Titan (moon)

From Wikipedia, the free encyclopedia

You have new messages (last change).
Titan
Titan in natural color
Titan seen from the Cassini-Huygens spacecraft.
Discovery
Discovered by: Christiaan Huygens
Discovery date: March 25, 1655
Orbital characteristics
Semi-major axis: 1,221,931 km[1]
Eccentricity: 0.028880 [2]
Orbital period: 15.94542 days
Inclination: 0.34854° (to Saturn's equator)
Satellite of: Saturn
Physical characteristics
Mean radius: 2575.50 ± 2.00 km (0.404 Earths) [3]
Surface area: 8.3×107 km²
Mass: 1.34520029 ± 0.00020155×1023 kg (0.0225 Earths) [3]
Mean density: 1.8798 ± 0.0044 g/cm³ [3]
Equatorial surface gravity: 1.352 m/s2,
or 0.14 g
Escape velocity: 2.639 km/s
Rotation period: (synchronous)
Axial tilt: zero
Albedo: 0.21
Temperature: 90 K (−297°F)
Atmosphere
Surface pressure: 146.7 kPa
Composition: 98.4% nitrogen
1.6% methane

Titan (/ˈtaɪ.tən/, from Ancient Greek Τῑτάν) or Saturn VI is the largest moon of Saturn and the second largest moon in the solar system,[4] after Jupiter's moon Ganymede. It is roughly 50% larger than Earth's moon by diameter, and is larger by diameter and mass than all known dwarf planets. It is also larger by diameter than the planet Mercury, though Mercury is more than twice as massive. It was discovered on March 25, 1655, by the Dutch astronomer Christiaan Huygens,[5] and was the first of Saturn's moons to be discovered.

Titan is the only moon in our solar system to have a dense atmosphere.[4] Until very recently, this atmosphere inhibited understanding of Titan's surface, but the moon is currently undergoing study by the Cassini-Huygens mission, and new information about it is accumulating, such as the discovery of liquid hydrocarbon lakes near its north pole. These are the only large, stable bodies of surface liquid known to exist anywhere other than Earth.

Titan is never visible to the naked eye, but can be observed through small telescopes (diameter greater than 5 cm) or strong binoculars. It has a maximum magnitude of +7.9, which is outshone by six asteroids (Vesta, Pallas, Iris, Hebe, Juno, Melpomene) and the dwarf planet Ceres. Titan reaches an angular distance of about 20 Saturn radii from Saturn and subtends a disk 0.8 arcseconds in diameter.

Contents

[edit] Name

Huygens named his discovery simply Saturni Luna (Latin for "Saturn's moon," which can also be written Luna Saturni) (De Saturni Luna observatio nova, 1656; XV). Later, Giovanni Domenico Cassini named the four moons he discovered (Tethys, Dione, Rhea and Iapetus) Sidera Lodoicea ("the stars of Louis") to honour king Louis XIV. Astronomers fell into the habit of referring to them as Saturn I through Saturn V. Other epithets used were the "Huygenian satellite of Saturn" (or "Huyghenian"), or the "sixth satellite of Saturn" (Saturn VI, still in use) (in order of distance from Saturn, once Mimas and Enceladus were also discovered in 1789).

The name "Titan" and the names of all seven satellites of Saturn then known come from John Herschel (son of William Herschel, discoverer of Mimas and Enceladus) in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope,[6] wherein he suggested the names of the Titans, sisters and brothers of Cronos (the Greek Saturn), be used.

[edit] Physical characteristics

Titan's internal structure.
Titan's internal structure.

At 5,150 km across, Titan is larger than the planet Mercury and is the second largest natural satellite in the solar system after Ganymede.[7] Prior to the arrival of Voyager 1 in 1980, Titan was thought to be slightly larger than Ganymede, an error resulting from the haze in its atmosphere which extends around 880 km above the surface and is almost opaque to visible light.[8] Hence, visual observations of Titan before discovery of this haze overestimated its diameter.

