[1] JOHNS HOPKINS UNIV,DEPT PHYS & ASTRON,BALTIMORE,MD 21218
[2] UNIV WISCONSIN,DEPT PHYS,MADISON,WI 53706
[3] UNIV COLORADO,CASA,BOULDER,CO 80309
[4] NASA,GODDARD SPACE FLIGHT CTR,GREENBELT,MD 20771
[5] CALTECH,DIV GEOL & PLANETARY SCI,PASADENA,CA 91125