Titan from Cassini-Huygens

Current models are still unable to render the complexity of seasonal phenomena or circulation patterns on Titan that could be responsible for such an upward shift. Cassini images also show a multilayer structure in the north polar hood region and at lower latitudes in some cases Porco These features could be due to gravity waves that have been detected on Titan at lower altitudes. Some of these layers may be related to the two global inversion layers observed in stellar occultations of Titan above km in altitude.

The observations estimate the monomer radius to be 0. However, contrary to previous assumptions, the DISR data show that the haze optical depth varies from about 2 at nm to only about 4. A value of for N gives a projected area equal to that of a sphere of radius 0. In any case, it seems that the size of the aggregate particles is several times as large as in some of the older models.

The methane mole fraction of 1. Cassini-Huygens has provided new information on the role of methane and the methane cycle in Titan's atmosphere. Clouds in Titan's troposphere were first suggested from variability in the methane spectrum observed from the ground by Griffith , Direct imaging of clouds on Titan has been achieved from Earth-based observatories since the turn of the century e.

Brown , Gendron Most of the currently detected clouds are located in Titan's southern hemisphere, as expected given the season on Titan summer in the south , which means that solar heating is concentrated there as well as rising motions. The large south polar system has been visible consistently essentially in the near-infrared at 2. It was extremely bright in — and recent Cassini images have shown that it is disappearing indeed it was visible only during the few first Titan flybys and not afterwards, see figure 5 and Porco Its shape is irregular and changing with time, recently resembling more a cluster of smaller-scale clouds than a large compact field.

Should it prove that this system's life was indeed on the order of five-to-six years fairly close to a Titan season , stringent constraints can be retrieved on seasonal and circulation patterns on Titan. A sequence of four methane continuum IRP0-IR3, nm images showing the temporal evolution over the period Three examples of discrete mid-latitude clouds arrows for which motions have been tracked in CB3 images.

This image was also viewed through an infrared polarizing filter. They may be related to some surface-atmosphere exchange such as geysering or cryovolcanism because they don't seem to be easily explained by a shift in global circulation. Note that DISR reported no definite detection of clouds during its descent through Titan's atmosphere. However, the data are compatible with a thin haze layer or cloud at around 21 km of altitude which could be due to methane condensation.

Perhaps the most intriguing part of Titan has been the determination of the nature of its surface. Besides remote sensing from the ground and observations from Cassini, this was investigated in situ by the Huygens probe on 14 January Titan's surface has been known to be covered with bright regions separated by darker material from ground-based and HST observations e. These variations are more readily attributed to the presence on the surface of constituents with different albedos rather than topography, although contribution from the latter is also expected.

The reason is that the Cassini camera Porco observing at 0.

The ISS and VIMS cameras confirmed these results and showed that the borders of these regions were linear but not smooth and that dramatic changes in surface albedo could be noted in the maps produced by these measurements. The best resolution achieved by ISS was of a few kilometres on Titan's surface.

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The large bright area around the equator first observed by the HST and the adaptive optics in was resolved and described by the Cassini instruments. The mid-latitude regions around the equator on Titan were found to be rather uniformly bright, while the southern pole is relatively dark.

What exactly is causing the albedo variations is still uncertain. A plausible candidate for the darker regions could be accumulations of hydrocarbons in liquid or solid form , precipitating down from the atmosphere. For the brighter regions the task of interpreting the data is more difficult. The exact ice that can satisfy the constraints imposed by all the observations is not easy to determine; hydrocarbon ice has been invoked on the basis of Xanadu appearing bright at all the near-infrared wavelengths observed to date Coustenis A bright circular structure about 30 km in diameter found in the VIMS hyperspectral images is interpreted as a cryovolcanic dome in an area dominated by extension.

These mechanisms are similar to those operating for silicate volcanism on Earth using tidal heating as an energy source and may lead to flows of non-H 2 O ices on Titan's surface. Following such eruptions, methane rain could produce the dendritic dark structures seen by Cassini-Huygens. If these structures are indeed channels, they could have dried out due to the short timescale for methane dissociation in the atmosphere, or this could be a seasonal phenomenon. Studying volcanism on Titan is important, not only to understand the thermal history of Titan which since it differs in its incorporation of volatiles from the Galilean satellites, must surely have evolved differently but also to realize how volatiles — in particular, methane — were delivered to the surface.

