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In October 2010, Sarah Horst of the University of Arizona reported finding the five nucleotide bases—building blocks of DNA and RNA—among the many compounds produced when energy was applied to a combination of gases like those in Titan's atmosphere. Horst also found amino acids, the building blocks of protein. HP Pavilion dv3-2155mx laptop keyboard

She said it was the first time nucleotide bases and amino acids had been found in such an experiment without liquid water being present.[129]

On April 3, 2013, NASA reported that complex organic chemicals could arise on Titan based on studies simulating the atmosphere of Titan. TOSHIBA PK130BH2A00 laptop keyboard

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. Although the analogy assumes the presence of liquid water for longer periods than is currently observable, several theories suggest that liquid water from an impact could be preserved under a frozen isolation layer.[130] SONY VAIO VGN-CR123E laptop keyboard

 It has also been theorized that liquid-ammonia oceans could exist deep below the surface;[123][131] 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 indeed survive.[124] Lenovo ThinkPad T510-4339 laptop keyboard

Heat transfer between the interior and upper layers would be critical in sustaining any subsurface oceanic life.[123] Detection of microbial life on Titan would depend on its biogenic effects. That the atmospheric methane and nitrogen might be of biological origin has been examined, for example. HP Pavilion dv6-2130ca laptop keyboard

It has been suggested that life could exist in the lakes of liquid methane on Titan, just as organisms on Earth live in water.[132] Such creatures would inhale H2 in place of O2, metabolize it with acetylene instead of glucose, and exhale methane instead of carbon dioxide.[132][133]

Although all living things on Earth (including methanogens) use liquid water as a solvent,

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it is speculated that life on Titan might instead use a liquid hydrocarbon, such as methane or ethane.[134] Water is a stronger solvent than methane.[135] However, water is also more chemically reactive, and can break down large organic molecules through hydrolysis.[134] A life-form whose solvent was a hydrocarbon would not face the risk of its biomolecules being destroyed in this way.[134] HP Pavilion DV6z artist edition 2 Laptop Keyboard

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.[132]

In 2010, Darrell Strobel, from Johns Hopkins University, identified a greater abundance of molecular HP G42-364LA Laptop Keyboard

hydrogen in the upper atmospheric layers of Titan compared to the lower layers, arguing for a downward flow at a rate of roughly 1025 molecules per second and disappearance of hydrogen near Titan's surface; as Strobel noted, his findings were in line with the effects Chris McKay had predicted if methanogenic life-forms were present.[132 DELL Vostro PP37L Laptop Keyboard

The same year, another study showed low levels of acetylene on Titan's surface, which were interpreted by Chris McKay as consistent with the hypothesis of organisms consuming hydrocarbons.[135] Although restating the biological hypothesis, McKay cautioned that other explanations for the hydrogen and acetylene findings are more likely:

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the possibilities of yet unidentified physical or chemical processes (e.g., a surface catalyst accepting hydrocarbon or hydrogen), or flaws in the current models of material flow.[137] Composition data and transport models need to be substantiated, and, per Occam's razor, a physical or chemical explanation is preferred a priori over one of biology (given the simplicity of chemical catalysts versus the complexity of biological forms). HP G42-364LA Laptop Keyboard

Even so, McKay notes that discovery of either, including simply of a catalyst effective at 95 K (−180 °C), would be an important discovery.[125]

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".[135]  TOSHIBA 9J.N7482.901 Laptop Keyboard

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."

Despite these biological possibilities, there are formidable obstacles to life on Titan, and any analogy to Earth is inexact. TOSHIBA Satellite U305-S2804 Laptop Keyboard

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 theories on the conditions that prevailed prior to the appearance of life on Earth.[138] HP 597635-001 Laptop Keyboard

 Although life itself may not exist, the prebiotic conditions of the Titanian environment and the associated organic chemistry remain of great interest in understanding the early history of the terrestrial biosphere.[126] Using Titan as a prebiotic experiment involves not only observation through spacecraft, but laboratory experiment, and chemical and photochemical modeling on Earth. Compaq Presario CQ57 Series Laptop Keyboard

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 transpermia. Calculations indicate that a number of these would encounter many of the bodies in the Solar System, including Titan.[139][140] DELL Vostro 1014 Laptop Keyboard

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.

