Voyager 1, which has traveled the farthest from Earth of any man-made object, is approaching the edge of the heliopause, the boundary between the sun’s solar winds and the interstellar medium. It is impossible to know when, exactly, the craft will reach interstellar space, since it will be the first man-made object ever to travel that far from Earth. It is anticipated, however, that the craft will cross the boundary within the next few months or years, reaching the heliopause roughly 10 years after crossing the Termination Shock, which it did in 2004. Voyager 2 crossed the termination shock in 2007.