| Piú votate - Titan: The "Foggy" Moon |
Titan-N00091172.jpgTitan56 visiteCaption NASA:"N00091172.jpg was taken on September 02, 2007 and received on Earth September 03, 2007. The camera was pointing toward TITAN that, at the time, was approximately 1.319.014 Km away, and the image was taken using the CL1 and CB3 filters. This image has not been validated or calibrated".MareKromium
(4 voti)
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Titan-Atmosphere-N00091073.jpgIn the Night of Titan - (possible natural colors; elab. Lunexit)56 visiteCaption NASA:"N00091073.jpg was taken on August 30, 2007 and received on Earth September 01, 2007. The camera was pointing toward TITAN that, at the time, was approx. 138.726 Km away, and the image was taken using the CL1 and UV3 filters. This image has not been validated or calibrated".MareKromium
(4 voti)
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Titan-Regions-Adiri_Region-PIA08995.jpgFlying over Adiri57 visiteCaption NASA:"Within the windswept wastes of Titan's Equatorial Dune Desert lies the 1.700-Km (1.050-mi) wide bright Region called Adiri, seen here at center.
The intrepid Huygens probe landed off the North-Eastern edge of Adiri in January 2005.
This view looks toward the Anti-Saturn side of Titan (5.150 Km, or about 3.200 miles across) -- the side that always faces away from Saturn as the moon orbits. North on Titan is up and rotated 26° to the right.
The image was taken using a spectral filter sensitive to wavelengths of infrared light centered at 939 nanometers. The view was acquired with the Cassini spacecraft wide-angle camera on June 14, 2007 at a distance of approx. 157.000 Km (about 98.000 miles) from Titan. Image scale is roughly 9 Km (about 6 miles) per pixel".MareKromium
(4 voti)
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Titan-N00084796.jpgInterpreting Titan (1)56 visite"Interpretare Titano". Difficile. Molto difficile. L'osservazione visuale di quella che la NASA chiama "foggy moon" non è gratificante, a causa dell'estrema turbolenza che caratterizza l' (alta e media) atmosfera di questo Mondo. Le nuvole di sabbia (che dovrebbero apparire giallastre) si confondono con quelle formate da ghiaccio d'acqua e/o da altri elementi organici; le nebbie che coprono perpetuamente la superficie di questo misterioso ed affascinante pianeta contribuiscono ad aumentare le difficoltà a noi "Interpreti". Se a questo aggiungiamo la grande distanza dalla quale le immagini sono state ottenute e la presenza costante di artefatti, il nostro lavoro diventa quasi impossibile. Le sole certezze che abbiamo attengono la colorazione di Titano il quale, se da una certa distanza (osservazioni telescopiche terrestri ed HST incluse) appare giallo, a mano a mano che ci si avvicina sembra "cedere" il colorito giallo in favore di varie gradazioni di celeste pallido, verde chiaro e marrone chiazzato.
Molte di queste colorazioni (dal celeste pallido, al giallo/arancio, al blu), forse, sono una conseguenza dell'interazione fra la debole (ma non insignificante!) illuminazione solare e gli elementi che compongono gli strati alti dell'atmosfera di Titano; altre di queste colorazioni (i verdi, i giallo-scuri, i bianchi ed i marroni), invece, potrebbero essere proprie degli strati bassi e/o (addirittura) della superficie di questo Mondo.
E noi...Noi interpretiamo. O meglio: proviamo ad interpretare...MareKromium
(4 voti)
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Titan-Regions-Omacati_Macula_Region-01-LS28_PSS_LASoderblom_VIMSRADAR20070323.jpgDunes in the "Omacati Macula" Region57 visiteThe first two images of Titan (from the top) were obtained by Cassini’s SAR radar and the VIMS imager, respectively. They cover an area about 300 by 1000 Km wide and centred at 20° North and 45° West in the Omacatl Macula Region.
Dunes are generally rare in this area, even if some of them can still be seen in the enlargement provided by the bottom right radar image (blue arrow). These dunes are correlated to the brown spot visible in the VIMS image.
