LANDING ON A FROZEN WORLD Cassini's main mission started with its Saturn orbit insertion on June 30, 2004 and was planned to last until June 2008. It was divided into six segments, each focusing on another aspect of the Saturnian system. In the first segment, the Huygens probe would separate from Cassini and land on the surface of Titan. Throughout the nominal mission, Cassini discovered new rings, new moons, and new Saturnian landmarks. Cassini would perform dozens of fly-bys, during 74 unique orbits around Saturn, using the gravity of Titan for shaping Cassini's path. Additionally, Cassini would perform close flybys of the moons Enceladus (4x), Phoebe, Hyperion, Dione, Rhea, and Iapetus. These moons were chosen as data from previous missions suggested that they could hold the keys to understanding the Saturnian system and possibly the origins of the Solar System.
However, researching Titan was the focus of the nominal Cassini mission. On December 23, 2004, the Huygens probe successfully detached from Cassini, and went on a trajectory to the surface of Titan. However, it would take a few weeks before the landing was completed. On January 14, 2005, Huygens entered the Titan atmosphere and landed on a plateau after a twoand-a-half-hour descent. After its landing, Huygens sent 700 pictures of its descent and landing site to Cassini, 350 of which were lost due to a software error. Some of the panoramas of Titan that were made during Huygens' descent can be seen in the timeline. During the descent, Huygens also performed measurements on Titan's atmosphere and as soon as Huygens landed, it used its instruments to analyze the landing region. The landing site was covered in pebbles of between five to fifteen centimeters across. These pebbles are thought to be made from water ice, coated with hydrocarbons. The pebbles were slightly rounded, which indicated a possible interaction with fluids. The surface was initially reported to be clay-like, but can probably be better described as 'sand' made of ice grains or snow that has been frozen on top. At the landing site, the temperature was 93.8K and the pressure was 1.5 times as high as that on the surface of the Earth. Due to the greater attenuation of blue light by Titan's atmosphere than that of red light, the color of the sky and the
scene on Titan appeared orange. Thirty minutes after Huygens' landing, Cassini rotated its antennas from Huygens to the Earth, as all the planned science activities had been carried out. However, very large radio telescopes at the Earth were not able to pick up signals that were sent by Huygens until two hours after the landing. This was longer than expected, but after almost two hours at the surface, Huygens' batteries died.
BUT WAIT, THERE’S MORE... Over the course of the nominal mission, not only did Huygens land on Titan, Cassini also investigated the surface of Titan during its numerous Titan flybys. After Huygens' images made already clear that there could be fluids at Titan's surface, Cassini's observations clearly showed lakes and seas of possibly ethane or methane scattered over the polar regions of Titan. An image showing some of these lakes is given in the timeline. Furthermore, in some of the valleys, rivers were flowing. As clouds were present above the lakes, it was suspected that the liquid hydrocarbons evaporate during summer and rain down during winter. This final phenomenon had not been proven, but possible mission extensions would be able to delve more deeply into the seasonal changes at Titan. After Cassini dropped Huygens off at Titan, it performed a flyby of the moon Iapetus, which was discovered in 1671. This was a very interesting flyby, as it was discovered NASA
In the final three months until orbit insertion, Cassini already discovered two new moons, of three and five kilometers in diameter. It also observed two storms merging into one larger storm on the southern hemisphere of the Saturnian atmosphere. This was only the second time that the merging of storms was observed on the planet. Also, Cassini performed its first flyby of a Saturnian moon, Phoebe. Finally, on June 30, 2004, Cassini became the first spacecraft to orbit Saturn, almost seven years after its launch. Cassini's prime mission was about to begin.
LEONARDO TIMES N°4 2017
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