The Voyager program consists of twin robotic probes, Voyager 1 and Voyager 2, launched by NASA in 1977 to survey the outer planets. Between them they made the first detailed studies of the Jupiter, Saturn, Uranus, and Neptune systems, and both are now the only operating spacecraft in interstellar space.[1][4]
Nearly 49 years after launch, the two probes still radio data home daily on shrinking power budgets. Voyager 1 is the most distant human-made object, about 173 astronomical units (AU) from Earth in mid-2026, and Voyager 2 remains the only spacecraft ever to visit Uranus or Neptune.[1][5]
The Grand Tour
In 1965, JPL engineer Gary Flandro calculated that a planetary alignment occurring once every 176 years would let a single spacecraft visit all four giant planets in the late 1970s, using each flyby as a gravity assist toward the next. Congress canceled the full "Grand Tour" program on cost grounds in 1972, but NASA approved a two-spacecraft mission to Jupiter and Saturn that preserved the option quietly: Voyager 2's trajectory could be extended to Uranus and Neptune if all went well.[4][5]
Each identical spacecraft carries ten science instruments, a 3.7-meter dish antenna, and three plutonium-fueled radioisotope thermoelectric generators. Voyager 2 launched first, on August 20, 1977; Voyager 1 followed on September 5 on a faster path that overtook its twin in the asteroid belt.[4]
Planetary encounters
| Target | Spacecraft | Closest approach |
|---|---|---|
| Jupiter | Voyager 1 | March 5, 1979 |
| Jupiter | Voyager 2 | July 9, 1979 |
| Saturn | Voyager 1 | November 12, 1980 |
| Saturn | Voyager 2 | August 25, 1981 |
| Uranus | Voyager 2 | January 24, 1986 |
| Neptune | Voyager 2 | August 25, 1989 |
At Jupiter the probes discovered erupting volcanoes on the moon Io, the first active volcanism seen beyond Earth, along with a faint ring around the planet and the fractured ice shell of Europa that hinted at a buried ocean.[4] At Saturn, Voyager 1 was deliberately steered close to the haze-covered moon Titan, confirming its dense nitrogen atmosphere; the maneuver bent the spacecraft's path north out of the plane of the planets and ended its planetary mission.[4]
Voyager 2 carried on alone. At Uranus in 1986 it found ten previously unknown moons and a magnetic field tilted far from the planet's rotation axis; at Neptune in 1989 it measured winds near 2,000 kilometers per hour, imaged the Great Dark Spot, and photographed geyser-like plumes on the frigid moon Triton.[5]
The Golden Record
Each spacecraft carries a 12-inch gold-plated copper phonograph record, a message for any intelligence that might find it. A committee chaired by astronomer Carl Sagan selected its contents: 115 encoded images, greetings in 55 languages, about 90 minutes of music from many cultures, and a library of natural sounds from Earth. The aluminum cover is etched with playback instructions and a pulsar map showing the Sun's location, plus a sample of uranium-238 whose decay serves as a clock.[7]
Into interstellar space
On February 14, 1990, Voyager 1 turned its cameras back for a final "family portrait" of the solar system, including the image of Earth that Sagan named the Pale Blue Dot. Voyager 1 passed Pioneer 10 in February 1998 to become the most distant human-made object.[4]
Voyager 1 crossed the heliopause, where the Sun's outflowing plasma gives way to the interstellar medium, on August 25, 2012, at about 122 AU; confirmation came a year later from plasma density measurements.[4] Voyager 2 followed on November 5, 2018, and its still-working plasma instrument returned the first direct measurements of the boundary crossing.[5] Both probes remain within the Sun's gravitational domain, however; on their present paths they will take tens of thousands of years to pass through the distant Oort cloud region.[4]
Power decline and instrument shutdowns
The radioisotope generators lose about 4 watts of output per year, and since 2024 JPL has been switching off instruments to keep the missions alive. Voyager 2's plasma science instrument was shut down in October 2024; Voyager 1's cosmic ray subsystem followed on February 25, 2025, and Voyager 2's low-energy charged particle instrument on March 24, 2025.[2]
On April 17, 2026, engineers powered down Voyager 1's low-energy charged particle experiment as well, leaving the spacecraft with two working instruments, its magnetometer and plasma wave subsystem. Voyager 2 still operates three, including the cosmic ray subsystem, which the team hopes to keep running through the mission's 50th anniversary in 2027.[3] Engineers have also prepared a coordinated power-system reconfiguration nicknamed "the Big Bang," tested on Voyager 2 in mid-2026 before any attempt on Voyager 1, in a bid to keep at least one instrument per spacecraft working into the 2030s.[2][3]
Distances and end of mission
In mid-2026 Voyager 1 is about 173 AU (25.9 billion kilometers) from Earth, far enough that its radio signal takes more than 23 hours to arrive; in November 2026 it is expected to become the first spacecraft one full light-day away.[1][6] Voyager 2 is about 143 AU (21.3 billion kilometers) out on a southerly course that only the 70-meter antenna at Canberra, Australia can command.[1][5] Voyager 1 recedes at roughly 17 kilometers per second, Voyager 2 at about 15.[4][5]
When power drops below what any instrument needs, likely sometime in the 2030s, the science mission will end and the probes will fall silent. Their trajectories continue regardless: in about 40,000 years Voyager 1 will pass within 1.6 light-years of the star Gliese 445, and Voyager 2 within about 1.7 light-years of Ross 248, each still carrying its Golden Record.[4][5]
References
- Where Are Voyager 1 and 2 Now? - NASA.
- NASA Turns Off 2 Voyager Science Instruments to Extend Mission - NASA Jet Propulsion Laboratory.
- The Little Probe That Could: Why Voyager 1 Matters, and Why NASA Just Switched Part of It Off - NPR.
- Voyager 1 - Wikipedia.
- Voyager 2 - Wikipedia.
- Voyager 1 will reach one light-day from Earth in 2026. Here's what that means - CNN.
- Voyager Golden Record - Wikipedia.
