# Solar System, technical/Titan

Depending on the astronomy technique used to view Titan, it may appear differently.
Titan has a mean radius of 2576 ± 2 km.
Titan is the largest object of any type in orbit around Saturn with an atmospheric pressure on the surface 50% greater than that on Earth.

## Notation

Notation: let the symbol Def. indicate that a definition is following.
Notation: let the symbols between [ and ] be replacement for that portion of a quoted text.

## Universals

To help with definitions, their meanings and intents, there is the learning resource theory of definition.
Def. evidence that demonstrates that a concept is possible is called proof of concept.
The proof-of-concept structure consists of
* background,
* procedures,
* findings, and
* interpretation.
The findings demonstrate a statistically systematic change from the status quo or the control group.

## Skygazing

"The most distant bright planet that one can observe with the refracting telescope is Saturn. If the conditions of observation are good, it unveils the very beautiful spectacle of its rings. One can follow the change of their appearance. In 2002, they were seen at their widest angle and best presentation, and will be seen in profile in 2010. They will then completely invisible for a few days, after which they will again appear as a thin, bright line as the angle gradually increases once more. Meanwhile, their appearance changes from year to year. With experience it is also possible to distinguish the large moon Titan."

## Source astronomy

Titan is an orange source in orbit around Saturn. When is Titan in Cancer? "Saturn takes 29.5 years to orbit the Sun, spending about 2.46 years in each sign of the zodiac."

## Radiation

"As spring continues to unfold at Saturn, April showers on the planet's largest moon, Titan, have brought methane rain to its equatorial deserts ... Extensive rain from large cloud systems ... has apparently darkened the surface of the moon."
“It's amazing to be watching such familiar activity as rainstorms and seasonal changes in weather patterns on a distant, icy satellite".
"The Saturn system experienced equinox, when the sun lies directly over a planet's equator and seasons change, in August 2009. (A full Saturn “year” is almost 30 Earth years.)"
"Clouds on Titan are formed of methane as part of an Earth-like cycle that uses methane instead of water. On Titan, methane fills lakes on the surface, saturates clouds in the atmosphere, and falls as rain. Though there is evidence that liquids have flowed on the surface at Titan's equator in the past, liquid hydrocarbons, such as methane and ethane, had only been observed on the surface in lakes at polar latitudes. The vast expanses of dunes that dominate Titan's equatorial regions require a predominantly arid climate."
"An arrow-shaped storm appeared in the equatorial regions on Sept. 27, 2010 -- the equivalent of early April in Titan's “year” -- and a broad band of clouds appeared the next month. ... A 193,000-square-mile (500,000-square-kilometer) region along the southern boundary of Titan’s Belet dune field, as well as smaller areas nearby, had become darker. ... this change in brightness is most likely the result of surface wetting by methane rain."
“These outbreaks may be the Titan equivalent of what creates Earth's tropical rainforest climates, even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of Earth's behavior over the tropical oceans than over tropical land areas”.
At right is an image that shows clouds over the equatorial region of Titan.
"Methane clouds in the troposphere, the lowest part of the atmosphere, appear white here and are mostly near Titan's equator. The darkest areas are surface features that have a low albedo, meaning they do not reflect much light. Cassini observations of clouds like these provide evidence of a seasonal shift of Titan's weather systems to low latitudes following the August 2009 equinox in the Saturnian system. (During equinox, the sun lies directly over the equator. See PIA11667 to learn how the sun's illumination of the Saturnian system changed during the equinox transition to spring in the northern hemispheres and to fall in the southern hemispheres of the planet and its moons.)"
"In 2004, during Titan's late southern summer, extensive cloud systems were common in Titan's south polar region (see PIA06110, PIA06124 and PIA06241). Since 2005, southern polar systems have been observed infrequently, and one year after the equinox, extensive near-equatorial clouds have been seen. This image was taken on Oct. 18, 2010, a little more than one Earth year after the Saturnian equinox, which happens once in roughly 15 Earth years."
"The cloud patterns observed from late southern summer to early southern fall on Titan suggest that Titan's global atmospheric circulation is influenced by both the atmosphere and the surface. The temperature of the surface responds more rapidly to changes in illumination than does the thick atmosphere. Outbreaks such as the clouds seen here may be the Titan equivalent of what creates the Earth's tropical rainforest climates, even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of the behavior over Earth's tropical oceans than over tropical land areas."
"A few clouds can be seen in Titan's southern latitudes here. See PIA12813 for a movie of clouds moving through the middle southern latitudes of Titan. Some clouds are also visible in the high northern latitudes here. See PIA12811 and PIA12812 for movies showing clouds near the moon's north pole. This view looks toward the Saturn-facing side of Titan (5,150 kilometers or 3,200 miles across). North is up. The image appears slightly grainy because it was re-projected to a scale of 6 kilometers (4 miles) per pixel. Scale in the original image was 15 kilometers (9 miles) per pixel. This view consists of an average of three images taken using a filter sensitive to near-infrared light centered at 938 nanometers, which allows for detection of Titan's surface and lower atmosphere, plus an image taken using a filter sensitive to visible light centered at 619 nanometers. The images were taken with the Cassini spacecraft's narrow-angle camera at a distance of approximately 2.5 million kilometers (1.6 million miles) from Titan and at a sun-Titan-spacecraft, or phase, angle of 56 degrees."

