Titan - new findings

The observations of the Cassini spacecraft that continues to scan Titan reveal more and more details of this moon and discover more parts of the face of this dark and freezing world

introduction

The observations of the Cassini spacecraft that continues to scan Titan reveal more and more details of this moon and discover more parts of the face of this dark and freezing world. These new details can serve as an extensive platform for new literary works by science fiction writers and oddly enough it has several parallels to Earth.

Surface

In the Xando area where the Huygens landed, geological forces parallel to those on Earth were identified. High mountains, vast plains, winding river channels, dunes and craters. 3 parallel ridges have been identified that look like broken lumps or a wrinkled crust. Their exposure to the surface gives them the appearance of high hills. The space between them is typical of places that have been compressed or stretched. Typical tectonic activity although plate tectonics has not been detected on Titan. Their direction is west-east and the distance between the ridges is 50 km(1). The height of the hills between the channels is 150-200 meters and their slopes are at a rate of 30°. Mountains made of water ice have been found that rise to a height of 2 km. According to estimates, this height indicates that they have undergone erosive processes (2). South of the equator there is a mountain range Its direction is southeast-northwest. Its length is 150 km, its width is 30 km and its height is 1.5 km, and it was probably created by the lifting of the surface by tectonic forces. Next to it there are sedimentary materials similar to a lava flow(3). A circular formation called Ganesa Macula was formed by cryovolcanism(4).

dunes

On Earth, grains of sand are formed as a result of the breaking and crumbling of rocks. On Titan the process is probably the opposite. The sand is built from very small materials. Part of this material is built from hydrocarbonate particles that reach the ground from the air as rain. When they reach the ground, they connect and become particles of granular size. If the inner part of the dunes is made of the same dark material as the outer part, they are of organic origin and more abundant than that created by erosive processes. The crystallization of the particles is done in a process called sintering - a slight heating that sticks particles together to a size that corresponds to that of grains of sand with sizes between 0.18-0.25 millimeters and no more, the same winds can carry and create dunes from them(5).

The composition of the soil

An unexpected return of radio waves from the ground allowed the researchers to estimate the size of the stones and gravel near the landing site of the Huygens when it landed on January 14.1.2005, 71. The lander survived the contact with the ground and continued to transmit data to the Cassini spacecraft. Part of the radio waves "leaked" to the sides and hit the ground of the star before being transmitted to Cassini and then "turned" towards it. What was received on Earth was not understood at first. Throughout the transmission, a constant pattern of signals repeated itself. The strength of reception increases and falls after that. The changes in the reception strength led the researchers to think that there is probably some kind of direct interaction between the transmitted signal and the one reflected from the environment. As Cassini moved away from the landing site, the angle between it and the Huygens changed. This angular gap changed the way in which the transmission beams reflected from the stones merge and the beam travels directly towards Cassini To understand the phenomenon, several computer models were tried. It turned out that signals could be generated and returned from the ground to estimate the size of the gravel on the ground. Cassini received signals from the Huygens for 1 minutes. The return range of the waves from the stones west of the landing site was 2 meter - 5 km and the size of the stones measured in this way was 10-6 cm. In the future it will be possible to use this unexpected technique on other planets and moons in the solar system(XNUMX).

In a comparison between photographs taken by Huygens and photographs of the same area taken by Cassini, no topographical correlation was found. The solution to this is found in comparing two dunes 30 km north of the landing site that were observed by both the lander and the compass. It is estimated that they are made of hydrocarbon grains between 100-300 microns in size. Based on this comparison, it became clear that around the landing site there is a large plain of dirty water ice covered with organic matter deposits. It turned out that this material covers the light areas and the dark dunes. The bright areas are not visible to Cassini's radar. The radar waves penetrate through them to the layer below the dirty water ice, which is rough in some places and slippery in others. The precipitation is formed when ultraviolet radiation from the sun and charged particles react at high altitudes with the methane that is common in the atmosphere and form hydrocarbon molecules such as ethane and acetylene. These reach the ground in the form of aerosols in the same way that smog particles on Earth cover the ground. On Titan, these precipitations can accumulate in layers hundreds of meters thick .

The dunes are made of material the size of grains of sand that accumulate either in the form of particles that reach the ground from the air or as a result of geological processes that shape the surface. The landscape made of ice or organic matter are very different from each other. Several channels were created by a process called spring sapping, a process in which methane flows under to the ground before coming to the surface, near the base of the hills. This burst of methane causes erosion of the hillsides, collapses and the formation of cliffs. Another place that was noticed is a dark plain made mainly of water ice mixed with a substance called tholin - organic aerosols formed from simple compounds such as methane and nitrogen . According to the assessment, the darkness of these areas was created due to occasional flooding from east to west and not from drainage channels to the highlands (7).