Conditions on Titan could become far more habitable in the far future. Lenovo 3000 N200 Laptop Keyboard

Five billion years from now, as the Sun becomes a red giant, surface temperatures could rise enough for Titan to support liquid water on its surface making it habitable.[142] 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.  HP Pavilion zv6223ea Laptop Keyboard

These conditions together could create a habitable environment, and could persist for several hundred million years. This was sufficient time for simple life to evolve on Earth, although the presence of ammonia on Titan would cause chemical reactions to proceed more slowly.

According to Cassini data from 2008, Titan has hundreds of times more liquid hydrocarbons than all the known oil and natural gas reserves on Earth.  Lenovo Thinkpad T520 Laptop Keyboard

These hydrocarbons rain from the sky and collect in vast deposits that form lakes and dunes.[1] "Titan is just covered in carbon-bearing material—it’s a giant factory of organic chemicals," said Ralph Lorenz, who leads the study of Titan based on radar data from Cassini. “This vast carbon inventory is an important window into the geology and climate history of Titan.” ACER Aspire 4736Z laptop keyboard

Several hundred lakes and seas have been observed, with several dozen estimated to contain more hydrocarbon liquid than Earth's oil and gas reserves. The dark dunes that run along the equator contain a volume of organics several hundred times larger than Earth's coal reserves.  HP Pavilion DV7t-3100 laptop keyboard

Radar images obtained on July 21, 2006 appear to show lakes of liquid hydrocarbon (such as methane and ethane) in Titan's northern latitudes. This is the first discovery of currently existing lakes beyond Earth. The lakes range in size from about a kilometer in width to one hundred kilometers across.[3] HP Pavilion dv6-2150es laptop keyboard

On March 13, 2007, JPL announced that it found strong evidence of seas of methane and ethane in the northern hemisphere. At least one of these is larger than any of the Great Lakes in North America.

The American aerospace engineer and author Robert Zubrin identified Saturn as the most important and valuable of the four gas giants in the solar system, HP Pavilion dv6-3107ax laptop keyboard

because of its relative proximity, low radiation, and excellent system of moons. He also named Titan as the most important moon on which to establish a base to develop the resources of the Saturn system.

Robert Zubrin has pointed out that Titan possesses an abundance of all the elements necessary to support life, saying "In certain ways,  SONY VAIO VGN-FS415E laptop keyboard

Titan is the most hospitable extraterrestrial world within our solar system for human colonization." [6] The atmosphere contains plentiful nitrogen and methane, and strong evidence indicates that liquid methane is on the surface and, liquid water, and ammonia are present under the surface and are often delivered to the surface by volcanic activity. HP Pavilion DV7-3165dx laptop keyboard

Water can easily be used to generate breathable oxygen. Nitrogen is ideal to add buffer gas partial pressure to breathable air; indeed, nitrogen forms about 78% of Earth's atmosphere.[7] Nitrogen, methane and ammonia can all be used to produce fertilizer for growing food.

Additionally, Titan has an atmospheric pressure one and a half times that of Earth. SONY VAIO VGN-NW25GF laptop keyboard

This means that the interior air pressure of landing craft and habitats could be set equal or close to the exterior pressure,reducing the difficulty and complexity of structural engineering for landing craft and habitats compared with low or zero pressure environments such as on the Moon, Mars, or the asteroids. Compaq Presario CQ71-317EA laptop keyboard

The thick atmosphere would also make radiation a non-issue, unlike on the Moon, Mars, or the asteroids. While Titan's atmosphere does contain trace amounts of hydrogen cyanide, in the event that an astronaut's respiration system is breached, the concentration would not inflict more than a slight headache. HP Pavilion dv6-2129ev laptop keyboard

A greater danger is that the gases of the atmosphere can generate an explosive mixture with oxygen, which requires special measures in the event that a leak occurs in a habitable module or a spacesuit.

