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Titan (moon)

Titan is the largest moon of Saturn and the second-largest in the Solar System. It is the only moon known to have an atmosphere denser than the Earth's and is the only known object in space—other than Earth—on which clear evidence of stable bodies of surface liquid has been found. Titan is one of seven gravitationally rounded moons of Saturn and the second-most distant among them. Frequently described as a planet-like moon, Titan is 50% larger in diameter than Earth's Moon and 80% more massive. It is the second-largest moon in the Solar System after Jupiter's Ganymede and is larger than Mercury, but only 40% as massive due to the latter being composed mainly of dense iron and rock, while a large portion of Titan is less-dense ice.

Discovered in 1655 by the Dutch astronomer Christiaan Huygens, Titan was the first known moon of Saturn and the sixth known planetary satellite (after Earth's moon and the four Galilean moons of Jupiter). Titan orbits Saturn at 20 Saturn radii or 1,200,000 km above Saturn's apparent surface. From Titan's surface, Saturn subtends an arc of 5.09 degrees, and if it were visible through the moon's thick atmosphere, it would appear 11.4 times larger in the sky, in diameter, than the Moon from Earth, which subtends 0.48° of arc.

Titan is primarily composed of ice and rocky material, with a rocky core surrounded by various layers of ice, including a crust of ice Ih and a subsurface layer of ammonia-rich liquid water. Much as with Venus before the Space Age, the dense opaque atmosphere prevented understanding of Titan's surface until the Cassini–Huygens mission in 2004 provided new information, including the discovery of liquid hydrocarbon lakes in Titan's polar regions and the discovery of its atmospheric super-rotation. The geologically young surface is generally smooth, with few impact craters, although mountains and several possible cryovolcanoes have been found.

The atmosphere of Titan is mainly nitrogen and methane; minor components lead to the formation of hydrocarbon clouds and heavy organonitrogen haze. Its climate—including wind and rain—creates surface features similar to those of Earth, such as dunes, rivers, lakes, 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 nearly resembles Earth's water cycle, albeit at a much lower temperature of about 94 K. Due to these factors, Titan is called the most Earth-like celestial object in the Solar System.

Discovery and naming

The Dutch astronomer Christiaan Huygens discovered Titan on March 25, 1655. Fascinated by Galileo's 1610 discovery of Jupiter's four largest moons and his advancements in telescope technology, Huygens, with the help of his elder brother Constantijn Huygens Jr., began building telescopes around 1650 and discovered the first observed moon orbiting Saturn with one of the telescopes they built.

Huygens named his discovery Saturni Luna (or Luna Saturni, Latin for "moon of Saturn"), publishing in the 1655 tract De Saturni Luna Observatio Nova (A New Observation of Saturn's Moon). After Giovanni Domenico Cassini published his discoveries of four more moons of Saturn between 1673 and 1686, astronomers began referring to these and Titan as Saturn I through V (with Titan then in fourth position). Other early epithets for Titan include "Saturn's ordinary satellite." The International Astronomical Union officially numbers Titan as "Saturn VI."

The name Titan, and the names of all seven satellites of Saturn then known, came from John Herschel (son of William Herschel, discoverer of two other Saturnian moons, Mimas and Enceladus), in his 1847 publication Results of Astronomical Observations Made during the Years 1834, 5, 6, 7, 8, at the Cape of Good Hope. Numerous small moons have been discovered around Saturn since then. Saturnian moons are named after mythological giants. The name Titan comes from the Titans, a race of immortals in Greek mythology.

Formation
The regular moons of Jupiter and Saturn probably formed through co-accretion, a similar process to that believed to have formed the planets in the Solar System. As the young gas giants formed, they were surrounded by discs of material that gradually coalesced into moons. Whereas Jupiter possesses four large satellites in highly regular, planet-like orbits, Titan overwhelmingly dominates Saturn's system and has a high orbital eccentricity not immediately explained by co-accretion alone. A proposed model for the formation of Titan is that Saturn's system began with a group of moons similar to Jupiter's Galilean satellites, but that they were disrupted by a series of giant impacts, which would go on to form Titan. Saturn's mid-sized moons, such as Iapetus and Rhea, were formed from the debris of these collisions. Such a violent beginning would also explain Titan's orbital eccentricity. A 2014 analysis of Titan's atmospheric nitrogen suggested that it was possibly sourced from material similar to that found in the Oort cloud and not from sources present during the co-accretion of materials around Saturn.

Orbit and rotation
Titan orbits Saturn once every 15 days and 22 hours. Like Earth's Moon and many of the satellites of the giant planets, its rotational period (its day) is identical to its orbital period; Titan is tidally locked in synchronous rotation with Saturn, and permanently shows one face to the planet. Longitudes on Titan are measured westward, starting from the meridian passing through this point. Its orbital eccentricity is 0.0288, and the orbital plane is inclined 0.348 degrees relative to the Saturnian equator, hence also about a third of a degree off of the equatorial ring plane.

The small and irregularly shaped satellite Hyperion is locked in a 3:4 orbital resonance with Titan—that is, Hyperion orbits three times for every four times Titan orbits. Hyperion probably formed in a stable orbital island, whereas the massive Titan absorbed or ejected any other bodies that made close approaches.

Bulk characteristics
Titan is 5149.46 km in diameter, 1.06 times that of the planet Mercury, 1.48 that of the Moon, and 0.40 that of Earth. Titan is the tenth-largest object in the solar system, including the Sun. Before the arrival of Voyager 1 in 1980, Titan was thought to be slightly larger than Ganymede, which has a diameter 5262 km, and thus the largest moon in the Solar System. This was an overestimation caused by Titan's dense, opaque atmosphere, with a haze layer 100-200 kilometers above its surface. This increases its apparent diameter. Titan's diameter and mass (and thus its density) are similar to those of the Jovian moons Ganymede and Callisto. Based on its bulk density of 1.88 g/cm3, Titan's composition is half ice and half rocky material. Though similar in composition to Dione and Enceladus, it is denser due to gravitational compression.

Titan is probably partially differentiated into distinct layers with a 3400 km rocky center. This rocky center is believed to be surrounded by several layers composed of different crystalline forms of ice, and/or water. The exact structure depends heavily on the heat flux from within Titan itself, which is poorly constrained. The interior may still be hot enough for a liquid layer consisting of a "magma" composed of water and ammonia between the ice Ih crust and deeper ice layers made of high-pressure forms of ice. The heat flow from inside Titan may even be too high for high pressure ices to form, with the outermost layers instead consisting primarily of liquid water underneath a surface crust. The presence of ammonia allows water to remain liquid even at a temperature as low as 176 K (for eutectic mixture with water). The Cassini probe discovered evidence for the layered structure in the form of natural extremely-low-frequency radio waves in Titan's atmosphere. Titan's surface is thought to be a poor reflector of extremely-low-frequency radio waves, so they may instead be reflecting off the liquid–ice boundary of a subsurface ocean. Surface features were observed by the Cassini spacecraft to systematically shift by up to 30 km between October 2005 and May 2007, which suggests that the crust is decoupled from the interior, and provides additional evidence for an interior liquid layer. Further supporting evidence for a liquid layer and ice shell decoupled from the solid core comes from the way the gravity field varies as Titan orbits Saturn. Comparison of the gravity field with the RADAR-based topography observations also suggests that the ice shell may be substantially rigid.

Atmosphere
Titan is one of two known moons with a significant atmosphere, with Triton hosting the other, and its atmosphere is the only nitrogen-rich dense atmosphere in the Solar System aside from Earth's. Observations of it made in 2004 by Cassini suggest that Titan is a "super rotator", like Venus, with an atmosphere that rotates much faster than its surface. Observations from the Voyager space probes have shown that Titan's atmosphere is denser than Earth's, with a surface pressure about 1.45 atm. It is also about 1.19 times as massive as Earth's overall, or about 7.3 times more massive on a per surface area basis. Opaque haze layers block most visible light from the Sun and other sources and obscure Titan's surface features. Titan's lower gravity means that its atmosphere is far more extended than Earth's. The atmosphere of Titan is opaque at many wavelengths and as a result, a complete reflectance spectrum of the surface is impossible to acquire from orbit. It was not until the arrival of the Cassini–Huygens spacecraft in 2004 that the first direct images of Titan's surface were obtained.

Titan's atmospheric composition is nitrogen (97%), methane (2.7±0.1%), and hydrogen (0.1–0.2%), with trace amounts of other gases. There are trace amounts of other hydrocarbons, such as ethane, diacetylene, methylacetylene, acetylene, and propane; and of other gases, such as cyanoacetylene, hydrogen cyanide, carbon dioxide, carbon monoxide, cyanogen, argon, and helium. The hydrocarbons are thought to form in Titan's upper atmosphere in reactions resulting from the breakup of methane by the Sun's ultraviolet light, producing a thick orange smog. Titan spends 95% of its time within Saturn's magnetosphere, which may help shield it from the solar wind.

