Scientists with the U.S. space agency NASA say the Voyager 1 spacecraft, launched 33 years ago, is on the edge of our solar system where there is no outward motion of solar wind.
NASA says the spacecraft is now more than 17 billion kilometers from the sun and has reached an area where the velocity of the solar wind - the hot, ionized particles flowing outward from the sun - has diminished to near zero.
The scientists say Voyager is preparing to exit the heliosheath, the turbulent outer shell of the sun's sphere of influence. In about four years, the spacecraft will fully reach interstellar space and come under the influence of another star system.
Voyager 1 was launched in 1977 and throughout its journey, has sent back data about the planets in our solar system and the solar wind that is helping to push it through space.
A separate spacecraft, Voyager 2, was launched a month before Voyager 1. It is now about 14 billion kilometers from the sun, traveling at a different path and different speed than Voyager 1.