The Cassini spacecraft continues its endless journey around Saturn and with the abundant information transmitted from Titan, it slowly removes the curtain that covers it and allows us to view its face
The Cassini spacecraft continues its endless journey around Saturn and with the abundant information transmitted from Titan, it is slowly removing the curtain that covers it and allows us to observe it. To say that we understand what is happening there is certainly impossible, but the new information serves as an infrastructure for placing milestones for future research that will be done using telescopes and spacecraft and in particular In the first, space is given for new and challenging astronomical insights. These are no less important and perhaps the most important in terms of understanding the solar system and everything that awaits us around the corner.
The surface of Titan
In an overall look at the surface, one of the things that stands out is the significant difference between the side facing Saturn and the side hidden from it. It turns out that the hidden surface is more complex. The radar photographs do not make it possible to distinguish between natural landscape colors and the only thing that can testify to the shades of the various landscape items is their degree of brightness. It turned out that one side of Titan is brighter than the other, which raises the possibility that this material is permanent and not subject to weathering. It is estimated that this is methane ice (26.2.05: Mullen M. web). Is the material really not subject to weathering? It is hard to believe that this is indeed the way things are. It may be more resistant to weathering, but time still takes its toll. The weathering is only at a slower rate, which can indicate that it is "older" than everything around it .
A large area unit located mostly in the southern hemisphere resembles the shape of the letter H and its parts also received names within the Titan mapping framework. This unit is between latitudes Nº15-Sº20 and longitudes º90-º360
The northern and wide part of the formation was named Fensal and the southern and narrow part was named Aztalen. The formation on both sides is dark and within it are "islands" of light formations. In Fensal there are small islands with sizes between 5-40 km. It is estimated that they originate from the water ice raised above the surface surrounded by low land that originates from dark matter that comes from the atmosphere. A number of "islands" were also distinguished, one of them Buarato Facula and inside it there is probably a crater. Also in the southern wing of the formation there are several bright islands. The largest of them is called Sotra Facula and its dimensions are 120-240 km.
The number of craters that have been photographed so far is small, the largest of which appears in photograph 07365 PIA and inside it a crater with a diameter of 440 km and a number of smaller craters tens of kilometers long. In photograph 08425 PIA a similar configuration is visible to a crater, 90 km in diameter and named Guabonito and located northwest of the Xando area . The other craters are in descending order of diameter. The Sinlap crater that appears in photo 07368 PIA has a diameter of 60 km and its location is Wº16 Nº11 and there is no bulge in its center. In an infrared photograph, its floor is dark compared to the environment and this corresponds to the hypothesis that the dark material is probably made of complex hydrocarbons that probably originated from atmospheric precipitation and when they reached the ground flowed from the low places.
In photo 01429 PIA there is a crater with a diameter of 70 km and a relief in the center. At the bottom of the photo you can see another smaller crater and several channels indicating the flow of liquid. In photo 08426 PIA there is a crater with a diameter of 35 km and a dark material on its floor, the place of the photo is Shikoka Facula. As for volcanoes, so far no direct evidence of volcanic activity has been found and no formation of volcanoes has been observed, although it is possible that future observations of the Cassini will show. The assessment is that these are not known volcanoes like on Earth and Mars, but a different type of volcanic activity, cryovolcanism, water emission or a mixture of liquid water and ammonia.
A terrestrial phenomenon observed in many photographs is the formation of rivers. These formations are reminiscent of rivers on Earth, the probability gives place to the opinion that indeed in the past liquids flowed here, it is not flowing water, but liquid methane and the viscosity of this on Titan is 1/5 that of water on Earth. We will describe here photographs in which these formations are visible. Photo 07366 PIA Several channels are visible on the slopes of Circus Maximus, the largest of which is 200 km long. In photo 03555 PIA, you see formations of drainage basins that include winding channels 1-2 km wide and up to 200 km long. The formation of the drainage basin is related to a basin that is 450 km wide and part of its rim has undergone weathering. In photo 03564 PIA you see channels that are 1 km wide, 200 meters deep and some of them reach 200 km in length, some of them have angular sections originating from creases in the lunar crust. The high resolution of the photos makes it possible to sort the channels. In this photograph you see long valleys with many tributaries. The center of the photograph is at Nº 75-Sº53. In photo 03565 PIA you notice a dense network of channels, which can indicate rains. The center of this photograph is Nº14 – Sº48. Along with these rivers, long rivers were also found, the length of which reaches 1500 km (10.3.05: web "Cassini Images").