Titan has a surface gravity of 0.14 g, slightly less than that of the Moon. FUJITSU Lifebook P1610 laptop keyboard

Managing long-term effects of low gravity on human health would therefore be a significant issue for long-term occupation of Titan, more so than on Mars. These effects are still an active field of study. They can include symptoms such as loss of bone density, loss of muscle density, and a weakened immune system.SONY VAIO VGN-FS640/W laptop keyboard

 Astronauts in Earth orbit have remained in microgravity for up to a year or more at a time. Effective countermeasures for the negative effects of low gravity are well-established, particularly an aggressive regime of daily physical exercise or weighted clothing. The variation in the negative effects of low gravity as a function of different levels of low gravity are not known,  HP 405963-001 laptop keyboard

since all research in this area is restricted to humans in zero gravity. The same goes for the potential effects of low gravity on fetal and pediatric development. It has been hypothesized that children born and raised in low gravity such as on Titan would not be well adapted for life under the higher gravity of Earth.  HP Pavilion G6-1223TX Laptop Keyboard

The temperature on Titan is about 94 K (−179 °C, or −290.2 °F), so insulation and heat generation and management would be significant concerns. Although the air pressure at Titan's surface is about 1.5 times that of Earth at sea level, because of the colder temperature the density of the air is closer to 4.5 times that of Earth sea level. HP Pavilion dv6-3001so laptop keyboard

At this density, temperature shifts over time and between one locale and another would be far smaller than comparable types of temperature changes present on Earth. The corresponding narrow range of temperature variation reduces the difficulties in structural engineering.

Relative thickness of the atmosphere combined with extreme cold makes additional troubles for human habitation. HP HDX18-1100 CTO laptop keyboard

Unlike in a vacuum, the high atmospheric density makes thermoinsulation a significant engineering problem.

The very high ratio of atmospheric density to surface gravity also greatly reduces the wingspan needed for an aircraft to maintain lift, so much so that a human would be able to strap on wings and easily fly through the atmosphere.[6] SONY VAIO VGN-N21E/W laptop keyboard

However, due to Titan's extremely low temperatures, heating of a flight-bound vehicle becomes a key obstacle.

The lakes of Titan, a moon of Saturn, are bodies of liquid ethane and methane that have been detected by theCassini–Huygens space probe, and had been suspected long before.[2] HP Pavilion dv5-1118tx laptop keyboard

The large ones are known as maria (seas) and the small ones as lacūs (lakes).

The possibility that there were seas on Titan was first suggested based on Voyager 1 and 2 data. The data showed Titan to have a thick atmosphere of approximately the correct temperature and composition to support them. HP AEUT5U00010 laptop keyboard

Direct evidence was not obtained until 1995 when data from the Hubble Space Telescope and other observations had already 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.[4]

The Cassini mission affirmed the former hypothesis, although not immediately. HP Mini 110-3504tu laptop keyboard

When the probe arrived in the Saturnian system in 2004, it was hoped that hydrocarbon lakes or oceans might be detectable by reflected sunlight from the surface of any liquid bodies, but no specular reflections were initially observed.[5]

The possibility remained that liquid ethane and methane might be found on Titan's polar regions, where they were expected to be abundant and stable.[6] SONY VGN-FE21H laptop keyboard

 In Titan's south polar region, an enigmatic dark feature named Ontario Lacus was the first suspected lake identified, possibly created by clouds that are observed to cluster in the area.[7] A possible shoreline was also identified near the pole via radar imagery.[8] Following a flyby on July 22, 2006, in which the Cassini spacecraft's radar imaged the northern latitudes  HP G72-b60SF laptop keyboard

 (which were at the time in winter), a number of large, smooth (and thus dark to radar) patches were seen dotting the surface near the pole.[9] Based on the observations, scientists announced "definitive evidence of lakes filled with methane on Saturn's moon Titan" in January 2007.[6][10] HP Mini 110-3180sv laptop keyboard

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 off Earth. Some appear to have channels associated with liquid and lie in topographical depressions.[6] Channels in some regions have created surprisingly little erosion, LENOVO IdeaPad S10 20015 laptop keyboard

suggesting erosion on Titan is extremely slow, or some other recent phenomena may have wiped out older riverbeds and landforms.[11] Overall, the Cassini radar observations have shown that lakes cover only a few percent of the surface and are concentrated near the poles, making Titan much drier than Earth.[12] HP Mini 110-3180sv laptop keyboard