Energy from the Sun should have converted all traces of methane in Titan's atmosphere into more complex hydrocarbons within 50 million years—a short time compared to the age of the Solar System. This suggests that methane must be replenished by a reservoir on or within Titan itself. The ultimate origin of the methane in its atmosphere may be its interior, released via eruptions from cryovolcanoes. On April 3, 2013, NASA reported that complex organic chemicals, collectively called tholins, likely arise on Titan, based on studies simulating the atmosphere of Titan.

On June 6, 2013, scientists at the IAA-CSIC reported the detection of polycyclic aromatic hydrocarbons in the upper atmosphere of Titan.

On September 30, 2013, propene was detected in the atmosphere of Titan by NASA's Cassini spacecraft, using its composite infrared spectrometer (CIRS). This is the first time propene has been found on any moon or planet other than Earth and is the first chemical found by the CIRS. The detection of propene fills a mysterious gap in observations that date back to NASA's Voyager 1 spacecraft's first close planetary flyby of Titan in 1980, during which it was discovered that many of the gases that make up Titan's brown haze were hydrocarbons, theoretically formed via the recombination of radicals created by the Sun's ultraviolet photolysis of methane.

On October 24, 2014, methane was found in polar clouds on Titan. On December 1, 2022, astronomers reported viewing clouds, likely made of methane, moving across Titan, using the James Webb Space Telescope.

Climate
Titan's surface temperature is about 94 K. At this temperature, water ice has an extremely low vapor pressure, so the little water vapor present appears limited to the stratosphere. Titan receives about 1% as much sunlight as Earth. Before sunlight reaches the surface, about 90% has been absorbed by the thick atmosphere, leaving only 0.1% of the amount of light Earth receives.

Atmospheric methane creates a greenhouse effect on Titan's surface, without which Titan would be much colder. Conversely, haze in Titan's atmosphere contributes to an anti-greenhouse effect by absorbing sunlight, canceling a portion of the greenhouse effect and making its surface significantly colder than its upper atmosphere.

Titan's clouds, probably composed of methane, ethane or other simple organics, are scattered and variable, punctuating the overall haze. The findings of the Huygens probe indicate that Titan's atmosphere periodically rains liquid methane and other organic compounds onto its surface.

Clouds typically cover 1% of Titan's disk, though outburst events have been observed in which the cloud cover rapidly expands to as much as 8%. One hypothesis asserts that the southern clouds are formed when heightened levels of sunlight during the southern summer generate uplift in the atmosphere, resulting in convection. This explanation is complicated by the fact that cloud formation has been observed not only after the southern summer solstice but also during mid-spring. Increased methane humidity at the south pole possibly contributes to the rapid increases in cloud size. It was summer in Titan's southern hemisphere until 2010, when Saturn's orbit, which governs Titan's motion, moved Titan's northern hemisphere into the sunlight. When the seasons switch, it is expected that ethane will begin to condense over the south pole.

Surface features
The surface of Titan has been described as "complex, fluid-processed, [and] geologically young". Titan has been around since the Solar System's formation, but its surface is much younger, between 100 million and 1 billion years old. Geological processes may have reshaped Titan's surface. Titan's atmosphere is four times as thick as Earth's, making it difficult for astronomical instruments to image its surface in the visible light spectrum. The Cassini spacecraft used infrared instruments, radar altimetry and synthetic aperture radar (SAR) imaging to map portions of Titan during its close fly-bys. The first images revealed a diverse geology, with both rough and smooth areas. There are features that may be volcanic in origin, disgorging water mixed with ammonia onto the surface. There is also evidence that Titan's ice shell may be substantially rigid, which would suggest little geologic activity.

There are also streaky features, some of them hundreds of kilometers in length, that appear to be caused by windblown particles. Examination has also shown the surface to be relatively smooth; the few objects that seem to be impact craters appeared to have been filled in, perhaps by raining hydrocarbons or volcanoes. Radar altimetry suggests height variation is low, typically no more than 150 meters. Occasional elevation changes of 500 meters have been discovered and Titan has mountains that sometimes reach several hundred meters to more than 1 kilometer in height.

Titan's surface is marked by broad regions of bright and dark terrain. These include Xanadu, a large, reflective equatorial area about the size of Australia. It was first identified in infrared images from the Hubble Space Telescope in 1994, and later viewed by the Cassini spacecraft. The convoluted region is filled with hills and cut by valleys and chasms. It is criss-crossed in places by dark lineaments—sinuous topographical features resembling ridges or crevices. These may represent tectonic activity, which would indicate that Xanadu is geologically young. Alternatively, the lineaments may be liquid-formed channels, suggesting old terrain that has been cut through by stream systems. There are dark areas of similar size elsewhere on Titan, observed from the ground and by Cassini; at least one of these, Ligeia Mare, Titan's second-largest sea, is almost a pure methane sea.

Lakes

The possibility of hydrocarbon seas on Titan was first suggested based on Voyager 1 and 2 data that showed Titan to have a thick atmosphere of approximately the correct temperature and composition to support them, but direct evidence was not obtained until 1995 when data from Hubble and other observations suggested the existence of liquid methane on Titan, either in disconnected pockets or on the scale of satellite-wide oceans, similar to water on Earth.

The Cassini mission confirmed the former hypothesis. When the probe arrived in the Saturnian system in 2004, it was hoped that hydrocarbon lakes or oceans would be detected from the sunlight reflected off their surface, but no specular reflections were initially observed. Near Titan's south pole, an enigmatic dark feature named Ontario Lacus was identified (and later confirmed to be a lake). A possible shoreline was also identified near the pole via radar imagery. Following a flyby on July 22, 2006, in which the Cassini spacecraft's radar imaged the northern latitudes (that were then in winter), several large, smooth (and thus dark to radar) patches were seen dotting the surface near the pole. Based on the observations, scientists announced "definitive evidence of lakes filled with methane on Saturn's moon Titan" in January 2007. The Cassini–Huygens team concluded that the imaged features are almost certainly the long-sought hydrocarbon lakes, the first stable bodies of surface liquid found outside Earth. Some appear to have channels associated with liquid and lie in topographical depressions. The liquid erosion features appear to be a very recent occurrence: channels in some regions have created surprisingly little erosion, suggesting erosion on Titan is extremely slow, or some other recent phenomena may have wiped out older riverbeds and landforms. Overall, the Cassini radar observations have shown that lakes cover only a small percentage of the surface, making Titan much drier than Earth. Most of the lakes are concentrated near the poles (where the relative lack of sunlight prevents evaporation), but several long-standing hydrocarbon lakes in the equatorial desert regions have also been discovered, including one near the Huygens landing site in the Shangri-La region, which is about half the size of the Great Salt Lake in Utah, USA. The equatorial lakes are probably "oases", i.e. the likely supplier is underground aquifers.

In June 2008, the Visual and Infrared Mapping Spectrometer on Cassini confirmed the presence of liquid ethane beyond doubt in Ontario Lacus. On December 21, 2008, Cassini passed directly over Ontario Lacus and observed specular reflection in radar. The strength of the reflection saturated the probe's receiver, indicating that the lake level did not vary by more than 3 mm (implying either that surface winds were minimal, or the lake's hydrocarbon fluid is viscous).

On July 8, 2009, Cassini's VIMS observed a specular reflection indicative of a smooth, mirror-like surface, off what today is called Jingpo Lacus, a lake in the north polar region shortly after the area emerged from 15 years of winter darkness. Specular reflections are indicative of a smooth, mirror-like surface, so the observation corroborated the inference of the presence of a large liquid body drawn from radar imaging.

Early radar measurements made in July 2009 and January 2010 indicated that Ontario Lacus was extremely shallow, with an average depth of 0.4–3 m, and a maximum depth of 3 to 7 m. In contrast, the northern hemisphere's Ligeia Mare was initially mapped to depths exceeding 8 m, the maximum discernable by the radar instrument and the analysis techniques of the time. Later science analysis, released in 2014, more fully mapped the depths of Titan's three methane seas and showed depths of more than 200 m. Ligeia Mare averages from 20 to 40 m in depth, while other parts of Ligeia did not register any radar reflection at all, indicating a depth of more than 200 m. While only the second-largest of Titan's methane seas, Ligeia "contains enough liquid methane to fill three Lake Michigans".