## Planetary science

Titan like Venus is another gas dwarf when viewed in visible light. "Much as with Venus prior to the Space Age, the dense, opaque atmosphere prevented understanding of Titan's surface until new information accumulated with the arrival of the Cassini–Huygens mission in 2004, including the discovery of liquid hydrocarbon lakes in the ... polar regions."
It is larger by volume than Mercury.
Seasonal changes in the atmosphere of Saturn's largest moon Titan are captured in this natural colour image at right. It shows Titan with a slightly darker top half and a slightly lighter bottom half. Titan's atmosphere has a seasonal hemispheric dichotomy, and this image was taken shortly after Saturn's August 2009 equinox. Images taken using red, green and blue spectral filters were combined to create this natural colour view. The winter hemisphere typically appears to have more high-altitude haze, making it darker at shorter wavelengths (ultraviolet through blue) and brighter at infra-red wavelengths. The switch between dark and bright occurs over the course of a year or two around the last equinox. Scientists are studying the mechanism responsible for this change, and will monitor the dark-light difference as it flip-flops now that the 2009 equinox has signalled the coming of spring and then summer in the northern hemisphere. Although this hemispheric boundary appears to run directly east-west near the equator, its position is not level with latitude and is actually offset from the equator by about 10 degrees. This view looks toward the Saturn-facing side of Titan (5150 kilometres across). North on Titan is up. The images were obtained with the Cassini spacecraft wide-angle camera at a distance of approximately 174,000 kilometres from Titan.
"The atmosphere of Titan is largely composed of nitrogen; minor components lead to the formation of methane and ethane clouds and nitrogen-rich organic smog."
There is clear evidence that Titan has stable bodies of surface liquid.
"Titan is primarily composed of water ice and rocky material." "[M]ountains and several possible cryovolcanoes have been discovered". The surface "is smooth and few impact craters have been found."
"The climate—including wind and rain—creates surface features similar to those of Earth, such as sand dunes, rivers, lakes and seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan's methane cycle is viewed as an analog to Earth's water cycle, although at a much lower temperature."

