Saturn's Moon: Iapetus Rotation

Iapetus (pronounced /aɪˈæpɨtəs/, or as Greek Ιαπετός), occasionally Japetus (pronounced /ˈdʒæpɨtəs/), is the third-largest moon of Saturn, and eleventh in the solar system, Iapetus is best known for its dramatic 'two-tone' coloration, but recent discoveries by the Cassini mission have revealed several other unusual physical characteristics, such as an equatorial ridge that runs about halfway around the moon.
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 magnitudes dimmer 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 Regio in 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 (see naming of natural satellites). Geological features on Iapetus are named after characters and places from the French epic poem The Song of Roland. Examples of names used include the craters Charlemagne and Baligant, and the northern bright region, Roncevaux Terra. The one exception is Cassini Regio, the dark region of the moon, named after the region's discoverer, Giovanni Cassini. 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 scarp about 15 km high.

Discovered by G. D. Cassini
Discovery date October 25, 1671
Designations
Alternate name Saturn VIII
Adjective Iapetian, Japetian
Orbital characteristics
Semi-major axis 3 560 820 km
Eccentricity 0.028 612 5
Orbital period 79.321 5 d
Inclination 17.28° (to the ecliptic)
15.47° (to Saturn's equator)
8.13° (to Laplace plane)
Satellite of Saturn
Physical characteristics
Dimensions 1494.8×1424.8 km
Mean radius 735.60 ± 3 km
Surface area 6 700 000 km²
Mass (1.805 635 ± 0.000 375) × 1021 kg
Mean density 1.083 0 ± 0.006 6 g/cm³
Equatorial surface gravity 0.223 m/s2
Escape velocity 0.572 km/s
Rotation period 79.321 5 d
(synchronous)
Axial tilt zero
Albedo 0.05-0.5
Apparent magnitude 10.2-11.9

Category:

Science & Technology

Tags:

• Iapetus Rotation
• Saturn moon Iapetus
• Iapetus
• Rhea
• Phoebe
• Saturn
• Titan
• Dione
• saturn rings
• cassini spacecraft
• Huygens spacecraft
• rings of saturn
• eceladus
• astronomy
• NASA
• ESA
• kurd
• kurdistan

[tanarus77]

I have always found it strange for the size of earth's moon is compared to planet to moon ratio of the rest of the solar system planets . Anyone have a theory on that ?

[KurdstanPlanetarium]

@tanarus77 To me its just chance...in the early days of Solar System creations it is said there were about 100 planets. then most of them collided with each other, creating our planets and thier moons...the gaseous planets are giants but their moons too, some of them bigger than Planet Mercury, but the ratio to the parent planet is smaller than that of Earth - Moon System. BTW Pluto - Charon is just like Earth - Moon, with higher ratio. but who knows maybe there are more than chance to it !

[tanarus77]

@KurdstanPlanetarium thanks for you response. Can you imagine how big a moon of jupiter would be if it had one like earth that was 1/80th its size

[KurdstanPlanetarium]

@tanarus77 Nice point, when we talk a bout King of the Planets Jupiter, we talk about huge size. just imagine Jupiter itself 384 times bigger than Earth, i.e you can have 384 Earth like planets inside Jupiter, so if we to imagine a Moon with size 1/80th of Jupiter than we talk about a Moon nearly 5 times bigger than Earth.

what a fascinating world would be.

BTW you know the Great Red Spot a Hurriacan more than 300 years raging since we know it, it is 3 times the size of Earth, just imagine!

[MadeInOregon27]

@KurdstanPlanetarium Is mars really a baron desert red planet IYO?

[KurdstanPlanetarium]

@MadeInOregon27 Mars certainy a desert but I wouldn't call it baron, I do belive in existing of live on Mars, not higher form of live but microbic bacteria !!!

[kaderoder]

@tanarus77 Great question! I favour the Biblical ideology, just to add to your observation that the suns size and distance from the earth, compared to the moons size and distance from the earth, give us the exact same size bodys- from our perspective, which seems like an improbable 'fluke'. Angular momentum would suggest the planets would spin slower than the sun, they dont, and that the outer planets should be smaller than the inner, they're not. Lol, its a funny world we live in. :o)

[IapetusTitan]

The cool thing is that Saturn is the Roman name for Cronus (the Greek Titan) and the planet has moons like Titan and Tethys and Rhea and Iapetus (those three Greek Titans also) and many others.

[TheMelanx]

Tarda en completar una vuelta alrededor de Saturno 79,33 días, a una distancia media de 3.561.300 km.

Uno de los hemisferios del satélite es mucho más oscuro que el otro, peculiar característica que se podría deber a la una composición distinta del material de la superficie, proveniente del interior de la propia luna o bien de materia de otros satélites o anillos: no se conoce con certeza el motivo real, aunque la segunda hipótesis cada vez es más apoyada por evidencias observacionales.