Sunday, September 15, 2013

Conversely,haze in Titan's atmosphere

 Conversely,haze in Titan's atmosphere contributes to an anti-greenhouse effect by reflecting sunlight back into space, cancelling a portion of the greenhouse effect warming and making its surface significantly colder than its upper atmosphere.[43] HP Pavilion DV6-1122us laptop keyboard

Titan's clouds, probably composed of methane, ethane or other simple organics, are scattered and variable, punctuating the overall haze.[19] The findings of the Huygens probe indicate that Titan's atmosphere periodically rains liquid methane and other organic compounds onto its surface.[44] SONY VAIO VGN-FS315M laptop keyboard

Clouds typically cover 1% of Titan's disk, though outburst events have been observed in which the cloud cover rapidly expands to as much as 8%. One hypothesis asserts that the southern clouds are formed when heightened levels of sunlight during the Titanian summer generate uplift in the atmosphere, resulting in convection.  DELL PK130801B00 laptop keyboard

This explanation is complicated by the fact that cloud formation has been observed not only post–summer solstice but also at mid-spring. Increased methane humidity at the south pole possibly contributes to the rapid increases in cloud size.[45] It was summer in Titan's southern hemisphere until 2010, TOSHIBA Satellite L655-S5163 laptop keyboard

when Saturn's orbit, which governs Titan's motion, moved Titan's northern hemisphere into the sunlight.[46] When the seasons switch, it is expected that ethane will begin to condense over the south pole.

The surface of Titan has been described as "complex, fluid-processed, [and] geologically young".[48] HP Pavilion dv5t-1200se CTO laptop keyboard

 Titan has been around since the Solar System's formation, but its surface is much younger, between 100 million and 1 billion years old. Geological processes may have reshaped Titan's surface.[49] Titan's atmosphere is twice as thick as the Earth's, making it difficult for astronomical instruments to image its surface in the visible light spectrum.[50]  COMPAQ Presario C700 Laptop Keyboard

The Cassini spacecraft is using infrared instruments, radar altimetry and synthetic aperture radar(SAR) imaging to map portions of Titan during its close fly-bys of Titan. The first images revealed a diverse geology, with both rough and smooth areas. There are features that seem volcanic in origin, which probably disgorge water mixed with ammonia.  HP G72-b60US Laptop Keyboard

There are also streaky features, some of them hundreds of kilometers in length, that appear to be caused by windblown particles.[51][52] Examination has also shown the surface to be relatively smooth; the few objects that seem to be impact craters appeared to have been filled in, perhaps by raining hydrocarbons or volcanoes. HP 519265-001 Laptop Keyboard

Radar altimetry suggests height variation is low, typically no more than 150 meters. Occasional elevation changes of 500 meters have been discovered and Titan has mountains that sometimes reach several hundred meters to more than 1 kilometer in height.[53]

Titan's surface is marked by broad regions of bright and dark terrain. COMPAQ Presario C700 Laptop Keyboard

These include Xanadu, a large, reflective equatorial area about the size of Australia. It was first identified in infrared images from the Hubble Space Telescope in 1994, and later viewed by the Cassini spacecraft. The convoluted region is filled with hills and cut by valleys and chasms.[54] It is criss-crossed in places by dark lineaments—sinuous topographical features resembling ridges or crevices. Lenovo Thinkpad T420 Laptop Keyboard

These may represent tectonic activity, which would indicate that Xanadu is geologically young. Alternatively, the lineaments may be liquid-formed channels, suggesting old terrain that has been cut through by stream systems.[55] There are dark areas of similar size elsewhere on Titan, observed from the ground and byCassini; TOSHIBA Satellite A305 Laptop Keyboard

The possibility of hydrocarbon seas on Titan was first suggested based on Voyager 1 and 2 data that showed Titan to have a thick atmosphere of approximately the correct temperature and composition to support them, but direct evidence was not obtained until 1995 when data from Hubble and other observations suggested the existence of liquid methane on Titan, Compaq Presario CQ57 Series Laptop Keyboard

either in disconnected pockets or on the scale of satellite-wide oceans, similar to water on Earth.[56]