The green arrows linking the lower left radar image with the VIMS image illustrate that in this region the dark blue units are correlated to with sinuous channels and flow features.MareKromium
(4 voti)
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Titan-PIA09034_H-1.jpgCrescent Titan73 visiteHuygens scored a first in 2005 by measuring the electrical conductivity of Titan’s atmosphere. The results hint at a new way to investigate the subsurface layers of Titan and could provide insight into whether or not Titan has a subsurface ocean.
The Permittivity, Waves and Altimetry (PWA) sensor on the Huygens Atmosphere Structure Instrument (HASI) detected an extremely low frequency (ELF) radio wave during the descent. It was oscillating very slowly for a radio wave, just 36 times a second, and increased slightly in frequency as the probe reached lower altitudes.
If the PWA team confirms that the signal is a natural phenomenon and not an artefact of the way the instrument worked, they will have discovered a powerful new way to probe not just the atmosphere of Titan but its subsurface as well.
The only other world on which ELF waves were detected before was Earth. They are reflected by both the surface of the Earth and its ionosphere, the rarefied region of the atmosphere where most particles are electrically charged. This turns the atmosphere into a giant ‘sound box’ where certain frequencies of ELF waves resonate and are reinforced, whilst other die away.
On Titan, however, the surface is a poor reflector because of its low conductivity and so these waves penetrate the interior. “The wave could have been reflected by the liquid-ice boundary of a subsurface ocean of water and ammonia predicted by theoretical models,” says Fernando Simões, CETP/IPSL-CNRS, France, and a member of the PWA team.
If Simões is right, successful modelling of how ELF waves resonate on Titan could lend support to the ocean’s existence and tell scientists about the depth at which it sits. Understanding the resonance however, is difficult.
Above about 100 kilometres altitude on Earth, the ionosphere provides the upper reflecting layer of the resonating cavity. At Titan, PWA revealed that things are more complicated. Apart from the ionosphere, at a much higher altitude of about 1200 kilometres, Huygens found a layer of ionized particles consisting of electrons, at 63 kilometres. “This does not match any previous prediction for Titan,” says Simões. To some extent, it splits Titan’s atmosphere into two resonating chambers.
With so much at stake, the PWA team are checking to make sure the detection is real and not an artefact generated by the spacecraft. They have already ruled out electrical interference from the instrument itself.
Two small arms, one on either side of Huygens, create an antenna and the team’s next goal is to investigate whether the arms could have oscillated during the descent. Simões and colleagues are building a special chamber to hold a replica of the instrument at the low temperature of Titan’s atmosphere, between 100-200 degrees Kelvin (about -173 to -73 °C), in order to check whether the antenna resonates at 36 hertz. If it does, it probably means that the signal is an artefact. If it does not, confidence in the signal’s reality will increase and the investigation of the atmosphere and subsurface can begin.
But perhaps the biggest mystery is what generated the ELF wave in the first place. On Earth, they are initiated by lightning strikes that make electrons in the atmosphere oscillate, releasing the ELF waves.
The PWA was designed to search for ELF waves on Titan while a microphone on Huygens kept an ear out for thunder – a sure sign of lightning. Cassini has also been watching for lightning using its cameras.
However, Huygens suggests that there is no lightning, or very little. “If there is lightning on Titan, it is significantly less than the amount of lightning that Earth experiences,” says Simões. So what generated Titan’s ELF? No one is quite sure yet. “It might be generated by an interaction with Saturn’s magnetosphere or related to Titan’s intrinsic fields,” suggests Simões. “Titan is proving to be an intriguing environment.”
One thing is certain: there is plenty to investigate. “The measurement of atmospheric electricity is something really new and exciting,” says Jean-Pierre Lebreton, ESA Huygens Project Scientist. “We could send similar instruments to study atmospheric electricity on other celestial bodies, in particular Venus, Mars, and the giant planets,” adds Simões.
The PWA team expect to release more definitive results when their investigation is complete.
MareKromium
(4 voti)
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Titan-PIA08868.jpgTitanian "Bands"56 visiteCaption NASA:"Titan bears a distinct East-West banded pattern in this Cassini spacecraft image taken in the ultraviolet.
The ultraviolet wavelength allows Cassini to see Titan's stratosphere, where superrotation -- in which the atmosphere moves around the moon faster than Titan rotates -- is strong. The recent appearance of this feature may be a harbinger of seasonal change on Titan.
The moon's halo -- its detached, high-altitude global haze layer -- is visible here as well, and is often its most prominent feature in such ultraviolet views. North on Titan is up and rotated 6° to the right in this image.
