Titan - findings 2015

Towards the end of the mission of the Cassini spacecraft in the Saturn system, in the last year it accelerated the study of the moons and in particular the largest moon of Saturn - Titan

clouds

A very large cloud was discovered at the South Pole whose components are frozen. It extends from the lower to the middle atmosphere. In 2012, a cloud was discovered above this pole at a height of 300 km from the ground. The new cloud is at an altitude of 200 km from the ground, lower than the previous cloud. This discovery was made using the infrared observation device. This cloud is different from the clouds observed so far. The density of the cloud is low and similar to fog on Earth. The way of formation of clouds at the pole of Titan is different from the formation of clouds on Earth and they are straighter at their top. Circulation in the atmosphere moves gases from the pole in the warm hemisphere to the cold hemisphere. At the pole where cold prevails, the warm air sinks like water coming out of the opening at the bottom of a bathtub. This process is called subsidence. The gases that sink down, a mixture of fog-like hydrocarbons and nitrogen chemicals, meet cold air on their way to the ground. Different gases condense at different heights while forming layers of clouds at each height range. The height of the clouds from the ground, their size and composition allow researchers to understand the nature of winter on Titan. Based on this data, the researchers concluded that the cloud discovered in 2012 in the southern hemisphere has its temperature dropping to 0 150 below zero. The new cloud is larger than its predecessor, is in the lower part of the stratosphere and contains ice particles of hydrogen, carbon and nitrogen. These characteristics are also found in the North Pole but with a weaker intensity. The stronger intensity at the South Pole strengthens the hypothesis that the beginning of winter is stronger than the end (1).

dunes

From earlier observations it became clear that the direction of movement of the dunes is west-east, the opposite of what was thought until then. An opinion was put forward that the reason for this is violent methane storms that are at high altitude creating strong gusts of wind in the east direction which are of great strength in the direction of movement to the west. These strong gusts of wind are responsible for moving the sand and this is the reason for the direction of movement to the east. The speed of these winds reaches 35 km/h, 10 times stronger than Titan's gentle ground winds. The storms only occur when Titan is at its equinox every 14.75 Earth years (2).

lakes

Usually the lakes on Titan are not connected to rivers.. They are filled by rainfall and underground sources. Some lakes dry up and fill up in 30-year seasonal cycles. It is not clear how the depressions in which the lakes are found were formed. Recently, it has been hypothesized that the explanation is surprisingly found on Earth. It turned out that Titan's lakes resemble the karst landscapes on Earth. On Earth the karst limestone and gypsum rocks are formed following the sealing by rains and underground water seeping through the rocks. Over time depressions and caves form in humid climates and salt clusters in places where the climate is arid. The rate of erosion of these landscape forms depends on various factors such as the chemistry of the rocks, the amount of rainfall and the temperature of the surface. A similar process probably also occurs on Titan. Based on a mathematical model, they tried to estimate how long different areas of the surface melt and create these formations. The assumption was that the surface was covered with solid organic materials. The main dissolving agent is liquid hydrocarbons. The conclusion they reached is that it takes 50 million years to create a depression 100 meters deep. A comparison was made between the erosion rate of organic materials in hydrocarbonic liquids on Titan and carbonates and volatile chemicals in water on Earth. It turned out that the rate of melting on Titan is 30 times smaller than that of Earth. The reason for this is the length of the year on Titan and rainfall only in the summer. Melting is believed to play an important role in shaping these landscapes. A question raised is how long it will take to create a lake depression in low latitudes, places where the amount of rainfall is less. The number obtained is 375 million years (3).

the wind of the sun

For 95% of its time orbiting Saturn, Titan is inside Saturn's magnetosphere. During the observation on 1.12.2013, Titan was on the side of Saturn facing the Sun when the eruption of the solar wind was very strong. When the solar wind reached Saturn it squeezed the sun-facing side of Saturn's magnetosphere so that the outer edge of the magnetic field bubble was squeezed into Titan's orbit. The result was that the moon was exposed to the energetic stream of particles from the solar wind. In most cases the Hexini observations were inside Saturn's magnetosphere. Because of this it was impossible to detect a magnetic field from the direction of Titan itself. This time Saturn's influence was not present, so the Cassini magnetometer could observe Titan as it interacted directly with the solar wind. It was possible to observe the shock wave created around Titan when it hits its atmosphere. The researchers' assessment was that it would be possible to examine Titan's response to the solar wind in a different approach due to the chemistry and haze of the dense and complex atmosphere. The hope of the researchers is that in addition to the new study about Titan, it will be possible to use this method also about other bodies in the solar system and how they behave in the interaction with the solar wind (4).

Sources
1. "NASA Cassini finds monstrous ice clouds in Titan's polar south region" 11.11.2015
http://saturn.jpl.nasa.gov/news/cassinifeature/feature/20151111/
2. "Violent Methane storms on Titan may solve dune direction mystery" 13.4.2015
http://sciencedaily.com/releases/2015/04/150413183758.htm
3. Baldwin Emily - "The mysterious lakes on Saturn's moon Titan" 19.6.2015
http://www.jpl.nasa.gov/news/news.php?release=215-213$rn=news.xml$rst=4635JUNE19,2015
4."Cassini catches Titan naked in the solar wind" 28.1.2015
http://saturn.jpl.nasa.gov/news/newsreleases/newsreleases20150128