Wednesday, May 25, 2005

Science special issue on Titan

A few weeks ago, when the Science special issue on Titan came out, I gave an outline of the RADAR paper for the benefit of those who don't have access to the paper. I promised to do the same for the other papers, but I have to admit, some of this stuff went over my head. I'm a geology major, I am no magnetospheres person or an atmospheres person, unless it has direct bearing on the surface. For example, the troposphere and weather within such layer can create erosional landforms on the surface, so good knowledge of that layer is important. But all the atmospheres papers were on the stratosphere and mesosphere, or higher. Finding a magnetic field, be it intrinsic or induced, is important for knowing the internal structure of a body. MAG and MIMI didn't find one. So I'm just going to post the abstracts here. I know, weasily...

Flasar et al. Titan's Atmospheric Temperatures, Winds, and Composition. Science 308 (5724), 975-978.
Temperatures obtained from early Cassini infrared observations of Titan show a stratopause at an altitude of 310 kilometers (and 186 kelvin at 15°S). Stratospheric temperatures are coldest in the winter northern hemisphere, with zonal winds reaching 160 meters per second. The concentrations of several stratospheric organic compounds are enhanced at mid- and high northern latitudes, and the strong zonal winds may inhibit mixing between these latitudes and the rest of Titan. Above the south pole, temperatures in the stratosphere are 4 to 5 kelvin cooler than at the equator. The stratospheric mole fractions of methane and carbon monoxide are (1.6 ± 0.5) x 10-2 and (4.5 ± 1.5) x 10-5, respectively.
Shemansky et al. The Cassini UVIS Stellar Probe of the Titan Atmosphere. Science 308 (5724), 978-982.
The Cassini Ultraviolet Imaging Spectrometer (UVIS) observed the extinction of photons from two stars by the atmosphere of Titan during the Titan flyby. Six species were identified and measured: methane, acetylene, ethylene, ethane, diacetylene, and hydrogen cyanide. The observations cover altitudes from 450 to 1600 kilometers above the surface. A mesopause is inferred from extraction of the temperature structure of methane, located at 615 km with a temperature minimum of 114 kelvin. The asymptotic kinetic temperature at the top of the atmosphere determined from this experiment is 151 kelvin. The higher order hydrocarbons and hydrogen cyanide peak sharply in abundance and are undetectable below altitudes ranging from 750 to 600 km, leaving methane as the only identifiable carbonaceous molecule in this experiment below 600 km.
Waite et al. Ion Neutral Mass Spectrometer Results from the First Flyby of Titan. Science 308 (5724), 982-986.
The Cassini Ion Neutral Mass Spectrometer (INMS) has obtained the first in situ composition measurements of the neutral densities of molecular nitrogen, methane, molecular hydrogen, argon, and a host of stable carbon-nitrile compounds in Titan's upper atmosphere. INMS in situ mass spectrometry has also provided evidence for atmospheric waves in the upper atmosphere and the first direct measurements of isotopes of nitrogen, carbon, and argon, which reveal interesting clues about the evolution of the atmosphere. The bulk composition and thermal structure of the moon's upper atmosphere do not appear to have changed considerably since the Voyager 1 flyby.
Wahlund et al. Cassini Measurements of Cold Plasma in the Ionosphere of Titan. Science 308 (5724), 986-989.
The Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP) sensor observed the cold plasma environment around Titan during the first two flybys. The data show that conditions in Saturn's magnetosphere affect the structure and dynamics deep in the ionosphere of Titan. The maximum measured ionospheric electron number density reached 3800 per cubic centimeter near closest approach, and a complex chemistry was indicated. The electron temperature profiles are consistent with electron heat conduction from the hotter Titan wake. The ionospheric escape flux was estimated to be 1025 ions per second.
Mitchell et al. Energetic Neutral Atom Emissions from Titan Interaction with Saturn's Magnetosphere. Science 308 (5724), 989-992.
The Cassini Magnetospheric Imaging Instrument (MIMI) observed the interaction of Saturn's largest moon, Titan, with Saturn's magnetosphere during two close flybys of Titan on 26 October and 13 December 2004. The MIMI Ion and Neutral Camera (INCA) continuously imaged the energetic neutral atoms (ENAs) generated by charge exchange reactions between the energetic, singly ionized trapped magnetospheric ions and the outer atmosphere, or exosphere, of Titan. The images reveal a halo of variable ENA emission about Titan's nearly collisionless outer atmosphere that fades at larger distances as the exospheric density decays exponentially. The altitude of the emissions varies, and they are not symmetrical about the moon, reflecting the complexity of the interactions between Titan's upper atmosphere and Saturn's space environment.
Backes et al. Titan's Magnetic Field Signature During the First Cassini Encounter. Science 308 (5724), 992-995.
The magnetic field signature obtained by Cassini during its first close encounter with Titan on 26 October 2004 is presented and explained in terms of an advanced model. Titan was inside the saturnian magnetosphere. A magnetic field minimum before closest approach marked Cassini's entry into the magnetic ionopause layer. Cassini then left the northern and entered the southern magnetic tail lobe. The magnetic field before and after the encounter was approximately constant for ~20 Titan radii, but the field orientation changed exactly at the location of Titan's orbit. No evidence of an internal magnetic field at Titan was detected.


Anonymous Gsnorgathon said...

I'm with you, Jason. I'd sure like to have someone who knows something about the atmospheric chemistry explain some of those results, especially "The higher order hydrocarbons and hydrogen cyanide peak sharply in abundance and are undetectable below altitudes ranging from 750 to 600 km, leaving methane as the only identifiable carbonaceous molecule in this experiment below 600 km." What's up with that?

5/25/2005 12:15:00 PM  
Blogger Bruce Moomaw said...

The complete articles have all been posted by ESA (bless its heart) in the "Latest Publications" section of their Space Science website's cover page at . ("Latest Publications" is one of the rare cases in which ESA has finally gotten on the ball, public-information-wise.)

5/26/2005 12:28:00 AM  

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