Voyager 1, the most distant spacecraft from Earth, has reached a new milestone in its quest to leave the Solar System. Now 10.8 billion miles) from home, the veteran probe has detected a distinct change in the flow of particles that surround it. These particles, which emanate from the Sun, are no longer travelling outwards but are moving sideways.
It means Voyager must be very close to making the jump to interstellar space - the space between the stars. The newly reported observation comes from Voyager 1's Low-Energy Charged Particle Instrument, which has been monitoring the velocity of the solar wind. This stream of charged particles forms a bubble around our Solar System known as the heliosphere. The wind travels at "supersonic" speed until it crosses a shockwave called the termination shock. At this point, the wind then slows dramatically and heats up in a region termed the heliosheath. Voyager has determined the velocity of the wind at its location has now slowed to zero.