In May 2013, Cassini's radar altimeter observed Titan's Vid Flumina channels, defined as a drainage network connected to Titan's second-largest hydrocarbon sea, Ligeia Mare. Analysis of the received altimeter echoes showed that the channels are located in deep (up to ~570 m), steep-sided, canyons and have strong specular surface reflections that indicate they are currently filled with liquid. Elevations of the liquid in these channels are at the same level as Ligeia Mare to within a vertical precision of about 0.7 m, consistent with the interpretation of drowned river valleys. Specular reflections are also observed in lower order tributaries elevated above the level of Ligeia Mare, consistent with drainage feeding into the main channel system. This is likely the first direct evidence of the presence of liquid channels on Titan and the first observation of hundred-meter deep canyons on Titan. Vid Flumina canyons are thus drowned by the sea but there are a few isolated observations to attest to the presence of surface liquids standing at higher elevations.

During six flybys of Titan from 2006 to 2011, Cassini gathered radiometric tracking and optical navigation data from which investigators could roughly infer Titan's changing shape. The density of Titan is consistent with a body that is about 60% rock and 40% water. The team's analyzes suggest that Titan's surface can rise and fall by up to 10 metres during each orbit. That degree of warping suggests that Titan's interior is relatively deformable, and that the most likely model of Titan is one in which an icy shell dozens of kilometers thick floats atop a global ocean. The team's findings, together with the results of previous studies, hint that Titan's ocean may lie no more than 100 km below its surface. On July 2, 2014, NASA reported the ocean inside Titan may be as salty as the Dead Sea. On September 3, 2014, NASA reported studies suggesting methane rainfall on Titan may interact with a layer of icy materials underground, called an "alkanofer", to produce ethane and propane that may eventually feed into rivers and lakes.

In 2016, Cassini found the first evidence of fluid-filled channels on Titan, in a series of deep, steep-sided canyons flowing into Ligeia Mare. This network of canyons, dubbed Vid Flumina, ranges in depth from 240 to 570 m and has sides as steep as 40°. They are believed to have formed either by crustal uplifting, like Earth's Grand Canyon, a lowering of sea level, or perhaps a combination of the two. The depth of erosion suggests that liquid flows in this part of Titan are long-term features that persist for thousands of years.

Impact craters
Radar, SAR and imaging data from Cassini have revealed few impact craters on Titan's surface. These impacts appear to be relatively young, compared to Titan's age. The few impact craters discovered include a 392 km two-ring impact basin named Menrva seen by Cassini's ISS as a bright-dark concentric pattern. A smaller, 80 km, flat-floored crater named Sinlap and a 30 km crater with a central peak and dark floor named Ksa have also been observed. Radar and Cassini imaging have also revealed "crateriforms", circular features on the surface of Titan that may be impact related, but lack certain features that would make identification certain. For example, a 90 km ring of bright, rough material known as Guabonito has been observed by Cassini. This feature is thought to be an impact crater filled in by dark, windblown sediment. Several other similar features have been observed in the dark Shangri-La and Aaru regions. Radar observed several circular features that may be craters in the bright region Xanadu during Cassini's April 30, 2006, flyby of Titan. Many of Titan's craters or probable craters display evidence of extensive erosion, and all show some indication of modification. Most large craters have breached or incomplete rims, despite the fact that some craters on Titan have relatively more massive rims than those anywhere else in the Solar System. There is little evidence of formation of palimpsests through viscoelastic crustal relaxation, unlike on other large icy moons. Most craters lack central peaks and have smooth floors, possibly due to impact-generation or later eruption of cryovolcanic lava. Infill from various geological processes is one reason for Titan's relative deficiency of craters; atmospheric shielding also plays a role. It is estimated that Titan's atmosphere reduces the number of craters on its surface by a factor of two.

The limited high-resolution radar coverage of Titan obtained through 2007 (22%) suggested the existence of nonuniformities in its crater distribution. Xanadu has 2–9 times more craters than elsewhere. The leading hemisphere has a 30% higher density than the trailing hemisphere. There are lower crater densities in areas of equatorial dunes and in the north polar region (where hydrocarbon lakes and seas are most common).

Pre-Cassini models of impact trajectories and angles suggest that where the impactor strikes the water ice crust, a small amount of ejecta remains as liquid water within the crater. It may persist as liquid for centuries or longer, sufficient for "the synthesis of simple precursor molecules to the origin of life".

Cryovolcanism and mountains
Scientists have long speculated that conditions on Titan resemble those of early Earth, though at a much lower temperature. The detection of argon-40 in the atmosphere in 2004 indicated that volcanoes had spawned plumes of "lava" composed of water and ammonia. Global maps of the lake distribution on Titan's surface revealed that there is not enough surface methane to account for its continued presence in its atmosphere, and thus that a significant portion must be added through volcanic processes.

Still, there is a paucity of surface features that can be unambiguously interpreted as cryovolcanoes. One of the first of such features revealed by Cassini radar observations in 2004, called Ganesa Macula, resembles the geographic features called "pancake domes" found on Venus, and was thus initially thought to be cryovolcanic in origin, until Kirk et al. refuted this hypothesis at the American Geophysical Union annual meeting in December 2008. The feature was found to be not a dome at all, but appeared to result from accidental combination of light and dark patches. In 2004 Cassini also detected an unusually bright feature (called Tortola Facula), which was interpreted as a cryovolcanic dome. No similar features have been identified as of 2010. In December 2008, astronomers announced the discovery of two transient but unusually long-lived "bright spots" in Titan's atmosphere, which appear too persistent to be explained by mere weather patterns, suggesting they were the result of extended cryovolcanic episodes.

A mountain range measuring 150 km long, 30 km wide and 1.5 km high was also discovered by Cassini in 2006. This range lies in the southern hemisphere and is thought to be composed of icy material and covered in methane snow. The movement of tectonic plates, perhaps influenced by a nearby impact basin, could have opened a gap through which the mountain's material upweled. Prior to Cassini, scientists assumed that most of the topography on Titan would be impact structures, yet these findings reveal that similar to Earth, the mountains were formed through geological processes.

In 2008 Jeffrey Moore (planetary geologist of Ames Research Center) proposed an alternate view of Titan's geology. Noting that no volcanic features had been unambiguously identified on Titan so far, he asserted that Titan is a geologically dead world, whose surface is shaped only by impact cratering, fluvial and eolian erosion, mass wasting and other exogenic processes. According to this hypothesis, methane is not emitted by volcanoes but slowly diffuses out of Titan's cold and stiff interior. Ganesa Macula may be an eroded impact crater with a dark dune in the center. The mountainous ridges observed in some regions can be explained as heavily degraded scarps of large multi-ring impact structures or as a result of the global contraction due to the slow cooling of the interior. Even in this case, Titan may still have an internal ocean made of the eutectic water–ammonia mixture with a temperature of 176 K, which is low enough to be explained by the decay of radioactive elements in the core. The bright Xanadu terrain may be a degraded heavily cratered terrain similar to that observed on the surface of Callisto. Indeed, were it not for its lack of an atmosphere, Callisto could serve as a model for Titan's geology in this scenario. Jeffrey Moore even called Titan Callisto with weather.

In March 2009, structures resembling lava flows were announced in a region of Titan called Hotei Arcus, which appears to fluctuate in brightness over several months. Though many phenomena were suggested to explain this fluctuation, the lava flows were found to rise 200 m above Titan's surface, consistent with it having erupted from beneath the surface.

In December 2010, the Cassini mission team announced the most compelling possible cryovolcano yet found. Named Sotra Patera, it is one in a chain of at least three mountains, each between 1000 and 1500 m in height, several of which are topped by large craters. The ground around their bases appears to be overlaid by frozen lava flows.

Crater-like landforms possibly formed via explosive, maar-like or caldera-forming cryovolcanic eruptions have been identified in Titan's polar regions. These formations are sometimes nested or overlapping and have features suggestive of explosions and collapses, such as elevated rims, halos, and internal hills or mountains. The polar location of these features and their colocalization with Titan's lakes and seas suggests volatiles such as methane may help power them. Some of these features appear quite fresh, suggesting that such volcanic activity continues to the present.

Most of Titan's highest peaks occur near its equator in so-called "ridge belts". They are believed to be analogous to Earth's fold mountains such as the Rockies or the Himalayas, formed by the collision and buckling of tectonic plates, or to subduction zones like the Andes, where upweling lava (or cryolava) from a melting descending plate rises to the surface. One possible mechanism for their formation is tidal forces from Saturn. Because Titan's icy mantle is less viscous than Earth's magma mantle, and because its icy bedrock is softer than Earth's granite bedrock, mountains are unlikely to reach heights as great as those on Earth. In 2016, the Cassini team announced what they believe to be the tallest mountain on Titan. Located in the Mithrim Montes range, it is 3,337 m tall.

