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Doug Cornelius

Aug. 25, 1989: Voyager 2, Meet Neptune

1989: Voyager 2 makes its closest encounter with Neptune, passing just 3,000 miles above the cloud tops of the most distant planet in our solar system.

The Voyager 2 space probe has been our most productive unmanned space voyage. It visited all four of the outer planets and their systems of moons and rings, including the first visits to previously unexplored Uranus and Neptune.

What did the space probe discover about Neptune?

Originally it was thought that Neptune was too cold to support atmospheric disturbances, but Voyager 2 discovered large-scale storms, most notably the Great Dark Spot . It turned out to have a much shorter duration than Jupiter's persistent Great Red Spot. Neptune not only has storms, it happens to have the fastest winds in the solar system .

The space probe was plotted to perform a close encounter with Triton, the larger of Neptune's originally known moons. Along the way, Voyager 2 found six new moons (.pdf) orbiting the planet.

Voyager 2 found four rings and evidence for ring arcs, or incomplete rings, above Neptune. That means all four of the gas giants in our solar system have rings. Neptune's, however, are very meager compared to the magnificent rings around Saturn.

In the late 19th century, astronomers thought that an unseen Planet X was influencing the orbits of Uranus and Neptune. The observed positions of the two planets and their calculated positions differed. Among those astronomers convinced of the existence of Planet X was Clyde Tombaugh. In 1930 while scanning areas of the sky for Planet X, he found Pluto.

When Voyager 2 flew by Neptune, it took very precise measurements of Neptune's mass and found it to be about 0.5 percent less massive than previous estimates. When the orbits of Uranus and Neptune were recalculated using the more accurate mass figure, it became clear that the imprecise number for Neptune -- and not the gravity of an unseen planet -- had caused the observed orbital discrepancies.

After the International Astronomical Union demoted Pluto from planetary status in 2006, Voyager 2's 1989 Neptune flyby became the point when every planet in our solar system had been visited by a space probe.

(All you Pluto-is-a-planet advocates can still argue for reinstatement, but you will have to bring a few more celestial objects into the planet category along with Pluto.)

The twin Voyager space probes were launched in 1977 . Voyager 2 was actually launched first, on Aug. 20. Voyager 1 left two weeks later on Sept. 5. ( Voyager 6 was never launched, much to the chagrin of Star Trek fans .) Voyager 1's trajectory was a faster path, getting it to Jupiter in March 1979. Voyager 2 arrived about four months later in July 1979. Both then sped on to Saturn.

Neptune was Voyager 2's final planetary destination after passing Jupiter (closest approach July 9, 1979), Saturn (closest approach Aug. 26, 1981) and Uranus (closest approach Jan. 24, 1986).

Matt Burgess

Steven Levy

After its encounter with Neptune, the spacecraft was rechristened the Voyager Interstellar Mission by NASA to take measurements of the interplanetary magnetic field, plasma and charged-particle environment. But mostly it's searching for the heliopause , the distance at which the solar wind becomes subsumed by the more general interstellar wind. Voyager 2 is headed out of the solar system, diving below the ecliptic plane at an angle of about 48 degrees and a rate of about 300 million miles a year.

We may be able to communicate with Voyager 2 for another 10 years, when its radioactive power sources are predicted to become too weak to supply electricity to run the craft's critical systems. Then it will be out of our solar system and out of touch, racing to parts unknown and untold.

Doug Cornelius is a contributor to Wired.com's GeekDad .

Source: Various

Image: Voyager 2 and Neptune/NASA composite

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Brenda Stolyar

Nena Farrell

A New World: NASA Recalls Voyager 2 Probe's 1989 Neptune Encounter

A quarter-century ago, the world got its first good look at the solar system's other blue planet.

NASA's Voyager 2 spacecraft made the first-ever flyby of Neptune on Aug. 25, 1989, zipping by the "ice giant" and its frigid moon Triton in quick succession. The historic encounter gave a face to two worlds that until that time had dwelt in depth and shadow, mission team members said Monday (Aug. 25) during a NASA event commemorating the flyby's 25th anniversary.