Makhteshim

4 new craters were discovered. One crater with a diameter of 30 km with a relief in the center and its location W°70 N° 10(8). A second crater with a diameter of 180 km, its bottom is flat and dark. Its location is W °9 S °26.5 (9). A third crater with a diameter of 400 km was named Menrva (10). (112).

lakes

Cassini's long-term observations confirmed the hypothesis that there are lakes on the moon. These were found at both poles of Titan. At the north pole, hundreds of lakes were found. At both poles, the lakes were found at latitude 70° and above. It is estimated that the mere presence of lakes at both poles indicates that the climatic conditions are similar(12). The lakes in the North Pole are filled with liquid methane and ethane. Topographically they are in low places and are connected to them by channels. Some of the lakes are half full while others are completely. Those that are half full or not completely filled or have partially evaporated show no signs of erosion and look like terrestrial lakes inside impact craters or inside calderas. The edges of some of the lakes are steep and can indicate topographic margins. They seem to be related to breaking out of drainage basins. Other lakes are diffuse towards their centers, which can indicate that they are related to channels or are themselves drainage basins and others exits in the form of winding channels similar to flood channels of Rivers. In the winter, the lakes expand as methane rains fall. In the summer, the lakes partially dry up and shrink (13).

The area of ​​most lakes ranges from a few meters to dozens of kilometers, although there are particularly large lakes that resemble seas in their dimensions. Their area can reach up to 100,000 square kilometers and their depth is tens of meters (14). At the South Pole is a lake that is 235 kilometers long and which was named Ontario Lacus. It is full of ethane and solutions of methane, nitrogen and other low molecular weight hydrocarbons. Its area is 20,000 square kilometers (15).

atmosphere

Cassini's tracking of the moon's atmosphere revealed additional substances - benzene and large amounts of positive and negative ions. The discovery of the negative ions was somewhat of a surprise. This discovery is of great importance in the creation of tholins. These pigeons are found in large quantities near the landing site of the Huygens. The analysis of the data raises the possibility that the organic compounds are formed in a chemical process of neutral ions that increases the amount of complex negative ions(16). The ionosphere is at an altitude of 120 km. Another layer of ionized particles is at an altitude of 63 km, which to a certain extent splits the atmosphere into two resonating chambers (Resonating Chamber) (17).

Spirits

In terrestrial observations made on Titan prior to the Huygens landing, at an altitude of 200 km at latitude N °50, a wind was measured at a speed of 720 km/h and it circled the moon in less than one terrestrial day. This wind is similar to the terrestrial jet stream (18).

Tracking the winds during the Huygens' movement towards landing revealed different wind speeds along its flight path within the atmosphere. At an altitude of 120 km, a wind speed of 432 km/h was measured. Below an altitude of 60 km, the wind speed is significantly less. The wind speed was below 10 km/h. On the ground, a wind speed of 1.08 km/h was measured.

The winds blow with the direction of Titan's movement around itself from west to east. They reverse their direction twice. The first inversion occurs at an altitude of 6 km and the second inversion is done at an altitude of 700 meters. These reversal points are of great significance in understanding the circulation of the atmosphere. According to one explanation, the upper reversal is caused by temperature differences between the northern hemisphere and the southern hemisphere. The second reversal occurs at the launch point between the upper and lower circulation of a large air pocket known as the Hadley cell. This Hadley cell of air movement from the South Pole to the North Pole and back is very important in the way heat is distributed in Titan's atmosphere. The southern hemisphere is currently turned towards the sun, which means that it is summer season. Warm air from the south rises and moves towards the colder northern hemisphere, causing the cold northern air to move south. Since this air is heavier, it sinks downwards (19).

clouds

The first time clouds were observed on Titan was during a terrestrial observation of this moon in 2001 from the Keck II telescope that incorporated the Adaptive Optics technique. The observed clouds were methane clouds at a height of 30 km above the ground around the South Pole. Since then, ethane clouds have also been observed over the North Pole by the Cassini spacecraft. A combination between Cassini and the Keck II telescope resulted in the discovery of methane clouds in mid-latitudes in the southern hemisphere. In 2005, the Huygens lander, during its passage through the atmosphere, transmitted data to Israel on the relative humidity of methane. These data provided information regarding the existence of frozen methane clouds at altitudes between -25 30 km and clouds of liquid methane including what appears to be thin rain at an altitude between 15-25 km (20).
A Cassini radar observation in 2006 showed that the lakes in the North Pole were half full and some of them had evaporated and resulted in the formation of a cloud made of ethane and organic materials. A cirrus cloud was also discovered in a bright strip at heights between 30-60 km at the edge of Titan's arctic region between latitudes N °69 - N °51. Cassini observed only part of the cloud because the Northern Hemisphere is now in the winter shadow region and will be fully illuminated in 2010 (21).

