Photolytic production of CO2 on Iapetus

Details Photolytic production of CO2 on Iapetus Photolytic production of CO2 on Iapetus

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.6106p&link_type=abstract

American Astronomical Society, DPS meeting #40, #61.06; Bulletin of the American Astronomical Society, Vol. 40, p.511

Astronomy and Astrophysics

Astronomy

Scientific paper

Carbon Dioxide has been detected on the surface of Iapetus by Cassini's VIMS instrument at the 4.26 micron band. This CO2 is concentrated on the equatorial leading side, where we also see an abundance of dark material. The residence time of free CO2 on the surface of Iapetus is very short, thus the CO2 is unlikely to be in the form of frost; it is more likely that the CO2 is tightly bound in the form of complexed molecules.
We explore the possibility of photolytically generating CO2 from a mixture of the carbon rich material and water ice that matches the expected composition of the dark material on Iapetus' surface. An ice regolith was created with flash frozen water that was crushed into sub-millimeter shards and mixed with amorphous 13C. The regolith was placed in a vacuum chamber with a surface area of 10 cm2 and a thickness of 2 cm and exposed to UV light from a deuterium lamp with peaks of flux centered around 121 and 160 nm. Temperatures were varied between 60 and 130K at a pressure of 10-8 torr. Both CO and CO2 were produced by photolytic reactions and detected by a mass spectrometer.
Applying these results to Iapetus, Jeans escape calculations show that CO2 generated by photolysis will remain gravitationally bound to Iapetus for between 100 and 200 years, ballistically scattering across the surface until it is sequestered in a polar cold trap or escapes to space. The average particle will interact with the surface more than 1000 times before escaping unless interactions with surface grains causes it to become complexed, such as adsorption.
We are continuing to evaluate the photochemistry for this simulated Iapetus surface using a Nicolet IR spectrometer to identify all the products generated and estimate the associated production rate.

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