"I think in many ways, [a first planetary] encounter is almost like giving birth," said Bonnie Buratti of NASA's Jet Propulsion Laboratory in Pasadena, California. "First of all, you have no control over the time; it's going to come no matter what. And you go from just an idea in your mind to a whole new person, or a whole new world." [ 5 Facts About NASA's Voyager Spacecraft ]

The encounter revealed a storm the size of Earth swirling on Neptune, as well as winds topping 1,000 mph (1,600 km/h) — the fastest ever measured in the solar system. Such observations came as a surprise to mission scientists, because solar energy tends to drive atmospheric activity and Neptune lies so far from the sun.

Voyager 2's images of Triton also caused jaws to drop, showing incredibly complex terrain and active geysers blasting material into space.

In fact, the Triton encounter remains a highlight for Voyager project scientist Ed Stone, who has overseen  the science operations of the mission since its inception in the early 1970s.

"The Triton flyby was my favorite moment partly because it was a bookend. The journey really started with the discovery of volcanoes on [Jupiter's moon] Io with Voyager 1, 10 years earlier — the first bookend," Stone, who's based at the California Institute of Technology in Pasadena, said in a NASA statement . "We finished the planetary part of the mission with another bookend, the flyby of Triton, where we discovered a much colder, smaller world that was also geologically active."

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Voyager 2 launched in August 1977, a few weeks before its twin, Voyager 1. Together, the two probes pulled off an unprecedented "grand tour" of the solar system's big planets, flying by Jupiter, Saturn, Uranus and, finally, Neptune. NASA transformed its JPL television studio into Neptune mission control for the final flyby, with legendary singer Chuck Berry performing in a special concert at the center to commemorate the event.  

But after Neptune, the two Voyager spacecraft weren't finished. They kept right on flying, during an extended phase known as the Voyager Interstellar Mission. Voyager 1 entered interstellar space in August 2012, and Voyager 2, which took a different path through the solar system, should make it there soon as well. Both spacecraft are still going strong today.

As the two Voyagers streaked through space, lifting the veil on world after world, mission scientists marked off big milestones in their own lives.

"There was a personal aspect — relationships formed, marriages; people had babies," said David Grinspoon of the Planetary Science Institute in Tucson, Arizona, who worked on Voyager in the 1970s and '80s. "And so there was this really growing sense of a family gathering at each of these encounters in addition to the scientific excitement of the encounter."

In a strange but appropriate coincidence, NASA's New Horizons probe crossed the orbit of Neptune Monday, 25 years to the day after Voyager 2's encounter. New Horizons is speeding toward Pluto, which it will fly by on July 14, 2015.

Like Voyager 2, New Horizons will return the first up-close views of exotic and faraway worlds — in this case, the dwarf planet Pluto and its five known moons.

"We don't know a thing now, and a year from now we're going to write the textbooks," New Horizons principal investigator Alan Stern said during a news conference Monday. "It's going to be very exciting."

Stern referred to the Voyager team as "heroes," noting the influence they have had on space science and on researchers such as himself.

"We stand on the shoulders of giants — giants like Ed Stone and his Voyager science team that pioneered how to do the exploration of the deep outer solar system," he said.

Follow Mike Wall on Twitter  @michaeldwall  and  Google+ . Follow us @Spacedotcom , Facebook  or Google+ . Originally published on  Space.com .

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Michael Wall is a Senior Space Writer with  Space.com  and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.

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News | July 7, 1989

Voyager 2 discovers new neptune moon.

A new moon has been discovered orbiting Neptune, scientists on the Voyager Project at NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif., announced today.

The moon's discovery was confirmed Wednesday, July 5, when it was located in images returned from the Voyager 2 spacecraft enroute to Neptune. Temporarily designated 1989 N1, the new moon was initially seen in Voyager 2 images transmitted to Earth in mid-June. Later images showing the small body in its predicted orbit confirmed its existence.