If volcanism on Titan really exists, the hypothesis is that it is driven by energy released from the decay of radioactive elements within the mantle, as it is on Earth. Magma on Earth is made of liquid rock, which is less dense than the solid rocky crust through which it erupts. Because ice is less dense than water, Titan's watery magma would be denser than its solid icy crust. This means that cryovolcanism on Titan would require a large amount of additional energy to operate, possibly via tidal flexing from nearby Saturn. The low-pressure ice, overlaying a liquid layer of ammonium sulfate, ascends buoyantly, and the unstable system can produce dramatic plume events. Titan is resurfaced through the process by grain-sized ice and ammonium sulfate ash, which helps produce a wind-shaped landscape and sand dune features. Titan may have been much more geologically active in the past; models of Titan's internal evolution suggest that Titan's crust was only 10 kilometers thick until about 500 million years ago, allowing vigorous cryovolcanism with low viscosity water magmas to erase all surface features formed before that time. Titan's modern geology would have formed only after the crust thickened to 50 kilometers and thus impeded constant cryovolcanic resurfacing, with any cryovolcanism occurring since that time producing much more viscous water magma with larger fractions of ammonia and methanol; this would also suggest that Titan's methane is no longer being actively added to its atmosphere and could be depleted entirely within a few tens of millions of years.

Many of the more prominent mountains and hills have been given official names by the International Astronomical Union. According to JPL, "By convention, mountains on Titan are named for mountains from Middle-earth, the fictional setting in fantasy novels by J. R. R. Tolkien." Colles (collections of hills) are named for characters from the same Tolkien works.

Dark equatorial terrain
In the first images of Titan's surface taken by Earth-based telescopes in the early 2000s, large regions of dark terrain were revealed straddling Titan's equator. Prior to the arrival of Cassini, these regions were thought to be seas of liquid hydrocarbons. Radar images captured by the Cassini spacecraft have instead revealed some of these regions to be extensive plains covered in longitudinal dunes, up to 330 ft high, about a kilometer wide, and tens to hundreds of kilometers long. Dunes of this type are always aligned with average wind direction. In the case of Titan, steady zonal (eastward) winds combine with variable tidal winds (approximately 0.5 meters per second). The tidal winds are the result of tidal forces from Saturn on Titan's atmosphere, which are 400 times stronger than the tidal forces of the Moon on Earth and tend to drive wind toward the equator. This wind pattern, it was hypothesized, causes granular material on the surface to gradually build up in long parallel dunes aligned west-to-east. The dunes break up around mountains, where the wind direction shifts.

The longitudinal (or linear) dunes were initially presumed to be formed by moderately variable winds that either follow one mean direction or alternate between two different directions. Subsequent observations indicate that the dunes point to the east although climate simulations indicate Titan's surface winds blow toward the west. At less than 1 meter per second, they are not powerful enough to lift and transport surface material. Recent computer simulations indicate that the dunes may be the result of rare storm winds that happen only every fifteen years when Titan is in equinox. These storms produce strong downdrafts, flowing eastward at up to 10 meters per second when they reach the surface.

The "sand" on Titan is likely not made up of small grains of silicates like the sand on Earth, but rather might have formed when liquid methane rained and eroded the water-ice bedrock, possibly in the form of flash floods. Alternatively, the sand could also have come from organic solids called tholins, produced by photochemical reactions in Titan's atmosphere. Studies of dunes' composition in May 2008 revealed that they possessed less water than the rest of Titan, and are thus most likely derived from organic soot like hydrocarbon polymers clumping together after raining onto the surface. Calculations indicate the sand on Titan has a density of one-third that of terrestrial sand. The low density combined with the dryness of Titan's atmosphere might cause the grains to clump together because of static electricity buildup. The "stickiness" might make it difficult for the generally mild breeze close to Titan's surface to move the dunes although more powerful winds from seasonal storms could still blow them eastward.

Around equinox, strong downburst winds can lift micron-sized solid organic particles up from the dunes to create Titanian dust storms, observed as intense and short-lived brightenings in the infrared.

Observation and exploration
Titan is never visible to the naked eye, but can be observed through small telescopes or strong binoculars. Amateur observation is difficult because of the proximity of Titan to Saturn's brilliant globe and ring system; an occulting bar, covering part of the eyepiece and used to block the bright planet, greatly improves viewing. Titan has a maximum apparent magnitude of +8.2, and mean opposition magnitude 8.4. This compares to +4.6 for the similarly sized Ganymede, in the Jovian system.

Observations of Titan prior to the space age were limited. In 1907 Spanish astronomer Josep Comas i Solà observed limb darkening of Titan, the first evidence that the body has an atmosphere. In 1944 Gerard P. Kuiper used a spectroscopic technique to detect an atmosphere of methane.

Fly-by missions: Pioneer and Voyager
The first probe to visit the Saturnian system was Pioneer 11 in 1979, which revealed that Titan was probably too cold to support life. It took images of Titan, including Titan and Saturn together in mid to late 1979. The quality was soon surpassed by the two Voyagers.

Titan was examined by both Voyager 1 and 2 in 1980 and 1981, respectively. Voyager 1 ' s trajectory was designed to provide an optimized Titan flyby, during which the spacecraft was able to determine the density, composition, and temperature of the atmosphere, and obtain a precise measurement of Titan's mass. Atmospheric haze prevented direct imaging of the surface, though in 2004 intensive digital processing of images taken through Voyager 1 ' s orange filter did reveal hints of the light and dark features now known as Xanadu and Shangri-la, which had been observed in the infrared by the Hubble Space Telescope. Voyager 2, which would have been diverted to perform the Titan flyby if Voyager 1 had been unable to, did not pass near Titan and continued on to Uranus and Neptune.

Cassini–Huygens
The Cassini–Huygens spacecraft reached Saturn on July 1, 2004, and began the process of mapping Titan's surface by radar. A joint project of the European Space Agency (ESA) and NASA, Cassini–Huygens proved a very successful mission. The Cassini probe flew by Titan on October 26, 2004, and took the highest-resolution images ever of Titan's surface, at only 1200 km, discerning patches of light and dark that would be invisible to the human eye.

On July 22, 2006, Cassini made its first targeted, close fly-by at 950 km from Titan; the closest flyby was at 880 km on June 21, 2010. Liquid has been found in abundance on the surface in the north polar region, in the form of many lakes and seas discovered by Cassini.

Huygens landing
Huygens was an atmospheric probe that touched down on Titan on January 14, 2005, discovering that many of its surface features seem to have been formed by fluids at some point in the past. Titan is the most distant body from Earth to have a space probe land on its surface. The Huygens probe landed just off the easternmost tip of a bright region now called Adiri. The probe photographed pale hills with dark "rivers" running down to a dark plain. Current understanding is that the hills (also referred to as highlands) are composed mainly of water ice. Dark organic compounds, created in the upper atmosphere by the ultraviolet radiation of the Sun, may rain from Titan's atmosphere. They are washed down the hills with the methane rain and are deposited on the plains over geological time scales.

After landing, Huygens photographed a dark plain covered in small rocks and pebbles, which are composed of water ice. The two rocks just below the middle of the image on the right are smaller than they may appear: the left-hand one is 15 centimeters across, and the one in the center is 4 centimeters across, at a distance of about 85 centimeters from Huygens. There is evidence of erosion at the base of the rocks, indicating possible fluvial activity. The ground surface is darker than originally expected, consisting of a mixture of water and hydrocarbon ice.

In March 2007, NASA, ESA, and COSPAR decided to name the Huygens landing site the Hubert Curien Memorial Station in memory of the former president of the ESA.

Dragonfly
The Dragonfly mission, developed and operated by the Johns Hopkins Applied Physics Laboratory, will launch in July 2028. It consists of a large drone powered by an RTG to fly in the atmosphere of Titan as New Frontiers 4. Its instruments will study how far prebiotic chemistry may have progressed. The mission is planned to arrive at Titan in the mid-2030s.

Proposed or conceptual missions

There have been several conceptual missions proposed in recent years for returning a robotic space probe to Titan. Initial conceptual work has been completed for such missions by NASA (and JPL), and ESA. At present, none of these proposals have become funded missions.

The Titan Saturn System Mission (TSSM) was a joint NASA/ESA proposal for exploration of Saturn's moons. It envisions a hot-air balloon floating in Titan's atmosphere for six months. It was competing against the Europa Jupiter System Mission (EJSM) proposal for funding. In February 2009 it was announced that ESA/NASA had given the EJSM mission priority ahead of the TSSM.

The proposed Titan Mare Explorer (TiME) was a low-cost lander that would splash down in Ligeia Mare in Titan's northern hemisphere. The probe would float whilst investigating Titan's hydrocarbon cycle, sea chemistry, and Titan's origins. It was selected for a Phase-A design study in 2011 as a candidate mission for the 12th NASA Discovery Program opportunity, but was not selected for flight.

