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IL GRAND FINALE

Cassini, a meteor in Saturn's atmosphere

The Cassini mission, one of the most important in space history, in which the Italian Space Agency has played a crucial role, comes to an end in Saturn's atmosphere

The increase in ring-grazing orbits have caused the Cassini probe to fall into Saturn's atmosphere today, leaving a trail of light behind it, like a shooting star. This is the end of the 20-year-long adventure of one of the most important and ambitious missions in the history of the conquest of space, with Italy's joint participation, through the Italian Space Agency, with NASA and the ESA. Its images and the data collected have led to the re-writing of books not only about the ringed planet but about the entire Solar System.

After a seven-year journey and thirteen years of activity, the probe, through its large 4-metre diameter antenna, designed and built in Italy by Thales Alenia Space, has sent a quantity of information to Earth, which will keep scientists busy for the next few years, discovering the missing data on how Saturn was formed and about its rings. The antenna has also been an integral part of two instruments in which ASI and the Italian University have played a leading role, namely Radar and Radio-science.

It is a programme with unparalleled technological and scientific returns and extended longevity, lasting 9 years beyond what was initially expected to be its operational lifetime. Upon its arrival, Cassini was already sending spectacular images to Earth, of a little-known planet. However, the beauty of the close-up images of the rings around Saturn or of their shadows projected onto the Planet is just a part of the exceptional outcome of the mission that has revealed the surface of a previously unknown world to us: Titan, with its hydrocarbon seas, or Enceladus, which was believed to be a small, fairly unimportant frozen satellite but that instead, with its water geysers proving the existence of a subterranean sea, turned out to be a world in which the conditions for the development of life forms might exist.

Cassini's instruments gradually gave us the last, fundamental information as it approached its final plunge. The Camera sent the conclusive, detailed close-up images to Earth before being shutting down, with NIMS and VIMS, another instrument that saw Italy as protagonist, functioning right up until the end. Radio contact was lost a few seconds before Cassini dissolved into Saturn's atmosphere, sending us further data. The last traces of the mission during its final phase were followed from Earth by various watchful 'eyes'. Among these, there is also the Italian Space Agency's Sardinia Deep Space Antenna (SDSA), positioned in the province of Cagliari and the latest arrival but one of the most powerful antennae belonging to the Deep Space Network. SDSA saw the ASI team, well-supported by colleagues from INAF, equip the Sardinia Radio Telescope (SRT) rapidly but in a suitable way for “sensing” the missions in deep space. The Sardinia Radio Telescope (SRT) was built a few years ago by INAF (National Institute of Astrophyisics) in collaboration with the Italian Space Agency, the Sardinia Regional Authority and the Ministry of Education, Universities and Research. 

Cassini has broadened our knowledge of the solar system exponentially”, said Roberto Battiston, president of ASI. “Furthermore, this mission is an example of the best scientific language - the language of international cooperation and sharing of scientific data, essential for the success of space exploration. ASI has a great tradition of cooperation with the most important space agencies in the world and the agreements we made for the Sardinia Deep Space Antenna, which will enter into NASA's Deep Space network, raise Italy's space capabilities to a higher level. We had proof of this capability on 22 August with the first connection between Cassini and the Deep Space Antenna. We could define it a scientific love story: two Italian instruments that ‘kissed’ after twenty years, at a distance of over a billion kilometres.”

 

“The mission coming to an end today speaks a great deal of Italian: over 300 years have passed since the discovery of Saturn’s satellites by Giovanni Domenico Cassini and today a probe carrying his name is plunging into the atmosphere of this remote planet, after allowing us to get to know them closely”, said Nichi D’Amico, president of INAF. “INAF’s participation includes four members of the VIMS spectrometer Scientific Team and 3 Participating Scientists, all from INAF'S Institute of Astrophysics and Space Planetology in Rome, which has produced about 20% of the scientific publications generated using data from the instrument, one of the main ones on board the probe. This is a source of great satisfaction for our Institute, considering the astounding discoveries that have been made over these 10 years, thanks to the contribution made by VIMS: demonstrating that Phoebe was formed far from the Sun and that Saturn captured it in the Solar System's primordial phases, demonstrating that the lakes of Titan are formed by hydrocarbons, hypothesizing the presence of a liquid ocean beneath the frozen crust of Enceladus. Who knows what other surprises await us in this last plunge, taking us one step further forward in understanding our Universe. Another source of satisfaction is witnessing this event from our large telescope in Sardinia, specially equipped by ASI.” 

The result of collaboration that began in the second half of the 1980s between NASA, the European Space Agency and the Italian Space Agency, the Cassini-Huygens probe was launched from Cape Canaveral on 15 October 1997 on board the Titan IV-Centaur rocket that carried it, after a long journey with flybys around Venus, the Earth and Jupiter, into orbit around the ringed planet on 1 July 2004. Huygens detached at Christmas that same year and on 14 January 2005 it began its descent, slowed down by three parachutes in sequence, through the clouds of Titan, one of Saturn's Moons. The lander acquired data for two and a half hours during the descent and another half an hour on the surface, which is as much as the on-board batteries would allow. Nevertheless, this was enough to show us a world that we could never have imagined, where rocks are made of ice and the surface is formed by a mixture of hydrocarbons. A couple of years later, the radar also showed us the existence of lakes and seas of liquid methane at the north pole. Cassini was initially expected to operate for 4 years and it worked at a distance of almost one and a half billion kilometres, while its radio signal took 60 minutes on average to reach the Earth. 

The Mission was named after Italian astronomer Gian Domenico Cassini, whose role, around end of the seventeenth century, was fundamental in the study of Saturn and its rings and was also named after Christian Huygens. Huygens was called by Cassini, who had in the meantime become the first director of the Paris Observatory, and worked with him, discovering the existence of Titan. Gian Domenico Cassini died on 14 September 1712, a mere but meaningful coincidence.