 The high relative humidity of methane in Titan’s lower atmosphere could be maintained by evaporation from lakes covering only 0.002–0.02% of the whole surface.[13]

During a Cassini flyby in late February 2007, radar and camera observations revealed several large features in the north polar region interpreted as large expanses of liquid methane and/or ethane, Lenovo ThinkPad Edge E125 laptop keyboard

including one sea (Ligeia Mare) with an area of over 100,000 km² (larger thanLake Superior), and another incompletely imaged region potentially the size of the Caspian Sea (Kraken Mare).[14] A flyby of Titan's southern polar regions in October 2007 revealed similar, though far smaller, lakelike features.[15] HP Pavilion dv6-3230us laptop keyboard

Image of Titan taken duringHuygens' descent, showing hills and topographical features that resemble a shoreline and drainage channels.

During a close Cassini flyby in December 2007 the visual and mapping instrument observed a lake, Ontario Lacus, in Titan's south polar region. ACER K052030A1 laptop keyboard

This instrument identifies chemically different materials based on the way they absorb and reflect infrared light. Based on this instrument's observations, scientists concluded that at least one of the large lakes observed on Saturn's moon Titan does in fact contain liquid, that liquid being hydrocarbons, and have positively identified the presence of ethane.  DELL Inspiron 6400 Laptop Keyboard

And on July 8, 2009, a specular reflection in infrared was seen off Jingpo Lacus, a lake near Kraken Mare. This confirms the presence of liquid on the part of the moon dotted with many large, lake-shaped basins, in the northern regions of Titan.[16] This makes Titan the only other object than Earth in the solar system known to have stable liquid on its surface.[17] TOSHIBA NSK-TAJ01 Laptop Keyboard

This would make Titan a very interesting place to observe and study, to refine weather science, as differing liquid and gaseous materials and temperatures are at play there. This would help refine the science of Earth weather forecasting, allowing for better weather forecasts.[ Radar measurements made in July 2009 and January 2010 indicate that Ontario Lacus is extremely shallow, ACER Aspire 7741G Laptop Keyboard

with an average depth of 0.4–3.2 m, and a maximum depth of 2.9–7.4 m.[18] It may thus resemble a terrestrial mudflat. In contrast, the northern hemisphere's Ligeia Mare has depths exceeding 8 m, the maximum measurable by the radar instrument.

According to Cassini data, scientists announced on February 13, 2008, SONY KFRMBA152B Laptop Keyboard

that Titan hosts within its polar lakes "hundreds of times more natural gas and other liquid hydrocarbons than all the known oil and natural gas reserves on Earth." The desert sand dunes along the equator, while devoid of open liquid, nonetheless hold more organics than all of Earth's coal reserves.[19] HP Pavilion dv6-3001so Laptop Keyboard

In June 2008, Cassini's Visible and Infrared Mapping Spectrometer confirmed the presence of liquid ethane beyond doubt in a lake in Titan's southern hemisphere.[20] The exact blend of hydrocarbons in the lakes is unknown. In addition to ethane, methane is almost certainly present. Methane rain should fall on the lakes but it is vastly more volatile than ethane, HP HDX18-1100 CTO Laptop Keyboard

so it probably evaporates much faster from lakes, leaving the heavier hydrocarbons behind. Cyclonesdriven by this evaporation and involving rain as well as gale-force winds of up 20 meters per second are expected to form over the large northern seas only (Kraken Mare, Ligeia Mare, Punga Mare) in northern summer, lasting up to ten days.[21]  TOSHIBA Satellite C655-S9521D Laptop Keyboard

According to a computer model developed by Daniel Cordier of the University of Rennes, three-quarters of an average polar lake is ethane, with 10 per cent methane, 7 per cent propane and smaller amounts of hydrogen cyanide, butane, nitrogen and argon. The chemical composition and physical properties of the lakes probably varies from one lake to another. HP G42-380LA Laptop Keyboard

The lack of evidence of waves possibly indicates the lakes contain heavier tar like hydrocarbons making them more viscous than expected (calculations indicate wind speeds of less than 1 metre per second should whip up detectable waves in Titan's ethane lakes but none have been observed).[22] In such a case, GATEWAY NV-53 Laptop Keyboard

