Edward Stone Voyager Exploration Trail
About Ed Stone
Dr. Edward Stone was a world-renowned physicist and space scientist whose life’s work established crucial foundations for planetary science and space exploration. From his humble childhood spent along the banks of the Mississippi in Iowa to his tenure at Caltech and JPL, Stone’s passion for science and fearless curiosity led him into a distinguished career that would launch humanity’s scientific presence farther into the cosmos than ever before.
After spending most of the 1960s at Caltech, Stone joined JPL in 1972, where he was made project scientist for a mission initially called the Mariner Jupiter/Saturn 1977 (MJS77) project. The mission — renamed Voyager in March 1977 — would become the longest-running space mission in history, as well as one of the most publicly recognizable.
For 50 years (1972-2022), Stone maintained his position as Voyager’s project scientist on its 15-billion-mile (24-billion-kilometer) journey from Earth to the edge of our solar system and into interstellar space.
About the Trail
The Edward Stone Voyager Exploration Trail follows the two trajectory paths of the twin Voyager spacecraft, starting from launch and following their journeys as they ventured far beyond the outer reaches of our solar system. Starting on the JPL Mall, the trail’s twin paths are marked by a series of memorial plaques commemorating the mission milestones of the two Voyager spacecraft, which launched August 20 (Voyager 2) and September 5 (Voyager 1), 1977, as well as the distinguished milestones Dr. Stone achieved throughout his remarkable life. Known for his lifelong passion for exploration — whether strolling thoughtfully across JPL’s grounds or navigating the vastness of interstellar space — Dr. Stone embodied the essence of curiosity and dedication. This walking path invites visitors to walk in his footsteps, reflecting on the twin paths of Voyager 1 and Voyager 2 and the profound milestones they reached under Dr. Stone’s steady leadership.
Voyager 1 & 2 Shared Pathway
August 20 & September 5, 1977
Calculations made in summer 1965 revealed that a spacecraft launched in the late 1970s could potentially visit all four of the giant outer planets, using each planet’s gravity to propel the spacecraft to the next.
This rare opportunity was met by Voyager 1 and 2, which launched from NASA’s Kennedy Space Center in 1977. Although Voyager 2 was the first to launch — two weeks before its spacecraft counterpart — Voyager 1 was given its name because it was scheduled to reach Jupiter and Saturn first.
September 6, 1977
Wasting no time in its history-making endeavors, Voyager 1 sent back its first batch of images less than two weeks after it launched. Those images included a snapshot of Earth and its Moon in a single frame from a distance of 7.25 million miles (1.2 million kilometers) — the first image of its kind taken by a spacecraft in the history of space exploration.
March 5, 1979
Voyager 1’s closest flyby of Jupiter yielded several exciting discoveries about the planet and its moons. The spacecraft uncovered the Jovian ring system and two moons, Thebe and Metis, as well as grooved terrain on Jupiter’s largest moon, Ganymede, suggesting an early history of tectonic activity. The mission team also learned that the famed Great Red Spot is actually an enormous cyclone-like storm.
Ed Stone’s favorite moment occurred on March 9, when the spacecraft’s optical navigation images captured the first active volcanoes spotted beyond Earth on the moon Io. The spacecraft also found that this small moon’s orbit across Jupiter’s powerful magnetic lines of force turns Io into an electric generator capable of creating lightning in Jupiter’s upper atmosphere. Until this time, scientists had never detected lightning on a world beyond Earth.
July 9, 1979
A few months later, Voyager 2 made even more discoveries during its flyby of Jupiter. The spacecraft captured the first images of Jupiter’s ring system and discovered yet another Jovian moon (Adrastea). A close approach to the moon Europa revealed intersecting linear features on its surface, suggesting the formation of cracks in a crust of ice over a vast liquid water ocean.