[edit] Internal structure

Titan's diameter and mass (and thus its density) are similar to Jovian moons Ganymede and Callisto.[9] Based on its bulk density of 1.88 g/cm³, Titan's bulk composition is half water ice and half rocky material. It is probably differentiated into several layers with a 3400 km (2,040 mi) rocky center surrounded by several layers composed of different crystal forms of ice.[10] Its interior may still be hot and there may be a liquid layer consisting of water and ammonia between the ice crust and the rocky core. Though similar in composition to Rhea and the rest of Saturn's moons, it is denser due to gravitational compression.

[edit] Atmosphere

True-color image of layers of haze in Titan's atmosphere.
True-color image of layers of haze in Titan's atmosphere.

Titan is the only known moon with a fully developed atmosphere that consists of more than just trace gases. The presence of a significant atmosphere was first discovered by Gerard P. Kuiper in 1944 using a spectroscopic technique that yielded an estimate of an atmospheric partial pressure of methane of the order of 100 millibars (10 kPa).[11] Since that time, observations from Voyager space probes have shown that the Titanian atmosphere is denser than Earth's, with a surface pressure more than one and a half times that of our planet, and supports an opaque cloud layer that obscures Titan's surface features at visible wavelengths. The haze that can be seen in the picture to the right contributes to the moon's Anti-Greenhouse Effect and lowers the temperature by reflecting sunlight away from the satellite. The thick atmosphere blocks most visible wavelength light from the sun and other sources from reaching Titan's surface. It is so thick, in fact, and the gravity is so low, that humans could fly through it by flapping "wings" attached to their arms.[12] The Huygens probe was unable to detect the direction of the sun during its descent, and although it was able to take images from the surface, scientists say the process was like photographing asphalt at dusk.[13]

The atmosphere is 98.4% nitrogen—the only dense nitrogen-rich atmosphere in the solar system aside from our own—with the remaining 1.6% composed of methane and only trace amounts of other gases such as hydrocarbons (including ethane, diacetylene, methylacetylene, cyanoacetylene, acetylene, propane), argon, carbon dioxide, carbon monoxide, cyanogen, hydrogen cyanide and helium.[14] 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 has no magnetic field and sometimes orbits outside Saturn's magnetosphere, directly exposing it to the solar wind. This may ionize and carry away some molecules from the top of the atmosphere.

The nitrogen ratio of 14N to 15N is 183 compared with the Earth's average of 272.[14] In the methane the isotope ratio of 12C/13C is 82.3 compared with the earth standard of 89.9.[14] The isotope ratio of H/D is 3.6 x 103 compared with 3.0 x 103 on Earth. The depletion of the lighter isotope of nitrogen indicates atmospheric escapes whereas the carbon and the hydrogen are far less depleted. The ratio of argon to nitrogen is 100 times less than in Earth's atmosphere.[14]

Layers of haze seen in a colorized ultraviolet image of Titan's night-side limb
Layers of haze seen in a colorized ultraviolet image of Titan's night-side limb

From all available data several theoretical models and experiments for the development of the Titan atmosphere have been derived. The high UV-radiation and high energy electrons are an energy source for many chemical reactions in the atmosphere. The hydrogen compounds ammonia and methane undergo dehydrogenation, forming complex organic compounds, nitrogen and hydrogen which is lost over cosmological time. The absence of ammonia and the presence of methane, although they should have a similar half life, indicates a source for methane on Titan. Clathrates (methane incorporated into ice), comets, and a Fischer Tropsch like synthesis are suggestions for the abundance of methane.[15]

The most recent flyby has suggested the existence of a large cloud over Titan's north pole, existing at a height of 40 km. At this altitude it is cold enough for ethane to freeze and the detected size of these particles is only 1-3 microns, suggesting again ethane, rather than methane which is also known to condense in the atmosphere of Titan. The downdrafts at high northern latitudes are strong enough to drive these particles towards the surface. A theory is that it is currently raining (or if cool enough, snowing) on the north pole. When the seasons switch, ethane will begin to condense over the south pole.[16]

[edit] Climate

Possible cloud of ethane (red) over Titan's north pole (marked NP)
Possible cloud of ethane (red) over Titan's north pole (marked NP)

At the surface, Titan's temperature is about 94 K (−179 °C, or −290.2 °F). At this temperature water ice does not sublimate, so the atmosphere is nearly free of water vapor. Scattered variable clouds punctuate an overall haze in Titan's atmosphere. These clouds are probably composed of methane, ethane or other simple organics. Other more complex chemicals in small quantities must produce the orange color as seen from space.