The Cassini mission confirmed the former hypothesis, although not immediately. 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,  Lenovo 39T7417 Laptop Keyboard

but no specular reflections were initially observed.[57] Near Titan's south pole, an enigmatic dark feature named Ontario Lacus was identified[58] (and later confirmed to be a lake).[11] A possible shoreline was also identified near the pole via radar imagery.[59] Following a flyby on July 22, 2006, in which the Cassini spacecraft's radar imaged the northern latitudes (that were then in winter), DELL Vostro 3450 Laptop Keyboard

a number of large, smooth (and thus dark to radar) patches were seen dotting the surface near the pole.[60] Based on the observations, scientists announced "definitive evidence of lakes filled with methane on Saturn's moon Titan" in January 2007.[9][61] The Cassini–Huygens team concluded that the imaged features are almost certainly the long-sought hydrocarbon lakes, HP Mini 210-1014TU Laptop Keyboard

the first stable bodies of surface liquid found outside of Earth. Some appear to have channels associated with liquid and lie in topographical depressions.[9] The liquid erosion features appear to be a very recent occurrence: channels in some regions have created surprisingly little erosion, suggesting erosion on Titan is extremely slow, HP Pavilion DV6-1002tx Laptop Keyboard

or some other recent phenomena may have wiped out older riverbeds and landforms.[49] Overall, the Cassini radar observations have shown that lakes cover only a few percent of the surface, making Titan much drier than Earth.[62]Although most of the lakes are concentrated near the poles (where the relative lack of sunlight prevents evaporation), HP 519265-001 Laptop Keyboard

a number of long-standing hydrocarbon lakes in the equatorial desert regions have also been discovered, including one near the Huygens landing site in the Shangri-La region, which is about half the size of Utah's Great Salt Lake. The equatorial lakes are probably "oases", i.e. the likely supplier is underground aquifers.[63] DELL Precision M4500 Laptop Keyboard

In June 2008, the Visual and Infrared Mapping Spectrometer on Cassini confirmed the presence of liquid ethane beyond doubt in Ontario Lacus.[64] On December 21, 2008, Cassini passed directly over Ontario Lacus and observed specular reflection in radar. The strength of the reflection saturated the probe's receiver, DELL PK130801B00 Laptop Keyboard

indicating that the lake level did not vary by more than 3 mm (implying either that surface winds were minimal, or the lake's hydrocarbon fluid is viscous).[65][66]

Specular reflections are indicative of a smooth, mirror-like surface, so the observation corroborated the inference of the presence of a large liquid body drawn from radar imaging. HP Pavilion DV6-1030us Laptop Keyboard

The observation was made soon after the north polar region emerged from 15 years of winter darkness.

On July 8, 2009, Cassini's VIMS observed a specular reflection indicative of a smooth, mirror-like surface, off what today is called Jingpo Lacus, a lake in the north polar region shortly after the area emerged from 15 years of winter darkness.[67][68] HP Probook 4520S Laptop Keyboard

Radar measurements made in July 2009 and January 2010 indicate that Ontario Lacus is extremely shallow, with an average depth of 0.4–3.2 m, and a maximum depth of 2.9–7.4 m.[69] In contrast, the northern hemisphere's Ligeia Mare has depths exceeding 8 m, the maximum measurable by the radar instrument.[69] SONY 147977821 Laptop Keyboard

During a flyby on 26 September 2012, Cassini's radar detected in Titan's northern polar region what is likely a river with a length of more than 400 kilometers. It has been compared with the much larger Nile river on Earth. This feature ends in Ligeia Mare.[11] SONY 147963021 Laptop Keyboard

