Models of oscillations in Titan's atmospheric circulation

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