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10-12 years old: Ice plumes at the south pole of Enceladus

 Author: Buggenhout Ariadne

Qui aurait imaginé, lorsque Cassini quitta la terre en 1997, qu’en allant explorer une lune glacée de Saturne apparemment inerte, on trouverait l’endroit le plus prometteur pour abriter peut-être une vie extraterrestre ?

Avec le passage des sondes Voyager dans les années 1980, les scientifiques étaient étonnamment surpris par le résultat des photos d’Encelade, une des nombreuses lunes de Saturne. Une de ces photos montrait  qu’Encelade ne possédait pas de cratères au sud mais seulement au nord. Les scientifiques, n’arrivant pas à comprendre pourquoi, ont utilisé une autre sonde, nommée Cassini pour éclaircir ce mystère.

Cassini a été lancée en 1997 pour atteindre l’orbite de Saturne en 2004 et explorer la planète ainsi que ses anneaux et ses lunes. Il était prévu que la sonde Cassini achève sa mission en 2008, mais vu le succès de la mission et de ses expériences, elle a été prolongée jusqu’en 2017.
Parmi les observations remarquables de la sonde Cassini, on peut retenir les panaches de glace au pôle sud d’Encelade. Ces panaches, mesurant environ 50 km de hauteur, ont permis de comprendre l’absence de cratères au sud d’Encelade (ils font retomber de la matière sur la surface, ce qui recouvre les cratères) mais ont aussi amené une nouvelle énigme: d’où viennent-ils ? Encelade est située très loin du soleil et à cette distance les corps célestes sont notamment trop froids pour avoir une quelconque activité.  Les scientifiques pensaient donc qu’Encelade était une boule de glace inerte. L’hypothèse aujourd’hui est que les panaches proviennent d’une couche liquide sous la croute gelée et entourant un noyau solide probablement rocheux. L’existence de cette couche liquide est provoquée par un phénomène de marée dû à une autre lune nommée Dioné dont la période autour de Saturne est deux fois plus grande que celle d’Encelade, ce qui provoque un phénomène de résonnance et chauffe la couche liquide sous la glace d’Encelade.

Les astronomes ont aussi calculé que les panaches rejettent dans l’espace environ 20kg de cristaux microscopiques d’eau gelée. Ce sont ces cristaux qui forment l’anneau E de Saturne.

En survolant Encelade a moins de 50km d’altitude  Cassini est passée, à travers un panache et a analysé sa composition. On a détecté la présence d’eau (H2O), méthane (CH4), ammonium (NH3), dioxyde du carbone (CO2) et d’autres composés organiques ainsi que de l’argon (Ar) . Ces atomes, ces molécules ainsi que le phosphore qui n’a pas encore été détecté  par Cassini constituent la base nécessaire pour le développement de la vie. Mais peut-être que sur Encelade malgré l’absence de phosphore, d’autres éléments existent et pourraient permettre une autre forme de vie.

J’espère que dans le futur d’autres missions spatiales vont pouvoir répondre à toutes les questions posées sur Encelade et plus précisément à propos de l’eau supposée présente entre la roche et la couche de glace: constitue-t-elle un seul océan ou est-elle présente en plusieurs mers? J’espère que je pourrai suivre de plus près, en tant qu’astrophysicienne, les découvertes des missions futures en rapport avec Encelade.

10-12 years old: Ice plumes at the south pole of Enceladus

 Author: Rose O’Higgins

Cassini is a space-ship. It is exploring Saturn. The journey there took 7 years. It has been there for 13 years. During that time, it has discovered a lot of new things about Saturn. Now its mission is nearly over. In about 6 months, it will dive into the atmosphere of Saturn and be destroyed. But there is still time to learn some more things. What to choose?

