00-013

Jovian System Data Analysis Program

Analysis Program

Cover Page/Proposal Summary

ROSS-99    NRA 99-OSS-01

Date Due: 5/5/99

NASA PROCEDURE FOR HANDLING PROPOSALS

This proposal shall be used and disclosed for evaluation purposes only, and a copy of this Government notice shall be applied to any reproduction or abstract thereof. Any authorized restrictive notices that the submitter places on this proposal shall also be strictly complied with. Disclosure of this proposal for any reason outside the Government evaluation purposes shall be made only to the extent authorized by the Government.

Proposal Type: New Proposal

Proposal Category: Satellites and Rings

Major Equipment Proposal? No

Do you intend to submit an Education/Public Outreach (E/PO) proposal? No

Proposal Title:
Io Aurora Processes from Analysis of Galileo SSI and UVS Observations

Abbreviated Proposal Title:
Io Aurora Processes

Principal Investigator:
Dr. Joseph Ajello
UV Emission Processes Team Space Sciences Division MS 183-601
JPL
4800 Oak Grove Drive
Pasadena, CA 91109-8099
Phone: 818-354-2457   Fax: 818-393-4605   E-mail: jajello@jpluvs.jpl.nasa.gov

SignatureDate
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Co-Investigators and Collaborators:
Type    Name    Affiliation    E-mail
Sci Co-I   Dr. Paul E. Geissler   Univ. Arizona   geissler@lpl.arizona.edu
Sci Co-I   Dr. Amanda Hendrix   Univ. Colorado   hendrix@lasp.colorado.edu
Sci Collab   Dr. Geoffrey K. James   JPL   gkjames@pop.jpl.na sa.gov
Sci Collab   Dr. Louis Frank   Univ. Iowa   frank@iowasp.physics.uiowa.edu



Proposal Summary:

The Galileo Orbiter Prime and GEM missions have obtained middle ultraviolet (MUV) and visible observations of the Io aurora with the Solid State Imager (SSI) and the Ultraviolet Spectrometer (UVS)over a combined wavelength range from 280-900 nm. The spectral data and imaging observations provide important information about the atmospheric structure and energy output of the aurora. Galileo's SSI imaging system has shown colorful blue, green and red aurorae in visible wavelength pictures of Io on GEM orbit E15. Similarly the UVS successfully observed an N-channel (280-430 nm) aurora on G8. These emissions are most likely caused by the impact of electrons on SO2 vented from volcanoes. The electron impact emission spectroscopy of SO2 is not well understood. We propose to analyze medium resolution (0.05-0.1 nm FWHM)emission spectra of SO2 from 3-100 eV electron impact energies with a laboratory spectrometer and 1024-pixel CCD detector (200-900 nm). The electron energy range for the laboratory study spans the range of the Te~5 eV core and Te~100 eV suprathermal distributions. The spectral studies will define the excited states of SO2 and its dissociation/ionization products contributing to the aurora. Candidate excited states are SO2(a,A,B), SO2+(C) and SO(B). The second goal of the program is to use the cross sections and plasma science(PLS) electron distributions to model the SO2 column abundance and amend the Io aurora SSI brightnesses for emissions from MUV wavelengths below 380 nm, where the brightest MUV/visible emissions are found. Color Coordinated simultaneous UVS and SSI observations of Io with higher S/N on orbits C22-G29 are planned. Red, green and blue SSI filter intensity ratios over volcanoes will be compared to laboratory spectra to help define the electron currents at Io.