Winners - United Kingdom
10 - 12 years old - Dione
Author: Rahul Rahulan
The target that I have selected for the Cassini spacecraft, to take an image of is target number two: Dione. Below I will explain why I have chosen this outstanding satellite as the target of which the Cassini spacecraft should take an image of.
This marvelous moon of Saturn's is very mysterious and therefore, using the observations of the Cassini spacecraft, these mysteries could potentially be unlocked.
The mysteries of Dione include ice cliffs which look like wispy terrain. These ice cliffs can be several hundred metres high. These ice cliffs were probably caused through tectonic shifts. Cassini might help us to establish the precise cause.
There is also a question that I have been wondering about: the craters on Dione date back to billions of years ago, but are there any more recent or "young" craters on it? Cassini might help answer this question.
A few features of Dione can theoretically support life: a liquid substance below its surface, fields of "ice sand", and geysers that slow the rotation of the magnetic field of planets nearby. Evidence also shows that there is atmospheric oxygen on Dione - but just barely. This supports the idea that there is extraterrestrial life on the planets Jupiter and Saturn. This could be the answer to a question that scientists still cannot work out: is there life outside of Earth? Cassini might help solve these mysteries.
At the bottom of Dione, near its South Pole, Dione has canyons, which look more like lunar rilles than quake - cliffs. Lunar rilles are lava flows which could also suggest the existence of water, since water could have discharged the role of lava long ago. The observations of Cassini spacecraft would be able to identify in detail what these canyons really are.
Another question is: why Dione has spun at an angle of 180 degrees from its original position. Dione is very heavily cratered, more in some parts than in others. The heavily-cratered terrain is located on the trailing hemisphere and the less heavily- cratered terrain is located on the leading hemisphere. This suggests that during the period when Dione's craters were being formed, Dione was tidally locked to Saturn in the opposite orientation. As Dione is relatively small, an impact (from Saturn's rings) causing a crater of at least 35 kilometers length could have spun the satellite. Cassini's observations might help provide some answers.
In conclusion I think that Dione is the best target for the Cassini spacecraft to take an image of, and I think that NASA should use the opportunity presented by the Cassini spacecraft mission to photograph this moon. Dione could possibly hold the answers to, many things. After all, the Cassini spacecraft has the perfect camera angle for the necessary photographs, and this would therefore help to ensure that the best use is made of this extraordinary spacecraft.
13 - 15 years old - Iapetus
Author: Elanor Hinchsliff
All the possible targets for the Cassini spacecraft have their own special qualities and things to be discovered, however in my opinion there is just one that can be chosen. This is Iapetus, the seventeenth of Saturn's known moons. This moon has many interesting aspects, and is full of mysteries.
First seen in 1671 by Giovanni Cassini, this walnut shaped moon of Saturn has fascinated many since then, and we have made many discoveries. Yet there is still more to be found, which I is why I propose this moon as the one visited by the Cassini Spacecraft.
The ridge of mountains running 10km high around the equator of this moon gives it its distinctive walnut shape. There are two theories as to how these mountains came to be, but neither has yet been proved; further observation of the moon may give us more solid evidence for either theory.
One theory is that they formed when Iapetus rotated far faster that it does today, and the other is that they are made up of material left over from the collapse of one of the rings.
We know now that approximately three quarters of the surface of Iapetus is made up of ice, and one quarter rock. The fact that there is so much ice suggests that there is water on Iapetus. As water is the basis for all life, this begs the question; could this be another place in our solar system where life exists? Perhaps it is too cold, but until this is investigated, we cannot say for sure, as bacteria can survive in adverse conditions.
Perhaps Iapetus' most interesting aspect is its two differently coloured halves, one a bright white colour, the other a dark, coaly black. When Cassini first observed it, he saw a ‘winking' moon. About every forty days, this moon he was observing would simply disappear, and then reappear again, after approximately the same length of time.
Cassini theorized that this effect was caused by one hemisphere being brighter than the other, and that as it turned in its cycle, you saw the different sides. This peculiar quality is what gained Iapetus its nickname- The Yin Yang Moon.
As we now know Cassini's theory was correct, but quite how this phenomenon was formed is still worthy of investigation, although there are some theories. For example, some think that Iapetus is sweeping up particles from the more distant dark moon, Phoebe. If this is the case, then Iapetus must be continually renewing its dark surface, which could explain the fact that there are no brighter craters on that surface. Another is that some form of an ice volcanism spreading darker material across the surface.
Iapetus has many mysteries yet to be solved, theories yet to be proved. Sending the Cassini spacecraft to this moon, could help to provide evidence that could one day be used to consolidate theories and provide the world with the answers it longs for. Cassini discovered it. Can Cassini uncover its mysteries?
16 - 18 years old - Iapetus
Author: Elena Rastorgueva
My chosen target is Iapetus, a moon of two halves, a long-standing puzzle and, I feel, the worthiest candidate for further investigation. As tempting as Dione and Saturn are, Iapetus stands out because of its scientific mystery and distinctive appearance.
Giovanni Cassini himself was perplexed by this 'yin and yang' moon. The trailing side of Iapetus, which faces backwards, opposite to the direction of travel, is white. No surprises there: Iapetus is not very dense and so is probably composed mainly of frozen water, as well as some rock. However, the leading side, which faces forwards, is black with a hint of red. It's thought that this dark material is made up of various compounds containing carbon, including cyanides.
No other object in the solar system has such an extreme contrast. Even more intriguing is that the contrast is very distinct: the change from stark white to coal-black can occur in 20 metres.
There have been attempts at explanations.
Maybe the material was transferred from Phoebe, another distant moon, after a rogue object slammed into it and blasted the material into space. Then again, the colours don't quite match up.
Perhaps the material has been spewed out from within Iapetus due to volcanism. But then why haven't we seen these ice volcanoes?
Much uncertainty remains. Yet with newly-acquired evidence, we may get closer to the root of this 300-year-old problem.
Another mystery was only revealed in 2004, when the Cassini probe took its first detailed photos of Iapetus. They show the moon to look very much like a walnut, albeit with a radius of 700km. This similarity is because of a very tall and narrow ridge that stretches almost all the way round the moon's equator. How could the ridge have formed?
It may have been during an early period in the moon's history when it was spinning much faster and caused the ice and rock to form the ridge much like a salad spinner. Another explanation is that Iapetus had a moon of its own: a sub-satellite. Gradually, it spiralled in towards Iapetus and broke into pieces as it was torn apart by Iapetus's gravity. These pieces eventually landed along the equator and formed the ridge seen today.
This may sound odd, but then Iapetus is a very unusual moon in being so very far from its planet: we are yet to observe any moons with sub-satellites because they are too close to their planet. The planet has such a strong gravitational pull that it effectively takes all the moons for itself. It would be very exciting, both among the scientific community and the general public, if it was discovered that the sub-satellite had existed: a moon which orbits a moon, which orbits a planet, which orbits a star.
It is very difficult to resist the intrigue of Iapetus and its unique appearance. By focusing on this particular target in the Cassini probe's next fly-by, we may be able to unravel some more of its mystery