The findings of the Huygens probe indicate that Titan's atmosphere periodically rains liquid methane and other organic compounds onto the moon's surface.[17] It is possible that areas of Titan's surface may be coated in a tar-like layer of organic precipitate called tholin, but this has not been confirmed. The presence of argon 40 was also discovered in the atmosphere, evidence of cryovolcanism producing a "lava" of water ice and ammonia.[18] Later, a methane-spewing volcano was spotted in close-up images, and Titanian volcanism is now believed to be a significant source of the methane in the atmosphere. As of early 2007, liquid methane oceans appear to be present (see section below). This is a departure from the previously accepted theory that such oceans were all but entirely absent.[19]

The October 2004 Cassini flyby photographed bright, high clouds at Titan's south pole, but they do not appear to be methane, as had been expected. This discovery has baffled scientists and studies are currently underway to determine the composition of the clouds and decide whether our understanding of Titan's atmosphere needs to be revised.[20] Observations by Cassini of the atmosphere made in 2004 suggest that Titan is a "super rotator," like Venus, with an atmosphere that rotates much faster than its surface.

[edit] Surface features

Titan in false color showing surface details and atmosphere. "Xanadu" is the bright region at the centre-right
Titan in false color showing surface details and atmosphere. "Xanadu" is the bright region at the centre-right

The Cassini mission has revealed that Titan's surface is relatively smooth. The few objects that seem to be impact craters appeared to have been filled in, perhaps by raining hydrocarbons or volcanoes. The area mapped so far appears to have no height variation greater than 50 meters (165 feet);[21] however, radar altimetry has so far only covered part of the north polar region.

Titan's surface is marked by broad regions of bright and dark terrain. These include a large, highly reflective area about the size of Australia identified in infrared images from the Hubble Space Telescope and the Cassini spacecraft. This region is named Xanadu and appears to represent an area of relatively high ground. There are dark areas of similar size elsewhere on the moon, observed from the ground and by Cassini; it had been speculated that these are methane or ethane seas, but Cassini observations seem to indicate otherwise (see below). Cassini has also spotted some enigmatic linear markings, which some scientists have suggested may indicate tectonic activity, as well as regions of bright material cross cut by dark lineaments within the dark terrain.

In order to understand Titanian surface features better, the Cassini spacecraft is currently using radar altimetry and synthetic aperture radar imaging to map portions of Titan during its close fly-bys of the moon. The first images have revealed a complex, diverse geology with both rough and smooth areas. There are features that seem volcanic in origin, which probably disgorge water mixed with ammonia. There are also streaky features that appear to be caused by windblown particles.

[edit] Liquids on Titan

This section is related to a current event.
Information may change rapidly as the event progresses.
Pseudo-colored radar imaging data from a Cassini flyby of northern lattitudes, published in the journal Nature to illustrate the convincing evidence for large bodies of liquid. The false blue coloring indicates low radar reflectivity areas, likely caused by liquid.
Pseudo-colored radar imaging data from a Cassini flyby of northern lattitudes, published in the journal Nature to illustrate the convincing evidence for large bodies of liquid. The false blue coloring indicates low radar reflectivity areas, likely caused by liquid.

It has long been believed that lakes or even seas of methane might exist on Titan's surface but until recently, conclusive evidence has proven elusive.[22] When the Cassini probe arrived in the Saturnian system, 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. Cassini observed surface features that could be explained as the products of flowing liquids, but again, there were few conclusive observations.