## Meteor astronomy

"These mosaics [at right] of the south pole of Saturn's moon Titan, made from images taken almost one year apart, show changes in dark areas that may be lakes filled by seasonal rains of liquid hydrocarbons."
"The images on the left (unlabeled at top and labeled at bottom) were acquired July 3, 2004. Those on the right were taken June 6, 2005. In the 2005 images, new dark areas are visible and have been circled in the labeled version. The very bright features are clouds in the lower atmosphere (the troposphere). Titan's clouds behave similarly to those on Earth, changing rapidly on timescales of hours and appearing in different places from day to day. During the year that elapsed between these two observations, clouds were frequently observed at Titan's south pole by observers on Earth and by Cassini's imaging science subsystem (see PIA06124)."
"It is likely that rain from a large storm created the new dark areas that were observed in June 2005. Some features, such as Ontario Lacus, show differences in brightness between the two observations that are the result of differences in illumination between the two observations. These mosaics use images taken in infrared light at a wavelength of 938 nanometers. The images have been oriented with the south pole in the center (black cross) and the 0 degree meridian toward the top. Image resolutions are several kilometers (several miles) per pixel."

## Optical astronomy

"This image [at right] shows Titan in ultraviolet and infrared wavelengths. It was taken by Cassini's imaging science subsystem on Oct. 26, 2004, and is constructed from four images acquired through different color filters. Red and green colors represent infrared wavelengths and show areas where atmospheric methane absorbs light. These colors reveal a brighter (redder) northern hemisphere. Blue represents ultraviolet wavelengths and shows the high atmosphere and detached hazes."
"Titan has a gigantic atmosphere, extending hundreds of kilometers above the surface. The sharp variations in brightness on Titan's surface (and clouds near the south pole) are apparent at infrared wavelengths. The image scale of this picture is 6.4 kilometers (4 miles) per pixel."
"This [second image at right] shows the first flash of sunlight reflected off a hydrocarbon lake on Saturn's moon Titan. The glint off a mirror-like surface is known as a specular reflection. This kind of glint was detected by the visual and infrared mapping spectrometer (VIMS) on NASA's Cassini spacecraft on July 8, 2009. It confirmed the presence of liquid in the moon's northern hemisphere, where lakes are more numerous and larger than those in the southern hemisphere. Scientists using VIMS had confirmed the presence of liquid in Ontario Lacus, the largest lake in the southern hemisphere, in 2008."
"The northern hemisphere was shrouded in darkness for nearly 15 years, but the sun began to illuminate the area again as it approached its spring equinox in August 2009. VIMS was able to detect the glint as the viewing geometry changed. Titan's hazy atmosphere also scatters and absorbs many wavelengths of light, including most of the visible light spectrum. But the VIMS instrument enabled scientists to look for the glint in infrared wavelengths that were able to penetrate through the moon's atmosphere. This image was created using wavelengths of light in the 5 micron range."
"By comparing the new image to radar and near-infrared light images acquired from 2006 to 2008, Cassini scientists were able to correlate the reflection to a lake, later named Jingpo Lacus, near the western shores of the sea known as Kraken Mare. Jingpo Lacus covers an area of 20,800 square kilometers (8,000 square miles). The reflection appeared to come from a part of the lake near 71 degrees north latitude and 337 degrees west longitude."
"It was taken on Cassini's 59th flyby of Titan on July 8, 2009, at a distance of about 200,000 kilometers (120,000 miles). The image resolution was about 100 kilometers (60 miles) per pixel. Image processing was done at the German Aerospace Center in Berlin and the University of Arizona in Tucson."

## Violet astronomy

At right is an image of Titan showing a purple haze.
"With its thick, distended atmosphere, Titan's orange globe shines softly, encircled by a thin halo of purple light-scattering haze."
"Small particles that populate high hazes in Titan's atmosphere scatter short wavelengths more efficiently than longer visible or infrared wavelengths, so the best possible observations of the detached layer are made in ultraviolet light."
"The images in this view were taken by the Cassini narrow-angle camera on May 5, 2005, at a distance of approximately 1.4 million kilometers (900,000 miles) from Titan and at a sun-Titan-spacecraft, or phase, angle of 137 degrees. Image scale is 8 kilometers (5 miles) per pixel."