Another mission to Titan proposed in early 2012 by Jason Barnes, a scientist at the University of Idaho, is the Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR): an uncrewed plane (or drone) that would fly through Titan's atmosphere and take high-definition images of the surface of Titan. NASA did not approve the requested $715 million, and the future of the project is uncertain.

A conceptual design for another lake lander was proposed in late 2012 by the Spanish-based private engineering firm SENER and the Centro de Astrobiología in Madrid. The concept probe is called Titan Lake In-situ Sampling Propelled Explorer (TALISE). The major difference compared to the TiME probe would be that TALISE is envisioned with its own propulsion system and would therefore not be limited to simply drifting on the lake when it splashes down.

A Discovery Program contestant for its mission #13 is Journey to Enceladus and Titan (JET), an astrobiology Saturn orbiter that would assess the habitability potential of Enceladus and Titan.

In 2015, the NASA Innovative Advanced Concepts program (NIAC) awarded a Phase II grant to a design study of a Titan Submarine to explore the seas of Titan.

Prebiotic conditions and life
Titan is thought to be a prebiotic environment rich in complex organic compounds, but its surface is in a deep freeze at -179 C so it is currently understood that life cannot exist on the moon's frigid surface. However, Titan seems to contain a global ocean beneath its ice shell, and within this ocean, conditions are potentially suitable for microbial life.

The Cassini–Huygens mission was not equipped to provide evidence for biosignatures or complex organic compounds; it showed an environment on Titan that is similar, in some ways, to ones hypothesized for the primordial Earth. Scientists surmise that the atmosphere of early Earth was similar in composition to the current atmosphere on Titan, with the important exception of a lack of water vapor on Titan.

Formation of complex molecules
The Miller–Urey experiment and several following experiments have shown that with an atmosphere similar to that of Titan and the addition of UV radiation, complex molecules and polymer substances like tholins can be generated. The reaction starts with dissociation of nitrogen and methane, forming hydrogen cyanide and acetylene. Further reactions have been studied extensively.

It has been reported that when energy was applied to a combination of gases like those in Titan's atmosphere, five nucleotide bases, the building blocks of DNA and RNA, were among the many compounds produced. In addition, amino acids—the building blocks of protein—were found. It was the first time nucleotide bases and amino acids had been found in such an experiment without liquid water being present.

On April 3, 2013, NASA reported that complex organic chemicals could arise on Titan based on studies simulating the atmosphere of Titan.

On June 6, 2013, scientists at the IAA-CSIC reported the detection of polycyclic aromatic hydrocarbons (PAH) in the upper atmosphere of Titan.

On July 26, 2017, Cassini scientists positively identified the presence of carbon chain anions in Titan's upper atmosphere which appeared to be involved in the production of large complex organics. These highly reactive molecules were previously known to contribute to building complex organics in the Interstellar Medium, therefore highlighting a possibly universal stepping stone to producing complex organic material.

On July 28, 2017, scientists reported that acrylonitrile (C2H3CN), a chemical possibly essential for life by being related to cell membrane and vesicle structure formation, had been found on Titan.

In October 2018, researchers reported low-temperature chemical pathways from simple organic compounds to complex polycyclic aromatic hydrocarbon (PAH) chemicals. Such chemical pathways may help explain the presence of PAHs in the low-temperature atmosphere of Titan, and may be significant pathways, in terms of the PAH world hypothesis, in producing precursors to biochemicals related to life as we know it.

Possible subsurface habitats
Laboratory simulations have led to the suggestion that enough organic material exists on Titan to start a chemical evolution analogous to what is thought to have started life on Earth. The analogy assumes the presence of liquid water for longer periods than is currently observable; several hypotheses postulate that liquid water from an impact could be preserved under a frozen isolation layer. It has also been hypothesized that liquid-ammonia oceans could exist deep below the surface. Another model suggests an ammonia–water solution as much as 200 km deep beneath a water-ice crust with conditions that, although extreme by terrestrial standards, are such that life could survive. Heat transfer between the interior and upper layers would be critical in sustaining any subsurface oceanic life. Detection of microbial life on Titan would depend on its biogenic effects, with the atmospheric methane and nitrogen examined.

Methane and life at the surface
It has been speculated that life could exist in the lakes of liquid methane on Titan, just as organisms on Earth live in water. Such organisms would inhale H2 in place of O2, metabolize it with acetylene instead of glucose, and exhale methane instead of carbon dioxide. However, such hypothetical organisms would be required to metabolize at a deep freeze temperature of -179.2 C.

All life forms on Earth (including methanogens) use liquid water as a solvent; it is speculated that life on Titan might instead use a liquid hydrocarbon, such as methane or ethane, although water is a stronger solvent than methane. Water is also more chemically reactive, and can break down large organic molecules through hydrolysis. A life form whose solvent was a hydrocarbon would not face the risk of its biomolecules being destroyed in this way.

In 2005, astrobiologist Chris McKay argued that if methanogenic life did exist on the surface of Titan, it would likely have a measurable effect on the mixing ratio in the Titan troposphere: levels of hydrogen and acetylene would be measurably lower than otherwise expected. Assuming metabolic rates similar to those of methanogenic organisms on Earth, the concentration of molecular hydrogen would drop by a factor of 1000 on the Titanian surface solely due to a hypothetical biological sink. McKay noted that, if life is indeed present, the low temperatures on Titan would result in very slow metabolic processes, which could conceivably be hastened by the use of catalysts similar to enzymes. He also noted that the low solubility of organic compounds in methane presents a more significant challenge to any possible form of life. Forms of active transport, and organisms with large surface-to-volume ratios could theoretically lessen the disadvantages posed by this fact.

In 2010, Darrell Strobel, from Johns Hopkins University, identified a greater abundance of molecular hydrogen in the upper atmospheric layers of Titan compared to the lower layers, arguing for a downward flow at a rate of roughly 1028 molecules per second and disappearance of hydrogen near Titan's surface; as Strobel noted, his findings were in line with the effects McKay had predicted if methanogenic life-forms were present. The same year, another study showed low levels of acetylene on Titan's surface, which were interpreted by McKay as consistent with the hypothesis of organisms consuming hydrocarbons. Although restating the biological hypothesis, he cautioned that other explanations for the hydrogen and acetylene findings are more likely: the possibilities of yet unidentified physical or chemical processes (e.g. a surface catalyst accepting hydrocarbons or hydrogen), or flaws in the current models of material flow. Composition data and transport models need to be substantiated, etc. Even so, despite saying that a non-biological catalytic explanation would be less startling than a biological one, McKay noted that the discovery of a catalyst effective at 95 K would still be significant. With regards to the acetylene findings, Mark Allen, the principal investigator with the NASA Astrobiology Institute Titan team, provided a speculative, non-biological explanation: sunlight or cosmic rays could transform the acetylene in icy aerosols in the atmosphere into more complex molecules that would fall to the ground with no acetylene signature.

As NASA notes in its news article on the June 2010 findings: "To date, methane-based life forms are only hypothetical. Scientists have not yet detected this form of life anywhere." As the NASA statement also says: "some scientists believe these chemical signatures bolster the argument for a primitive, exotic form of life or precursor to life on Titan's surface."

In February 2015, a hypothetical cell membrane capable of functioning in liquid methane at cryogenic temperatures (deep freeze) conditions was modeled. Composed of small molecules containing carbon, hydrogen, and nitrogen, it would have the same stability and flexibility as cell membranes on Earth, which are composed of phospholipids, compounds of carbon, hydrogen, oxygen, and phosphorus. This hypothetical cell membrane was termed an "azotosome", a combination of "azote", French for nitrogen, and "liposome".

Obstacles
Despite these biological possibilities, there are formidable obstacles to life on Titan, and any analogy to Earth is inexact. At a vast distance from the Sun, Titan is frigid, and its atmosphere lacks CO2. At Titan's surface, water exists only in solid form. Because of these difficulties, scientists such as Jonathan Lunine have viewed Titan less as a likely habitat for life than as an experiment for examining hypotheses on the conditions that prevailed prior to the appearance of life on Earth. Although life itself may not exist, the prebiotic conditions on Titan and the associated organic chemistry remain of great interest in understanding the early history of the terrestrial biosphere. Using Titan as a prebiotic experiment involves not only observation through spacecraft, but laboratory experiments, and chemical and photochemical modeling on Earth.

Panspermia hypothesis
It is hypothesized that large asteroid and cometary impacts on Earth's surface may have caused fragments of microbe-laden rock to escape Earth's gravity, suggesting the possibility of panspermia. Calculations indicate that these would encounter many of the bodies in the Solar System, including Titan. On the other hand, Jonathan Lunine has argued that any living things in Titan's cryogenic hydrocarbon lakes would need to be so different chemically from Earth life that it would not be possible for one to be the ancestor of the other.