The amount of methane in Titan's atmosphere is 2% and the line of thought is that this methane reaches the ground as rain. It then evaporates and condenses back into the clouds, similar to the water cycle on Earth. The observations from the Cassini and the Huygens show that this was indeed the case in the past, except that no contemporary evidence of methane rain has been found. Proof from another direction of the correctness of this hypothesis is the invention of triangular slopes at the bottoms of canyons lined with pebbles several centimeters wide (9.9.05: Mckee M. web). Some of the photographs hint that Titan has a relief, although it is difficult to know what its height and its change are on a global scale. In photo 03566 PIA you see hills that are 100 km long and their origin is probably tectonic, a product of the folding of the moon's ice crust. The low areas between the hills are covered with dark spots, perhaps dunes. These spots are at intervals of 1-2 km from each other. In photo 08448PIA. In the Xandu area one sees a chain of hills or mountains lit from their northern side and in the intervals between them are extremely dark areas that may contain liquid. This liquid can be methane or ethane.
At the South Pole we see a dark spot that was and perhaps still is a lake of liquid hydrocarbonates. A possible corroboration for this hypothesis is the reality of what appears to be a coastline in its extent and the very fact that in this place a movement of
Cloud storm (in photo 06240 PIA the observed clouds are methane clouds).
The accumulation of photographs that came from Titan disproved the hypothesis that part of the surface is seas, as they thought, but rather dunes such as those found in the Arabian deserts or in Namibia (4.5.06: Stiles L. web) What contributed to disproving the seas hypothesis is the formation observed in these places "cat scratches" . Photographs in which this phenomenon is found are photograph 07009PIA which is located northeast of the Xando area, photograph 03555PIA Some of the dunes in this photograph are 500-1000 meters long, the spaces between them are 1-2 km and they are reminiscent of ice dunes in Antarctica, photograph 03568PIA which is located Wº292 - Sº10, photograph 03567PIA located At Wº300-Sº13. The interval between the dunes is 1-2 km and photo 08454PIA whose domain is between latitudes Sº18 - Nº7 and longitudes Wº320-Wº179. In radar images you see a series of dunes parallel to each other that are 100 meters high and hundreds of kilometers long. In the equatorial region, one dune field reaches a length of 1500 km. The shape of the dunes is linear, which is typical of the winds blowing from different directions. The tide causes the wind to change its direction towards the equator. When the tidal wind is with a local wind direction movement from west to east, dunes are created that are oriented west to east.
When you look at the dunes, the tidal winds can move sand around the moon several times and shape it into the shape of dunes at the equator. Tidal winds may transport dark sedimentary material from high latitudes to the equator, thus creating Titan's dark belt. The sand on Titan is somewhat rougher but less dense than the typical sand on Earth and Mars. The combination between the tidal winds and the equatorial wind in the west-east direction creates a land wind with a speed of 1.6 km/h.
Among the dunes there are those that bypass small mountains and rock formations as they move along Titan's equator in the same way that terrestrial dunes bypass obstacles.
atmosphere
The percentage of methane content in Titan's atmosphere is 2%, this is a high percentage. Methane belongs to the group of hydrocarbons and the diversity of those found in the high atmosphere of Titan such as Ethane - (C2H6) and Octane (C8H18) The discovery of these hydrocarbons was contrary to the accepted assumptions, since according to the accepted knowledge so far complex molecules cannot exist at low temperatures. The working assumption was that the nitrogen and methane components of the atmosphere produced large hydrocarbon molecules in response to sunlight (sunlight breaks down the methane and creates the large molecules) or to electromagnetic energy emitted from Saturn. Molecules reach the ground in the form of rain and here a new mystery emerged. What is the chemistry that creates hydrocarbons in the moon's atmosphere? Are we talking about similar processes that took place in the primordial atmosphere of the earth or are we talking about activity bustling with life on the ground (28.4.05: Baradelli P. web)? Other methane components found in the atmosphere are Propane (C3H8) and Acetylean (C2H2). Another gas found in the atmosphere and which is important in terms of the development of Titan's atmosphere is argon. The argon found here is argon 40, a gas that during its radioactive decay becomes krypton 40. The origin of the argon is the decay of potassium inside the planets which is later released to the surface. This means that Titan's atmosphere is not primordial but secondary (a secondary atmosphere is the one that comes from gases emitted from the interior of planets). The obvious conclusion is that when Titan solidified in the stages of its formation, it included among its components nitrogen and methane which were later emitted and created the atmosphere we know (8.10.05: MacKay C. web).