On 29.12.2006 and for 3 weeks during Cassini's 13th flyby, a cloud was observed over the North Pole that extended from the Pole to the N °60 latitude. Its diameter is 2400 km and covers the pole almost entirely. It is believed that this cloud filled the lakes a year before(22).

Surprisingly, at an altitude of 1000 km, a cloud made of heavy ions was discovered. The ions that were discovered are organic compounds created by exposure to the sun of methane and nitrogen molecules. These molecules gradually increase to a mass 8000 times heavier than a single hydrogen atom. These molecules sink towards the ground and form the tholins mentioned earlier (23).

climate

Despite Titan being very cold, its climate has structural characteristics similar to that of a tropical climate. The methane rains and its ice and tar dunes cover most of the arid regions and these conditions reflect terrestrial tropical climates. One reason for this climatic parallelism is that liquid methane at Titan's temperatures is much more volatile than water at Earth's temperatures. In this sense Titan as a whole is a tropical planet. A second reason is Titan's slow rotation around itself. On Earth, the tropical climate reaches up to 30° latitude on both sides of the equator. On Titan, this tropical climate covers the entire lunar body. The research significance is that to understand its climate the theories developed for understanding the global tropical climate can be used. Titan's atmosphere creates air currents that rise upward to where the ground winds converge. Air currents vaporize the methane to the region of cold temperatures and lower atmospheric pressure, where the methane condenses and forms clouds. This phenomenon is known on Earth as the ITCZ ​​(Inter Tropical Convergence Zone). On Earth, the oceans limit the ITCZ ​​to the low latitudes. According to several computer scenarios on Titan, the ITCZ ​​migrates almost from pole to pole. The clouds follow the ITCZ ​​(24).

The very fact that dry lake bottoms and many meandering rivers can be seen at both the north and south poles shows that many places on Titan are shaped more by climate than by tectonic events. The fact that one pole is humid while the other pole is dry raises the possibility that the climate changes during the seasons(25).

rain

The Huygens watched a cloud of methane and nitrogen that drops raindrops on the surface. Thin but constant rain all the time. It is this fact that explains why the Huygens landing was accompanied by a splash of methane mud. The amount of rain is equal to 50 mm per year (26). In a national observation from telescopes in Chile and Hawaii, they noticed for the first time a cloud with a global scope at high altitude that rains fine rain on the western slopes of the Xando region and that it rains in the morning hours and not always in the same area. This rain can reach the ground or become a misty vapor that dissipates shortly after dawn . In earthly terms this occurs 3 days after sunrise(20).

Large clouds of methane vapor create storms on the lunar surface. The hydrocarbon compounds play a role similar to that of water on Earth. According to calculations, these heavy clouds can reach a height of 35 km, create dense clouds of methane and be covered with precipitation of liquid drops of gaseous compounds similar to intense raindrops on Earth. It is these sediments that form accumulations and rivers of liquid methane observed by Cassini(27).

In addition to the methane rains, ethane rains were also found. A large cloud of ethane was found around the North Pole, which rains in this area. This ethane cloud was observed for the first time during the transit flights of the high northern latitudes in December 2004, August 2005 and September 2006. Based on these observations, they came to the conclusion that the ethane precipitation will be more common at the poles than on the entire moon. This is what can partially explain why there are no oceans and ethane clouds in the middle and low latitudes. Since it is now winter in the Northern Hemisphere, it seems that during this period it rains ethane and if the temperature is low enough, there is also ethane snow. In winter the methane lakes are enriched with ethane (21).

The totality of the data obtained regarding methane gave the researchers the impression that Titan has a methane cycle similar to the water cycle on Earth. The methane evaporates, cools, condenses and returns to the ground as rain and fills the liquid ground. It may also break out of the rocks to the surface. The methane cycles correspond to the seasons. In the winter the lakes expand and in the summer they shrink (13).

Sources

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2."BYU scientists leads discovery of mountains on Saturn's largest moon" 7.12.2007
http://byunewsbyu.edu/archive07-dec-titan.aspx

3.PIA09032:Titan's Sierras
http://photojournal.jpl.nasa.gov/catalog/ PIA09032

4.PIA09176: Ganesa Macula
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9.PIA09175:A new crater on Titan?
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10.PIA09846:Alien weather
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11.PIA10655: Impact craters
http://photojournal.jpl.nasa.gov/catalog/ PIA10655

12.PIA10018:Radar sees lakes in Titan's southern hemisphere
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14.PIA09183:Radar shows evidence of seas
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22."cassini images Mammoth cloud engulfing Titan's north pole" 2.2.2007
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25. Lakdawalla E.-"Titan's south pole pretty dry" 11.1.2008
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26. "Evidence strong that it rains on Titan" 28.7.2006

27.” A Titanic Methane cycle drives distant world” 2.8.2006
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