Future conditions
Conditions on Titan could become far more habitable in the far future. Five billion years from now, as the Sun becomes a sub-red giant, its surface temperature could rise enough for Titan to support liquid water on its surface, making it habitable. As the Sun's ultraviolet output decreases, the haze in Titan's upper atmosphere will be depleted, lessening the anti-greenhouse effect on the surface and enabling the greenhouse created by atmospheric methane to play a far greater role. These conditions together could create a habitable environment, and could persist for several hundred million years. This is proposed to have been sufficient time for simple life to spawn on Earth, though the higher viscosity of ammonia-water solutions coupled with low temperatures would cause chemical reactions to proceed more slowly on Titan.

title: Titan (moon)


text:
Instrumentation

Instrumentation is a collective term for measuring instruments, used for indicating, measuring, and recording physical quantities. It is also a field of study about the art and science about making measurement instruments, involving the related areas of metrology, automation, and control theory. The term has its origins in the art and science of scientific instrument-making.

Instrumentation can refer to devices as simple as direct-reading thermometers, or as complex as multi-sensor components of industrial control systems. Instruments can be found in laboratories, refineries, factories and vehicles, as well as in everyday household use (e.g., smoke detectors and thermostats)

Measurement parameters

Instrumentation is used to measure many parameters (physical values), including:
 * Pressure, either differential or static
 * Flow
 * Temperature
 * Levels of liquids, etc.
 * Moisture or humidity
 * Density
 * Viscosity
 * ionising radiation
 * Frequency
 * Current
 * Voltage
 * Inductance
 * Capacitance
 * Resistivity
 * Chemical composition
 * Chemical properties
 * Toxic gases
 * Position
 * Vibration
 * Weight

History
The history of instrumentation can be divided into several phases.

Pre-industrial
Elements of industrial instrumentation have long histories. Scales for comparing weights and simple pointers to indicate position are ancient technologies. Some of the earliest measurements were of time. One of the oldest water clocks was found in the tomb of the ancient Egyptian pharaoh Amenhotep I, buried around 1500 BCE. Improvements were incorporated in the clocks. By 270 BCE they had the rudiments of an automatic control system device.

In 1663 Christopher Wren presented the Royal Society with a design for a "weather clock". A drawing shows meteorological sensors moving pens over paper driven by clockwork. Such devices did not become standard in meteorology for two centuries. The concept has remained virtually unchanged as evidenced by pneumatic chart recorders, where a pressurized bellows displaces a pen. Integrating sensors, displays, recorders, and controls was uncommon until the industrial revolution, limited by both need and practicality.

Early industrial
Early systems used direct process connections to local control panels for control and indication, which from the early 1930s saw the introduction of pneumatic transmitters and automatic 3-term (PID) controllers.

The ranges of pneumatic transmitters were defined by the need to control valves and actuators in the field. Typically, a signal ranged from 3 to 15 psi (20 to 100kPa or 0.2 to 1.0 kg/cm2) as a standard, was standardized with 6 to 30 psi occasionally being used for larger valves. Transistor electronics enabled wiring to replace pipes, initially with a range of 20 to 100mA at up to 90V for loop powered devices, reducing to 4 to 20mA at 12 to 24V in more modern systems. A transmitter is a device that produces an output signal, often in the form of a 4–20 mA electrical current signal, although many other options using voltage, frequency, pressure, or ethernet are possible. The transistor was commercialized by the mid-1950s.

Instruments attached to a control system provided signals used to operate solenoids, valves, regulators, circuit breakers, relays and other devices. Such devices could control a desired output variable, and provide either remote monitoring or automated control capabilities.

Each instrument company introduced their own standard instrumentation signal, causing confusion until the 4–20 mA range was used as the standard electronic instrument signal for transmitters and valves. This signal was eventually standardized as ANSI/ISA S50, "Compatibility of Analog Signals for Electronic Industrial Process Instruments", in the 1970s. The transformation of instrumentation from mechanical pneumatic transmitters, controllers, and valves to electronic instruments reduced maintenance costs as electronic instruments were more dependable than mechanical instruments. This also increased efficiency and production due to their increase in accuracy. Pneumatics enjoyed some advantages, being favored in corrosive and explosive atmospheres.

Automatic process control
In the early years of process control, process indicators and control elements such as valves were monitored by an operator, that walked around the unit adjusting the valves to obtain the desired temperatures, pressures, and flows. As technology evolved pneumatic controllers were invented and mounted in the field that monitored the process and controlled the valves. This reduced the amount of time process operators needed to monitor the process. Latter years, the actual controllers were moved to a central room and signals were sent into the control room to monitor the process and outputs signals were sent to the final control element such as a valve to adjust the process as needed. These controllers and indicators were mounted on a wall called a control board. The operators stood in front of this board walking back and forth monitoring the process indicators. This again reduced the number and amount of time process operators were needed to walk around the units. The most standard pneumatic signal level used during these years was 3–15 psig.

Large integrated computer-based systems
Process control of large industrial plants has evolved through many stages. Initially, control would be from panels local to the process plant. However, this required a large manpower resource to attend to these dispersed panels, and there was no overall view of the process. The next logical development was the transmission of all plant measurements to a permanently staffed central control room. Effectively this was the centralization of all the localized panels, with the advantages of lower manning levels and easy overview of the process. Often the controllers were behind the control room panels, and all automatic and manual control outputs were transmitted back to plant.

However, whilst providing a central control focus, this arrangement was inflexible as each control loop had its own controller hardware, and continual operator movement within the control room was required to view different parts of the process. With coming of electronic processors and graphic displays it became possible to replace these discrete controllers with computer-based algorithms, hosted on a network of input/output racks with their own control processors. These could be distributed around plant, and communicate with the graphic display in the control room or rooms. The distributed control concept was born.

The introduction of DCSs and SCADA allowed easy interconnection and re-configuration of plant controls such as cascaded loops and interlocks, and easy interfacing with other production computer systems. It enabled sophisticated alarm handling, introduced automatic event logging, removed the need for physical records such as chart recorders, allowed the control racks to be networked and thereby located locally to plant to reduce cabling runs, and provided high level overviews of plant status and production levels.

Application
In some cases, the sensor is a very minor element of the mechanism. Digital cameras and wristwatches might technically meet the loose definition of instrumentation because they record and/or display sensed information. Under most circumstances neither would be called instrumentation, but when used to measure the elapsed time of a race and to document the winner at the finish line, both would be called instrumentation.

Household
A very simple example of an instrumentation system is a mechanical thermostat, used to control a household furnace and thus to control room temperature. A typical unit senses temperature with a bi-metallic strip. It displays temperature by a needle on the free end of the strip. It activates the furnace by a mercury switch. As the switch is rotated by the strip, the mercury makes physical (and thus electrical) contact between electrodes.

Another example of an instrumentation system is a home security system. Such a system consists of sensors (motion detection, switches to detect door openings), simple algorithms to detect intrusion, local control (arm/disarm) and remote monitoring of the system so that the police can be summoned. Communication is an inherent part of the design.

Kitchen appliances use sensors for control.
 * A refrigerator maintains a constant temperature by actuating the cooling system when the temperature becomes too high.
 * An automatic ice machine makes ice until a limit switch is thrown.
 * Pop-up bread toasters allow the time to be set.
 * Non-electronic gas ovens will regulate the temperature with a thermostat controlling the flow of gas to the gas burner. These may feature a sensor bulb sited within the main chamber of the oven.  In addition, there may be a safety cut-off flame supervision device: after ignition, the burner's control knob must be held for a short time in order for a sensor to become hot, and permit the flow of gas to the burner.  If the safety sensor becomes cold, this may indicate the flame on the burner has become extinguished, and to prevent a continuous leak of gas the flow is stopped.
 * Electric ovens use a temperature sensor and will turn on heating elements when the temperature is too low. More advanced ovens will actuate fans in response to temperature sensors, to distribute heat or to cool.
 * A common toilet refills the water tank until a float closes the valve. The float is acting as a water level sensor.

Automotive
Modern automobiles have complex instrumentation. In addition to displays of engine rotational speed and vehicle linear speed, there are also displays of battery voltage and current, fluid levels, fluid temperatures, distance traveled, and feedback of various controls (turn signals, parking brake, headlights, transmission position). Cautions may be displayed for special problems (fuel low, check engine, tire pressure low, door ajar, seat belt unfastened). Problems are recorded so they can be reported to diagnostic equipment. Navigation systems can provide voice commands to reach a destination. Automotive instrumentation must be cheap and reliable over long periods in harsh environments. There may be independent airbag systems that contain sensors, logic and actuators. Anti-skid braking systems use sensors to control the brakes, while cruise control affects throttle position. A wide variety of services can be provided via communication links on the OnStar system. Autonomous cars (with exotic instrumentation) have been shown.

