the water, is similar to that of Rhea, indicating a small quantity of rocky matter. Its hemisphere before, is very dark (albedo between 0,03 and 0,05) with a light reddish nuance, while its back hemisphere, is brilliant (albedo 0,5, almost as much as Europe).
This difference is so striking as Cassini had already noted that he could see Iapetus only of a single side of Saturn. The dark face could consist of matter got back by the space either resulting from the inside of the moon. The dark matter could be a fine layer of organic matter, maybe similar to complex substances found in the most primitive meteorites.
Cassini passed on in September, 2007 the images of its flying over Iapetus, the third satellite of Saturn.
The observations supplied by the probe are even more surprising and more enigmatic than that we could imagine for this moon, in the form of cockleshell, bizarrely separated in two faces, the one black and sooty, the other white and snow-covered.
Cassini glanced through Iapetus on Monday, September 10th, 2007.


The images arrived only some days later because of a very energy cosmic ray which crossed the probe. This one was grateful to put itself in sleep mode to limit the risks of disturbance.

Image: Image Cassini, Credit: NASA/JPL/Space Science Institute.


Universe of Iapetus


The data transmission was thus delayed to be finally broadcast without problem. The diverse systems of the probe recovered in functioning in the days which followed. The most close taken images were realized in only 1 640 kilometers of the surface, or 100 times closer of Iapetus that during the last meeting moved closer to Cassini in 2004.
These images are really stunning. Indeed, numerous photos of the mysterious chain of mountain 20 kilometers high, show of it. This chain of mountain runs during the equator of Iapetus, looking like the relief of a walnut.


Image: Image Cassini, Credit: NASA/JPL/Space Science Institute.

The yin and the yang of Iapetus


The transmission of hundreds of images of this mission showed the yin and the yang of Iapetus, a snow-white hemisphere and the other black as a tar.
"The flight above the surface of Iapetus looked like an unlimited free-fall, in the heart of a den of rabbit, to succeed directly in a magnificent Country! Very few places in our solar system are more bizarre than this patchwork of dark and glittering" said Carolyn Porco, the leader of the team to the Institute of the Spatial Sciences.


Image: This image shows the ground in the region of transition between the dark main hemisphere of the moon and its brilliant hemisphere.

The mission Cassini-Huygens is a cooperative project of the NASA, the European Space agency and the Italian Space agency. JPL, is a division of the Technological Institute of California in Pasadena, she manages the mission Cassini for the Direction of the NASA. The space probe Cassini and its two cameras on board were conceived, developed and assembled to JPL.


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