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 SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University

nachricht Molecule flash mob
19.01.2017 | Technische Universität Wien

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: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>