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International Edition Winners - 2013: Pakistan, Target 1, Grade 5-6

International Edition Winners - 2013: Pakistan, Target 1, Grade 5-6

Eisha Zafar
Target 1, Iapetus
Eisha Zafar

Army Public School & College, Humayun Road
Grade: 5

"Iapetus is the third largest natural satellite of Saturn and eleventh largest of the solar system. It has a radius of about 42, a density of about 32.5percent and a mass of about 25percent of that of the moon. I like lapetus because it is best known for its dramatic "two tone' coloration. Other striking characteristics that grab my attention include an equatorial ridge that runs halfway across it.

I chose lapetus because I found it very interesting. Reading about lapetus added to my knowledge immensely. Most importantly it is made of ice!

lapetus was discovered by an Italian-French astronomer named Giovanni Domenico Cassini on 25th October, 1871. lapetus has a bright hemisphere and a dark hemisphere that is tidally locked, always keeping the same face towards Saturn. This fascinates me.

lapetus is named after the Titan lapetus from Greek mythology.The name was suggested by John Herschel in his 1847 publication Results of Astronomical Observation made at the Cape of Good Hope in which he recommended naming the moons of Saturn after the Titans.

The low density of lapetus indicates that it is mostly composed of ice, with only 20% of rocky materials. Unlike most of the large moons, its overall shape is neither spherical nor ellipsoid, but has a bulging waistline and squashed poles; also, its unique equatorial ridge is so high that its visibility distorts lapetus' shape even when viewed from a distance. These features often lead it to be characterized as walnut-shaped.

Light debris outside lapetus' orbit either knocked free from the surface of a moon by micrometeoroid impacts or created in a collision, would spiral in as its orbit decays, it would have been darkened by exposure to sunlight. The largest reservoir of such in falling material is Phoebe, the largest of the outer moons. Although Pheobe's composition is close to that of the bright hemisphere of lapetus than the dark one, dust from Phoebe would only be needed to establish the contrast albedo, and presumably have been largely obscured by later sublimation.

According to my research the current triaxial measurements of lapetus give it dimensions of 746 x 764 x 712 km, with a mean radius of 734.5 km. However these measurements may be inaccurate on the kilometer scale as Iapetus' entire surface has not yet been imaged in high enough resolution.

A further mystery of Iapetus which intrigues me is the equatorial ridge that runs along the center of Cassini Regio, about 1300 km long 20 km wide and 13 km high. It was discovered when the Cassini spacecraft imaged it on December 31st, 2004. Peaks in ridge reach more than 20 km above the surrounding plains, making them some of the tallest mountains in the solar system.

Temperatures on the dark region's surface reach 130 K (-143' C, -226' F) at the equator as heating is made more effective by Iapetus' slow rotation. The brighter surfaces absorb less sunlight so temperatures there only reach about 100 K (-173'C, -280' F).

So being scientist for a day, I would definitely like to explore Iapetus."