Ng Jing Ni

Year: 2015-2016

School: Raffles Girls' School (Secondary)

City: Singapore

Target: Rings and Moons

Cassini should image Target Set 1, consisting of Tethys, Enceladus, Mimas, and Saturn's rings. I will focus on Enceladus in this essay.

Enceladus is Saturn's sixth largest moon, with a rocky core and icy crust. With suitable conditions, Enceladus is a promising candidate in the search for extra-terrestrial life, giving Cassini an opportunity to conduct more research. Cassini can also find out about Enceladus' geography, like its cryovolcanism and plate tectonics. Enceladus' interactions with Saturn's magnetosphere and ring system can be investigated too.

Firstly, Enceladus is suspected to harbour life. At Enceladus' south pole, cryovolcanoes of water ice have been observed, forming a thin but transient water vapour atmosphere on Enceladus. By measuring Enceladus' physical libration, scientists conclude that a subsurface ocean, about 26-31km deep, surrounds the moon, providing a liquid source for the cryovolcanoes. Several essential organic compounds and hydrocarbons, like sodium and
potassium salts, have also been found dissolved in the oceans. All these conditions point to the possibility of life on Enceladus. Spectra of gases and ice particles from the cryovolcanoes can be taken using Cassini's spectrometers to further study the oceans. Radar imaging technology can also help to track the depth of Enceladus' oceans to greater detail, and if possible, narrow down the possible locations where life may be found. These will give us a
better understanding of the composition and distribution of surface materials on Enceladus, and therefore, a more comprehensive evaluation of the moon.

Secondly, there are many geographical mysteries on Enceladus. Enceladus' oceans need a consistent heat source to remain liquid for such a long time. However, where does this heat come from? Cassini's radar and visible and infrared mapping spectrometer can map and investigate Enceladus' heat source. So far, there are 3 different theories - heat released by tidal forces of Saturn, tectonic activity, or decay of radioactive elements found in Enceladus'
rocks. More research is required to reconcile the drawbacks of each theory. Also, the composite infrared spectrometer in Cassini can observe the thermal properties of Enceladus' south pole to investigate its abnormal surface temperature, suspected to cause the increased activity on that part of the moon. The south pole also has a stronger gravitational pull than expected. The radio science subsystem of Cassini can study the gravitational field of Enceladus and hopefully shed some light on the geological history of Enceladus.

Lastly, Cassini can investigate the interactions of Enceladus with Saturn's magnetosphere and ring system. Saturn's magnetosphere is highly influenced by Enceladus' cryovolcanoes, so much that Enceladus can change the rotation of Saturn's magnetic field. Cassini's magnetometer can observe the pattern of this rotation, bringing the investigation one step further. Enceladus' cryovolcanoes also feed and maintain Saturn's E-ring, as discovered by the cosmic dust analyser on-board Cassini. With further analysis, the history of Saturn's ring system can be traced back to its origins.

Enceladus poses many mysteries to us. With Cassini's help, we will be able to solve these puzzles and gain a more comprehensive understanding of Saturn and its moons.

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