Winner - Czech Republic
Author: Kryštof Hes
I believe that Iapetus is the best target for the observation by the Cassini spacecraft. Iapetus is Saturn's third largest moon - not very dense, tidally locked to Saturn and definitely one of the most interesting in our Solar System. It was discovered in 1671 by the astronomer Giovanni Cassini and since then, there are many questions about it which hadn't been answered until now. Cassini spacecraft is our opportunity to do so.
One of the most interesting facts about Iapetus is its mountain range around its equator. This range includes mountains more than 10 km high and is more than 1 300 km long. But how was it formed? One theory suggests that its formation could be a result of a collapse of a ring. The other one explains the existence of the range with Iapetus' previous faster rotation. Shortly after it had been formed, the moon rotated much faster than today. It rotated about its axis once in approximately six hours compared to today's 79 days. According to the theory, an asteroid of about 800 to 1050 kilometers in diameter might have crashed into Iapetus, rapidly slowing down its rotation. This should have eventually caused the deformation of the moon and the formation of the equatorial mountain range. The further exploration of Iapetus could therefore help us to explain its geologic history and understand the processes which formed its shape.
However, maybe the most interesting feature of Iapetus is its surface. It was already Giovanni Cassini who discovered that one of Iapetus' hemispheres is much darker than the other one. Because of this fact, Iapetus is sometimes nicknamed the Yin-Yang Moon. There are several theories, which could explain the diversity in the color of the surface. One of them claims that the dark color is caused by particles coming from Saturn's moon Phoebe and hitting Iapetus' surface. The second theory explains the dark color with ice volcanism. Ice volcanoes are often found on the icy moons of our solar system and the mechanisms of their eruptions are still a bit of a mystery. In this case, methane-rich material could be released on Iapetus' surface and the absorption of UV-light could eventually darken it. However, the theory which is supported by previous thermal observations by the Cassini spacecraft is the temperature difference between the dark and the bright hemisphere. The dark material heats faster and causes the ice on Iapetus' surface to sublime and fall back on the cool, bright side of the moon.
All in all, further exploration of Iapetus could bring us impressive scientific facts. It could help us to understand its geological history, as well as all the processes which were involved in its formation. It could explain the color contrast between the two hemispheres and possibly also help us to understand cryovolcanoes. There are many theories about Iapetus' extraordinary features and we should use the chance to explore the moon by the Cassini spacecraft as long as it's in operation.