An isotopic test shows that the carbon 13C, 12C ratio in the atmosphere shows that there is a regular supply of methane to the atmosphere, possibly also biological, but there is still no evidence for this (28.2.05: Knight W. web). Several explanations are being tried for this high concentration of methane. One explanation focuses on clouds and according to which the presence and activity of most clouds is above the South Pole. It is estimated that this is where the methane cycle takes place: liquid methane seeps into the soil and evaporates into rain. A place where there is evidence of liquid methane is the landing site of the Huygens. Another explanation is vents in the ground from which the methane is emitted or volcanic sources emitting methane and indeed from earthly observations you can see large clouds coming from those methane vents (26.10.08: web "Cracks Or"). But here another question arises. Since no contemporary evidence of a liquid presence has been found, where did it come from anyway? It is estimated that the methane supply comes from ice rich in methane hydrate called Clathate Hydrogene which forms a crust over an ocean of water mixed with ammonia. Parts of the clathrate are broken from time to time by cryovolcanism releasing methane into the atmosphere. These gas bursts create temporary streams of liquid methane responsible for the river formations on the ground (1.3.06 : web "Does Titan"). The replenishment of the ice is on a cyclical basis.
climate
Since Titan's axis is also tilted like the Earth, the poles are also exposed to many hours of light or darkness, but here the process is slower for two reasons. One reason is that his day lasts 16 earthly days and his year is 30 earthly years, today winter prevails in the northern hemisphere. The observations show that there are significant temperature differences between the North Pole and the equator. Most likely, with the exposure of more parts of the surface, they will also find the connections between the topographic structure and the wind flow directions, and then try to understand in the most effective way as possible the structure of the moon's wind regime, an important contribution to this will be given with a better understanding of the dunes found on Titan. Summer temperatures bring cloud storms and rain to the South Pole and mean methane rains. The temperature on the ground is -178 C and at an altitude of 40 km it drops to -203 C. The atmospheric pressure on the ground is 1.5 bar and the average density of the atmosphere is 4 times higher than that of the Earth at sea level. Due to the thickness of the atmosphere there are no temperature differences at the equator between day and night. In photo 06204PIA sub-photo B there are spots that seem to have been created by winds moving from west to east. Evidence of an isolated polar vortex was found, similar to a parallel phenomenon on Earth. The observations show that strong winds moving around the North Pole insulate the atmosphere in place during the polar night. During these hours, the combination between the polar region and the lower regions of the atmosphere is inhibited. On Earth, the South Pole's atmosphere is isolated for months during the long Antarctic winter, thus enabling the formation of polar stratospheric clouds (12.5.05:web "Titans Atmosphere").
clouds
During the various flybys of Cassini near Titan, clouds were observed in different locations in the moon's atmosphere. In the passage made in October 2004 many clouds were seen near the South Pole. In December 2004, many clouds were seen in the mid-latitudes of the Southern Hemisphere and a few small clouds near the South Pole. Some of the clouds are 250 km long (photo 06157PIA). In an observation made in June 2005 (photo 07542PIA), several clouds were seen around the South Pole moving at a speed of several kilometers per hour. No clouds have been observed at the equator so far. Monitoring of 10 clouds showed a wind speed of 120 km/h, while the clouds rose from an altitude of 23 km to an altitude of 44 km at a speed of tens of meters per second, a new phenomenon was observed in them, which was given the name "abundant centers" "
(Vigorus Centers). At the end of their movement, the clouds dissipate or lose 10 km height for 30 minutes (9.9.05: McKee M. web). In the transit flight performed in December 2005, the clouds at the South Pole were particularly bright, while in the transits performed in October and January of the same year, the clouds were barely visible.