The first indication of the presence of a lake was observed at Titan's south pole, where clouds have been observed to cluster, and where an enigmatic dark feature at the pole, named Ontario Lacus was identified as a possible lake created by precipitation from them.[23] A possible shoreline has also been identified at the pole via radar imagery.[24] Then, on January 3, 2007, it was announced that scientists have "definitive evidence of lakes filled with methane on Saturn's moon Titan."[25][26]

Following a flyby on July 22, 2006, in which the Cassini spacecraft's radar imaged the northern latitudes (which are currently in winter), a number of large, dark (and thus smooth to radar) patches were seen dotting the surface near the pole.[27] The Cassini-Huygens team have now concluded that these features are almost certainly the long sought hydrocarbon lakes of Titan. Some of the lakes appear to have channels running in or out of them, which are just as smooth. Ethane and methane may be liquids near Titan's poles, which are cold enough for these gases to condense. Repeated coverage of these areas should prove whether they are truly liquid, as any changes that correspond with wind blowing on the surface of the liquid would alter the roughness of the surface and be visible in the radar. NASA recently confirmed that there is ice from hydrocarbon rain at the north polar area.

NASA image comparing a body of liquid on Titan with Lake Superior.
NASA image comparing a body of liquid on Titan with Lake Superior.
Image of Titan taken during Huygens' descent, showing hills and topographical features that resemble a shoreline and drainage channels.
Image of Titan taken during Huygens' descent, showing hills and topographical features that resemble a shoreline and drainage channels.

The strongest evidence yet of lakes on Titan came during a Cassini flyby in late February 2007, as observations by the radar and camera instruments revealed several large features in the north polar region that may be large expanses of liquid methane and/or ethane, including one sea with an area of over 100,000 square kilometers (larger than Lake Superior), and another (though less definite) region potentially the size of the Caspian Sea.[28]

The discoveries at the poles contrast with the findings of the Huygens probe, which landed near Titan's equator on January 14, 2005. The images taken by the probe during its descent show no open areas of liquid, but strongly indicate 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 tarry substance, but it is now clear that Huygens landed on the dark region, and that it is solid without any indication of liquids. A penetrometer studied the composition of the surface as the craft impacted it, and it was initially reported that the surface was similar to loose sand, wet clay, or perhaps crème brûlée (that is, a hard crust covering a sticky material). However, 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, which may be made of water ice, are somewhat rounded, which may indicate the action of fluids on them.[30]

A view of Titan centered on the large lake-like feature in Titan's north polar region, which lies just below the day-night line in this image.
A view of Titan centered on the large lake-like feature in Titan's north polar region, which lies just below the day-night line in this image.

Since the existence of lakes on Titan has only been recently confirmed, and the hypothesized vast methane oceans have not been found, some scientists now believe that many of the moon's features are caused by cryovolcanism rather than running liquids. Alternatively, it has been hypothesized that Huygens landed during a dry season on Titan, and that periods of heavy methane rain could form lakes that subsequently evaporate. The length of the intervals between rainy periods on Titan are unknown, and scientists stress that Huygens sampled only one small site on this planet-sized moon, which is insufficient for evaluating the entire body.[31]

[edit] Impact craters

Radar SAR and imaging data from Cassini have revealed a relative paucity of impact craters on Titan's surface, suggesting a youthful surface. To date, only three impact craters have been confirmed, which includes a 440 km wide multi-ring impact basin named Menrva (seen by Cassini's ISS as a bright-dark concentric pattern),[32] a smaller 80 km wide flat-floored crater named Sinlap,[33] and a 30 km crater with a central peak and dark floor named Ksa.[34] RADAR and Cassini imaging have also revealed a number of "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 wide ring of bright, rough material known as Guabonito has been observed by Cassini.[35] 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.[36]

[edit] Cryovolcanism

Main article: Cryovolcano
One of the first radar images of Titan's complex surface. The circular feature at left, Ganesa Macula, is thought to be a cryovolcanic dome.
One of the first radar images of Titan's complex surface. The circular feature at left, Ganesa Macula, is thought to be a cryovolcanic dome.