Titan's lakes are rather more like giant tar pits. Another possible explanation would be solidification of hydrocarbons. The optical properties of solid methane surface (close to the melting point) are quite close to the properties of liquid surface however the viscosity of solid methane, even near the melting point, is many orders of magnitude higher, which might explain extraordinary smoothness of the surface.[23]  HP 646568-001 Laptop Keyboard

Solid methane is denser than liquid methane so it will eventually sink. However, according to calculations presented in a 2012 paper by Jason Hofgartner[24] the methane ice is initially expected to float as it probably contains pockets of nitrogen gas from Titan's atmosphere. Temperatures close to the freezing point of methane (90.4 Kelvins) could lead to both floating and sinking ice - t ACER Aspire One D150-1920 Laptop Keyboard

hat is, a hydrocarbon ice crust above the liquid and blocks of hydrocarbon ice on the bottom of the lake bed. The ice is predicted to rise to the surface again at the onset of spring before melting.

On 21 December 2008, Cassini passed directly over Ontario Lacus at an altitude of 1900 km and was able to observe specular reflection in radar observations. HP AEUT5U00010 Laptop Keyboard

The signals were much stronger than anticipated and saturated the probe's receiver. The conclusion drawn from the strength of the reflection was that the lake level did not vary by more than 3 mm over a first Fresnel zone reflecting area only 100 m wide (smoother than any natural dry surface on Earth). From this it was surmised that surface winds in the area are minimal at that season and/or the lake fluid is more viscous than expected.[25][26] ACER Aspire One D150-1920 Laptop Keyboard

On 8 July 2009, Cassini's Visual and Infrared Mapping Spectrometer (VIMS) observed a specular reflection in 5 micron infraredlight off a northern hemisphere body of liquid at 71° N, 337° W. This has been described as at the southern shoreline of Kraken Mare,[27] but on a combined radar-VIMS image the location is shown as a separate lake (later named Jingpo Lacus).  HP AEUT5U00010 Laptop Keyboard

The observation was made shortly after the north polar region emerged from 15 years of winter darkness. Because of the polar location of the reflecting liquid body, the observation required a phase angle close to 180°.

The discoveries in the polar regions contrast with the findings of the Huygens probe, which landed near Titan's equator on January 14, 2005. APPLE A1278 Laptop Keyboard

The images taken by the probe during its descent showed no open areas of liquid, but strongly indicated the presence of liquids in the recent past, showing pale hills crisscrossed with dark drainage channels that lead into a wide, flat, darker region. It was initially thought that the dark region might be a lake of a fluid or at least tar-like substance, ACER 9J.N0F82.A1D Laptop Keyboard

but it is now clear that Huygens landed on the dark region, and that it is solid without any indication of liquids. Apenetrometer studied the composition of the surface as the craft impacted it, and it was initially reported that the surface was similar to wet clay, or perhaps crème brûlée (that is, a hard crust covering a sticky material). HP G72-b66US Laptop Keyboard

Subsequent analysis of the data suggests that this reading was likely caused by Huygens displacing a large pebble as it landed, and that the surface is better described as a "sand" made of ice grains.[29] The images taken after the probe's landing show a flat plain covered in pebbles. The pebbles may be made of water ice and are somewhat rounded, which may indicate the action of fluids.[30] ACER 9J.N0F82.A1D Laptop Keyboard

Thermometers indicated that heat was wicked away from Huygens so quickly that the ground must have been damp, and one image shows light reflected by a dewdrop as it falls across the camera's field of view. On Titan, the feeble sunlight allows only about one centimeter of evaporation per year (versus one meter of water on Earth),  HP G72-b66US Laptop Keyboard

but the atmosphere can hold the equivalent of about 10 meters of liquid before rain forms vs. only a few centimeters on Earth. So Titan's weather is expected to feature torrential downpours causing flash floods, interspersed by decades or centuries of drought.[31] Cassini has observed equatorial rainstorms only once since 2004. HP Mini 110-3180sv Laptop Keyboard