The Hexini observation of Titan's methane clouds was made in conjunction with terrestrial observations. Two telescopes were pointed at Titan for 82 nights. For 15 nights, 2 dozen bright clouds were observed in all middle latitudes in the southern hemisphere. The clouds usually dissipate the night after the observation night. In several night observations no clouds were seen the following night clouds were seen and the following night they disappeared. The length of some clouds reaches 2000 km. Although their exact height above the ground is unknown, it is estimated that their location above the lunar surface is between 10-35 km, within the lunar troposphere.
All the clouds in this observation were found in a relatively narrow band around the latitude Cº40 and most of them appear as clusters near the longitude º350. Their specific location and random appearance led the researchers to estimate that they are not the product of air currents resulting from heating by the sun (which creates the cover at the south pole of the moon), but that they are the product of some process on the ground, although it should be noted that other hypotheses have been put forward such as the rise of air over dark areas which absorb more heat from the sunlight, than bright areas or cloud formation as in the case of lightning on an earthly summer day. This hypothesis is problematic because no differences were found in the lightness of the soil at the latitude Sº 40. Another possibility is the increase in humidity through direct injection of methane into the atmosphere. This may be the most likely explanation (20.10.05: "Cracks Or" web).
At an altitude of 500 km above the surface, the moon is surrounded by a haze made of particles whose length is the length of ultraviolet waves - 338 nanometers. These particles scatter the sunlight more effectively in the direction opposite to the direction of the sunlight's movement. It is still not clear what caused the formation of this haze layer (8.11.05: web "Titans Ultraviolet"). At a lower altitude the haze becomes a fog of complex organic molecules. The color of the haze is an orange color and allows only 10% of the sunlight to reach the ground and we are unable to hold the infrared radiation and because of this the intensity of the greenhouse effect is much weaker than that of the earth, a phenomenon defined as the reverse greenhouse effect
(Anti-Greenhouse Effect) (4.11.05 : Field M. web).
discussion
The unveiling of Titan is similar to that done for the planet Venus. Both of these bodies are covered in clouds and there is no way to view their surface using sophisticated television cameras, however sophisticated they may be, and the proper way is to use radar images. This way turned out to be the most effective and the evidence for this is the Magellan spacecraft which allowed almost complete mapping of the surface of the planet Venus. Regarding Titan, the mapping will be partial and this is due to the way of work planned for the Cassini. Transit flights and directing its devices towards selected points. It is possible that in the future it will be necessary to launch a spacecraft that will be solely designed to focus on Titan. In any case, those parts of Titan's surface that are being exposed allow for a preliminary geological analysis and with careful use of extrapolation it will be possible to estimate what is happening in large parts of the surface.
If the very small number of craters discovered so far is a representative model of the complex of craters on Titan, then in this respect it quite resembles Venus. Here too, a small number of craters with a diameter of over 100 km in this case 2 and the rest of the craters are less than 100 km in diameter, the obvious question is where did the rest of the craters go. A possible explanation is that, like Venus, so also on Titan, volcanic activity renewed the surface. Lava that erupted from volcanoes or hot spots. In its flow it covered large areas including craters and those visible on the surface are new craters. The great crater, the rim of which is too high to allow lava to flow into it. But again a new problem arose. Although the Voyager photographs revealed very few craters with a diameter of hundreds of kilometers on the surface of Saturn's other moons, Cassini discovered more and more craters of this size on these moons, and hence it is likely that more craters of this size will be discovered on Titan. If this is indeed the case, is it possible that even in these craters you will find dunes (even though they have a different chemical composition) like the crater interior dunes that you find on Mars? Since very strong winds blow on Titan, these craters also undergo weathering resulting from erosion and erosion caused by the effect of dust carried by winds such as those found on the few craters found on Earth and the many craters of Mars.