Aircraft
Early aircraft had a few sensors. "Steam gauges" converted air pressures into needle deflections that could be interpreted as altitude and airspeed. A magnetic compass provided a sense of direction. The displays to the pilot were as critical as the measurements.

A modern aircraft has a far more sophisticated suite of sensors and displays, which are embedded into avionics systems. The aircraft may contain inertial navigation systems, global positioning systems, weather radar, autopilots, and aircraft stabilization systems. Redundant sensors are used for reliability. A subset of the information may be transferred to a crash recorder to aid mishap investigations. Modern pilot displays now include computer displays including head-up displays.

Air traffic control radar is a distributed instrumentation system. The ground part sends an electromagnetic pulse and receives an echo (at least). Aircraft carry transponders that transmit codes on reception of the pulse. The system displays an aircraft map location, an identifier and optionally altitude. The map location is based on sensed antenna direction and sensed time delay. The other information is embedded in the transponder transmission.

Laboratory instrumentation
Among the possible uses of the term is a collection of laboratory test equipment controlled by a computer through an IEEE-488 bus (also known as GPIB for General Purpose Instrument Bus or HPIB for Hewlitt Packard Instrument Bus). Laboratory equipment is available to measure many electrical and chemical quantities. Such a collection of equipment might be used to automate the testing of drinking water for pollutants.

Instrumentation engineering
Instrumentation engineering is the engineering specialization focused on the principle and operation of measuring instruments that are used in design and configuration of automated systems in areas such as electrical and pneumatic domains, and the control of quantities being measured. They typically work for industries with automated processes, such as chemical or manufacturing plants, with the goal of improving system productivity, reliability, safety, optimization and stability. To control the parameters in a process or in a particular system, devices such as microprocessors, microcontrollers or PLCs are used, but their ultimate aim is to control the parameters of a system.

Instrumentation engineering is loosely defined because the required tasks are very domain dependent. An expert in the biomedical instrumentation of laboratory rats has very different concerns than the expert in rocket instrumentation. Common concerns of both are the selection of appropriate sensors based on size, weight, cost, reliability, accuracy, longevity, environmental robustness, and frequency response. Some sensors are literally fired in artillery shells. Others sense thermonuclear explosions until destroyed. Invariably sensor data must be recorded, transmitted or displayed. Recording rates and capacities vary enormously. Transmission can be trivial or can be clandestine, encrypted and low power in the presence of jamming. Displays can be trivially simple or can require consultation with human factors experts. Control system design varies from trivial to a separate specialty.

Instrumentation engineers are responsible for integrating the sensors with the recorders, transmitters, displays or control systems, and producing the Piping and instrumentation diagram for the process. They may design or specify installation, wiring and signal conditioning. They may be responsible for commissioning, calibration, testing and maintenance of the system.

In a research environment it is common for subject matter experts to have substantial instrumentation system expertise. An astronomer knows the structure of the universe and a great deal about telescopes – optics, pointing and cameras (or other sensing elements). That often includes the hard-won knowledge of the operational procedures that provide the best results. For example, an astronomer is often knowledgeable of techniques to minimize temperature gradients that cause air turbulence within the telescope.

Instrumentation technologists, technicians and mechanics specialize in troubleshooting, repairing and maintaining instruments and instrumentation systems.

Typical industrial transmitter signal types

 * Pneumatic loop (20-100KPa/3-15PSI) – Pneumatic
 * Current loop (4-20mA) – Electrical
 * HART – Data signalling, often overlaid on a current loop
 * Foundation Fieldbus – Data signalling
 * Profibus – Data signalling

Impact of modern development
Ralph Müller (1940) stated, "That the history of physical science is largely the history of instruments and their intelligent use is well known. The broad generalizations and theories which have arisen from time to time have stood or fallen on the basis of accurate measurement, and in several instances new instruments have had to be devised for the purpose. There is little evidence to show that the mind of modern man is superior to that of the ancients. His tools are incomparably better."

Davis Baird has argued that the major change associated with Floris Cohen's identification of a "fourth big scientific revolution" after World War II is the development of scientific instrumentation, not only in chemistry but across the sciences. In chemistry, the introduction of new instrumentation in the 1940s was "nothing less than a scientific and technological revolution" in which classical wet-and-dry  methods of structural organic chemistry were discarded, and new areas of research opened up.

As early as 1954, W. A. Wildhack discussed both the productive and destructive potential inherent in process control. The ability to make precise, verifiable and reproducible measurements of the natural world, at levels that were not previously observable, using scientific instrumentation, has "provided a different texture of the world". This instrumentation revolution fundamentally changes human abilities to monitor and respond, as is illustrated in the examples of DDT monitoring and the use of UV spectrophotometry and gas chromatography to monitor water pollutants.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Instrumentation


text:
Anne of Cleves

Anne of Cleves (Anna von Kleve; 1515 – 16 July 1557) was Queen of England from 6 January to 12 July 1540 as the fourth wife of Henry VIII. Not much is known about Anne before 1527, when she became betrothed to Francis, Duke of Bar, son and heir of Antoine, Duke of Lorraine, although their marriage did not proceed. In March 1539, negotiations for Anne's marriage to Henry began, as Henry believed that he needed to form a political alliance with her brother, William, who was a leader of the Protestants of Western Germany, to strengthen his position against potential attacks from Catholic France and the Holy Roman Empire.

Anne arrived in England on 27 December 1539 and married Henry on 6 January 1540, but after six months, the marriage was declared unconsummated and, as a result, she was not crowned queen consort. Following the annulment, Henry gave her a generous settlement, and she was thereafter known as the King's Beloved Sister. Remaining in England, she lived to see the reign of Edward VI, and the coronation of Mary I, outliving the rest of Henry's wives.

Early life
Anne was born in 1515, on either 22 September, or 28 June. She was born in Düsseldorf, the second daughter of John III of the House of La Marck, Duke of Jülich jure uxoris, Cleves, Berg jure uxoris, Count of Mark, also known as de la Marck and Ravensberg jure uxoris (often referred to as Duke of Cleves) who died in 1538, and his wife Maria, Duchess of Jülich-Berg (1491–1543). She grew up in Schloss Burg on the edge of Solingen.

Anne's father was influenced by Erasmus and followed a moderate path within the Reformation. He decided to side with the Schmalkaldic League and opposed Emperor Charles V. After John's death, Anne's brother William became Duke of Jülich-Cleves-Berg, bearing the promising epithet "The Rich". In 1526, her elder sister Sibylle was married to John Frederick, Elector of Saxony, head of the Protestant Confederation of Germany and considered the "Champion of the Reformation."

In 1527, at the age of 11, Anne was betrothed to Francis, the 9-year-old son and heir of Antoine, Duke of Lorraine. But because Francis was under the age of consent (10 years old) at the time of the arrangement, the betrothal was considered unofficial and was cancelled in 1535. Her brother William was a Lutheran but the family was unaligned religiously, with her mother, the Duchess Maria, described as a "strict Catholic". Her father's ongoing dispute over Gelderland with Charles V made the family suitable allies for England's King Henry VIII in the wake of the Truce of Nice. The match with Anne was urged on the king by his chief minister, Thomas Cromwell.

Wedding preparations
The artist Hans Holbein the Younger was dispatched to Düren to paint portraits of Anne and her younger sister, Amalia, each of whom Henry VIII was considering as his fourth wife. Henry required the artist to be as accurate as possible, not to flatter the sisters. The portraits are now located in the Musée du Louvre in Paris and the Victoria and Albert Museum in London. Another 1539 portrait, by the school of Barthel Bruyn the Elder, is in the collection of Trinity College, Cambridge.

Negotiations to arrange the marriage were in full swing by March 1539. Thomas Cromwell oversaw the talks and a marriage treaty was signed on 4 October of that year.

Henry valued education and cultural sophistication in women, but Anne lacked these traits. She had received no formal education but was skilled in needlework and liked playing card games. She could read and write, but only in German. Nevertheless, Anne was considered gentle, virtuous and docile, which is why she was recommended as a suitable candidate for Henry.

Anne was described by French ambassador Charles de Marillac as tall and slim, "of medium beauty, and of very assured and resolute countenance." She was fair-haired and was said to have had a lovely face. In the words of the chronicler Edward Hall, "Her hair hanging down, which was fair, yellow and long ... she was apparelled after the English fashion, with a French hood, which so set forth her beauty and good visage, that every creature rejoiced to behold her." She appeared rather solemn by English standards, and looked old for her age. Holbein painted her with a high forehead, heavy-lidded eyes and a pointed chin.

