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Titan, the largest satellite of Saturn and the second-largest, after Ganymede, the solar system.

It was discovered by C. Huygens in 1655. It has a diameter of 5150 km. The semi-major axis measuring 1.222 million km, the orbital period is 15.94 days. Its surface has a reflectivity of about 20%. From the value of the average density, it shows that it consists of more than 60% of the ice and the residual part of rocky materials. Titan is the only moon that possesses a dense atmosphere (Io and Triton have one, but extremely thin).

For this characteristic, has been chosen as one of the priority objectives of the Voyager mission I: to carry with it a close encounter (which took place on 11 November 1980) has had to give up to achieve with this probe Uranus and Neptune, which are We were visited only by twin probe Voyager II.

Further exploration of Titan was taken on the Cassini mission (launched in October 1997) that, in addition to an orbiting observatory around Saturn, has been equipped with a capsule (Huygens) landed on the surface of the satellite in January 2005.

Titan’s atmosphere was discovered in 1944 by G. Kuiper, who singled, in the spectrum of sunlight reflected from the satellite, the absorption bands of methane.

However, only the probes Voyager I and Cassini have given reliable information about its composition and structure. It turned out that it consists of at least 90% nitrogen. As the second component, the observations indicate methane; It is possible, however, that most abundant is argon, although this gas was not revealed by the experiments carried out on the board of the probes. Several other gases are present in traces in the atmosphere: hydrogen, carbon monoxide, carbon dioxide, various hydrocarbons and nitrogen compounds. On the surface of the satellite, the temperature is 94 K and the pressure 1.6 bar. As the altitude increases, the temperature initially decreases, reaching a minimum at an altitude of about 50 km, and then increases again toward the outside. In the atmosphere, they are identified as two layers (the troposphere and the mesosphere), separated by a surface thermal inversion (the tropopause). Given the temperatures and pressures existing in the atmosphere and on the surface of Titan, methane should exist in all three states (solid, liquid and gaseous), giving place to a cycle, similar to the water cycle that takes place on the Land.

Meteorology could therefore present phenomena (rain, snow) similar to those on Earth. There are large uncertainties on the nature of the surface of the satellite: it could be filled by an immense ocean, mainly composed of ethane and methane, or possess, however, a solid crust, with liquid hydrocarbon basins of limited size (lakes, seas).

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Titan, the largest satellite of Saturn and the second-largest.