Another form of landscape familiar to us from our world is rivers. Obviously water cannot flow on Titan. The temperatures are too low. The option they are thinking about is liquid methane. No evidence of methane flow was found in the locations photographed recently. These rivers, if that is the face of things, are dry rivers. When was it? Water at a pressure of one atmosphere freezes at Cº0 and boils at Cº100. The range of existence of water in liquid phase is quite wide. Methane freezes at Cº-183 and boils at Cº-164. Compared to water, the range of existence of liquid methane is very narrow. That is, any change greater than C º19 will result in large changes in the volume of liquid methane and an increase in its amount as vapors and clouds in the atmosphere. Is Titan subject to acute climatic changes and random or cyclical climatic instabilities and what causes this? Supporting evidence for these possibilities is the presence of propane, methane, octane and acetylene in the atmosphere. In order to understand what we are talking about, we will look at the following table:
Boiling temperature Gas melting temperature
-42.09 º C -187.6 º C propane
-88.6º C -182.76º C Ethane
125.5º C -57º C octane
-80º C -84º C Acetlane
According to the Kasini action plan, it still has two years of operation left. It's a lot of time. It is possible that, as in other space missions such as Galileo and the spacecraft operating around and on the surface of Mars, it will be possible to continue the journey of the spacecraft while setting new goals. An action plan worth considering is a long-term climate study of Titan as possible. An example of a possible program is the monitoring of explosives and the atmospheric location of hydrocarbons in the atmosphere since, based on the melting and boiling temperatures of the gases found in the atmosphere, it will be possible to draw isothermal maps of Titan, including dynamic mapping of vertical thermal changes of the atmosphere and to have another tool for monitoring the development and movement of winds on Titan.
In terms of the existence range of liquid methane on Titan, one must take into account the atmospheric pressure of Titan that is greater than that of the Earth. If, for example, on Earth the atmospheric pressure was like that on Titan, water would boil at a temperature higher than Cº100. The range of gases shown in the table is at a pressure of 1 atmosphere, so it must be taken into account that in Titan's atmosphere, the duration of their stability is higher. What does this mean? Any slight change in the average temperature on Titan will cause huge changes in the accumulation state of the methane. It will stop flowing in rivers immediately, or turn into a liquid, or evaporate. 3 reasons can cause these dramatic changes. The first reason is powerful volcanic eruptions that release hot currents coming from within the crust. A second reason is energy bursts from Saturn. It is known that Saturn emits more energy than it absorbs from the Sun. Any release of energy from Saturn can affect Titan's atmosphere and heat it up. The third reason is cyclical change, climatic changes like on Earth. When cyclical change is combined with random change for one of the other reasons, climate change is cataclysmic.
When climate change occurs, some of the methane evaporates, increasing the molecular methane content in the atmosphere and in this case, as on Earth, the humidity is high. In the opposite direction, the methane can freeze and accumulate on the ground. It would not be surprising to see ice glaciers sliding down mountain slopes and creating moraine effects. Another possibility is dry rivers. As a result of a cataclysmic change. Lakes or seas can dry up completely for extended periods as happened in the past in the Mediterranean Sea. This model allows daily monitoring of the planet's atmosphere and reaching several conclusions regarding the lifespan of methane rivers, lakes or oceans on Titan. Based on similarities to desertification processes on Earth such as in the Sahara.
Another means of examining climatic stability or instability is to examine the configuration of the rivers on Titan. The construction of rivers is a process that lasts thousands of years. The longer the life span of the liquid, the greater the likelihood of longer rivers forming. If we take an example from Israel, the time required for the development of the Jordan River is longer than that required for the development of the Yarkon. From this we can also learn something about the lifespan of methane rivers on Titan, and therefore many years of climatic stability can allow the development of rivers. This model is somewhat simplistic, but it allows more than a glimpse of knowledge of what is happening on the surface of Titan.
There is also room for comparison with the planet Venus. Both of these bodies have low axial velocities. Venus has an unusual day in that it is longer than his year. An hour that orbits the sun once in 225 days is 243 days. Its rotation speed around itself is 6.46 km/h and that of Titan is 41.7 km/h. That is, Titan moves faster around itself than Venus. Due to its short distance from Saturn, Titan shows only one side of its face. In both bodies, the high clouds surround them at a higher speed than the speed of their rotation around themselves. These data enable the performance of interesting comparative studies.
Summary
The discussion we opened to understand the phenomenon on Titan shows that it contains elements that exist on two other bodies in the solar system, namely the Earth and Venus. This is a new situation in terms of astronomical knowledge. No longer a comparison to one planet or another moon, but a comparison to two bodies. This comparison can open new and surprising research horizons, another moon that can be thought of with high probability with similar climatic characteristics is Neptune's moon Triton.
The numbers refer to the images found in
http://photojournal.jpl.nasa.gov/index.html
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