The Cassini instruments have found no obvious evidence for heavy cratering on the bright or the dark areas of Titan so far.

A few features interpreted as impact craters or volcanoes have been announced to date: One such multi-ringed impact basin was named Circus Maximus by the science team. A smaller crater of about 40 km was also observed, exhibiting a parabolic-shaped ejecta blanket. Recent features observed by the Cassini orbiter include large areas similar to the dunes as observed on Earth Lorenz These formations are aligned west to east covering hundreds of kilometres and rising to about m. They are expected to have formed for the major part due to the influence of Saturn through tidal forces times greater than on Earth, causing winds of about 0.

In the images recorded, various dark patches are observed, some of which extend outwards or inwards by means of channels, seemingly carved by liquid. The missing reservoir of liquid methane or ethane, that scientists have speculated on for a long time, may indeed — at least partly — be found in such areas. The most resolved features in these images are about m across. The probe flew over an icy surface, floated down and drifted eastwards for about km.

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Several of the instruments on board contributed to our knowledge of Titan's surface conditions. Density and accelerometry measurements were made by the HASI instrument and then translated into temperature-versus-pressure profiles throughout the atmosphere and with surface conditions at the landing site found to be: The fact that the surface is solid but unconsolidated was verified by all the data. The first part of the probe to touch the surface was the SSP penetrometer, whose data are now interpreted as indicative of the probe first hitting one of the icy pebbles littering the landing area before sinking into the softer darker ground material.

The SSP detected the ground from 88 m in altitude by acoustic sounding, revealing a relatively smooth but not flat surface, for which the best current hypothesis is gravel wet sand. Huygens landed on an organic-rich surface, with trace organic species such as cyanogens and ethane detected on the ground.

The data collection included surface images from 49—0 km, with impressive snapshots of the Huygens landing site. Panoramic mosaics were constructed from the images taken at different altitudes and show bright and darker regions separated by an impressive drainage system with various-sized channels figure 7. This dendritic network can be caused by rainfall methane? Some of the bright linear streaks seen on the images could be due to icy flows from the interior of Titan emerging through fissures perhaps cryovolcanism?

The spectra acquired by DISR during the descent gave information on the atmospheric properties, but also on the surface properties. The spectra taken by DISR are compatible with the presence of water ice on Titan's surface Tomasko , something that had already been suggested from ground-based observations. However, the most intriguing feature found in the spectra was the featureless quasi-linear unidentified blue slope observed between and nm.

Unique insights into a ringed world

No combination of any ice and organic material from laboratory measurements has been adequate in reproducing this characteristic and we may be looking at a new component. No biotic signatures have been found on Titan. Titan has proven to be simultaneously more and less like our own planet than expected. In view of the recent findings also pertaining to Enceladus Khurana , we're discovering that there are many surprises awaiting us in the Saturnian system and even one such long-lived successful mission like Cassini-Huygens may not be enough. Returning to Titan with various future high-technology instruments will, in particular, be extremely useful in order to determine the physical process on, above and under the surface.

Although the mission's objectives span the entire Saturnian system, for Cassini as for Voyager before it Titan is a privileged target and the mission is designed to address our principal questions about the satellite. The spacecraft is equipped with 18 science instruments 12 on the orbiter and 6 carried by the probe , gathering both remote sensing and in situ data figure 4. Because of its massive weight, Cassini could not be sent directly to Saturn but used the gravity assist technique to gain the energy required by looping twice around the Sun.

Cassini-Huygens reached Saturn in July and performed a flawless orbit insertion, becoming trapped forever in orbit like one of Saturn's moons. The Cassini spacecraft carries a host of instruments designed to perform in situ studies of elements of Saturn, its atmosphere, moons, rings and magnetosphere. It communicates through one high-gain and two low-gain antennas. The instruments study the temperatures in various locations, the plasma levels, the neutral and charged particles, the surface composition, the atmospheres and rings, the solar wind, and even the dust grains in the Saturn system.

Other instruments perform spectral mapping for high-quality images of the ringed planet, its moons and rings. The images returned of the various icy satellites with the limestone-like Hyperion surface Porco , the tiger-stripes and the water atmosphere generated from the plumes on Enceladus Khurana are a few of the amazing new results. As for Titan, some of the flybys came as close as less than km from the surface Voyager 1 flew by at km and allowed direct measurements with the visible, infrared and radar instruments.

