I have to say that I had no idea this was still being debated: Voyager spacecraft might not have reached interstellar space.
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.
Now, two Voyager team scientists have developed a test that they say could prove once and for all if Voyager 1 has crossed the boundary. The new test is outlined in a study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
It’s interesting that the line between interplanetary and interstellar space appears to have become the boundary of the heliosphere. It’s worth remembering that the Voyager probes are well beyond the orbits of Neptune and Pluto, or the overall Kuiper belt. Both probes are currently over 100 AU away, over 100 times the distance between the Earth and the Sun. By many standards, they entered interstellar space long ago.
By other standards, they still have a long way to go. They haven’t passed the orbits of all of the scattered disk objects, and they still have millenia to go before they’re out of the Oort Cloud or beyond the point where the Sun’s gravitational influence dominates, both of which extend for light years. If the Voyager probes were headed for the nearest star (which they’re not), they would have covered less than 0.04% of the distance so far.
Whether or not Voyager 1 has actually exited the Heliosphere, it is definitely near or at the boundary. It still amazes me that human created objects are that far out. And that we’ll have instruments observing what the environment out there is like.