Dr. Stephen P. Synnott, Voyager imaging team scientist at JPL, found the small, bright smudge in Voyager pictures that led to the moon's discovery. According to Synnott, the new Neptunian satellite could range in diameter from 200 to 600 kilometers (about 125 to 400 miles) and orbits in very nearly circular and equatorial orbit about 92,700 kilometers (about 57,600 miles) from the planet's cloud tops (or about 117,500 kilometers (73,000 miles) from the planet's center).

At this point, the moon is too indistinct to appear in photographic prints made from the Voyager images. Pictures taken in coming weeks will show the moon more clearly.

1989 N1 cannot be seen from Earth because the moon is so close to Neptune that the brightness of the planet itself masks the tiny point of light. Voyager 2 will continue to study the moon and conduct searches for others as it approaches the planet.

Neptune has two other known moons: Triton, discovered in 1846, and Nereid, discovered in 1949. Triton is between 2,500 and 4,000 kilometers (1,500 to 2,500 miles) in diameter; Nereid probably is somewhere between 300 and 1,100 kilometers (200 to 700 miles) in diameter.

Voyager 2 is now 45 million miles away from Neptune and will make close pass of the planet on Aug. 24, 1989. The spacecraft was launched in 1977 and flew past Jupiter in 1979, Saturn in 1981 and Uranus in 1986. The Neptune encounter will be the final planetary flyby of the Voyager mission, which also included Jupiter and Saturn flybys conducted by twin spacecraft, Voyager 1.

The Voyager mission is managed by JPL for NASA's Office of Space Science and Applications.

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Voyager 2 and neptune.

Voyager 2 is a mission launched by NASA in 1977 to explore Uranus and Neptune . Voyager 2 came in close contact with Neptune and its moon Triton , gathering a lot of information about its moon. Voyager is now providing direct measurements of the temperature and density of interstellar plasma, as it became the first human-made object to venture into interstellar space.

The Deep Space Network provides communication and tracking services to Voyager 2 through its 34 and 70 meter antennas.

› SCaN Network Image Gallery

Voyager 2 Discovers Eruption on Triton

five-mile-tall, geyser-like plume of dark material has been discovered erupting from the surface of Neptune's moon Triton in one of the images returned last month to the Jet Propulsion Laboratory, Pasadena, Calif., by NASA's Voyager 2 spacecraft.

The discovery comes just as the Neptune encounter -- Voyager 2's fourth and final planetary flyby in 12 years -- officially ends today (Oct. 2).

This is the first time geyser-like phenomena have been seen on any solar system object (other than Earth) since Voyager discovered eight active geysers shooting sulfur above the surface of Jupiter's moon, Io. The new finding -- Voyager's last hurrah in its journey past the planets -- augments Triton's emerging reputation as the most perplexing of all the dozens of moons Voyager 1 and 2 have explored.

Voyager's camera captured the eruption shooting dark particles high into Triton's thin atmosphere on August 24 from distance of 99,920 kilometers (about 62,000 miles).

Resembling smokestack, the narrow stem of the dark plume, measured using stereo images, rises vertically nearly eight kilometers (five miles), forming cloud that drifts 150 kilometers (90 miles) westward in Triton's winds.

The feature was recognized by examining several images taken from different angles and analyzed through stereoscopic techniques.

While Voyager scientists are still trying to determine the mechanism responsible for the eruption, one possibility being considered is that pressurized gas, probably nitrogen, rises from beneath the surface and carries aloft dark particles and possibly ice crystals. Whatever the cause, the plume takes the particles to an altitude where they are left suspended to form cloud that drifts westward.

Voyager 2's working life among the planets may be at an end, but the spacecraft and its twin, Voyager 1, are expected to continue returning information about the various fields and particles they encounter while approaching, and eventually crossing, the boundary of our solar system. The plutonium-based generators that provide electricity to the spacecraft are expected to keep alive the computers, science instruments and radio transmitter for up to 25 or 30 more years.

As of today, the long-lived project will be known as the Voyager Interstellar Mission.

The Voyager Project is managed for NASA's Office of Space Science by the Jet Propulsion Laboratory, Pasadena, Calif.