Despite this, a number of long-standing tropical hydrocarbon lakes were unexpectedly discovered in 2012 (including one near the Huygens landing site in the Shangri-La region which is about half the size of Utah's Great Salt Lake, with a depth of at least 1 meter). As on Earth, the likely supplier is probably undergroundaquifers, in other words the arid equatorial deserts of Titan contain "oases".[32] Lenovo 3000 N200 Laptop Keyboard

Models of oscillations in Titan's atmospheric circulation suggest that over the course of a Saturnian year, liquid is transported from the equatorial region to the poles, where it falls as rain. This might account for the equatorial region's relative dryness.[33] According to a computer model developed by researchers at the California Institute of Technology (Caltech),[32] DELL Vostro 3450 Laptop Keyboard

 intense rainstorms should occur in normally rainless equatorial areas during Titan's vernal and autumnal equinoxes—enough liquid to carve out the type of channels that Huygens found. The CalTech model also predicts energy from the Sun will evaporate liquid methane from Titan's surface except at the poles,  DELL Vostro 3550 Laptop Keyboard

where the relative absence of sunlight makes it easier for liquid methane to accumulate into permanent lakes. The model also apparently explains why there are more lakes in the northern hemisphere. Due to the eccentricity of Saturn's orbit, the northern summer is longer than the southern summer and consequently the rainy season is longer in the north. HP Pavilion dv6-2125ef laptop keyboard

Whether there is life on Titan, the largest moon of Saturn, is at present an open question and a topic of scientific evaluation and research.

Titan is far colder than Earth, and its surface seems to lack liquid water; factors which have led some scientists to consider life there unlikely. HP Pavilion dv6-2110ev laptop keyboard

On the other hand, the following points have been made in favor of Titan's suitability to sustain some form of life:

Titan appears to have lakes of liquid ethane and/or liquid methane on its surface, as well as rivers and seas, which some scientific models (still tentative and debated) suggest could support non-water-based life.[1][2][3] SONY VAIO VGN-N31Z/W laptop keyboard

  • t has also been suggested that life may exist in a sub-surface ocean consisting of water and ammonia.[4] Recent data from NASA's Cassini spacecraft have strengthened evidence that Titan likely harbors a layer of liquid water under its ice shell.[5]

Titan is the only known natural satellite (moon) in the Solar System that is known to have a fully developed atmosphere that consists of more than trace gases. ACER TravelMate 6252 laptop keyboard

  • Titan's atmosphere is thick, chemically active, and is known to be rich in organic compounds; this has led to speculation about whether chemical precursors of life may have been generated there.[1][2][3]

The atmosphere also contains hydrogen gas, which is cycling through the atmosphere and the surface environment, and which living things comparable to Earthmethanogens could combine with some of the organic compounds (such as acetylene) to obtain energy.[1][2][3] SONY VGN-FE11M laptop keyboard

In June 2010, scientists analysing data from the Cassini–Huygens mission reported anomalies in the atmosphere near the surface which could be consistent with the presence of methane-producing organisms, but may alternatively be due to non-living chemical or meteorological processes.[6] The Cassini–Huygens mission was not equipped to provide direct evidence for biology or complex organics. TOSHIBA Satellite L750-ST4NX1 laptop keyboard

Due to its distance from the Sun, Titan is much colder than the Earth. Its surface temperature is about 90 K (−179 °C, or −290 °F). At these temperatures, water ice does not melt, evaporate or sublime, but remains solid.

Because of the extreme cold and also because of lack of carbon dioxide (CO2) in the atmosphere, ASUS X53S laptop keyboard

scientists such as Jonathan Lunine have viewed Titan less as a likely habitat for extraterrestrial life, than as an experiment for examining theories on the conditions that prevailed prior to the appearance of life on Earth.[7] However Lunine does not rule out life in an environment of liquid methane and ethane, and has written about what discovery of such a life form (even if very primitive) would imply about the prevalence of life in the universe. Acer eMachines E640 laptop keyboard

In the 1970s, astronomers found unexpectedly high levels of infrared emissions from Titan.[9] One possible explanation for this was the surface was warmer than expected, due to a greenhouse effect. Some estimates of the surface temperature even approached temperatures in the cooler regions of the Earth. TOSHIBA Satellite L655-S5107 laptop keyboard

There was, however, another possible explanation for the infrared emissions: Titan's surface was very cold, but the upper atmosphere was heated due to absorption of ultraviolet light by molecules such as ethane, ethylene and acetylene.[9]

In September 1979, Pioneer 11, the first space probe to conduct fly-by observations of Saturn and its moons, HP Pavilion DV6z artist edition 2 laptop keyboard

sent data showing Titan's surface to be extremely cold by Earth standards, and much below the temperatures generally associated with planetary habitability.

