The European Huygens probe, which flew to the planet Saturn on board the American Cassini probe for 7 years and entered the atmosphere of the mysterious Titan on January 14, 2005, was only active for a few hours, but the small probe provided invaluable data.
The first data and images were already collected during the parachute glide (2 h and 28 min), showing that Saturn's moon Titan is an extraordinary world that resembles Earth in many respects. In particular, the meteorology, the geomorphology and the mysterious river-like activity (probably liquid methane) on the moon are reminiscent of our own planet.
Before the Cassini - Huygens mission, there were not many reliable facts about the second largest moon in the solar system, as the entire moon is shrouded in an orange haze that optical wavelengths cannot penetrate.
Even the first Cassini radar images revealed bright (plateaus) and dark areas (lower-lying areas, possibly representing dried-up river courses or lake landscapes). Huygens landed in a dark area and found water ice the size of pebbles scattered around the landing site. These pebbles varied in size (up to a few centimeters in diameter) and were rounded, suggesting that liquid hydrocarbons may have shaped them over time. Furthermore, a soil analysis revealed that the surface here has the same consistency as loose wet sand.
The wind conditions on the moon were also a surprise. Winds blow mainly in the direction of Titan's rotation from west to east with wind speeds of 450 km/h at an altitude of 120 kilometers. The wind speed decreases with lower altitudes and even changes direction close to the surface. Unusually strong gusts of wind have been detected at altitudes of 100 and 60 kilometers.
Huygens also surprised the scientists by discovering a second lower ionospheric layer between 140 and 40 kilometers. Furthermore, Huygens' instruments detected electrical conductivity at an altitude of about 60 kilometers, indicating traces of lightning.
And contrary to assumptions, the haze extends to just before the surface, as it was previously assumed that the lower stratosphere no longer contained any haze. Fortunately, however, the haze was no longer so strong from an altitude of 40 kilometers, which is why the first images could be taken from here.
Huygens discovered that Titan's atmosphere is rich in nitrogen, similar to the Earth's atmosphere, but also contains significant amounts of methane and other organic compounds. Huygens also found a rich variety of organic particles and aerosols in the atmosphere, which are similar to the building blocks of life on Earth.
Huygens confirmed the existence of an active methane cycle on Titan, similar to the water cycle on Earth. Methane, which condenses on the cold surface and is present as a liquid, plays a central role in Titan's geology and possibly also in its hydrological cycles.
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