Anne was initially to travel to England alone with her cortège – the death of her father prevented her brother and mother from travelling – but there were concerns about a beautiful, sheltered young woman who had never traveled by sea making such a journey, especially during the winter. She traveled from Düsseldorf to Cleves, and then to Antwerp where she was received by fifty English merchants.

Henry met her privately on New Year's Day 1540 at Rochester Abbey in Rochester on her journey from Dover. Henry and some of his courtiers, following a courtly-love tradition, went disguised into the room where Anne was staying. Eustace Chapuys reported:

"[The King] so went up into the chamber where the said Lady Anne was looking out of a window to see the bull-baiting which was going on in the courtyard, and suddenly he embraced and kissed her, and showed her a token which the king had sent her for New Year’s gift, and she being abashed and not knowing who it was thanked him, and so he spoke with her. But she regarded him little, but always looked out the window .... and when the king saw that she took so little notice of his coming he went into another chamber and took off his cloak and came in again in a coat of purple velvet. And when the lords and knights saw his grace they did him reverence."

According to the testimony of Henry's companions, he was disappointed with Anne, feeling that she was not as described. According to the chronicler Charles Wriothesley, Anne "regarded him little", though it is unknown whether she knew this was the king. Henry then revealed his true identity to Anne, although he is said to have been put off the marriage from then on. Henry and Anne then met officially on 3 January on Blackheath outside the gates of Greenwich Park, where a grand reception was laid out.

Most historians believe that Henry's misgivings about the marriage were because of Anne's unsatisfactory appearance, which did not inspire him to consummate the marriage. He felt that he had been misled after his advisors had praised Anne's beauty: "She is nothing so fair as she hath been reported", he complained. He went even further to tell others in his court that if "it were not that she had come so far into my realm, and the great preparations and state that my people have made for her, and for fear of making a ruffle in the world and of driving her brother into the arms of the Emperor and the French King, I would not now marry her. But now it is too far gone, wherefore I am sorry."

Cromwell received some blame for the Holbein portrait, which Henry believed had not been an accurate representation of Anne, and for some of the exaggerated reports of her beauty. Henry urged Cromwell to find a legal way to avoid the marriage but, by this point, doing so was impossible without endangering the vital alliance with the Germans. In his anger and frustration, the King turned on Cromwell, to his subsequent regret.

Marriage
Despite Henry's very vocal misgivings, the two were married on 6 January 1540 at the royal Palace of Placentia in Greenwich, London, by Archbishop Thomas Cranmer. The phrase "God send me well to keep" was engraved around Anne's wedding ring. According to Edward Hall, she wore a "gowne of ryche cloth of gold set full of large flowers of great and Orient pearl, made after the Duche fassion rownde". A round gown had no train. On the Sunday after the wedding there were jousts, Anne dressed in the English fashion, with a French hood.

Immediately after arriving in England, Anne conformed to the Catholic form of worship which Henry had retained after his break with Rome. The couple's first night as husband and wife was not a successful one. Henry confided to Cromwell that he had not consummated the marriage, saying, "I liked her before not well, but now I like her much worse".

In February 1540, speaking to the Countess of Rutland, Anne praised the King as a kind husband, saying: "When he comes to bed he kisseth me, and he taketh me by the hand, and biddeth me 'Good night, sweetheart'; and in the morning kisseth me and biddeth 'Farewell, darling. Lady Rutland responded: "Madam, there must be more than this, or it will be long ere we have a duke of York, which all this realm most desireth."

Anne was commanded to leave the Court on 24 June, and on 6 July she was informed of her husband's decision to reconsider the marriage. Witness statements were taken from a number of courtiers and two physicians which register the king's disappointment at her appearance. Henry had also commented to Thomas Heneage and Anthony Denny that he could not believe she was a virgin.

Shortly afterwards, Anne was asked for her consent to an annulment, to which she agreed. Cromwell, the moving force behind the marriage, was attainted for treason. The marriage was annulled on 12 July 1540, on the grounds of non-consummation and her pre-contract to Francis of Lorraine. Henry VIII's physician stated that after the wedding night, Henry said he was not impotent because he experienced "duas pollutiones nocturnas in somno" (two nocturnal pollutions while in sleep).

After the annulment

Anne had been given dower lands in January 1540 to fund her household, including manors in Hampshire formerly owned by Breamore Priory and Southwick Priory. As former queen, she received a generous settlement, including Richmond Palace, and Hever Castle, home of Henry's former in-laws, the Boleyns. Anne of Cleves House, in Lewes, East Sussex, is just one of many properties she owned, though she never lived there. Henry and Anne became friendly—she was an honorary member of the king's family and was referred to as "the King's Beloved Sister". She was invited to court often and, out of gratitude for her not contesting the annulment, Henry decreed that she would be given precedence over all women in England save his own wife and daughters.

After Catherine Howard was beheaded, Anne and her brother, William, Duke of Jülich-Cleves-Berg, pressed the king to remarry Anne. Henry quickly refused to do so. She seems to have disliked Catherine Parr, and reportedly reacted to the news of Henry's sixth marriage with the remark "Madam Parr is taking a great burden on herself."

In March 1547, Edward VI's Privy Council asked her to move out of Bletchingley Palace, her usual residence, to Penshurst Place to make way for Thomas Cawarden, Master of Revels. They pointed out that Penshurst was nearer to Hever and the move had been Henry VIII's will. On 4 August 1553, Anne wrote to Mary I to congratulate her on her marriage to Philip of Spain. On 28 September 1553, when Mary left St James's Palace for Whitehall, she was accompanied by her sister Elizabeth and Anne of Cleves. Anne also took part in Mary I's coronation procession, and may have been present at her coronation at Westminster Abbey. These seem to have been her last public appearances, although there is an account of Anne at Westminster Abbey in August 1554 after the wedding of Mary and Philip. As the new queen was a strict Catholic, Anne yet again changed religion, now becoming a Roman Catholic.

After a brief return to prominence, she lost royal favour in 1554, following Wyatt's rebellion. According to Simon Renard, the imperial ambassador, Anne's close association with Elizabeth had convinced the Queen that "the Lady [Anne] of Cleves was of the plot and intrigued with the Duke of Cleves to obtain help for Elizabeth: matters in which the king of France was the prime mover". There is no evidence that Anne was invited back to court after 1554. She was compelled to live a quiet and obscure life on her estates. After her arrival as the King's bride, Anne never left England. Despite occasional feelings of homesickness, Anne was generally content in England and was described by Holinshed as "a ladie of right commendable regards, courteous, gentle, a good housekeeper and verie bountifull to her servants."

In the summer of 1556, Anne's brother, William, Duke of Jülich-Cleves-Berg, complained about some of her servants. He had heard that Otto Wylick, Jasper Brockhausen, and his wife, Gertrude, made difficulties in Anne's household. Gertrude was said to have beguiled Anne with impostures and incantations. The matter came before Queen Mary and the English council of Philip II, and in September Brockhausen and Wylick were expelled.

Death
When Anne's health began to fail, Mary allowed her to live at Chelsea Old Manor, where Henry's last wife, Catherine Parr, had lived after her remarriage. Here, in the middle of July 1557, Anne dictated her last will. In it, she mentions her brother, sister, and sister-in-law, as well as the future Queen Elizabeth, the Duchess of Suffolk, and the Countess of Arundel. She left some money to her servants and asked Mary and Elizabeth to employ them in their households. She was remembered by everyone who served her as a particularly generous and easy-going mistress.

Anne died at Chelsea Old Manor on 16 July 1557. The most likely cause of her death was cancer. She was buried in Westminster Abbey, on 3 August, in what has been described as a "somewhat hard-to-find tomb" on the opposite side of Edward the Confessor's shrine and slightly above eye level for a person of average height.

Anne's epitaph in Westminster Abbey, which is in English, reads simply:

ANNE OF CLEVES QUEEN OF ENGLAND BORN 1515 • DIED 1557

She was the last of Henry VIII's wives to die.

Fictional portrayals
The role of Anne of Cleves was played by:
 * Elsa Lanchester in The Private Life of Henry VIII, which was released in 1933. Lanchester's husband Charles Laughton played Henry VIII and won an Academy Award for his portrayal.
 * Elvi Hale in the episode Anne of Cleves in the 1971 television series The Six Wives of Henry VIII.
 * Jenny Bos in the 1972 British film Henry VIII and His Six Wives
 * Pia Girard in the 2003 ITV series Henry VIII.
 * Joss Stone in the Showtime cable television series The Tudors.
 * Rebecca Dyson-Smith in the BBC documentary mini-series Six Wives with Lucy Worsley
 * Genesis Lynea originated the role of Cleves in the musical Six.
 * Dana Herfurth will portray her in the forthcoming BBC miniseries Wolf Hall: The Mirror and the Light.

title: Anne of Cleves