Scientists have speculated that conditions on Titan resemble those of early Earth, though at a much lower temperature. Evidence of volcanic activity from the latest Cassini mission suggests that temperatures are probably much higher in hotbeds, enough for liquid water to exist. Argon 40 detection in the atmosphere indicates that volcanoes spew plumes of water and ammonia.[37]

[edit] Mountains

A mountain range measuring 150 km long (93 miles), 30 km (19 miles) wide and 1.5 km (1 mile) high was 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 that the mountain's material upwelled through.[38]

[edit] Dark terrain

Titan's sand dunes (below), compared with dunes on Earth's surface (above)
Titan's sand dunes (below), compared with dunes on Earth's surface (above)

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.[39] Prior to the arrival of Cassini, these regions were thought to be seas of organic matter like tar or seas of liquid hydrocarbons.[40] However, radar images captured by the Cassini spacecraft has instead revealed some of these regions to be extensive plains covered in longitudinal sand dunes. The sand dunes are believed to be formed by wind generated as a result of tidal forces from Saturn on Titan's atmosphere, which are 400 times stronger than the tidal forces of the Moon on Earth. The tidal winds cause dunes to build up in long parallel lines, with Titan's zonal winds aligning the dunes west-to-east. The dunes break this pattern around mountains, where the wind direction is shifted.

Widespread evidence has also recently been found to support the claim that lakes of hydrocarbons do in fact exist on Titan's North pole during the second of several planned Cassini spacecraft flybys.[41]

The sand on Titan might have formed when liquid methane rained and eroded the ice bedrock, possibly in the form of flash floods. Alternatively, the sand could also have come from organic solids produced by photochemical reactions in Titan's atmosphere.[42][43][44]

[edit] Huygens landing site

Main article: Huygens probe
Huygens image from Titan's surface
Huygens image from Titan's surface

The Huygens probe landed just off the easternmost tip of a bright region now called Adiri, and 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.[45]

Huygens landed on a dark plain covered in small rocks and pebbles, which are composed of water ice.[45] 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 (about 6 inches) across, and the one in the center is 4 centimeters (about 1.5 inches) across, at a distance of about 85 centimeters (about 33 inches) from Huygens. There is evidence of erosion at the base of the rocks, indicating possible fluvial activity. The surface is darker than originally expected, consisting of a mixture of water and hydrocarbon ice. It is believed that the 'soil' visible in the images is precipitation from the hydrocarbon haze above.

See also: list of geological features on Titan

[edit] Exploration of Titan

Cassini image of Epimetheus and Titan
Cassini image of Epimetheus and Titan

Titan was examined by both Voyager 1 and Voyager 2, with Voyager 1's course being diverted specifically to make a closer pass of Titan. Unfortunately Voyager 1 did not possess any instruments that could penetrate Titan's haze, an unforeseen factor. Many years later, 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 the Sickle,[46] but by then they had already been observed in the infrared by the Hubble Space Telescope. Voyager 2 took only a cursory look at Titan. The Voyager 2 team had the option of steering the spacecraft to take a detailed look at Titan or to use another trajectory which would allow it to visit Uranus and Neptune. Given the lack of surface features seen by Voyager 1, the latter plan was implemented. The Cassini-Huygens spacecraft reached Saturn on July 1, 2004 and has begun the process of mapping Titan's surface by radar; The Cassini probe flew by Titan on October 26, 2004[47] and took the highest-resolution images ever of the moon's surface, at only 1,200 kilometers,[47] discerning patches of light and dark that would be invisible to the human eye from the Earth. Huygens landed on Titan on January 14, 2005,[48] discovering that many of the moon's surface features seem to have been formed by flowing fluids at some point in the past. Present liquid on the surface may be found near the north pole, in the form of many lakes that were recently discovered by Cassini.[27]

[edit] Life on Titan

Scientists believe that the atmosphere of early Earth was similar in composition to the current atmosphere on Titan. Many hypotheses have developed that attempt to bridge the step from chemical to biological evolution. 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 hydrocyan and ethyne. Further reactions have been studied extensively.[49]

All of these experiments 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.[50] It has also been suggested that liquid ammonia oceans could exist deep below the surface.[51] Furthermore, Titan's distance from the sun and the anti-greenhouse effect of its cloud cover, as well as the absence of CO2, would further limit the option for a fully analogous environment. With these many obstacles, the topic of life on Titan may best be described as a thought experiment for examining theories for life's origin on Earth.[52] In other words, if life were able to develop on Titan, it would provide a mirror for examining the evolution of life on Earth. This line of reasoning has been challenged, however, by an alternate explanation for life's hypothetical existence on Titan. It has been proposed that, if life were to be found on Titan, that it would be statistically more likely to have originated from Earth than to have appeared independently. Research conducted by Brett Gladman of the University of British Columbia theorizes 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. Further calculations indicate that a number of these would encounter many of the bodies in the solar system, including Titan.[53][54]