On Io, Voyager 2 observed that six of the moon’s volcanoes that had been erupting during Voyager 1’s encounter were still erupting, suggesting that their active periods could last several months and that Io’s volcanoes erupted intermittently
November 12, 1980
A little more than a year after its flyby of Jupiter, Voyager 1 narrowed in on the famously ringed planet of Saturn. The spacecraft discovered three moons: Atlas, Prometheus, and Pandora.
Voyager 1’s encounter with Saturn’s largest moon, Titan, revealed a thick, nitrogen-rich atmosphere. Titan’s Earth-like atmosphere — the first found beyond our planet — suggested that seas of liquid methane and ethane may exist on its surface.
After the Saturn flyby, Voyager 1 veered upward and out of the planetary plane toward the edge of the solar system. Unlike Voyager 2, it would not visit the two remaining gas giants.
August 26, 1981
Fifteen months behind Voyager 1, Voyager 2 finally reached Saturn. The flyby included close encounters with several of the planet’s icy moons, including Tethys, Iapetus, and Enceladus. The spacecraft took snapshots of Enceladus’ half-young, half-old, yet surprisingly bright terrain, which suggested the strong possibility that it was geologically active. The spacecraft captured additional images of Saturn’s north pole from Enceladus which were later stitched together to reveal for the first time the massive hexagonal storm circulating around the planet’s pole.
Unlike its twin spacecraft, Voyager 2 would continue its planetary tour, visiting the final two gas giants, Uranus and Neptune, before setting its trajectory toward the outer boundary between our solar system and interstellar space — a journey that would take 37 years from this point.
From this point, Voyager 1 & 2 take separate paths to interstellar space, and across JPL.
Voyager 1 Pathway
September 12, 1985
In the late 1980s and through the 1990s, Ed Stone served as vice chairman and chairman of the Board of Directors of the California Association for Research in Astronomy. During this time, Stone oversaw the creation and operation of the W.M. Keck Observatory on Mauna Kea, Hawaii — one of the most productive ground-based astronomical observatories on Earth. He also served as director of the W.M. Keck Foundation; in 2023, this foundation honored Stone’s scientific achievements and leadership with a $4 million gift to endow the Edward C. Stone Professorship at Caltech.
February 14, 1990
At a distance of 3.7 billion miles (6 billion kilometers) from the Sun, Voyager 1 took its final snapshots of the mission, which would soon become known as the “Solar System Family Portrait.” It was the first series of images capturing Venus, Earth, Jupiter, Saturn, Uranus, and Neptune arrayed about the Sun. Earth was captured as a tiny speck in a beam of scattered sunlight — an image that would inspire Carl Sagan to think about the fragility and uniqueness of our “pale blue dot” of a home planet.
After the images were transmitted from the spacecraft, engineers turned off Voyager 1’s cameras so they could use the power, computer memory, and data rate for other instruments that collect key data on the solar wind and interstellar space.
January 1, 1991
Ed Stone was made director of JPL in 1991, roughly two years after the Voyagers completed their planetary flybys. Under his leadership, JPL was responsible for more than two dozen missions and instruments, including the NASA-ESA Cassini/Huygens mission in 1997. Cassini was a direct outgrowth of the scientific questions that arose from Voyager’s two flybys, and it carried the only probe that has ever landed in the outer solar system (at Titan).
After retiring from JPL in 2001, Stone returned to Caltech as a teacher and researcher
September 16, 1991
The same year he was made director of JPL, Ed Stone was awarded the National Medal of Science in the Physical Sciences category. The award was presented by President George H. W. Bush in recognition of Stone’s outstanding leadership as project scientist for the Voyager space mission and its exploration of the outer solar system.
July 4, 1997
As JPL director, Ed Stone oversaw the Mars Pathfinder mission, which had launched from Cape Canaveral in December 1996 and landed on the Red Planet seven months later. After demonstrating a new way to safely land on the rough terrain of Mars, Pathfinder successfully delivered the first-ever robotic rover, Sojourner, to land and operate on the Martian surface.
The level of public engagement was unprecedented at the time. Although the internet was still in its infancy, the mission’s activities captured the imaginations of millions of viewers, who watched as engineers and scientists in Mission Control landed and operated the instrument.
