Data has confirmed that the space probe is now encountering an area in the cosmos that is dense with plasma particles.
Scientists have always believed that there is a distinct boundary at the edge of our solar system where the solar wind with a density of around 1,000 particles per square meter ends and gives away to cooler, denser interstellar space with around 80,000 plasma particles per square meter. Data beamed back to NASA from Voyager 1 confirms the hypothesis.
Below is an artist's concept depicting Voyager 1 entering interstellar space, which is the area between stars. Within a solar system "bubble" that encircles a sun -- the influence of the star is dominated by solar wind particles. Interstellar space is instead dominated by plasma, or ionized gas, that was ejected by the death of stars when they exploded as supernovas millions of years ago. In the drawing below, the interstellar plasma is shown with an orange glow.
Voyager II flew near Jupiter and Saturn and then went on to pass by Uranus and Neptune. It has not travelled as far from the Earth as its sister space probe.
Although Voyager I is now in interstellar space, it hasn’t technically left the solar system. The spacecraft will now continue travelling through the Kuiper Belt toward the Oort cloud — a region of comets in orbit around the sun.
Voyager 1 will not reach the inner edge of the Oort cloud for another 300 years. Unfortunately, the spacecraft will run out of fuel, which consists of the radioactive decay of Plutonium 238. NASA expects to prolong some use of the probe by turning off instruments in 2020. Voyager I probably will go dark by 2025. Although it will no longer be transmitting data, the spacecraft will continue on and pass through the far side of the Oort cloud in about 30,000 years.