This mission's flyby photos remain the only close-ups we have of two planets

The 176-Year Window

Voyager 2 launched from Cape Canaveral on August 20, 1977, sixteen days before its twin Voyager 1, but followed a slower trajectory that would take it past all four gas giants. NASA designed the mission around a planetary alignment that hadn't occurred since Thomas Jefferson was president and wouldn't repeat until the 22nd century: Jupiter, Saturn, Uranus, and Neptune lined up in an arc that allowed a single spacecraft to visit each one using gravity assists, slingshotting from planet to planet without carrying enough fuel for the journey on its own. The alternative—a direct flight to Neptune—would have required a spacecraft the size of a building and taken thirty years. Voyager 2's route cut the travel time to twelve years and fit on a Titan IIIE rocket. Engineers at the Jet Propulsion Laboratory calculated the trajectories by hand and on early computers, plotting a path that threaded through the moons of four planets with margins measured in hundreds of kilometers across billions of kilometers of space.

Uranus in January 1986

Voyager 2 reached Uranus on January 24, 1986, flying within 81,500 kilometers of the planet's cloud tops at 9:00 a.m. Pacific time. The encounter revealed a world nothing like the other gas giants: Uranus rotates on its side, its axis tilted 98 degrees, so its poles point nearly directly at the sun during its 84-year orbit. The spacecraft discovered ten new moons, measured a magnetic field offset 60 degrees from the rotational axis, and photographed Miranda, a moon whose surface looks like it was shattered and reassembled, with cliffs ten times deeper than the Grand Canyon. Voyager 2's cameras captured images in near-total darkness—Uranus receives 1/400th the sunlight Earth does—requiring exposure times so long that engineers had to rotate the entire spacecraft during the shot to avoid blurring. The flyby lasted just five and a half hours; the spacecraft spent decades traveling to Uranus and had only a few hours to gather data before hurtling past at 15 kilometers per second, never to return.

Neptune in August 1989

Voyager 2 arrived at Neptune on August 25, 1989, the only spacecraft ever to visit the solar system's outermost major planet. Flying within 4,950 kilometers of Neptune's north pole, closer than it had approached any other planet, Voyager 2 discovered six moons, four rings, and the Great Dark Spot, a storm system the size of Earth. Winds on Neptune blow at 2,100 kilometers per hour, the fastest in the solar system, on a planet so distant it receives 1/900th Earth's sunlight. The spacecraft photographed Triton, Neptune's largest moon, revealing geysers of nitrogen erupting through surface ice at minus 235 degrees Celsius, the coldest known temperature on any solid surface. Voyager 2's final planetary encounter used Neptune's gravity to bend the spacecraft's path southward, sending it diving below the plane of the solar system at 470 million kilometers per day, leaving the planets behind forever. The mission returned 4,950 images of Neptune and Triton in under 24 hours, then fell silent on the planetary stage.

The Only Visitor

No spacecraft has returned to Uranus or Neptune since 1989, and none is currently funded or scheduled. Voyager 2's images remain the highest-resolution pictures we have of two entire planets, one-quarter of the major worlds in our solar system. A 2023 National Academies report recommended a Uranus orbiter and probe as NASA's top priority for the next decade, but the earliest launch date would be 2031, arriving in 2044—55 years after Voyager 2's flyby. Neptune would wait even longer; no serious mission proposal exists beyond preliminary concept studies. The problem is distance and money: a Uranus mission costs over four billion dollars and requires nuclear power sources, of which NASA produces only one per decade. Voyager 2 itself continues operating, now over 20 billion kilometers from Earth in interstellar space, sending data through a transmitter powered by decaying plutonium-238. The spacecraft carries a golden record with greetings in 55 languages and images of Earth, a message to no one in particular from a species that visited four worlds in twelve years and hasn't gone back.