February 17, 1998
Pioneer 10 may have had a five-year head start, but Voyager 1 still managed to surpass it in February 1998. At 69.4 astronomical units (6.5 billion miles; 10.4 billion kilometers) from the Sun — traveling at a rate of over 1 au per year faster than Pioneer 10 — Voyager 1 became the most distant human-made object from the Sun.
December 16, 2004
Twenty-four years after its flyby of Saturn, Voyager 1 crossed the termination shock, where the solar wind abruptly slows down and heats up as it encounters the interstellar wind. The termination shock marks the inner boundary of the heliosheath, which is the turbulent outer atmosphere of solar wind the Sun creates around the planets.
Voyager 1’s crossing also clarified the location of the termination shock, which was unknown until this time. Unfortunately, on the day Voyager 1 crossed the shock, ground antennas were not scheduled to listen for the data the spacecraft was transmitting.
August 25, 2012
Eight years after crossing the termination shock, Voyager 1 exited the heliosphere — the boundary between our solar bubble and the matter ejected by explosions of other stars — and became the first human-made object to cross the threshold of interstellar space.
Since the spacecraft was continually collecting data, Voyager detected the full intensity of the cosmic rays in interstellar space for the first time on this day. It also made the first measurement of the interstellar magnetic field wrapped around the outside of the heliosheath.
The crossing itself, however, was not confirmed until April 9, 2013, when Voyager 1 made its first measurement of the density of the interstellar medium, capturing a wave caused by a coronal mass ejection from the Sun and causing the plasma in interstellar space to ring.
December 3, 2013
NASA bestowed its highest honor upon Ed Stone in December 2013, awarding him the Distinguished Service Medal. The award was presented to Stone by Stephen Colbert during an episode of the comedy news show The Colbert Report.
April 20, 2024
In a historic first, the Deep Space Network (DSN) used all six radio frequency antennas at the Madrid Deep Space Communications Complex to carry out a test to recover the signal from Voyager 1, which was at a distance of 163 au (15.2 billion miles; 24.4 billion kilometers) from Earth. The six-antenna array combined the receiving power of six enormous antennas, allowing the DSN to successfully collect the faraway spacecraft’s very faint signals.
January 23, 1936 – June 9, 2024
Ed Stone’s steadfast leadership and pursuit of scientific knowledge expanded humanity’s understanding of the universe and left a deep impact on the space community. His legacy lives on through the Voyager mission, as well as the myriad other contributions he made to space exploration and planetary science.
Stone’s colleagues continue to describe him as a trailblazer who dared mighty things and took NASA and the rest of humankind on a planetary tour of our solar system and beyond, where no spacecraft had gone before. His energetic leadership has sparked our collective imaginations about the mysteries and wonders of deep space, and his legacy will continue to inspire future generations to explore the great cosmic landscape that is our home.
Voyager 2 Pathway
September 19, 1982
At Caltech’s Palomar Observatory atop Palomar Mountain, California, JPL’s famed asteroid hunter Eleanor F. Helin discovered a new asteroid in the inner main belt, which contains objects orbiting between Mars and Jupiter within the inner portion of the asteroid belt. Helin named the asteroid “5841 Stone” in honor of Ed Stone
January 24, 1986
Unlike its twin spacecraft, which veered away from the solar system’s remaining two gas giants en route to interstellar space, Voyager 2 powered through the five-year trip to do a flyby of Uranus, the first time the seventh planet from the Sun had been seen up close.
Upon approach, Voyager 2 images revealed 11 new moons: Puck, Juliet, Portia, Cressida, Desdemona, Rosalind, Belinda, Perdita, Cordelia, Ophelia, and Bianca. The Voyager team also learned that Uranus has a tilted magnetic field. Consequently, the poles of its magnetic field are closer to the equator, unlike Earth where the magnetic pole and the rotational poles are nearly aligned.
