Iapetus is the seventeenth of Saturn's known satellites and the third largest:
orbit: 3,561,300 km from Saturn
diameter: 1460 km
mass: 1.88e21 kg
In Greek mythology Iapetus was a Titan, the son of Uranus, the father of Prometheus and Atlas and an ancestor of the human race.
Discovered by Cassini in 1671.
With a density of only 1.1, Iapetus must be composed almost entirely of water ice.
Trailing side of Iapetus from Voyager 2 The leading and trailing hemispheres of Iapetus are radically different. The albedo of most of the leading hemisphere is about .04, as dark as lampblack, whereas the trailing hemisphere's albedo is .6, as bright as Europa. This difference is so striking that Cassini noted that he could see Iapetus only on one side of Saturn and not on the other.
One explanation of this is that the leading hemisphere is dusted with a coating of material knocked off of Phoebe or some other Saturnian body. However, the color of the leading half of Iapetus and that of Phoebe don't quite match. Another possibility is that some active process within Iapetus is responsible. The puzzle is compounded by the fact that the dividing line between the two sides is inexplicably sharp.
Near the edge of the dark overlaying material On the last day of 2004, Cassini made its first close encounter with Iapetus. The images show that the dark material overlays the topography, indicating that it is relatively young. And as in the image to the left, along the edge of the dark area there are many craters where only one side is covered by the dark material; the boundary between the two regions isn't so sharp after all. So far the Cassini's data do not resolve the puzzle of the origin of the dark material but there's more to come!
Iapetus's giant equatorial ridge Cassini's first encounter with Iapetus also revealed another striking feature not seen before: a ridge 13 kilometers higher than the surrounding terrain that extends at least 1300 km almost almost exactly parallel with Iapetus's equator.
All of Saturn's moons except for Iapetus and Phoebe are very nearly in the plane of Saturn's equator. Iapetus is inclined almost 15 degrees.
Iapetus 是土星已知衛(wèi)星中距土星第十七近、第三大的一顆：
公轉(zhuǎn)軌道：距土星 3,561,300 千米
衛(wèi)星直徑：1460 千米
質(zhì)量：1.88e21 千克
希臘神話中，Iapetus是一個巨人，烏拉若斯的兒子，普羅米修斯和Atlas的父親，人類的祖先。
它由卡西尼于1671年發(fā)現(xiàn)。
密度僅為1.1，土衛(wèi)八的大部分肯定是由冰水組成的。
正對公轉(zhuǎn)和反對公轉(zhuǎn)的半球完全不同。正轉(zhuǎn)半球的反照率在0.03到0.05之間，與煤煙一樣暗，反面為1.5，幾乎同木衛(wèi)四一樣亮。這些不同點太明顯，使得卡西尼注意到了，說出了“我只能見到土衛(wèi)八的一面，另一面則不能?！钡脑挕?BR> 對此的一個解釋是正轉(zhuǎn)半球被土衛(wèi)九上撒下的煤質(zhì)塵埃覆蓋。然而，土衛(wèi)八的顏色與土衛(wèi)九的并不相配。另一個可能是因為土衛(wèi)八內(nèi)部的活躍作用引起。這個難題加上這兩個半球分界處的線是無法形容的形狀，增添了人們的疑惑。
所有的土星的衛(wèi)星，除了土衛(wèi)八與土衛(wèi)九，處于土星赤道平面。土衛(wèi)八的傾斜角近15度。
orbit: 3,561,300 km from Saturn
diameter: 1460 km
mass: 1.88e21 kg
In Greek mythology Iapetus was a Titan, the son of Uranus, the father of Prometheus and Atlas and an ancestor of the human race.
Discovered by Cassini in 1671.
With a density of only 1.1, Iapetus must be composed almost entirely of water ice.
Trailing side of Iapetus from Voyager 2 The leading and trailing hemispheres of Iapetus are radically different. The albedo of most of the leading hemisphere is about .04, as dark as lampblack, whereas the trailing hemisphere's albedo is .6, as bright as Europa. This difference is so striking that Cassini noted that he could see Iapetus only on one side of Saturn and not on the other.
One explanation of this is that the leading hemisphere is dusted with a coating of material knocked off of Phoebe or some other Saturnian body. However, the color of the leading half of Iapetus and that of Phoebe don't quite match. Another possibility is that some active process within Iapetus is responsible. The puzzle is compounded by the fact that the dividing line between the two sides is inexplicably sharp.
Near the edge of the dark overlaying material On the last day of 2004, Cassini made its first close encounter with Iapetus. The images show that the dark material overlays the topography, indicating that it is relatively young. And as in the image to the left, along the edge of the dark area there are many craters where only one side is covered by the dark material; the boundary between the two regions isn't so sharp after all. So far the Cassini's data do not resolve the puzzle of the origin of the dark material but there's more to come!
Iapetus's giant equatorial ridge Cassini's first encounter with Iapetus also revealed another striking feature not seen before: a ridge 13 kilometers higher than the surrounding terrain that extends at least 1300 km almost almost exactly parallel with Iapetus's equator.
All of Saturn's moons except for Iapetus and Phoebe are very nearly in the plane of Saturn's equator. Iapetus is inclined almost 15 degrees.
Iapetus 是土星已知衛(wèi)星中距土星第十七近、第三大的一顆：
公轉(zhuǎn)軌道：距土星 3,561,300 千米
衛(wèi)星直徑：1460 千米
質(zhì)量：1.88e21 千克
希臘神話中，Iapetus是一個巨人，烏拉若斯的兒子，普羅米修斯和Atlas的父親，人類的祖先。
它由卡西尼于1671年發(fā)現(xiàn)。
密度僅為1.1，土衛(wèi)八的大部分肯定是由冰水組成的。
正對公轉(zhuǎn)和反對公轉(zhuǎn)的半球完全不同。正轉(zhuǎn)半球的反照率在0.03到0.05之間，與煤煙一樣暗，反面為1.5，幾乎同木衛(wèi)四一樣亮。這些不同點太明顯，使得卡西尼注意到了，說出了“我只能見到土衛(wèi)八的一面，另一面則不能?！钡脑挕?BR> 對此的一個解釋是正轉(zhuǎn)半球被土衛(wèi)九上撒下的煤質(zhì)塵埃覆蓋。然而，土衛(wèi)八的顏色與土衛(wèi)九的并不相配。另一個可能是因為土衛(wèi)八內(nèi)部的活躍作用引起。這個難題加上這兩個半球分界處的線是無法形容的形狀，增添了人們的疑惑。
所有的土星的衛(wèi)星，除了土衛(wèi)八與土衛(wèi)九，處于土星赤道平面。土衛(wèi)八的傾斜角近15度。