MAPPING THE HELIOPAUSE FROM EARTH might be possible by deciphering reflected solar ultraviolet radiation. The heliopause is the boundary where the outgoing solar wind meets the incoming plasma of the local interstellar medium. The Voyager 1 spacecraft, now at a distance of 67 astronomical units, might actually sample the heliopause (at an expected distance of 125 AU or more) in the future, but scientists at USC and the University of Bonn contend that UV rays bouncing off the heliopause and returning toward the Earth might be brighter than the general UV background, and hence would offer a way of probing the heliopause shape, which is expected to be nonspherical, and the magnetic field of the interstellar medium. (Gruntman and Fahr, Geophysical Review Letters, 15 April.)