The first choice is to learn more about the plumes of Enceladus.
Enceladus is a moon of Saturn. It is made of rock, water and ice. Cassini has been able to fly very close to the surface of Enceladus. It took pictures and did a lot of scientific experiments. In fact, thanks to Cassini they now believe that the inside of the planet is one big ocean. Plumes come out of its south pole. Here again Cassini has found out a lot of new things. It discovered that this part of Enceladus is quite warm. This was a surprise. It would be good to know more about these plumes. Maybe they could find out if very simple things live there. If Cassini could help with this, this would be a very big discovery. Even if they send another space-ship to Enceladus in the future, Cassini could already help by finding as many new things as possible over the next 6 months. This would help prepare the new mission.

The second choice is to learn more about the lakes of Titan.
Titan is the largest moon of Saturn. Cassini also flew very close to Titan and was able to take a lot of detailed pictures which were sent back to Earth. It launched a small probe, called Huygens, which landed on Titan and Huygens found out even more about this moon. It is very cold on Titan. One of the interesting things is that it has lakes. Even if they are not made of water, but of liquid gas, these are the first lakes found outside of Earth. It would be interesting to find out more about these lakes. One reason for this is that a long, long time ago the Earth was also very cold. By studying the lakes of Titan, we could learn more about how life started on Earth. There are many lakes and some of them are quite big, so there is a lot of work to be done.

The third choice is to view Saturn’s hexagon
Saturn’s hexagon is a strange pattern of clouds formed around the North Pole of the planet. The clouds are in the shape of a hexagon. Not so much is known about these clouds. During its mission so far, Cassini has not been able to get very close to them. It was able to see that the clouds change colour. However, they don’t know why this happened. Now at the end of the Cassini mission, it could be the chance to find out more about this strange shape on Saturn.

13-15 years old: The lakes of Titan

 Authors: Anirudhh Ramesh, Jakub Filcak

The largest of Saturn’s moons, Titan has long been an object of fascination to the scientific community. It is with good reason, as this moon could provide us with scientific insights into potential extraterrestrial life and a further understanding of the processes which would have played a key part in the formation of Earth’s biosphere, early in its life.

Titan has a dense atmosphere composed of nitrogen (98.4%), methane (1.4%) and hydrogen (0.1-0.2%), one of few atmospheres in our solar system to primarily be composed of nitrogen. The pressure of the atmosphere, being 1.6 bars, is not completely dissimilar to our own, of 1 bar. Due to the relative abundance of methane in Titan’s atmosphere, haze- a state of matter that occurs when light photons break up the gaseous methane- is common. Like the smog on Earth, this has made it difficult to observe the happenings on Titan’s surface and a significant amount of the information we have today was only uncovered after the Huygens probe landed on it in 2005.

This moon is equipped with a tepid core, with vast oceans of liquid water existing between the high-pressure ice mantles and the ice sheets that cover its surface. The existence of liquid water feeds into theories of organic compounds forming within the moon, but the boundless oceans may not be the most interesting secret of the astronomical titan that is Titan. On its surface, Titan’s temperature hovers around 94 kelvin, 17 kelvin below methane’s boiling point. This has allowed the formation of liquid methane lakes across Titan yet also a methane cycle analogous to the hydrological cycle on Earth, as in the formation of rain droplets due to evaporation. These unique features are same as the reasons that make Titan such an intriguing world, as it could perhaps harbour pre-biotic substances and hold key insights into the formation of rudimentary cells and compounds.
Although the nature of life on Titan will probably be different to that on Earth, it would nevertheless enhance our understanding of Earth’s primordial evolution. A closer examination of Titan’s lakes and the processes within them would also enlighten us as of the behaviour of compounds in prehistoric environments. While Titan is similar enough to Earth to provide us with significant knowledge about how these reactions would have happened, it is also diverse enough to present us with the behaviour of the reactions in an environment with certain factors changed.

In conclusion, Titan’s methane lakes could provide us with knowledge about processes that take place in an environment, with conditions comparable to those once present on Earth. It will also give us a broader view of their occurrence and their dependence on environmental factors, which could substantially aid our understanding of the origins of life. Perhaps it might put to rest a question we have been asking ourselves since humanity's conception, whether we are alone in the universe. It could also hold exciting prospects such as eventually serving as a refuelling station for future, methane-powered rockets.

Last Update: 1 September 2019
23-Sep-2020 06:33 UT

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