HR: 1340h
AN: P53B-1248    [Abstracts]
TI: Consequence of Electron Mobility in Icy Grains on Solar System Objects
AU: * Gudipati, M S
EM: gudipati@jpl.nasa.gov
AF: Jet Propulsion Laboratory / California Institute of Technology, Mail Stop 183-301 4800 Oak Grove Dr., Pasadena, CA 91109, United States
AU: Allamandola, L J
EM: louis.j.allamandola@nasa.gov
AF: NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035, United States
AU: Cooper, J F
EM: John.F.Cooper@nasa.gov
AF: NASA Goddard Space Flight Center, Heliospheric Physics Laboratory, Code 672, Greenbelt, MD 20771, United States
AU: Sturner, S J
EM: Steven.J.Sturner@nasa.gov
AF: CRREST/UMBC, NASA Goddard Space Flight Center, Astroparticle Physics Laboratory, Code 661, Greenbelt, MD 20771, United States
AU: Johnson, R E
EM: rej@virginia.edu
AF: University of Virginia, Materials Science & Engineering, Charlottesville, VA 22904, United States
AB: Solar system ices have been shown to contain organic molecules, whether in the ice on Mars, comets such as Tempel-1 (from the Deep Impact mission) or on the surfaces of Europa, Ganymede, and Callisto. Sub-surface oceans containing ionic salts have been proposed to interpret the induced components of the local magnetic fields at these Galilean moons. Presence of liquid water is thought to be a requirement for potential astrobiological habilitability, particularly on Europa where the putative subsurface ocean is likely closest to the outer surface. Recent laboratory studies have shown that radiation processing of water-rich ices containing aromatic organic impurities readily ionizes organic molecules imbedded in an ice matrix. As a result, transient charge separation is produced more efficiently in ices containing organic impurities. This charge separation is partially stabilized by electron trapping. This could have important consequences since the icy moons of the giant planets are imbedded in both the magnetic field and trapped particle radiation environments of the planetary magnetospheres. Internal discharges of accumulated free charges (i.e. ice lightning) could significantly affect molecular chemistry of the irradiated outer layer beyond the direct effects of irradiation. Here we present new experimental results and theoretical modelling that deals with mobility of electrons produced by photoionization of PAHs (polycyclic aromatic hydrocarbons) in an ice matrix. We find that a small portion of the electrons (about 5% of the originally generated) are weakly trapped in the impurity-containing ices and can be made mobile at temperatures between 50 K and 125 K. Current flow of these mobile electrons could affect electrical conductivity of the irradiated surfaces and contribute to induced magnetic fields. This solid-state micro-ionospheric environment, comparable to a thin metallic conducting shell, may then need to be taken into account, along with the above-surface ionosphere, in modelling background variations affecting detection of induced magnetic fields from the sub-surface oceans.
References:
1. M. S. Gudipati, L. J. Allamandola, J. F. Cooper, S. Sturner, R. E. Johnson (in preparation)
2. J. F. Cooper, R. E. Johnson, B. H. Mauk, H. B. Garrett, N. Gehrels, Icarus 149, 133 (2001).
3. M. S. Gudipati, Journal of Physical Chemistry A 108, 4412 (2004).
4. M. S. Gudipati, L. J. Allamandola, Astrophysical Journal Letters 615, L177 (2004).
5. M. S. Gudipati, L. J. Allamandola, Astrophysical Journal 638, 286 (2006).
6. M. S. Gudipati, L. J. Allamandola, Journal of Physical Chemistry A 110, 9020 (2006).
DE: 2423 Ionization processes (7823)
DE: 5443 Magnetospheres (2756)
DE: 6060 Radiation and chemistry
DE: 6218 Jovian satellites
DE: 6280 Saturnian satellites
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting