Mevsim ÖZKAN

Year: 2015-2016

School: Kadikoy Anatolian High School

Teacher: Metin Tevetoglu

Grade: 9

City: Moda, Kad köy - Istanbul

Target: Rhea and Tethys

"There are a lot of things that we do not know about space. Even a phenomenon that happened in a remote corner of the universe can lead us to great enlightenments towards science. Which is why we should observe these kinds of scientific occurrences closely. The occultation between Tethys and Rhea is a great example to that and it should be observed by the Cassini spacecraft.

Tethys and Rhea were discovered separately by Giovanni Domenico Cassini spacecraft in 1684 and 1672.They are two of the many moons of Saturn. Although they were observed multiple times, there are things that human kind still cannot explain. If we observe the occultation we can find answers to some of our questions. This observation can give us a very accurate way to assess the orbits of these moons, which change slowly over time. Also to understand the reason why their orbits change.

Tethys has a very low density, according to its structure that contains; water ice, small fraction of rock and a small amount of an unidentified dark material. The most unusual part of this moon is the reddish strikes called "tiger scratches" that were found on the moon that doesn't match the surface. There are many theories on how they were made. Taking a close look to the occultation and Tethys can help us understand the origin of those mysterious tiger scratches and the unidentified dark material. Rhea is also intriguing, just like Tethys, Rhea has a low density which indicates that it is made of twenty five percent rock and seventy five percent water ice. It was assumed that Rhea had a rocky core in the center however the measurements taken by the Cassini orbiter in 2005 cast this into doubt. After this, there were many different theories about Rhea's center. Rhea has a tenuous atmosphere-exosphere which consists oxygen and carbon .In 2008 NASA made an announcement about a possible tenuous ring system around Rhea that would have marked the first discovery of the rings about a moon but there were not any reliable evidence. Observing the occultation can possibly lead to accurate information's about these matters and it can help us observe the reflection of light that will happen during the occultation and help us investigate the interaction of Tethys and Rhea with Saturn's magnetosphere and ring system.

The occultation Cassini should observe will help to determine; general characteristics and geological features of Tethys and Rhea, the occultation itself and the outcomes of this event. That is why I believe observing the occultation that will happen between Tethys and Rhea will be the most logical and useful choice for the Cassini to observe."

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