Voyager 1, which left the Earth 33 years ago, is now at the edge of our solar system. It is today 17.4 billion kilometers away from the Sun (about 116 times farther than the Earth is from the Sun), where it reached an area where the radial speed of the solar wind is 0.
The Voyager mission, formed of 2 spacecrafts, was originally designed to study the outer solar system, specifically the gas giants Jupiter and Saturn. The mission was later extended to study the boundaries of the solar system and interstellar space.
The Voyager 1 probe is today the most remote human made object. It is located in an area called the heliosheath, which it entered 6 years ago. This is the outer shell of the Sun’s sphere of influence, before interstellar space. In this outer shell, part of the heliosphere (a ‘bubble’ in space blown by the solar wind), the solar wind slows down and heats up. Even though the outward speed of the solar wind is 0, scientists think Voyager 1 hasn’t reached interstellar space yet: a sudden drop in the density of hot particles and an increase in the density of cold particles that should occur when leaving the heliosheath hasn’t been observed yet. Scientists suspect the solar wind has been slowed down by the pressure of the interstellar wind. According to the current estimations, Voyager 1 should cross that frontier in about 4 years.
Voyager 2, traveling slower and located about 14.2 billion kilometers away from the Sun, will probably encounter the same phenomenon. Fortunately, Voyager 1 and 2 will have enough power to send us data until 2025, well after they have left the solar system.