Advanced | Help | Encyclopedia
Directory


Titan (moon)

This page is about the moon of Saturn. For other meanings, see Titan (disambiguation).

Titan (tye'-tun, IPA [ˈtaɪt ən]; Greek Τιτάνας) is the largest moon of Saturn and the second largest moon in the solar system[1], after Jupiter's moon Ganymede. It was discovered on March 25 1655 by the Dutch astronomer Christiaan Huygens[2], and was the first satellite in the Solar System to be discovered after the Galilean moons of Jupiter. Titan is the only moon in our solar system to have a dense atmosphere[3]. 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 continuously accumulating.

Titan
Discovery
Discoverer Christiaan Huygens
Date March 25, 1655
Orbital characteristics
Semimajor axis 1,221,931 km
Eccentricity 0.028880 [4]
Orbital period 15.94542 d
Inclination 0.34854° (to Saturn's equator)
Is a satellite of Saturn
Physical characteristics
Mean diameter 5150 km
Surface area 83×106km2
Mass 1.345×1023 kg
Mean density 1.88 g/cm3
Equatorial surface
gravity
1.35 m/s2,
or .14 gee
Rotation period (synchronous)
Axial tilt zero
Albedo 0.21
Surface temp.
min mean max
 ?K 94 K  ?K
Atmospheric characteristics
Pressure 160 kPa
Nitrogen 94 percent
Methane 6 percent

Table of contents

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, Jean-Dominique Cassini named the four moons he discovered (Tethys, Dione, Rhea and Iapetus) Lodicea Sidera ("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[5], wherein he suggested the names of the Titans, sisters and brothers of Cronos (the Greek Saturn), be used.

Visibility from Earth

Titan has a magnitude between +7.9 and +8.7 and reaches an angular distance of about 20 Saturn radii from Saturn. It can be observed through small telescopes (diameter greater than 5cm) or strong binoculars. It subtends a disk of 0.8" in diameter.

Physical characteristics

Titan is larger than the planet Mercury[6] (though less massive) and is the second largest natural satellite in the solar system after Ganymede[7]. It was originally thought to be slightly larger than Ganymede, but recent observations have shown that its thick atmosphere reflects a large amount of light causing an overestimation of its diameter. Like several other satellites, Titan is also larger and more massive than Pluto.

Titan is similar in bulk properties to Ganymede, Callisto, Triton, and (probably) Pluto. Titan is about half water ice and half rocky material. It is probably differentiated into several layers with a 3400 km rocky center surrounded by several layers composed of different crystal forms of ice. Its interior may still be hot. Though similar in composition to Rhea and the rest of Saturn's moons, it is denser due to gravitational compression.

Atmosphere

Titan in false colour showing surface details and atmosphere. Photographed on October 26, 2004 by the Cassini spacecraft

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. Since that time, observations from Voyager space probes have shown that Titan's 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. It is thought that Titan may possess bodies of liquid ethane. Recent radar measurements from Earth suggest that there is no large-scale ocean of ethane on Titan, but it may still be present in smaller lakes.

The atmosphere is 94% nitrogen — the only dense nitrogen-rich atmosphere in the solar system aside from our own — with significant traces of various hydrocarbons making up much of the remainder (including methane, ethane, diacetylene, methylacetylene, cyanoacetylene, acetylene, propane, along with carbon dioxide, carbon monoxide, cyanogen, hydrogen cyanide, and helium). These 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.

At the surface, Titan's temperature is about -179.15 °C. At this temperature water ice does not sublimate, effecting a nearly water-vaporless atmosphere. 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 thick atmosphere blocks most sunlight from reaching Titan's surface. 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 [8]. It is therefore unlikely that Saturn is ever visible from the surface of Titan. The findings of the Huygens probe indicate that Titan's atmosphere periodically rains liquid methane and other organic compounds onto the moon's surface [9]. 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 [10]. 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 [11]. 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.

Surface features

Overall topography

"Xanadu" is the bright region at the centre-right of this Cassini image

At present, maps of Titan's surface show broad regions of bright and dark terrain, including a large, highly reflective area about the size of Australia identified in infra-red images from the Hubble Space Telescope and the Cassini spacecraft. This region has been officially named Xanadu; it is not certain what kind of terrain it represents. There are similarly-sized dark areas elsewhere on the moon, observed by Hubble, the Keck telescopes, and the Very Large Telescope, which some speculated may be methane or ethane seas, though Cassini observations seem to indicate otherwise. Cassini has taken higher-resolution pictures of all these features, and 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 Titan's 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. The few objects that seem to be impact craters appeared to have been filled in, perhaps by raining hydrocarbons. The area mapped so far appears to be fairly smooth with no height variation greater than 50 metres [12]; however, radar altimetry has so far only covered part of the north polar region.

