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2013 Edition -- Target 1: Iapetus, Grade 9 to 12 Winner

2013 Edition -- Target 1, Grade 9 to 12 Winner

Simran Parwani
Target 1, Iapetus
Simran Parwani

Fox Chapel Area High School
11th Grade
Pittsburgh, Pennsylvania

Teacher: Jennifer Klein

"In Chinese philosophy, Yin-Yang describes how contrasting forces are interrelated. In that same complementary manner, the Saturnian moon Iapetus has a jet black leading hemisphere that contrasts with its bright trailing hemisphere. The beauty of this moon and the mysteries that its “Yin-Yang” hemispheres hold are only a few of the reasons why the Cassini probe should point its telescopes to Iapetus to garner more knowledge and unravel the mysteries behind the paradoxical face of lapetus.

In September 2007, the Cassini flyby indicated that the process of thermal segregation was a factor for the darkened side of Iapetus. Like Earth and the Moon, Iapetus is tidally locked by Saturn, so it always presents the same face towards Saturn. The icy surface is warmed by the sun so the dark material absorbs more heat than the bright material, sublimates, and then migrates to colder regions, thus increasing the contrast between the black and white material. Another Cassini flyby of Iapetus would yield more evidence to support or modify the thermal segregation theory and solve one of the fascinating enigmas surrounding Iapetus.

Iapetus has a unique walnut shape due to the chain of six mile high mountains that encircles the moon’s equator. It has been a tough nut to crack to discover why the ridge formed, though it is possible that the formation occurred before Iapetus’ rotation slowed. The flattened shape of the moon indicates that, at some point in time, Iapetus had a more rapid rotation around Saturn. Some researchers suggest this rotation to have been as fast as sixteen hours, which is indubitably faster than its current seventy-nine day rotation. It may also be plausible that Iapetus had a sub-moon formed from the surface of Iapetus after a colossal impact, just like how some believe Earth’s moon was formed, as well as Pluto’s satellite Charon. This sub-moon would have orbited for several thousand, or maybe million, years, but would have gradually lost energy until it was broken into chunks by Iapetus’ tidal forces. These moonlets could have orbited Iapetus’ equator as a ring, and collapsed onto Iapetus’ surface, forming the ridge.

Through further Cassini imaging of Iapetus, it could be determined why the equatorial ridge is unique to Iapetus in the Solar System. On its journey, the Cassini probe could also discover more about the dark material on Iapetus since similar contaminant material is found on Phoebe and in Saturn’s rings. Through such further investigation, the Cassini probe’s findings of Iapetus could provide greater insight about the origins of Saturn’s famous rings. It is clear that Iapetus has many distinctive and mysterious features that pose questions about the universe surrounding us. However, unlike the “Yin-Yang moon” itself, the answers to these questions will not be so black and white."