While the Cassini-Huygens mission was not equipped to provide evidence for biology or complex organics, it did support the existence of an environment on Titan that is similar, in some ways, to that of the primordial Earth. However, at this time future missions and experiments are not currently being planned to research the question. Considering the time required for executing such a voyage, further scientific data would be decades away.[55]

[edit] Titan in fiction

Main article: Titan in fiction
Artistic representation of a view from the surface of Titan, with dune fields, lakes, channels and Saturn in the background.
Artistic representation of a view from the surface of Titan, with dune fields, lakes, channels and Saturn in the background.

Since Titan has a substantial atmosphere and is the most Earth-like satellite in the Solar System, it has become one of the most popular extraterrestrial settings in science fiction other than Earth's Moon and the planets. It has featured in and provided the backdrop for many stories in literature, film and television, and in more recent times computer games.

[edit] See also

[edit] Further reading

  • Lorenz, Ralph; Jacqueline Mitton (May 2002). Lifting Titan's Veil: Exploring the Giant Moon of Saturn. Cambridge University Press. ISBN 0-521-79348-3. 

[edit] References

  1. ^ Computed using the Natural Satellites Ephemeris Service µ value, Natural Satellites Ephemeris Service. Retrieved on 2006-10-14.
  2. ^ Orbital elements. Pseudo-MPEC for Saturn VI. Retrieved on 2006-10-14.
  3. ^ a b c Jacobson, R. A.; Antreasian, P. G.; Bordi, J. J.; Criddle, K. E.; et.al. (December 2006). "The gravity field of the saturnian system from satellite observations and spacecraft tracking data". The Astronomical Journal 132: 2520-2526. 
  4. ^ a b NASA page: News-Features-the Story of Saturn saturn.jpl.nasa.gov. Retrieved 8 January 2007.
  5. ^ NASA page: The Story of Saturn/The moons "On March 24, 1655, ... The next day, Christiaan Huygens ... discovered its largest moon, Titan." States the date of discovery. Retrieved 29 March 2005
  6. ^ Satellites of Saturn; Observations of Mimas, the closest and most interior satellite of Saturn, Mr Lassell, Monthly Notices of the Royal Astronomical Society, volume 8, page 42, 1847-11-12. Retrieved 29 March 2005.
  7. ^ *Bill Arnett (2005). Titan. Retrieved 10 April 2005. "Titan is nevertheless larger in diameter than Mercury"; "It was long thought that Titan was the largest satellite in the solar system but recent observations have shown that Titan's atmosphere is so thick that its solid surface is slightly smaller than Ganymede's."
  8. ^ Mori K., Tsunemi H., Katayama H., Burrows D.N., Garmire G.P., Metzger A.E. (2004), An X-Ray Measurement of Titan's Atmospheric Extent from Its Transit of the Crab Nebula, Astrophysical Journal, v. 607, pp. 1065-1069. Chandra images used by Mori et al can be viewed here.
  9. ^ Lunine, J. "Comparing the Triad of Great Moons." Astrobiology Magazine: 2005-03-21. Retrieved 2006-07-20.
  10. ^ G. Tobie, O. Grasset, J. I. Lunine, A. Mocquet, C. Sotin (2005). "Titan's internal structure inferred from a coupled thermal-orbital model". Icarus 175 (2): 496-502. DOI:10.1016/j.icarus.2004.12.007. 
  11. ^ G. P. Kuiper (1944). "Titan: a Satellite with an Atmosphere". Astrophysical Journal: 378. DOI:10.1086/144679. 