One of the first radar images of Titan's complex surface

During the October 26 2004 fly-by of Titan by Cassini, a smooth surface with few impact craters was observed, marked by strongly differentiated light and dark regions. This suggests that the moon has an active surface that is constantly being resurfaced, possibly by hydrocarbon rain or snow filling in the craters or by volcanic activity.

RADAR SAR data taken during a flyby on February 15 2005 revealed even more intriguing surface features, including a 440-km wide multi-ring impact basin (seen by ISS as a bright-dark concentric pattern), a smaller 60-km wide flat-floored crater, and regions of roughly parallel bright and dark lineaments which maybe ice- or hydrocarbon-rich sand dunes.

The Huygens probe photographed pale hills with dark 'rivers' running down to a dark plain. Current understanding is that the hills are composed of water ice. Dark organic compounds rain from Titan's atmosphere and flow down the hills to form the dark plains [13].

Liquids on Titan

It has long been believed that lakes or even seas of methane might exist on Titan's surface. However, while many of Titan's surface features could be explained as the products of flowing liquids, no conclusive evidence has yet been found for the presence of liquids on Titan's surface at the present time. [14] 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 observed.

Image taken during the descent of Huygens, showing an apparent shoreline and hills riddled with channels

The findings of the January 14 2005 landing on Titan by the Huygens probe do not show any open areas of liquid. However, they strongly indicate the presence of liquids in the recent past. The Huygens images show pale hills crisscrossed with dark drainage channels. The channels 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. However, it is now clear that Huygens landed on the dark region, and it is solid.

There is no immediate trace of liquid on the Huygens landing site. A penetrometer studied the composition of the surface as the craft impacted it, and it was initially reported that the surface is 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 [15]. 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 [16].

The existence of lakes on Titan thus remains unconfirmed. However, it has been hypothesized that Huygens landed during a dry season on Titan, and that periods of heavy methane rain in the recent past 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 tiny site on this planet-sized moon, which is insufficient for evaluating the entire body [17].

Panoramic image created by artist and amateur astronomer Christian Waldvogel from raw images (released by ESA/NASA/U of Arizona) taken by the Huygens probe's DISR (Descent Imager/Spectral Radiometer) with a 660nm-1000nm filter.

Titan's volcanic hotbeds

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. Argon 40 detection in the atmosphere indicates that volcanoes spew flumes of water and ammonia.

Features of the Huygens landing site

Huygens image from Titan's surface, colorized in accordance with measurements taken by the probe

Huygens landed on a dark plain covered in small rocks or pebbles, which are composed of water ice [18]. 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 list of geological features on Titan.

Exploration of 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, which had not been known about until then. Many years later, heavy digital processing of images taken through Voyager 1's orange filter did reveal hints of the light and dark features known as Xanadu and the Sickle [19], 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[20] and took the highest-resolution images ever of the moon's surface, at only 1,200 kilometers away from the planet[21], discerning patches of light and dark that would be invisible to the human eye. Huygens landed on Titan on January 14 2005[22], discovering that much of the moon's surface features seem to have been formed by flowing fluids at some point in the past; however, the presence of actual open fluids on Titan today has not been confirmed at present.

Titan in culture

Titan is one of the most popular settings in science fiction other than Earth's Moon and the planets.

Titan in literature

  • 1935: Flight on Titan, a short story by Stanley G. Weinbaum
  • 1954: There is a novel by Alan E. Nourse, the American Science Fiction writer, that appeared in English on December 1954 called Trouble on Titan, translated into French as Revolte sur Titan in 1971.
  • 1959: Kurt Vonnegut's novel The Sirens of Titan features a journey that climaxes on Titan.
  • 1963: In Philip K. Dick's post-apocalyptic novel The Game-Players of Titan, a neurotic and suicidal man named Pete Garden must roll a three in Bluff, the game that's become a blinding obsession for the last inhabitants of Earth, against opponents who are from Titan.
  • 1976: In Arthur C. Clarke's novel Imperial Earth, Titan is home to a human colony with a population of 250,000 and provides an important role in the Solar System's economics; Titan's atmosphere supplies the hydrogen needed to support interplanetary travel.
  • 1983: In James P. Hogan's novel Code of the Lifemaker, Titan is inhabited by a race of Clanking Replicators
  • 1986: Stanislaw Lem's novel Fiasco contains several chapters set on Titan, and a character who ends up frozen on the surface for several hundred years.
  • 1997: In Stephen Baxter's novel Titan, a NASA mission to Titan must struggle to survive after a disastrous landing.
  • 2000: In Michael McCollum's novel, The Clouds of Saturn (ISBN 0740805282), Titan is a homeworld of Envon and Kimber Crawford, and Arvin Taggart.
  • (unknown year): In the novel Shattered Faith by Trevor Mark, Titan is the center of a vast extraterrestrial civilization that is angered by an ancient injustice, and aims for Earth to seek revenge.
  • with potential for confusion: John Varley's science fiction novel Titan is set aboard an expedition to Saturn. The "Titan" here is not the moon of Saturn, but something entirely different.

