On September 10, 2007 the Cassini orbiter passed within 1,227 km (762 miles) of Iapetus and returned images showing that both hemispheres are heavily cratered. The color dichotomy of scattered patches of light and dark material in the transition zone between Cassini Regio and the bright areas exists at very small scales, down to the imaging resolution of 30 metres (98 ft).
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Iapetus was discovered by Giovanni Domenico Cassini, an Italian/French astronomer, in October 1671. He had discovered the moon on the western side of Saturn and tried viewing it on the eastern side some months later, but was unsuccessful. The pattern continued the following year as he was able to observe it on the western side, but not the eastern side. Cassini finally observed Iapetus on the eastern side in 1705 with the help of an improved telescope, finding it two magnitudesdimmer on that side. Cassini correctly surmised that Iapetus has a bright hemisphere and a dark hemisphere, and that it is tidally locked, always keeping the same face towards Saturn. This means that the bright hemisphere is visible from Earth when Iapetus is on the western side of Saturn, and that the dark hemisphere is visible when Iapetus is on the eastern side. The dark hemisphere was later named Cassini Regioin his honour.
Iapetus is named after the Titan Iapetus from Greek mythology. In fact, all Saturnian moons are named after Titans. The name was suggested by John Herschel (son of William Herschel, discoverer of Mimas and Enceladus) in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope, in which he advocated naming the moons of Saturn after the Titans, sisters and brothers of the Titan Cronus (whom the Romans equated with their god Saturn). When first discovered, Iapetus was among four Saturnian moons labelled the Sidera Lodoicea by their discoverer Giovanni Cassini after King Louis XIV (the other three were Tethys, Dione and Rhea). However, astronomers fell into the habit of referring to them using Roman numerals, with Iapetus being Saturn V. Once Mimas and Enceladus were discovered in 1789, the numbering scheme was extended and Iapetus became Saturn VII. And with the discovery of Hyperion in 1848, Iapetus became Saturn VIII, which it is still known by today (s...
The low density of Iapetus indicates that it is mostly composed of ice, with only a small (~20%) amount of rocky materials. Unlike most moons, its overall shape is neither spherical nor ellipsoid, but has a bulging waistline and squashed poles; also, its unique equatorial ridge (see below) is so high that it visibly distorts the moon's shape even when viewed from a distance. These features often lead it to be characterized as walnut-shaped. Iapetus is heavily cratered, and Cassini images have revealed large impact basins in the dark region, at least five of which are over 350 km wide. The largest, Turgis, has a diameter of 580 km; its rim is extremely steep and includes a scarpabout 15 km high.
Temperatures on the dark region's surface reach 130 K (Template:Convert/C F) at the equator, as heating is made more effective by Iapetus's slow rotation. The brighter surfaces absorb less sunlight so temperatures there only reach about 100 K (Template:Convert/C F).
The orbit of Iapetus is somewhat unusual. Although it is Saturn's third-largest moon, it orbits much farther from Saturn than the next closest major moon, Titan. It has also the most inclined orbital plane of the regular satellites; only the irregular outer satellites like Phoebehave more inclined orbits. The cause of this is unknown. Because of this distant, inclined orbit, Iapetus is the only large moon from which the rings of Saturn would be clearly visible; from the other inner moons, the rings would be edge-on and difficult to see. From Iapetus, Saturn would appear to be 1°56' in diameter (four times that of the Moon viewed from Earth).
Iapetus has been imaged multiple times from moderate distances by the Cassini orbiter. However, its orbit makes close observation difficult. There has been one close targeted fly-by, at 1227 km on September 10, 2007; there are no plans for any others.Iapetus in fictionList of geological features on Iapetus
1. Cassini mission page - Iapetus 2. Discussion of Iapetus dated October 2007 3. Iapetus Global Maps 4. Iapetus Profile by NASA's Solar System Exploration 5. The Planetary Society: Iapetus 6. Astronomy Picture of the Dayarticle on Iapetus 7. Mirror Objects in the Solar System? - refereed article discussing the speculative mirror matter, and Iapetus in this context 8. A Moon with a View - Richard C. Hoagland's imaginative discussion of Iapetus's oddities 9. New attempts to crack Saturn's 'walnut' moon- equatorial ridge formation theories 10. Movie of Iapetusat National Oceanic and Atmospheric Administration bg:Япет (спътник)ca:Jàpet (satèl·lit)cs:Iapetus (měsíc)cy:Iapetws (lloeren)da:Iapetus (måne)el:Ιαπετός (δορυφόρος)eu:Japeto sateliteagl:Iapeto (lúa)hr:Japet (mjesec)id:Iapetusit:Giapeto (astronomia)he:יאפטוס (ירח)la:Iapetus (satelles)lv:Japets (pavadonis)lt:Japetas (palydovas)hu:Iapetus (hold)ms:Iapetus (bulan)nl:Iapetus (maan)no:Iapetus (måne)nn:Saturnmånen Iapetuspl:Japet...
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Dec 17, 2004 · Light & Dark on Iapetus. Saturn's outermost large moon, Iapetus, has a bright, heavily cratered icy terrain and a dark terrain, as shown in this Voyager 2 image taken on August 22, 1981. For more information go to the photojournal website.
Iapetus is composed mainly of water-ice and very little rocky material with a low density of 1.20 g/cm 3. The interior structure is composed of a small frozen solid rocky core that is less than 1/4 of its total mass. The surface is dark, heavily cratered, and grooved with the presence of equatorial ridges.
The view was obtained by the Cassini spacecraft narrow-angle camera on March 27, 2015 at a distance of approximately 621,000 miles (1 million kilometers) from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 38 degrees. Image scale on Iapetus is about 4 miles (6 kilometers).
Saturn's outermost large moon, Iapetus, has a bright, heavily cratered icy terrain and a dark terrain, as shown in this Voyager 2 image taken on August 22, 1981. Amazingly, the dark material covers precisely the side of Iapetus that leads in the direction of orbital motion around Saturn (except for the poles), whereas the bright material occurs ...
Half of Iapetus is so dark that it can nearly disappear when viewed from Earth. Recent observations show that the degree of darkness of the terrain is strangely uniform, like a dark coating was somehow recently applied to an ancient and highly cratered surface.
Saturn's moon Iapetus has a long, 20-kilometer-high ridge running along most of its equator. It was discovered by the Cassini probe in 2004. The ridge's origin is unknown. There are bright areas on the sides of the equatorial ridge near Iapetus' bright trailing hemisphere, which were already visible in Voyager 2 images appearing like mountains and were nicknamed the "Voyager Mountai
Iapetus Temperature Variation Map Full Resolution: TIFF (179 kB) JPEG (42.93 kB) 2005-01-10: Iapetus: Cassini-Huygens: Composite Infrared Spectrometer: 664x568x3: PIA07005: Iapetus Temperature Map Full Resolution: TIFF (268.2 kB) JPEG (35.24 kB)
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