The view was obtained by the Cassini spacecraft narrow-angle camera using a spectral filter sensitive to wavelengths of polarized ultraviolet light.
The view was acquired on Dec. 25, 2006 at a distance of approx. 1,3 MKM (about 800.000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 123°.
Image scale is roughly 8 Km per pixel".
(4 voti)
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Titan-Regions-Xanadu_Region-PIA06107.jpgXanadu Region56 visiteThis image taken on Oct. 24, 2004, reveals Titan's bright "continent-sized" terrain known as Xanadu. It was acquired with the narrow angle camera on Cassini's imaging science subsystem through a spectral filter centered at 938 nnmts, a wavelength region at which Titan's surface can be most easily detected. The surface is seen at a higher contrast than in previously released imaging science subsystem images due to a lower phase angle (Sun-Titan-Cassini angle), which minimizes scattering by the haze.
The image shows details about 10 times smaller than those seen from Earth. Surface materials with different brightness properties (or albedos) rather than topographic shading are highlighted. The image has been calibrated and slightly enhanced for contrast. It will be further processed to reduce atmospheric blurring and to optimize mapping of surface features. The origin and geography of Xanadu remain mysteries at this range. Bright features near the South Pole (bottom) are clouds.
(4 voti)
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Titan-Clouds-White_Clouds-PIA06112.jpgWhite Clouds61 visiteCaption NASA:"Shown here is a blowup of a region of Titan imaged on July 2, 2004. This image was taken at a distance of 339.000 Km (about 210.600 miles) and shows brightness variations on the surface of Titan and a bright field of clouds near the South Pole. The field of clouds is 450 Km (about 280 miles) across and is the about the size of Arizona. Features as small as 10 Km (a little more than 6 miles) can be discerned".
(4 voti)
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Titan-PIA08351.jpgClose "Friends"...55 visiteCaption NASA originale:"Cassini peers around the hazy limb of Titan to spy the sunlit South Pole of Saturn in the distance beyond.
The thick, smog-like atmosphere of frigid Titan is a major source of interest for the Cassini mission. The moon is 5.150 Km (about 3.200 miles) across.
Images taken using red, green and blue spectral filters were combined to create this natural-color view. The image was taken with the Cassini spacecraft narrow-angle camera on Dec. 26, 2005, at a distance of approx. 26.000 Km (about 16.000 miles) from Titan. Image scale is roughly 1 Km (4.643 feet) per pixel".
(4 voti)
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Titan-Clouds-PIA09036.jpgTitanian Clouds and Surface55 visiteCaption NASA originale:"This image composite contains a radar image taken during a February 2005 (T3) flyby, and overlaid are images from the Visual and Infrared Mapping Spectrometer (VIMS) taken on Sept. 7, 2006, (T17) and Oct. 25, 2006 (T20).
The thin strip is the infrared image taken on the inbound leg of the T20 flyby and crosses the radar image near an area with a small, crater-like feature. In the radar image a faint fan of material seems to originate at the crater and the portion of the infrared image that crosses the faint fan shows both a large brightness contrast and very sharp boundaries. The fan-like deposit has such sharp boundaries and strong contrast with its surroundings that it supports the idea that the deposit seen in the radar images is a flow of material erupted from the small crater. This may be the strongest evidence yet of cryovolcanism on Titan.
The infrared image was taken at a distance of about 1100 Km (680 miles) from the surface of Titan and resolves features as small as 400 mt (1300 feet)".MareKromium
(4 voti)
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Titan-PIA08221.jpgWhen Giants meet...56 visiteCaption NASA originale:"Saturn's two largest moons meet in the sky in a rare embrace. Smog-enshrouded Titan (5.150 Km, or 3,200 miles across) glows to the left of airless Rhea (1.528 Km, or 949 miles across).
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 11, 2006 at a distance of approx. 3,6 MKM (about 2,2 MMs) from Rhea and 5,3 MKM (about 3,3 MMs) from Titan.
The Sun-Rhea-spacecraft, or phase, angle is 157° on Rhea.
Image scale is about 22 Km (approx. 13 miles) per pixel on Rhea and 32 Km (approx. 20 miles) per pixel on Titan".
(4 voti)
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