  12. ^ Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Titan, pp. 163-166, Tarcher/Putnam, 1999, ISBN 1-58542-036-0
  13. ^ Huygens Probe Sheds New Light on Titan, Petre de Selding, Space News, 21 January 2005, verified 28 March 2005
  14. ^ a b c d H. B. Niemann, S. K. Atreya, S. J. Bauer, G. R. Carignan, J. E. Demick, R. L. Frost, D. Gautier, J. A. Haberman, D. N. Harpold, D. M. Hunten, G. Israel, J. I. Lunine, W. T. Kasprzak, T. C. Owen, M. Paulkovich, F. Raulin, E. Raaen, S. H. Way (2005). "The abundances of constituents of Titan’s atmosphere from the GCMS instrument on the Huygens probe". Nature 438: 779-784. DOI:10.1038/nature04122. 
  15. ^ A. Coustenis (2005). "Formation and evolution of Titan’s atmosphere". Space Science Reviews 116: 171 – 184. DOI:10.1007/s11214-005-1954-2. 
  16. ^ David Shiga (2006). "Huge ethane cloud discovered on Titan". New Scientist 313: 1620,. 
  17. ^ Titan: Arizona in an Icebox?, Emily Lakdawalla, 2004-01-21, verified 2005-03-28
  18. ^ Seeing, touching and smelling the extraordinarily Earth-like world of Titan, ESA News, European Space Agency, 2005-01-21, verified 2005-03-28
  19. ^ Hydrocarbon volcano discovered on Titan, David L. Chandler, NewScientist.com news service, New Scientist, 2005-06-08
  20. ^ New Images of Titan Baffle Astronomers, Henry Bortman, Astrobiology Magazine, 2004-10-28, verified 2005-03-28
  21. ^ Titan's complex and strange world revealed, Stephen Battersby, NewScientist.com news service, New Scientist, 2004-10-29, verified 2005-03-28
  22. ^ S. F.Dermott, C. Sagan, (1995). "Tidal effects of disconnected hydrocarbon seas on Titan". Nature 374: 238-240. 
  23. ^ Dark Spot Near the South Pole:A Candidate Lake on Titan?. Planetary.org. Retrieved on 2006-10-14.
  24. ^ Jet Propulsion Laboratory (September 16, 2005). NASA Cassini Radar Images Show Dramatic Shoreline on Titan. Press release. Retrieved on 2006-10-14.
  25. ^ 'Proof' of methane lakes on Titan BBC news, 4 January 2007.
  26. ^ Titan Has Liquid Lakes, Scientists Report in Nature saturn.jpl.nasa.gov, 3 January 2007. Retrieved 8 January 2007.
  27. ^ a b PIA08630: Lakes on Titan. NASA/JPL. Retrieved on 2006-10-14.
  28. ^ "Cassini Spacecraft Images Seas on Saturn's Moon Titan", NASA, 2007-03-13. Retrieved on 2007-03-14.
  29. ^ Titan probe's pebble 'bash-down', BBC News, 10 April 2005.
  30. ^ New Images from the Huygens Probe: Shorelines and Channels, But an Apparently Dry Surface, Emily Lakdawalla, 2005-01-15, verified 2005-03-28
  31. ^ Titan: Arizona in an Icebox?, Emily Lakdawalla, 2004-01-21, verified 2005-03-28
  32. ^ PIA07365: Circus Maximus. NASA Planetary Photojournal. Retrieved on 2006-05-04.
  33. ^ PIA07368: Impact Crater with Ejecta Blanket. NASA Planetary Photojournal. Retrieved on 2006-05-04.
  34. ^ PIA08737: Crater Studies on Titan. NASA Planetary Photojournal. Retrieved on 2006-09-15.
  35. ^ PIA08425: Radar Images the Margin of Xanadu. NASA Planetary Photojournal. Retrieved on 2006-09-26.
  36. ^ PIA08429: Impact Craters on Xanadu. NASA Planetary Photojournal. Retrieved on 2006-09-26.
  37. ^ Tobias Owen. "Planetary science: Huygens rediscovers Titan". Nature 438: 756-757. DOI:10.1038/438756a. 
  38. ^ Mountain range spotted on Titan. BBC News (2006-12-13).
  39. ^ H. G. Roe et al. (2004). "A new 1.6-micron map of Titan's surface". Geophys. Res. Lett. 31 (17): CiteID L17S03.