## Blue astronomy

At right is an image of the blue haze layer near the south polar region of Titan. "The moon's high altitude haze layer appears blue here whereas the main atmospheric haze is orange. The difference in color could be due to particle size of the haze. The blue haze likely consists of smaller particles than the orange haze."
"The depressed or attenuated layer appears in the transition area between the orange and blue hazes about a third of the way in from the left edge of the narrow-angle image. The moon's south pole is in the upper right of this image."
"The southern pole of Titan is going into darkness as the sun advances towards the north with each passing day. The upper layer of Titan's hazes is still illuminated by sunlight."
"Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained on Sept. 11, 2011 at a distance of approximately 83,000 miles (134,000 kilometers) from Titan. Image scale is 2,581 feet (787 meters) per pixel."

## Orange astronomy

"Much as with Venus prior to the Space Age, the dense, opaque atmosphere prevented understanding of Titan's surface until new information accumulated with the arrival of the Cassini–Huygens mission in 2004, including the discovery of liquid hydrocarbon lakes in the ... polar regions."
"The atmosphere of Titan is largely composed of nitrogen; minor components lead to the formation of methane and ethane clouds and nitrogen-rich organic smog."
"With its thick, distended atmosphere, Titan's orange globe shines softly".

## Infrared astronomy

"[N]ear-infrared spectrum clearly exhibited a methane absorption band at 2 micrometres, a feature ... observed in gas giant atmospheres and the atmosphere of Saturn's moon, Titan."
"This mosaic [at right] of Titan's surface was made from 16 images. The individual images have been specially processed to remove effects of Titan's hazy atmosphere and to improve visibility of the surface near the terminator (the boundary between day and night)."
"During Cassini's first close flyby of Titan in October 2004, many clouds were seen near the south pole; in the December flyby many clouds were seen at mid-latitudes (see PIA06157). During this flyby, only a few small clouds near the south pole were noted."
"Imaging coverage during this flyby included improved looks at territory to the north and west of Xanadu, the large bright white area."
"The images were taken with the Cassini spacecraft narrow angle camera through a filter sensitive to wavelengths of polarized infrared light and were acquired at distances ranging from approximately 226,000 to 242,000 kilometers (140,000 to 150,000 miles) from Titan. Resolution in the images is about 1.3 kilometers (0.8 miles) per pixel."

## Radio astronomy

"The Permittivity, Waves and Altimetry (PWA) sensor on the Huygens Atmosphere Structure Instrument (HASI) detected an extremely low frequency (ELF) radio wave during the descent. It was oscillating very slowly for a radio wave, just 36 times a second, and increased slightly in frequency as the probe reached lower altitudes."

## Radar astronomy

Radar detection of Titan "from Arecibo Observatory, [included] mapping of Titan's surface".
"This Cassini false-color mosaic [at right] shows all synthetic-aperture radar images to date of Titan's north polar region. Approximately 60 percent of Titan's north polar region, above 60 degrees north latitude, is now mapped with radar. About 14 percent of the mapped region is covered by what is interpreted as liquid hydrocarbon lakes."
"Features thought to be liquid are shown in blue and black, and the areas likely to be solid surface are tinted brown. The terrain in the upper left of this mosaic is imaged at lower resolution than the remainder of the image".
"Most of the many lakes and seas seen so far are contained in this image, including the largest known body of liquid on Titan. These seas are most likely filled with liquid ethane, methane and dissolved nitrogen."
"Many bays, islands and presumed tributary networks are associated with the seas. The large feature in the upper right center of this image is at least 100,000 square kilometers (40,000 square miles) in area, greater in extent than Lake Superior (82,000 square kilometers or 32,000 square miles), one of Earth's largest lakes. This Titan feature covers a greater fraction of the surface, at least 0.12 percent, than the Black Sea, Earth's largest terrestrial inland sea, at 0.085 percent. Larger seas may exist, as it is probable that some of these bodies are connected, either in areas unmapped by radar or under the surface (see PIA08365)."
"Of the 400 observed lakes and seas, 70 percent of their area is taken up by large "seas" greater than 26,000 square kilometers (10,000 square miles)."
In the second image at right is another radar image of Titan's surface. "The existence of oceans or lakes of liquid methane on Saturn's moon Titan was predicted more than 20 years ago. But with a dense haze preventing a closer look it has not been possible to confirm their presence. Until the Cassini flyby of July 22, 2006, that is."
"Radar imaging data from the flyby, published this week in the journal Nature, provide convincing evidence for large bodies of liquid. This image, used on the journal's cover, gives a taste of what Cassini saw. Intensity in this colorized image is proportional to how much radar brightness is returned, or more specifically, the logarithm of the radar backscatter cross-section. The colors are not a representation of what the human eye would see."
"The lakes, darker than the surrounding terrain, are emphasized here by tinting regions of low backscatter in blue. Radar-brighter regions are shown in tan. The strip of radar imagery is foreshortened to simulate an oblique view of the highest latitude region, seen from a point to its west."
"This radar image was acquired by the Cassini radar instrument in synthetic aperture mode on July 22, 2006. The image is centered near 80 degrees north, 35 degrees west and is about 140 kilometers (84 miles) across. Smallest details in this image are about 500 meters (1,640 feet) across."