Titan may become warmer in the future.[11] Six billion years from now, as the Sun becomes a red giant, surface temperatures could rise to ~200 K (−70 °C), TOSHIBA Satellite L750-ST5N02 laptop keyboard

high enough for stable oceans of water/ammonia mixture to exist on the surface. 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. HP Pavilion DV6-1160ed laptop keyboard

These conditions together could create an environment agreeable to exotic forms of life, and will persist for several hundred million years.[11] This was sufficient time for simple life to evolve on Earth, although the presence of ammonia on Titan will cause the same chemical reactions to proceed more slowly. SONY VAIO VGN-FS195VP laptop keyboard

Apparent lack of liquid water on Titan's surface has been cited by NASA astrobiologist Andrew Pohorille as an argument against life there. Pohorille considers that water is important not only as the solvent used by "the only life we know" but also because its chemical properties are "uniquely suited to promote self-organization of organic matter". IBM ThinkPad T42 laptop keyboard

He has questioned whether prospects for finding life on Titan's surface are sufficient to justify the expense of a mission which would look for it.

While the Cassini–Huygens mission was not equipped to provide evidence for biosignatures or complex organics, it showed an environment on Titan that is similar, in some ways, to ones theorized for the primordial Earth.[13] DELL Inspiron N4050 laptop keyboard

 Scientists think 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.[14] Many hypotheses have developed that attempt to bridge the step from chemical to biological evolution. GATEWAY MT3707 laptop keyboard

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 cyanideand acetylene. Further reactions have been studied extensively.[15] HP Pavilion dv6-3050tx laptop keyboard

In October 2010, Sarah Horst of the University of Arizona reported finding the five nucleotide bases—building blocks of DNA and RNA—among the many compounds produced when energy was applied to a combination of gases like those in Titan's atmosphere. Horst also found amino acids, the building blocks of protein. SONY VGN-FE48E laptop keyboard

She said it was the first time nucleotide bases and amino acids had been found in such an experiment without liquid water being present.[16]

On April 3, 2013, NASA reported that complex organic chemicals could arise on Titan based on studies simulating the atmosphere of Titan.  Lenovo Thinkpad T520 laptop keyboard

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. While the analogy assumes the presence of liquid water for longer periods than is currently observable, several theories suggest that liquid water from an impact could be preserved under a frozen isolation layer.[18Compaq Presario CQ71-403SA laptop keyboard

] It has also been observed that liquid ammonia oceans could exist deep below the surface;[19][20] one model suggests an ammonia–water solution as much as 200 km deep beneath a water ice crust, conditions that, "while extreme by terrestrial standards, are such that life could indeed survive".[4] HP Pavilion dv6-2150us laptop keyboard

Heat transfer between the interior and upper layers would be critical in sustaining any sub-surface oceanic life.[19] Detection of microbial life on Titan would depend on its biogenic effects. That the atmospheric methane and nitrogen could be examined for biogenic origin, for example. HP Pavilion dv6-2030ev laptop keyboard

It has also been suggested that life could exist in the liquid methane and ethane that form rivers and lakes on Titan's surface, just as organisms on Earth live in water.[21] Such creatures would take in H2 in place of O2, react it with acetylene instead of glucose, and produce methane instead of carbon dioxide.[21] TOSHIBA Satellite L655-S5083 laptop keyboard

By comparison, somemethanogens on Earth obtain energy by reacting hydrogen with carbon dioxide, producing methane and water.

Although all living things on Earth (including methanogens) use liquid water as a solvent, it is conceivable that life on Titan might instead use a liquid hydrocarbon, such as methane or ethane.[22] Water is a stronger solvent than the hydrocarbons.[23] TOSHIBA Satellite L655-S5160 laptop keyboard

 However, water is also more chemically reactive, and can break down large organic molecules through hydrolysis.[22] A life-form whose solvent was a hydrocarbon would not face the risk of its biomolecules being destroyed in this way.

