This Day in History — Voyager 1 Launches

The Off-Key Bard watches a rocket climb from Cape Canaveral carrying a spacecraft designed to explore Jupiter and Saturn. Nearly half a century later, that spacecraft is still traveling.

"Voyager 1 was sent to explore the outer planets. It just never stopped."

On this day in 1977, at 12:56:01 UTC, NASA launched Voyager 1 from Launch Complex 41 at Cape Canaveral, Florida, aboard a Titan IIIE-Centaur rocket. It was the second of the twin Voyager spacecraft to leave Earth — Voyager 2 had launched 16 days earlier on August 20. But Voyager 1 flew a faster trajectory and overtook its twin on December 19, 1977, just over three months after launch. It would reach Jupiter and Saturn first.

The mission's timing exploited the same rare planetary alignment that made Voyager 2's Grand Tour possible — the once-per-176-years window in which Jupiter, Saturn, Uranus, and Neptune fell into an arc that allowed gravity assists to carry a spacecraft from one to the next with far less fuel than a direct trajectory would require. Unlike Voyager 2, which was sent on the slower path to visit all four outer planets, Voyager 1 was placed on a trajectory optimized for speed and for a crucial scientific detour: a close flyby of Saturn's moon Titan.

That choice had consequences that shaped the entire mission.

Jupiter: The Solar System's Most Violent Moon

Voyager 1 reached Jupiter on March 5, 1979, passing within 348,890 kilometers of the planet's cloud tops. The encounter transformed planetary science. Jupiter's atmosphere proved far more complex than ground-based observations had suggested — the Great Red Spot revealed its structure in extraordinary detail, the thin Jovian ring system was confirmed, and lightning was detected in the cloud banks.

But the single most astonishing image came from Io.

On March 8, 1979, navigation engineer Linda Morabito was processing a long-exposure image of Io taken for star-position calibration when she noticed a large umbrella-shaped plume erupting from the moon's surface — 280 kilometers high, arching back toward the camera. It was a volcanic eruption. Active volcanism, driven by the immense tidal forces of Jupiter's gravity kneading Io's interior, was producing eruptions ten times taller than anything on Earth. It was the first active volcanism ever observed beyond Earth.

The Voyager team found nine active eruptions on Io over the course of the flyby. The moon scientists had expected to be a dead, cratered ball of rock turned out to be the most volcanically active body in the solar system.

Saturn: The Titan Decision

Voyager 1 reached Saturn on November 12, 1980. The close flyby of Titan — a priority from mission design because Titan's thick atmosphere made it one of the most scientifically compelling targets in the outer solar system — revealed a moon blanketed in nitrogen-rich haze so thick that the cameras could not see the surface. Titan's atmosphere, Voyager showed, resembled Earth's primordial atmosphere in its basic chemistry, with nitrogen as the dominant component and complex organic chemistry occurring in the upper layers.

The Titan flyby dictated what came next. The gravitational path required for the close Titan encounter bent Voyager 1's trajectory steeply northward, out of the plane in which the planets orbit. The spacecraft would never reach Uranus or Neptune. Its planetary tour was complete.

Its journey was not.

The Pale Blue Dot

In 1990, NASA turned Voyager 1's cameras back toward the inner solar system for a final family portrait — a sequence of images capturing the Sun and as many planets as could be seen from 6 billion kilometers away. On February 14, 1990, one of those frames captured Earth: a 0.12-pixel point of light, suspended in a sunbeam scattered by the camera's optics, barely distinguishable from the darkness around it.

The image became known as the Pale Blue Dot. Carl Sagan, who had championed the idea of taking it, reflected on what it showed: every human being who had ever lived, every war ever fought, every great empire, had played out on that barely visible speck. The cameras were shut off after the portrait. There was nothing further that way worth photographing. Everything interesting lay ahead.

Interstellar Space

On February 17, 1998, Voyager 1 overtook Pioneer 10 to become the most distant human-made object ever built. The spacecraft continued outward, its instruments studying the thinning solar wind and the approaching boundary of the Sun's influence.

On August 25, 2012 — confirmed by scientists on September 12, 2013 — Voyager 1 crossed the heliopause into interstellar space. For the first time in history, something built by human hands was sailing through the medium between the stars. It remains there today, now more than 24 billion kilometers from Earth, its signals taking over 22 hours to reach us at the speed of light.

What It Carries

Bolted to the side of the spacecraft is a gold-plated copper phonograph disc — the Golden Record. It contains 115 images, sounds of Earth from rain to surf to music to laughter, spoken greetings in 55 languages, and 90 minutes of music selected by a committee that included Carl Sagan. It was designed as a message should Voyager 1 ever be intercepted by another intelligence.

The odds of that happening in any human-relevant timeframe are effectively zero. The nearest star system is thousands of years away even at Voyager's speed. But that is, in some ways, beside the point. The Golden Record is what the species chose to say about itself at the moment it first sent something into the dark between the stars.

Voyager 1's radioisotope generators continue to decline. Individual instruments have been shut down to conserve power. Eventually, sometime in the 2030s, the last signal will fade. The spacecraft itself will coast silently through the Milky Way, carrying its message, long after there is anyone left at the Deep Space Network to listen.

"Past giant worlds the traveler flew,
Beyond the Sun's familiar blue.
And when its final signals cease,
It sails the stars, a message-piece."

History reminds us: in 1977 we launched a machine toward the planets — and it became humanity's first emissary into interstellar space. Forty-nine years ago today.

Sources

• Voyager 1 — NASA Science — NASA
• Voyager 1 — Wikipedia — Wikipedia
• The Voyager Golden Record — NASA JPL — NASA Jet Propulsion Laboratory
• Voyager 1: Where It Is Now — KeepTrack — KeepTrack