Direct Observations of Interstellar Neutral Atoms from IMAGE 

Simpson, D.G., Collier, M.R., Moore, T.E., Fok, M.H., Fuselier, S.A., Wurz, P.


The Imager for Magnetosphere-to-Aurora Global Exploration (IMAGE) spacecraft was 
launched in early 2000. Its Low-Energy Neutral Atom (LENA) imager, designed 
primarily for remote sensing of terrestrial neutral atom emissions generated by 
plasma heating, has an energy range of 10 to 1000 eV. We report direct LENA 
observations of interstellar neutral atoms detected by the LENA imager during 
certain times of the year when the IMAGE orbit geometry is favorable. This is 
when the spacecraft is "downwind" of the Sun, within the Sun's gravitational 
focusing cone for interstellar neutral atoms, and beginning to turn into the 
"upwind" direction. Comparison of LENA observations with numerical models 
indicates that the LENA instrument has detected primarily interstellar neutral 
helium, which can be observed by sputtering of adsorbed atoms from the LENA 
instrument's conversion surface. A summary of the LENA observations of 
interstellar neutral atoms will be presented, along with a description of the 
numerical models with which they have been compared. 
 
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Presented at the 2002 Spring A.G.U. Meeting, 
Washington, D.C., U.S.A., 28-31 May 2002