In 2005, astrobiologists Chris McKay and Heather Smith predicted that if methanogenic life is consuming atmospheric hydrogen in sufficient volume,Lenovo 3000 G430 4152 laptop keyboard

it will have a measurable effect on the mixing ratio in thetroposphere of Titan. The effects predicted included a level of acetylene much lower than otherwise expected, as well as a reduction in the concentration of hydrogen itself.[21]

Evidence consistent with the predictions was reported in June 2010 by Darrell Strobel of Johns Hopkins University, Acer eMachines E640 laptop keyboard

who noted an overabundance of molecular hydrogen in the upper atmospheric layers, which leads to a downward flow at a rate of roughly 1025 molecules per second. Near the surface the hydrogen apparently disappears.[21][23][24] Another paper released the same month showed very low levels of acetylene on Titan's surface.[23] HP Mini 110-3504tu laptop keyboard

Chris McKay agreed with Strobel that presence of life, as suggested in McKay's 2005 article, is a possible explanation for the findings about hydrogen and acetylene; but also cautioned that other explanations are currently more likely: namely the possibility that the results are due to human error, to a meteorological process, or to the presence of some mineral catalyst.[6][25] Lenovo Thinkpad T520 Laptop Keyboard

He noted that such a catalyst, effective at -178°C (95K), is presently unknown, and would in itself be a startling discovery, though less startling than discovery of an extraterrestrial life form.[6]

The June 2010 findings gave rise to considerable media interest, including a report in the British newspaper, the Telegraph, which spoke of clues to the existence of "primitive aliens".COMPAQ Presario C700 Laptop Keyboard

In order to assess the likelihood of finding any sort of life on various planets and moons, Dirk Schulze-Makuch and other scientists have developed a Planetary Habitability Index which takes into account factors including characteristics of the surface and atmosphere, availability of energy, solvents and organic compounds.[27] Lenovo 45N2240 Laptop Keyboard

Using this index, based on data available in late 2011, the scientists found that Titan has the highest current habitability rating of any known world, other than Earth.

Titan is presented as a test case for the relation between chemical reactivity and life, in a 2007 report on life's limiting conditions prepared by a committee of scientists under the United States National Research Council. Lenovo IdeaPad Y710 Laptop Keyboard

The committee, chaired by John A. Baross, considered that "if life is an intrinsic property of chemical reactivity, life should exist on Titan. Indeed, for life not to exist on Titan, we would have to argue that life is not an intrinsic property of the reactivity of carbon-containing molecules under conditions where they are stable... DELL Latitude D830 Laptop Keyboard

David Grinspoon, one of the scientists who in 2005 proposed that hypothetical organisms on Titan might use hydrogen and acetylene as an energy source,[29] has mentioned the Gaia hypothesis in the context of discussion about Titan life. He suggests that, just as Earth's environment and its organisms have evolved together, TOSHIBA Satellite U305-S2812 Laptop Keyboard

the same thing is likely to have happened on other worlds with life on them. In Grinspoon's view, worlds which are "geologically and meteorologically alive are much more likely to be biologically alive as well".

An alternate explanation for life's hypothetical existence on Titan has been proposed: GATEWAY M-6319 Laptop Keyboard

if life were to be found on Titan, it could have originated from Earth in a process called panspermia. It is theorized that large asteroid and cometary impacts on Earth's surface have caused hundreds of millions of fragments of microbe-laden rock to escape Earth's gravity. Calculations indicate that a number of these would encounter many of the bodies in the Solar System, including Titan.[ HP 634139-001 Laptop Keyboard

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.[33] In Lunine's view, presence of organisms in Titan's lakes would mean a second, independent origin of life within the Solar System, TOSHIBA Satellite L655-S5083 Laptop Keyboard

implying that life has a high probability of emerging on habitable worlds throughout the cosmos. HP pavilion DV7-1000 Laptop Keyboard,TOSHIBA Satellite A300 Laptop Keyboard,TOSHIBA Satellite A110 Series Laptop Keyboard

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