During six flybys of Titan from 2006 to 2011, Cassini gathered radio-metric tracking and optical navigation data from which investigators could roughly infer Titan's changing shape. The density of Titan is consistent with a body that is about 60% rock and 40% water. The team's analyses suggest that Titan's surface can rise and fall by up to 10 metres during each orbit. SONY VAIO VGN-FS315M Laptop Keyboard

That degree of warping suggests that Titan's interior is relatively deformable, and that the most likely model of Titan is one in which an icy shell dozens of kilometres thick floats atop a global ocean.[70] The team's findings, together with the results of previous studies, hint that Titan's ocean may lie no more than 100 km below its surface. TOSHIBA Satellite C650-182 Laptop Keyboard

Radar, SAR and imaging data from Cassini have revealed few impact craters on Titan's surface.[49] These impacts appear to be relatively young, opposed to Titan's age.[49] The few impact craters discovered include a 440 km wide two-ring impact basin named Menrva seen by Cassini's ISS as a bright-dark concentric pattern.[73] ASUS F3M Laptop Keyboard

A smaller, 60 km wide, flat-floored crater named Sinlap[74] and a 30 km crater with a central peak and dark floor named Ksa have also been observed.[75] Radar and Cassiniimaging 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. Lenovo 63Y0047 Laptop Keyboard

For example, a 90 km wide ring of bright, rough material known as Guabonito has been observed by Cassini.[76] 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.[77]  HP Pavilion dv6-3107ax Laptop Keyboard

Many of Titan's craters or probable craters display evidence of extensive erosion, and all show some indication of modification.[72] Most large craters have breached or incomplete rims, despite the fact that some craters on Titan have relatively more massive rims than those anywhere else in the Solar System.HP 488590-001 Laptop Keyboard

However, there is little evidence of formation ofpalimpsests through viscoelastic crustal relaxation, unlike on other large icy moons.[72] Most craters lack central peaks and have smooth floors, possibly due to impact-generation or later eruption of cryovolcanic lava. Although infill from various geological processes is one reason for Titan's relative deficiency of craters, atmospheric shielding also plays a role; TOSHIBA P000482730 Laptop Keyboard

it is estimated that Titan's atmosphere reduces the number of craters on its surface by a factor of two.[78]

The limited high-resolution radar coverage of Titan obtained through 2007 (22%) suggested the existence of a number of nonuniformities in its crater distribution. Xanadu has 2–9 times more craters than elsewhere.  SONY 147977821 Laptop Keyboard

The leading hemisphere has a 30% higher density than the trailing hemisphere. There are lower crater densities in areas of equatorial dunes and in the north polar region (where hydrocarbon lakes and seas are most common).[72]

Pre-Cassini models of impact trajectories and angles suggest that where the impactor strikes the water ice crust, TOSHIBA Tecra M9-S5514 Laptop Keyboard

a small amount of ejecta remains as liquid water within the crater. It may persist as liquid for centuries or longer, sufficient for "the synthesis of simple precursor molecules to the origin of life".

Scientists have long speculated that conditions on Titan resemble those of early Earth, though at a much lower temperature.  GATEWAY NV-54 Laptop Keyboard

The detection of Argon 40 in the atmosphere in 2004 indicated that volcanoes had spawned plumes of "lava" composed of water and ammonia.[80] Global maps of the lake distribution on Titan's surface revealed that there is not enough surface methane to account for its continued presence in its atmosphere, and thus that a significant portion must be added through volcanic processes.[81] FUJITSU Lifebook P1510 Laptop Keyboard

Still there is a paucity of surface features that can be unambiguously interpreted as cryovolcanoes.[82] One of the first of such features revealed by Cassini radar observations in 2004, called Ganesa Macula, resembles the geographic features called "pancake domes" found on Venus, and was thus initially thought to be cryovolcanic in origin,  FUJITSU Lifebook P1610 Laptop Keyboard

although the American Geophysical Union refuted this hypothesis in December 2008. The feature was found to be not a dome at all, but appeared to result from accidental combination of light and dark patches.[83][84] In 2004 Cassini also detected an unusually bright feature (called Tortola Facula), which was interpreted as a cryovolcanic dome.[85]  DELL Precision M4500 Laptop Keyboard