Looking Back On The Cassini-Huygens Mission to Saturn

Additionally, the mission saw the deployment of the European-built Huygens probe. After release from the Cassini orbiter, on 25 December , this kg probe plunged into Titan's atmosphere on 14 January at The five batteries onboard the probe lasted much longer than expected, allowing Huygens to collect descent data for 2 hrs and 27 mns and surface data for 1 hr and 12 mns. During its descent, Huygens' Descent Imager Spectral Radiometer DISR returned more than images, while the probe's other five instruments sampled Titan's atmosphere to help determine its composition and structure.

The telemetry data from Huygens was stored onboard Cassini's solid state recorders SSRs at a rate of 8 kbps, while the spacecraft was at an altitude of 60 km from Titan. Although some data from Huygens was lost during its transmission to Cassini, none of the science was lost in the end because Titan's weak signal was captured by Earth-based radio telescopes which allowed, among other things, retrieval of the wind profile missed by Cassini's Doppler Wind Experiment DWE Bird As well as studying the atmosphere and surface, the probe took samples of the haze and aerosols.

These in situ measurements complement measurements made from the orbiter. Among them is a multimode radar, which completely penetrates the hazy atmosphere of Titan and images Titan's surface at 0. Other filters are able to probe different altitudes in the atmosphere. The Composite Infrared Spectrometer CIRS instrument allows the temperature to be profiled at different locations in the atmosphere, as well as spatially resolved composition measurements. These data are invaluable for verifying and refining models of chemistry, photochemistry and atmospheric circulation.

The latter instrument searches also for radio emissions from lightning on Titan, although a similar search by Voyager failed to indicate any such emission, while the Cosmic Dust Analyzer CDA measures the mass, velocity and composition of particles in Titan's vicinity. The radio system on the orbiter is used to study Titan in two ways — first by tracking the spacecraft from Earth, to determine Titan's gravity field. This in turn constrains its internal structure e.

These will measure a temperature profile, and indicate the extent of Titan's ionosphere. These, and spacecraft dynamics measurements, allow direct comparison with the density profile measured by the entry deceleration of the Huygens probe. Direct measurements of the composition of Titan's atmosphere versus altitude were made above the Huygens landing site by the Gas Chromatograph Mass Spectrometer GCMS on the probe — as Titan's atmosphere has so many components, separation in two dimensions by chromatography as well as mass spectroscopy is required. The GCMS also analysed the pyrolysis products from the Aerosol Collector and Pyrolyser ACP , which sucked haze particles into the probe and trapped them in a filter which was subsequently baked in an oven to break down the haze macromolecules into smaller fragments for the GCMS.

The GCMS also had a heated inlet, to find the volatile component of the surface material at the landing site.

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But this intimacy peaked on Jan. The mission began with two conjoined spacecraft — an orbiter and a lander — but on Dec. Huygens had its own destiny: Titan is an oddity; no other moon in the solar system possesses a thick atmosphere , and planetary scientists are deeply fascinated with this mysterious world. Three weeks after leaving Cassini and coasting to Titan, the 9-foot-wide 2. But Huygens was descending into the unknown. But as the lander continued to sail deeper into the eerie depths , eventually passing under the haze, it captured hundreds of aerial images of the alien world and saw a surprisingly diverse — and strikingly Earth-like — landscape filled with mountains, dry floodplains and what appeared to be river deltas.

Scientists then realized that though Huygens had landed on something solid, liquid methane did flow there: Huygens' cameras could see intricate channels cutting into the surface. When Huygens touched down, it did so with a soft thud and a short slide across the frozen surface. Later analysis of the lander's telemetry showed that Huygens sank around 4. Reflecting on the landing in , Erich Karkoschka, of the University of Arizona's Lunar and Planetary Laboratory, likened the strange surface to snow with a frozen crust. Huygens had landed on a dry floodplain littered with eroded, icy rocks covered in a dusty material that was likely organic aerosols that are now known to form in Titan's atmosphere and precipitate onto the surface.

For 72 minutes, the lander returned valuable data from the moon's surface and atmosphere.