Titan in cinema and television

  • In the BBC television show Red Dwarf, the character Lister illegally imports a cat from Titan that, through the action of hard radiation over millions of years, becomes the progenitor of a well-dressed, but not particularly intelligent species called Felis sapiens.
  • In the film Gattaca (1997), Titan is the goal for a space mission, which is seen lifting off in the final sequence.
  • In the television show Starhunter, Titan features prominently as the former home of the character Dante, and is the site of a large colony.
  • In the 1985 horror film Creature, Titan is where ancient aliens preserved dormant creatures from all over the galaxy.

Titan in comics and anime

  • In the Marvel Comics Universe, Titan is home to a colony of Eternals, a godlike race of men and women.
  • In the 2000 AD comic series Judge Dredd, Titan is used as a penal colony, but, due to a writer's error, is in orbit around Jupiter. This was later explained as being due to a scientific experiment in teleportation.
  • In the anime Cowboy Bebop (1998), Titan was once the site of a war. It is unclear whether there was a colony on the moon.

Titan in computer games

  • An Apple II game called Titan Empire had human inhabitants of this moon attempting to take over the solar system.
  • In the table-top science fiction game Warhammer 40,000 the Grey Knights Space Marine chapter keep their Fortress-Monastery on Titan.
  • In the C64 computer game Project Firestart the setting of the story is located on a scientific space vessel which is floating near Titan in the Saturn system.
  • In the 1998 Activision video game Battlezone, Titan is the site of a Soviet base and several battles between the American, Soviet, and "Fury" forces.
  • The 1992 computer game Flashback takes place mostly on Titan.
  • Interplay's 1998 computer game Hardwar takes place in a fictionalized city called Misplaced Optimism, which is in Titan.

External links

Wikimedia Commons has more media related to:
Titan (moon)

Notes

  1. NASA page: News-Features-the Story of Saturn "Titan is the second-largest moon in the entire solar system."
  2. 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. verified 22:00, 29 Mar 2005 (UTC)
  3. NASA page: News-Features-the Story of Saturn "it's the only moon with a dense atmosphere."
  4. NASA Astronomy Picture of the Day of Titan, Book: Lifting Titan's Veil NASA: "Huygens discovered Luna Saturni – now known as...Titan" Book: Huygens discovered Luna Saturni – now known as Saturn's moon Titan
  5. 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, verified 2005–03–29
  6. *Bill Arnett (2005). Titan. Retrieved April 10, 2005. "Titan is nevertheless larger in diameter than Mercury"
  7. ibid. "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. Huygens Probe Sheds New Light on Titan, Peter de Selding, Space News, 2005–01–21, verified 2005–03–28
  9. Titan: Arizona in an Icebox?, Emily Lakdawalla, 2004–01–21, verified 2005–03–28
  10. Seeing, touching and smelling the extraordinarily Earth-like world of Titan, ESA News, European Space Agency, 2005–01–21, verified 2005–03–28
  11. New Images of Titan Baffle Astronomers, Henry Bortman, Astrobiology Magazine, 2004–10–28, verified 2005–03–28
  12. Titan's complex and strange world revealed, Stephen Battersby, NewScientist.com news service, New Scientist, 2004–10–29, verified 2005–03–28
  13. Seeing, touching and smelling the extraordinarily Earth-like world of Titan, ESA News, European Space Agency, 2005–01–21, verified 2005–03–28
  14. Early Huygens Results: Titan Threw Curves at ESA Probe, Emily Lakdawalla, The Planetary Society, 2005–03–19, verified 2005–03–28
  15. New Images from the Huygens Probe: Shorelines and Channels, But an Apparently Dry Surface, Emily Lakdawalla, 2005–01–15, verified 2005–03–28
  16. Titan: Arizona in an Icebox?, Emily Lakdawalla, 2004–01–21, verified 2005–03–28
  17. Seeing, touching and smelling the extraordinarily Earth-like world of Titan, ESA News, European Space Agency, 2005–01–21, verified 2005–03–28
  18. 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
  19. 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."
  20. ibid.
  21. 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."


... | Rhea | Titan | (Themis) | Hyperion | ...


Saturn's natural satellites
Janus' group | Mimas | Enceladus | Tethys | Dione | Rhea | Titan | Hyperion | Iapetus | Inuit group | Gallic group | Norse group







Links: Addme | Keyword Research | Paid Inclusion | Femail | Software | Completive Intelligence

Add URL | About Slider | FREE Slider Toolbar - Simply Amazing
Copyright © 2000-2008 Slider.com. All rights reserved.
Content is distributed under the GNU Free Documentation License.