This artist's concept depicts NASA's Voyager 1 spacecraft entering interstellar space. Interstellar space is dominated by the plasma, or ionized gas, that was ejected by the death of nearby giant stars millions of years ago, indicated here in orange. The Voyager 1 probe was launched by NASA in 1977 to study the outer Solar System, and crossed the heliopause and entered interstellar space in 2012. The probe is expected to continue its mission until 2025, when it it will no longer be able to generate enough power to continue operation.