"In 2012, the Voyager mission team announced that the Voyager 1 spacecraft had passed into interstellar space, traveling further from Earth than any other manmade object.
But, in the nearly two years since that historic announcement, and despite subsequent observations backing it up, uncertainty about whether Voyager 1 really crossed the threshold continues. There are some scientists who say that the spacecraft is still within the heliosphere - the region of space dominated by the Sun and its wind of energetic particles - and has not yet reached the space between the stars."
NASA Responds: NASA Voyager Statement About Solar Wind Models
"A paper recently published in the journal Geophysical Research Letters describes an alternate model for the interaction between the heliosphere -- a "bubble" around our planets and sun -- and the interstellar medium. It also proposes a test for whether Voyager 1 has, indeed, left the heliosphere.
NASA's Voyager project scientist, Ed Stone of the California Institute of Technology in Pasadena, responds."
Related: Voyager 1 stories on SpaceRef