  40. ^ R. Lorenz (2003). "The Glitter of Distant Seas". Science 302: 403 - 404. DOI:10.1126/science.1090464. 
  41. ^ Chang, Alicia. "Evidence of Hydrocarbon Lakes on Titan", Associated Press, 25 July 2006. Retrieved on 2006-10-14.
  42. ^ N. Lancaster (2006). "Linear Dunes on Titan". Science 312: 702 - 703. DOI:10.1126/science.1126292. 
  43. ^ Goudarzi, Sara. "Saharan Sand Dunes Found on Saturn's Moon Titan", space.com, 04 May 2006.
  44. ^ Lorenz RD, Wall S, Radebaugh J, Boubin G, Reffet E, Janssen M, Stofan E, Lopes R, Kirk R, Elachi C, Lunine J, Mitchell K, Paganelli F, Soderblom L, Wood C, Wye L, Zebker H, Anderson Y, Ostro S, Allison M, Boehmer R, Callahan P, Encrenaz P, Ori GG, Francescetti G, Gim Y, Hamilton G, Hensley S, Johnson W, Kelleher K, Muhleman D, Picardi G, Posa F, Roth L, Seu R, Shaffer S, Stiles B, Vetrella S, Flamini E, West R (2006). "The sand seas of Titan: Cassini RADAR observations of longitudinal dunes". Science 312: 724-727. DOI:10.1126/science.1123257. 
  45. ^ a b "Seeing, touching and smelling the extraordinarily Earth-like world of Titan", ESA News, European Space Agency, 2005-01-21. Retrieved on 2005-03-28.
  46. ^ Titan's Surface and Rotation: New Results from Voyager 1 Images James Richardson, Ralph Lorenz, & Alfred McEwen, Icarus, July 2004, Vol. 170/1, pp. 113-124 verified 2005-03-28.
  47. ^ a b NASA Page: Cassini-Huygens: Operations "Oct. 26, 2004: Cassini makes its first close pass by Titan. Cruising by at a distance of only 1,200 kilometers (750 miles), the spacecrafts radar provides the first detailed glimpses of the moon's mysterious surface."
  48. ^ ibid. "Jan. 14, 2005: The European Space Agency's Huygens probe descends through Titan's cloudy atmosphere, touching down on the surface about two and half hours later."
  49. ^ Raulin F., Owen T. (2002). "Organic chemistry and exobiology on Titan". Space Science Review 104 (1-2): 377-394. DOI:10.1023/A:1023636623006. 
  50. ^ Artemivia N., Lunine J, (2003). "Createring on Titan: Impact melt ejecta and the fate of surface organics". Icarus 164: 471-480. DOI:10.1016/S0019-1035(03)00148-9. 
  51. ^ Grasset, O., Sotin C., Deschamps F., (2000). "On the internal structure and dynamic of Titan". Planetary and Space Science 48: 617-636. DOI:10.1016/S0032-0633(00)00039-8. 
  52. ^ Saturn's Moon Titan: Prebiotic Laboratory. astrobio.net. Retrieved on 2004-08-11.
  53. ^ Earth could seed Titan with life. news.bbc.co.uk. Retrieved on 2007-03-10.
  54. ^ Gladman, Brett; Dones, Luke; Levinson, Harold F.; Burns, Joseph A. (2005). "Impact Seeding and Reseeding in the Inner Solar System". Astrobiology 5: 483-496. 
  55. ^ Raulin F. (2005). "Exo-astrobiological aspects of Europa and Titan: From observations to speculations". Space Science Review 116 (1-2): 471-487. DOI:10.1007/s11214-005-1967-x. 

[edit] External links

Wikimedia Commons has media related to:
... | Rhea | Titan | Hyperion | ...


v • d • e
Natural satellites of the Solar System
Planetary satellites Terrestrial · Martian · Jovian · Saturnian · Uranian · Neptunian
Other satellite systems Plutonian · Eridian · Asteroid satellites
Largest satellites Ganymede · Titan · Callisto · Io · Moon · Europa · Triton
Titania · Rhea · Oberon · Iapetus · Charon · Umbriel · Ariel · Dione · Tethys  · Enceladus · Miranda · Proteus · Mimas

Retrieved from "http://en.wikipedia.org../../../t/i/t/Titan_%28moon%29.html"