Tuesday, July 06, 2004
Titan tantilizes...
The T-0 flyby, which had Cassini arcing under Titan, has confirmed some suspicions (ISS observations of Titan's south pole has a small system of cloulds, indicating that locally the temperatures in the moon's nitrogen atmosphere dive below the triple point of methane), but provided other problems. Scattering in the atmosphere will apparenly limit the use of the ISS cameras in two ways - scattering of reflected light from the surface as photochemical smog blurs abedlo details, and the same overcast washing out the sun as seen from the surface - meaning no shadows. All this means the believability of Titanian photointerpretation is going to be somewhere between Mars as seen by Lowell and Mariner 4.
VIMS, the lower resolution spectometer, however has managed to throw a spanner in the works. Previously, the thinking had been that the darker equatorial areas might be seas of ethane, produced by the photolysis of the methane in Titan's atmosphere (e.g. see Roe et al. 2004 , paragraph 11, or here (Ethane is liquid in the conditions predicted at Titan's surface). Apparently, though, these dark bands are composed of water (which at 94K is no way liquid), while organic material is strewn over the 'bright' temperate regions. Which means we literally had Titan backwards...
If it is true that the dark bands are solid, it increases the chances that the probe Hugyens will survive on the surface - liquid ethane's high thermal conductivity would quickly freeze the probe to death. Although the scientists involved might trade those minutes on the surface for a glimpse of an alien ocean...
The lack of obvious craters in the ISS images is also intriguing*, although the lack of shadows means that this hasnt been confirmed. The decider will be the RADAR instrument, a SAR much like than on Magellan operating at 2.2 cm wavelength that will scan Titan on the frequent flybys (at 338,922 km, this particular encounter was too distant). RADAR and ISS point in different, fixed directions, so they cannot be used at the same time. The results of this flyby may make the choice easier.
*a standard scientific word meaning we dont even begin to understand the data yet, but give us more money and we might be able to invent something.
VIMS, the lower resolution spectometer, however has managed to throw a spanner in the works. Previously, the thinking had been that the darker equatorial areas might be seas of ethane, produced by the photolysis of the methane in Titan's atmosphere (e.g. see Roe et al. 2004 , paragraph 11, or here (Ethane is liquid in the conditions predicted at Titan's surface). Apparently, though, these dark bands are composed of water (which at 94K is no way liquid), while organic material is strewn over the 'bright' temperate regions. Which means we literally had Titan backwards...
If it is true that the dark bands are solid, it increases the chances that the probe Hugyens will survive on the surface - liquid ethane's high thermal conductivity would quickly freeze the probe to death. Although the scientists involved might trade those minutes on the surface for a glimpse of an alien ocean...
The lack of obvious craters in the ISS images is also intriguing*, although the lack of shadows means that this hasnt been confirmed. The decider will be the RADAR instrument, a SAR much like than on Magellan operating at 2.2 cm wavelength that will scan Titan on the frequent flybys (at 338,922 km, this particular encounter was too distant). RADAR and ISS point in different, fixed directions, so they cannot be used at the same time. The results of this flyby may make the choice easier.
*a standard scientific word meaning we dont even begin to understand the data yet, but give us more money and we might be able to invent something.
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