## Atmospheric astronomy

"This natural color image [at right] shows Titan's upper atmosphere -- an active place where methane molecules are being broken apart by solar ultraviolet light and the byproducts combine to form compounds like ethane and acetylene. The haze preferentially scatters blue and ultraviolet wavelengths of light, making its complex layered structure more easily visible at the shorter wavelengths used in this image."
"Lower down in the atmosphere, the haze turns into a globe-enshrouding smog of complex organic molecules. This thick, orange-colored haze absorbs visible sunlight, allowing only perhaps 10 percent of the light to reach the surface. The thick haze is also inefficient at holding in and then re-radiating infrared (thermal) energy back down to the surface. Thus, despite the fact that Titan has a thicker atmosphere than Earth, the thick global haze causes the greenhouse effect there to be somewhat weaker than it is on Earth."
"Images taken with the Cassini spacecraft wide-angle camera using red, green and blue spectral filters were combined to create this natural color view. The images were obtained at a distance of approximately 9,500 kilometers (5,900 miles) from Titan on March 31, 2005. The image scale is approximately 400 meters (1,300 feet) per pixel."
The second image at right is of the south pole.
"What's happening over the south pole of Titan? A vortex of haze appears to be forming, although no one is sure why. The [second at right] natural-color image shows the light-colored feature. The vortex was found on images taken last month when the robotic Cassini spacecraft flew by the unusual atmosphere-shrouded moon of Saturn. Cassini was only able to see the southern vortex because its orbit around Saturn was recently boosted out of the plane where the rings and moons move. Clues as to what created the enigmatic feature are accumulating, including that Titan's air appears to be sinking in the center and rising around the edges. Winter, however, is slowly descending on the south of Titan, so that the vortex, if it survives, will be plunged into darkness over the next few years."

