Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rain, winds and haze during the descent to Titan

01.12.2005


The high-resolution images taken in Titan’s atmosphere by the Descent Imager/Spectral Radiometer (DISR) were spectacular, but not the only surprises obtained during descent. Both DISR and the Doppler Wind Experiment data have given Huygens scientists much to think about.



The irreversible conversion of methane into other hydrocarbons in Titan’s stratosphere implies a surface or subsurface ’reservoir’ of methane. Although the NASA/ESA/ASI Cassini orbiter has not seen a global surface reservoir, and DISR images do not show liquid hydrocarbon pools on the surface either, this instrument’s images do reveal the traces of flowing liquid.

The DISR imagers provided views of Titan’s previously unseen surface, thus allowing a deeper understanding of the moon’s geology. Surprisingly like Earth, the brighter highland regions show complex systems draining into flat, dark lowlands, possibly dry lake or river beds.


Images taken after landing in one of these lowland areas show more than 50 stones which vary between 3 mm and 15 cm in diameter. No rocks larger than 15 cm are seen. This size distribution suggests that rocks larger than 15 cm cannot be transported to the lakebed, while small pebbles (less than 5 cm) are quickly removed from the surface.

From these features, along with apparent ’ponds’ and elongated ’islands’ oriented parallel to the ’coastline’, the scientists can propose explanations for the nature of the brightness variations spread throughout the images.

They appear to be controlled by a flow of ’runny’ liquids (consistent with methane, ethane or both) down slopes, whether caused by precipitation or springs.

The light–dark brightness difference can be explained by the ’irrigation’ of the bright terrain, with darker material being removed and carried into the channels, which discharge into the region ’offshore’, thereby darkening it.

’Aeolian’ (wind) processes, such as gusts, and Titan’s low gravity may aid this migration.

The surface science lamp worked exactly as planned, permitting surface reflection measurements even in strong methane absorption bands. Operations after landing included the collection of successive images as well as spectral reflectance measurements of the surface illuminated by the lamp from an assumed height of roughly 30 cm.

The infrared reflectance spectrum — the rise and fall of brightness at different wavelengths of light — measured for the surface is unlike any other in the Solar System. There are signs of organic materials such as ’tholins’, and dips in the brightness consistent with water ice are also seen. However, the most intriguing feature in the surface spectrum is an infrared signature of a material not matched by any combination of spectra of ices and complex organics found on Earth.

These spectra also show a methane abundance near the surface of 5 +/-1%, which is in precise agreement with the 4.9% in situ measurements made by the probe’s Gas Chromatograph Mass Spectrometer. The corresponding relative humidity of methane is about 50%.

Therefore, the surface is not ’bone dry’, but this does rule out extensive ground fogs in the vicinity of the landing site caused by methane alone.

Taken together, these new observations make clearer the role of methane in shaping the surface of Titan and how it is recycled into the atmosphere. The substantial relative humidity of methane and the obvious evidence of fluid flow on the surface provide evidence for methane ’rain’ and subsequent evaporation. Some hints of ’cryovolcanic’ flows may also be present in the images.

By assembling the panoramic mosaics, the Huygens scientists could determine the descent trajectory as part of an iterative process of image reconstruction. The trajectory could be used to derive the probe ground track and see how wind speeds changed with altitude.

They found that the probe drifted steadily east-northeast due to Titan’s ’prograde’ (in the direction of rotation of the moon) winds. It slowed from near 30 to 10 m/s between altitudes of 50 and 30 km and then slowed more rapidly (from 10 to 4 m/s) between altitudes of 30 and 20 km.

The winds dropped to zero and reversed at around 7 km, near the expected top of the planetary boundary layer, producing a west-northwestwardly motion for about 1 km during the last 15 minutes of the descent.

The Doppler Wind Experiment (DWE) data which were obtained from two Earth-based telescopes have confirmed the findings of the DISR and provided a high-resolution vertical profile of Titan’s winds.

The DWE not only confirmed the considerable turbulence above 120 km and the eastward drift in prograde winds, but also the weak retrograde (westward) winds near the surface.

Significantly, this experiment provided the first in situ confirmation of Titan’s ’superrotation’ (the atmosphere is moving faster than the surface). Unexpectedly, it also found a layer of very low wind velocity between 60 and 100 km altitude, which is presently unexplained.

Franco Bonacina | alfa
Further information:
http://www.esa.int/SPECIALS/Results_from_Mars_Express_and_Huygens/SEM23TULWFE_0.html

More articles from Physics and Astronomy:

nachricht What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin

nachricht Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Global study of world's beaches shows threat to protected areas

19.07.2018 | Earth Sciences

New creepy, crawly search and rescue robot developed at Ben-Gurion U

19.07.2018 | Power and Electrical Engineering

Metal too 'gummy' to cut? Draw on it with a Sharpie or glue stick, science says

19.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>