Beyond the Solar System's edge
When engineers designed the Voyager spacecraft in the 1970s, a nominal mission life of five years was planned. Nearly fifty years later, both probes remain operational — the only spacecraft ever to have crossed the heliopause, the boundary where the Sun's outward-streaming solar wind is finally halted by the pressure of the interstellar medium.
The most recent data reveals that the interstellar medium is not the quiet, uniform medium scientists once assumed. Voyager has detected plasma waves propagating through interstellar space — triggered by coronal mass ejections from the Sun that take over a year to travel out and disturb the interstellar plasma. The measurements provide the first direct data on the density and temperature of the local interstellar medium, previously only inferred from remote observations.
What the probes are measuring
Voyager 1 carries a working Plasma Wave System and a cosmic ray detector. Data show that cosmic ray flux increases sharply beyond the heliopause — confirming that the heliopause shields the inner Solar System from a significant portion of galactic cosmic radiation. This has direct implications for understanding the radiation environment that future deep-space crewed missions — and any life-bearing planets around other stars — would experience.
To understand the broader context of where Voyager sits, see our guide to measuring cosmic distances and our solar wind and magnetosphere guide, which explains what the probes crossed to reach interstellar space.
Key figures
NASA's Jet Propulsion Laboratory manages both missions. The official Voyager mission page publishes current distance and status data updated daily.