Voyager 2 was the first spacecraft to capture snapshots of Uranus’ very dark rings and detect temperatures as low as -353 F (59 K; -214 C), making Uranus the coldest planet in our solar system. This encounter also marked the first time NASA’s Deep Space Network arrayed its antennas together to improve our ability to capture the weak radio signals from very distant spacecraft.
August 25, 1989
Three years after its encounter with Uranus, Voyager 2 finally arrived for its flyby of Neptune, making it the first spacecraft to observe the planet up close and the first to visit four planets beyond Earth. Like any good tourist, Voyager 2 snapped as many photos as it could, discovering six new moons in its images: Despina, Galatea, Larissa, Proteus, Naiad, and Thalassa. It also captured the first images of Neptune’s rings and found a huge, counterclockwise rotating storm in Neptune’s southern hemisphere, dubbed “The Great Dark Spot.”
Five hours after its closest approach to Neptune, Voyager 2 gave us our first close-up views of Triton, a bitterly cold, fractured moon with terrain the texture of a cantaloupe rind and geysers erupting from pinkish-hued nitrogen ice that forms the moon’s southern polar cap. After the Neptune encounter, Voyager 2 bid farewell to the last planet in our solar system, veering south from the ecliptic plane on its trip to the edge of the solar system.
October 10 & December 5, 1989
Two years after NASA’s Deep Space Network expanded its 64-meter dishes to 70 meters wide at all three communications complexes (Goldstone, California; Madrid, Spain; and Canberra, Australia) — improving our ability to capture the weak radio signals Voyager was expected to send back from Neptune — engineers turned off Voyager 2’s wide-angle and narrow-angle cameras as well as its spectrometers. This would allow the Voyager team to use the spacecraft’s power, computer memory, and data rate for other instruments that collect key data on the solar wind and interstellar space.
August 25, 1997
Ed Stone served as principal investigator for the Advanced Composition Explorer (ACE) mission, which was designed to collect and analyze particles from solar, interplanetary, interstellar, and galactic origins. Since its August 1997 launch from Cape Canaveral, the ACE spacecraft, aided by its nine science instruments, has provided a wealth of data contributing to our understanding of our Sun, its interaction with Earth, and the formation and evolution of our solar system.
ACE’s instruments have a collecting power that is 10 to 10,000 times greater than anything previously flown, allowing the spacecraft to provide real-time space weather data and advanced warning of geomagnetic storms.
November 16, 1999
Ed Stone received the American Astronomical Society’s prestigious Carl Sagan Memorial Award for his demonstrated leadership in research and policies that have advanced humankind’s exploration of the cosmos.
August 30, 2007
Eighteen years after its flyby of Neptune, Voyager 2 crossed the termination shock into the heliosheath, which is the turbulent outer atmosphere of the solar wind the Sun creates around the planets. Learning from what happened with Voyager 1 three years earlier, the team made sure that antennas on Earth were listening for Voyager 2’s data transmissions, allowing scientists to finally analyze the first measurements of the passage through the termination shock.
August 13, 2012
Voyager 2 surpassed NASA’s longest operating mission in August 2013, breaking the previous record for continuous operation held by Pioneer 6, which operated 12,758 days after launching in December 1965.
August 20, 2012
Ed Stone received many awards and honors throughout his prestigious career, but among the honors he treasured most was when the Burlington School Board in his Iowa hometown decided to name its new middle school on Mason Road in his honor. Stone attended the grand opening of Edward Stone Middle School in August 2020, and he was deeply proud to be known as an inspiration to young learners.
November 5, 2018
Eleven years after crossing the termination shock, and six years after its twin spacecraft accomplished the same feat, Voyager 2 exited the heliosphere in November 2018, becoming the second human-made object in history to break through the interstellar medium and reach the space between the stars. At the time of its crossing, it had traveled slightly more than 11 billion miles (18 billion kilometers) from Earth.
As of 2024, Voyager 2 is the only spacecraft that has studied all four of our solar system’s gas giant planets at close range.