## Crater astronomy

"This radar image [at right] of Titan shows a semi-circular feature that may be part of an impact crater. Very few impact craters have been seen on Titan so far, implying that the surface is young. Each new crater identified on Titan helps scientists to constrain the age of the surface."
"Taken by Cassini's radar mapper on Jan. 13, 2007, during a flyby of Titan, the image swath revealed what appeared to be the northernmost half of an impact crater. This crater is roughly 180 kilometers (110 miles) wide. Only three impact craters have been identified on Titan and several others, like this one, are likely to also have been caused by impact. The bright material is interpreted to be part of the crater’s ejecta blanket, and is likely topographically higher than the surrounding plains. The inner part of the crater is dark, and may represent smooth deposits that have covered the inside of the crater."
"This image was taken in synthetic aperture mode and has a resolution of approximately 350 meters (1,150 feet). North is toward the top left corner of the image, which is approximately 240 kilometers (150 miles) wide by 140 kilometers (90 miles) high. The image is centered at about 26.5 degrees north and 9 degrees west."
The second image at right may show a cryovolcano.
"This high-resolution infrared image was taken during the Cassini spacecraft's closest approach to Titan on Oct. 26, 2004. These images were obtained by Cassini's visual and infrared mapping spectrometer instrument and show a bright, circular feature (8.5 degrees latitude, minus 143.5 degrees longitude) with two elongated wings extending westwards. Scientists think this feature might be a volcano."
"The resolution in the image varies from 2.6 kilometers (1.6 miles) per pixel to 1.8 kilometers (1.1 miles) per pixel."
The third image at right is of a feature around a high peak called Doom Mons.
"Scientists have named the highest peak in this area Doom Mons, after a volcano that appears in J.R.R. Tolkien's fiction, and the depression next to it Sotra Patera. Scientists believe this region makes the best case yet for an ice volcano -- or cryovolcano -- region on Titan. The flyover shows two peaks more than 1,000 meters (3,000 feet) tall. Doom Mons is estimated to stand about 1,450 meters (4,760 feet) high, with a diameter of about 70 kilometers (40 miles). Multiple craters can also be seen, including Sotra Petera, which is about 1,700 meters (5,600 feet) deep and 30 kilometers (20 miles) wide. The region also features finger-like flows, named Mohini Fluctus. All of these are land features that indicate cryovolcanism. The 3-D topography comes from Cassini's radar instrument. Topography has been vertically exaggerated by a factor of 10. The false color in the initial frames shows different compositions of surface material as detected by Cassini's visual and infrared mapping spectrometer. In this color scheme, dunes tend to look relatively brown-blue. Blue suggests the presence of some exposed ice. Scientists think the bright areas have an organic coating that hides the ice and is different and lighter than the dunes. The finger-like flows appear bright yellowish-white, like the mountain and caldera. The second set of colors shows elevation, with blue being lowest and yellow and white being the highest. Dunes here appear blue because they tend to occupy low areas. The finger-like flows are harder to see in the elevation data, indicating that they are thin, maybe less than about 100 meters (300 feet) thick."

## Geography

"These updated maps of Saturn's moon Titan [at right], consisting of data from the Cassini imaging science subsystem, include Cassini's August 2008 imaging of the moon's northern hemisphere."
"Evidence from Cassini's imaging science subsystem, radar, and visual and infrared mapping spectrometer instruments strongly suggests that dark areas near the poles are lakes of liquid hydrocarbons-an analysis affirmed by images capturing those changes in the lakes thought to be brought on by rainfall."
"Colored lines in the polar portions of these maps illustrate the boundaries between surface regions having different albedos— or differences in surface brightness—which Cassini scientists have interpreted as potential shorelines. Blue outlines indicate features that changed between observations made one year apart (see PIA11147)."
"Atmospheric effects complicate incorporation of data from high northern latitudes, which are shown separately in a polar view. The map at bottom left is a north polar projection showing latitudes 55 degrees to 90 degrees. The bottom right map is a south polar projection showing latitudes minus 55 degrees to minus 90 degrees."
"The maps are compiled from images dating from April 2004 through August 2008, and their resolutions vary from a few meters to a few tens of kilometers per pixel. Brightness variations are due to differences in surface albedo rather than topographic shading."

## Rocky-object rocketry

"Cassini–Huygens is ... NASA-ESA-ASI robotic spacecraft sent to the Saturn system. ... It launched on October 15, 1997 on a Titan IVB/Centaur and entered into orbit around Saturn on July 1, 2004 ... On December 25, 2004, Huygens separated from the orbiter at approximately 02:00 UTC. It reached Saturn's moon Titan on January 14, 2005, when it entered Titan's atmosphere and descended downward to the surface. It successfully returned data to Earth, using the orbiter as a relay."
"Cassini released the Huygens probe on December 25, 2004, by means of a spring and spiral rails intended to rotate the probe for greater stability. It entered the atmosphere of Titan on January 14, 2005, and after a two-and-a-half-hour descent landed on solid ground. Although Cassini successfully relayed 350 of the pictures that it received from Huygens of its descent and landing site, a software error failed to turn on one of the Cassini receivers and caused the loss of the other 350 pictures."