And the end of Voyager 2’s planetary tour on August 25, 1989, concluded with a dazzling display of Neptune and it’s moon, Triton. The images and scientific data returned by Voyager 2 would change our understanding of the solar system.
Voyager 2 is still the only spacecraft to visit the outer planets of Neptune and Uranus.
The Voyager probes launched in 1977. Together, they visited Saturn and Jupiter and their moons. But then, Voyager 2 had a unique opportunity.
“We had the opportunity to get a close flyby with Voyager 2,” said Suzanne Dodd, Voyager Project Manager. “Because of the planetary alignment when the probes launched in 1977, the four giant outer planets were all aligned on the same side of the sun, so we could go from one to the next to the next. It was a really great opportunity.”
This allowed the spacecraft to use a gravity assist from one planet to visit the next one, allow the Voyager program to visit four planets in four years. This alignment only occurs once every 176 years.
Trina Ray was working at NASA’s Jet Propulsion Laboratory for the Neptune flyby of the Voyager 2 mission. She joined the General Science Data team as her first job out of college.
There were monitors everywhere in the laboratory for Voyager operations in Building 264 at JPL, with the teams spread over multiple floors. Because Voyager 2 was always pointing antenna back to Earth, it was constantly relaying back data.
Chris Jones helped develop the flight software for the Voyager mission and helped the agency determine the best ways to manage the ever-increasing distance for communicating with the spacecraft. He also helped the mission overcome the issue of decreasing light levels to return clear images of Neptune.
The images would come across the monitors, line by line. On the slow approach to Neptune, the planet started out as several pixels, a fuzzy blue dot that grew a little each day.
As the approach grew closer, everything changed.
Ray would be sitting at her desk and someone would say, “Wow,” causing everyone to look up at the monitors.
“That’s the best image of Neptune we’ve ever seen,” one of the scientists would say. They would go back to work until someone else exclaimed, and another image would come to life.
“The incredible flow of the encounter was tremendously exciting,” Ray said. “Over the course of the month leading up to the closest approach, you really got caught up in what was happening. It had this feeling of acceleration. I’ve never seen another spacecraft mission profile have that building intensity over months, resulting in an incredible data set from the days around the closest approach.”
During the week of the flyby, Ray didn’t want to go to sleep or even step away from the monitors for a second. Everyone else was the same way. While the spacecraft was briefly out of communication, Ray used one of the showers on site and took a nap. No one she knew went home.
Media from around the world were camped out in the JPL parking lot, showing up for the daily press conference to discuss the new images and scientific findings.
“It was five days of unbelievable science,” Ray said. “And there was this intense emotion of knowing this was the last flyby. It was the end of an era.”
A new look at Neptune
The Voyager team has been working together between 20 and 30 years, a smooth functioning machine full of people who knew each other well and what each other was capable of.
Ray was a new addition. Voyager would set all of her expectations for how teams work together for the rest of Ray’s 30-year career at NASA, which is ongoing. It lit a spark in her and she would spend the next 20 years working on the Cassini orbiter at Saturn, which was inspired by Voyager.
The science gathered during the Neptune flyby revealed that their existing models for the gas giant were too simple to show what was really happening.
They discovered that Neptune’s magnetic field was tipped on its side. They found a giant spot called the Great Dark Spot on the planet, similar to Jupiter’s Great Red Spot. But the event was passing, because it was no longer there when the Hubble Space Telescope looked four years later. Neptune was found to possess some of the fastest and coldest winds in the solar system.
Four rings were found around the planet.
And when Voyager 2 flew by Triton, Neptune’s moon, the scientists discovered it was orbiting backwards. Unlike Neptune’s other moons formed from the leftovers after Neptune became a planet, Triton was a captured object that was pulled into a retrograde orbit.
During the flyby, six additional moons were discovered.
Triton was the coldest object Voyager 2 ever witnessed, reaching negative 391 degrees Fahrenheit. The wild-looking surface proved to be geologically active, with geysers erupting from the frozen nitrogen ice on Triton.
Understanding the diversity of our solar system came from the Voyager flybys.
“Time after time, we found objects doing things we hadn’t expected,” said Ed Stone, Voyager project scientist since 1975 and physics professor at the California Institute of Technology. “It changed our view of the solar system.”
“Its been a wonderful experience because there was so much to be learned,” Stone said, reflecting on his time with the Voyager mission. “We’ve been able to share this journey over many decades with the public. We could bring people along on the journey as we were discovering things at each of the flybys.”
Stone believes three aspects of Voyager contributed to NASA’s continuing legacy of spacecraft: innovative engineering, transformative science and the extraordinary inspiration of learning what’s “out there.”
Voyager 1 and 2 are the longest-flying spacecraft in history; 42 years after they launched, both are still going strong and sending back data as they explore interstellar space. It’s the farthest we’ve ever pushed into space. And the spacecraft were initially designed to last only five years.
Dodd began working on Voyager in 1984 and stayed on the project to see the Uranus and Neptune encounters. After that, Dodd would work on missions inspired by the information gleaned by Voyager’s data. And now, Dodd has returned to helm Voyager once again.
Dodd’s team of 12 people look after both spacecraft to make sure the probes are healthy, safe, operating well and not getting too cold.
Jones, who has returned to help look after the spacecraft as chief engineer, describes himself as a “doctor with a permanent housecall,” for Voyager. “You never know when you might be needed,” he said.
The Voyager flybys inspired orbiter missions like Cassini to Saturn and its moons, Galileo and Juno to Jupiter and its moons and future planned missions as well.
“I describe Voyager as a grandparent of the missions that have flown since,” Dodd said.
No missions have followed up on Uranus or Neptune, however. If a mission were ready to launch right now, it would take ten years to reach Neptune. But nothing is currently in the works, although Voyager’s intriguing scientific discoveries have given cause to return and investigate further.
“We need to develop an orbiter for each of those planets,” Dodd said. “At Uranus, the five major moons are very different. They have unique geological history, so we need to understand how they were formed or captured. Uranus has a rotational pole that is tipped on its side more than the Earth, so we need an understanding of why that happened. At Neptune, there are a great amount of features in atmosphere similar to Jupiter and Saturn. And Neptune’s moon Triton is of interest because of the methane geysers on it.”
When the Voyager spacecraft flew by the planets in our solar system, they helped answer some questions while creating more, Ray said.
But missions to the outer planets take longer, so the teams working on them know that they will probably only get to work on one or two of them in their lifetime.
“We absorb into our soul the fact that we’re going to launch and it will take seven years to get there,” Ray said, who is now working on the Europa Clipper mission to explore Jupiter’s moon Europa.
Those who worked on the Voyager mission and now assist with Europa Clipper’s development know they may not be able to see the mission through. But they’re contributing everything they learned from Voyager and other missions to ensure it will be the best it can be. And they will hand off to a new generation of scientists.
For everyone still working on Voyager, they take pride in the longest-running spacecraft in human history that is now exploring the uncharted territory of the heliosphere.
“You only send a robot emissary that exits the solar system once, and that’s Voyager,” Ray said. “That’s a milestone for mankind. Just look at these little robots and how long they’ve been going. Boy, she’s a trooper.”