No similar features have been identified as of 2010.[86] In December 2008, astronomers announced the discovery of two transient but unusually long-lived "bright spots" in Titan's atmosphere, which appear too persistent to be explained by mere weather patterns, suggesting they were the result of extended cryovolcanic episodes.[22]  SONY VAIO VGN-N325QE/W Laptop Keyboard

In March, 2009, structures resembling lava flows were announced in a region of Titan called Hotei Arcus, which appears to fluctuate in brightness over several months. Though many phenomena were suggested to explain this fluctuation, the lava flows were found to rise 200 meters above Titan's surface, consistent with it having been erupted from beneath the surface.[87]  TOSHIBA Satellite A205-S4618 Laptop Keyboard

A mountain range measuring 150 km long, 30 km wide and 1.5 km high was also discovered by Cassini in 2006. This range lies in the southern hemisphere and is thought to be composed of icy material and covered in methane snow. The movement of tectonic plates, perhaps influenced by a nearby impact basin, could have opened a gap through which the mountain's material upwelled.[88] HP G61-424CA laptop keyboard

 Prior to Cassini, scientists assumed that most of the topography on Titan would be impact structures, yet these findings reveal that similar to Earth, the mountains were formed through geological processes.[89] In December 2010, theCassini mission team announced the most compelling possible cryovolcano yet found.HP G61-424CA laptop keyboard

Named Sotra Patera, it is one in a chain of at least three mountains, each between 1000 and 1500 m in height, several of which are topped by large craters. The ground around their bases appears to be overlaid by frozen lava flows.[90]

If volcanism on Titan really exists, the hypothesis is that it is driven by energy released from the decay of radioactive elements within the mantle, as it is on the Earth.[22] Compaq Presario CQ56-102SE laptop keyboard

Magma on Earth is made of liquid rock, which is less dense than the solid rocky crust through which it erupts. Because ice is less dense than water, Titan's watery magma would be denser than its solid icy crust. This means that cryovolcanism on Titan would require a large amount of additional energy to operate, possibly via tidal flexing from nearby Saturn.[22] HP G42-265LA laptop keyboard

Alternatively, the pressure necessary to drive the cryovolcanoes may be caused by ice Ih "underplating" Titan's outer shell. The low-pressure ice, overlaying a liquid layer of ammonium sulfate, ascends buoyantly, and the unstable system can produce dramatic plume events. Titan is resurfaced through the process by grain-sized ice and ammonium sulfate ash, which helps produce a wind-shaped landscape and sand dune features.[91] TOSHIBA Satellite A305-S6841 laptop keyboard

In 2008 Jeffrey Moore (planetary geologist of Ames Research Center) proposed an alternate view of Titan's geology. Noting that no volcanic features had been unambiguously identified on Titan so far, he asserted that Titan is a geologically dead world, whose surface is shaped only by impact cratering, fluvial andeolian erosion, mass wasting and other exogenic processes. HP Mini 210-1081NR laptop keyboard

According to this hypothesis, methane is not emitted by volcanoes but slowly diffuses out of Titan's cold and stiff interior. Ganesa Macula may be an eroded impact crater with a dark dune in the center. The mountainous ridges observed in some regions can be explained as heavily degraded scarps of large multi-ring impact structures or as a result of the global contraction due to the slow cooling of the interior. HP G42-265LA laptop keyboard

Even in this case Titan may still have an internal ocean made of the eutectic water–ammonia mixture with the temperature of 176 K (−97 °C), which is low enough to be explained by the decay of radioactive elements in the core. The bright Xanadu terrain may be a degraded heavily cratered terrain similar to that observed on the surface of Callisto. TOSHIBA Satellite A305-S6829 laptop keyboard

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