Interstellar atom and neutral solar wind observations from IMAGE                  

T.E. Moore (1), M.R. Collier (1), M-C. Fok (1), S.A. Fuselier (2), 
D.G. Simpson (1), P. Wurz (3)                                   
                                          
1 - NASA's Goddard Space Flight Center, Interplanetary Physics Branch, Code 692, 
    Greenbelt, MD 20771, United States       
2 - Lockheed Martin Advanced Technology Center, Dept. H1-11, Bldg. 255, 
    Palo Alto, CA 94304, United States            
3 - University of Bern, Physikalisches Institut, Bern CH-3012, Switzerland
                                          
Designed for observations of low energy neutral atoms generated by plasma 
heating in the Earth's ionosphere, the low energy neutral atom imager (LENA) has 
also made direct observations of interstellar neutral atoms and of a neutral 
atom component of the solar wind. Orbiting in a 8 x 1.15 Re polar orbit, IMAGE 
and LENA have operated since May 2000, and have sampled these populations on 
time scales as short as the spacecraft spin period of 2 minutes.  The 
interstellar neutral atoms have been observed for several weeks in each of two 
consecutive winter seasons in the region downstream of the interstellar flow. 
The observed flux reveals the Helium focusing cone structure, with the ions 
actually detected having been created by sputtering from impact on the coated, 
polished Tungsten conversion surface. The neutral solar wind component is 
observed to be modulated on time scales as short as the fluctuations associated 
with passing CME structures.  This owes largely to a component created by charge 
exchange with the outer geocorona. A large (factor of 100) annual variation in 
the neutral solar wind flux is thought to result from depletion of the 
interstellar gas in the downstream cavity created by solar photo-ionization and 
charge exchange [Collier et al., poster session]. Inferred characteristics of 
the interstellar gas and dust distribution in the inner heliosphere will be 
summarized for comparison with theoretical models.

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To be presented at the 2002 Spring A.G.U. Meeting, 
Washington, D.C., U.S.A., 28-31 May 2002