Titan – Part 3: Lakes

It turned out that in the Northern Hemisphere there are more reserves of liquid methane than in the Southern Hemisphere. Some of these lakes are very large

Comparing photographs of the South Pole taken in 2008 and those taken in 2007 revealed new lakes that were not observed in 2007. A comparison was also made between that part of the moon that always faces Saturn and the other side that is hidden from Saturn (Titan, similar to the Earth's moon, only shows one side of it to Saturn).

It turned out that in the Northern Hemisphere there are more reservoirs of liquid methane than in the Southern Hemisphere. Some of these lakes are very large. The area of ​​Kraken Mare in Milou reaches 400,000 square kilometers (1). The location of the lake is at W0 331-N 0 71. This is the first lake in which reflection of light was observed (2). Comparing with photographs taken in 2006, it became clear that the shoreline of the lake has been stable in terms of its area in the last 3 years. Along the drainage basins of the lake, deep cuts were found in the icy ground of Titan. Because of this, it was hypothesized that these hydrocarbon streams drain into lakes. Following these findings, it was concluded that liquid ethane filled a lake in the southern hemisphere (3).

On 22.5 several lakes in the northern hemisphere were photographed. Their width is 35-45 km each. They can be divided into two groups. Lakes filled with hydrocarbonate liquids and lakes which are only partially filled with these liquids or whose soil is saturated with liquids (4). From the set of findings regarding the lakes, the possibility of the existence of an underground reservoir of hydrocarbonate ocean was also raised (5). In the high latitudes is one of the largest lakes of the moon. This is Lake Mare Ligeia, whose area is larger than that of Lake Superior in the Great Lakes region of the USA (6).

In the observations made in 2009, it became clear that there is a larger reservoir of lakes in the North Pole than in the South Pole. At the equator the land surface is dry. There are no lakes in them and because in this area it rains a lot. Comparing observations made in 2005 and those made in 2009, it became clear that in this area there are channels cut by the flow of liquids, probably due to rains. The measurements made in 2009 show that following strong storms that were there, it started to rain in the dry areas. The obvious question is what caused the accumulation of lakes near the North Pole? According to an explanation given for this phenomenon, it has to do with the geometry of Saturn's orbit around the Sun.

Saturn's orbit is somewhat elongated and the meaning is that Titan is far from the sun when in the summer season the sunlight reaches the north pole. As a result the summer in the Northern Hemisphere is longer than the summer in the Southern Hemisphere. And it rains more since the summer is the rainy season and a bigger draw is longer and because of this there are more lakes in this pole (7).

Today there are a small number of lakes in the South Pole. 50,000 years ago the situation was reversed. There were few lakes in the North Pole and many lakes in the South. The largest lake in the South Pole is Lake Ontario (Ontario Lacus). A combination of photographs of the lake taken in July 2009 and January 2010 show that its dimensions are 235-80 km and its depth is at least 10 meters. Based on these photographs, the researchers came to the conclusion that in the past the lake was larger and its dimensions were 280-475 km (8). In another comparison made with photographs taken between June 2005 and July 2009, it became clear that during these 5 years the shoreline of the lake receded by 10 km until it reached the dimensions observed in 2009. The retreat in the coastline as well as in other lakes in this pole occurred due to seasonal evaporation of the liquid methane (9).

A dried out soil looks like a hard salt pan on the earth. Evidence was found in the photographs of the existence of long-lived channels connected to the bottom of the lake at its southern border. It is believed that the lake dried up and filled completely in previous years with hydrocarbon fluids that came from underground sources while exposing areas that have fluids surrounded by materials or muddy sand soil. In this way, the lake is reminiscent of the salt floor of Etoshia in Namibia, the bottom of a shallow water lake, the water in which comes from an underground source that rises to the surface during the rainy season. At the end of this season, the layer evaporates and leaves sediments on the ground like tide marks that show the limit of the spread of water in the previous season (10).

Contrary to predictions that lakes would only be found at the poles of Titan, lakes were also found at the equator in its tropical regions. The size of one of the lakes is like the Great Salt Lake in Utah, USA and is 1 meter deep. It is estimated that the source of the liquids is in an underground aquifer. In a sense Titan has oases and these lakes are stable in size over time. In the observations between 2004-2012 there was no change in them. In one of the observations, they noticed the rain, which after a while evaporated (11).

The analysis of the photographs taken between 2008-2011 raises the possibility that in the geological past there were large and shallow seas at the South Pole. One of these lakes is the previously mentioned Lake Ontario. A second lake that has not yet been named has dimensions of 280-485 km and is hundreds of meters deep. It seems that in the past there were large cycles of warming and cooling similar to those of the Earth and their origin is in the geometry of the Earth's orbit around the Sun. Such large time cycles can transport hydrocarbons from pole to pole. It is hypothesized that 50,000 years ago there were extensive lakes in the South Pole (12).

Sources
1. "Cassini finds Hydrocarbon rains may fill Titan lakes" 30.1.2009
http://www.saturndaily.com/reports/Cassini_Finds_Hydrocarbon_Rains_May_Fill _Titan_ Lakes_999.html
2. "Sunlight glints off liquid lake on Saturn's moon Titan" 18.12.2009
http://www.spaceflightnow.com/news/n0912/18titan
3. "A reflective surface of a lake on Saturn's moon Titan" 22.12.2009
http://www.saturndaily.com/reports/A_Reflective_Surface_Of_A_Lake_On Saturn_ Moon_ Titan_999.html
4. PIA16635: Different looks of Titan lakes
http://photojournal.jpl.nasa.gov/catalog/PIA16635
5. "Titan's tropy-turvy topography" 8.4.2009

http://www.saturndaily.com/reports/Titan_Tropy_Turvy_ topography
6. Mann A. – “Titan a wet world not far from Earth” 28.12.2011
http;//www.wiredcom/wiredscience/2011/12/titan-lake-rivers/
7. "New computer model explains lakes and storms on Titan" 5.1.2012
http://www.saturndaily.com/reports/New_Computer_Model_Explains_Lakes_Land _Storm_ On_ Titan_999.html
8. PIA16166: Outline of an ancient sea on Titan
http://photojournal.jpl.nasa.gov/catalog/PIA16166
9. "Caltech scientists measure changing lake depths on Titan" 16.7.2010
http://www.spacedaily.com/reports/Caltech_Scientists_Measure_Changing_Lake _Depths_On_Titan_999.html
10. "Cassini finds Titan lake is like a Namibia mudflat" 23.4.2012
http://www.spacedaily.com/reports/Cassini_finds_Titan_Isl_like_A_Namibia_ Mudflat_999.html
11. "Cassini sees tropical lakes on Saturn moon" 13.6.2012
http://saturn.jpl.nasa.gov/news/release/newsrelease20120613/
12. "What's baking on Titan?" 17.10.2012
http://www.spacedaily.com/reports/Whats_Baking_On_Titan_999.html