Neptune's Rings: Discovered 25 Years Ago!

Golden record from Voyager 2.

Today marks the 25th anniversary of closest approach to Neptune by the incredible robotic explorer, Voyager 2. Voyager 2 is still the only spacecraft to explore the vast reaches of our solar system beyond Saturn. The pictures it took of Uranus and Neptune are still the best pictures we have of those frigid gas giants. Before the Voyager missions, all images of these planets were taken from Earth. Because Earth's atmosphere blurs the image, and Neptune is really, really, really far away, you can imagine that those pictures were not very good. I couldn't even find an image of Neptune from before the Voyager missions.

Voyager 1 launched in 1977, visiting Jupiter in 1979, and Saturn in 1980. Voyager 2 also launched in 1977, and after visiting Jupiter in 1979 and Saturn in 1981, went on to Uranus in 1986. Each of these flybys advanced our knowledge of the outer solar system by leaps and bounds. As Voyager 2 silently approached Neptune, scientists were awed by the first images. Neptune was finally coming into focus. 

June 1989. Image Credit: NASA/JPL

In June of 1989, the Great Dark Spot was first observed. What was originally thought to be great storm (like Jupiter's Great Red Spot) is now considered a hole in the clouds in the upper atmosphere. It is not visible in later images of Neptune taken from Hubble.

In July, Voyager 2 captured an image of Neptune and its largest moon, Triton. It also discovered 4 new moons. 

Neptune and Triton, July 1989. Image Credit: NASA/JPL

The major discoveries happened in August, as the spacecraft got closer and closer to the planet. Neptune's faint rings were discovered by Voyager 2, with detailed images taken on August 22, 1989. 

Scientists didn't know Neptune had rings until Voyager 2 sped by in 1989. Image Credit: NASA/JPL

Finally, detailed pictures of the outermost gas giant! Image credit: NASA/JPL

Streaks of clouds in Neptune's outer atmosphere. Scientists discovered that Neptune's winds move at incredible speeds, about 1340 mph! Image Credit: NASA/JPL

True color of Neptune's clouds. Image Credit: NASA/JPL

The Great Dark Spot in high resolution. Image Credit: NASA/JPL

Before leaving the Neptune system, Voyager 2 flew by Triton, Neptune's largest and most interesting moon. Triton is the only large moon in the solar system that orbits its planet opposite of the planet's rotation. This is a telltale sign that it must not have formed out of the same disk of materials from which the planet formed, but rather is an object from the Kuiper Belt (a belt of icy asteroids orbiting out beyond Neptune) that was captured by Neptune's gravity.

Triton is super cold (-391F). It is so cold that nitrogen, a gas here on Earth, freezes solid to its surface. Image Credit: NASA/JPL

Speaking of the Kuiper belt, Pluto was the first Kuiper belt object ever discovered. It is home to at least two other dwarf planets, Haumea and Makemake. Below is the best picture ever taken of Pluto:

Don't you want to know more about Pluto?! Well, get excited, because in less then a year, a robotic explorer will fly by the dwarf planet and its moons, and then on to something else in the Kuiper belt. New Horizons has already imaged Jupiter, as it flew by to get a gravity assist. 

Jupiter and its erupting moon Io. This is a near-infrared image, so the reds are exaggerated. Image Credit:
NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

New Horizons will help us better understand the objects in the Kuiper belt. Scientists don't know how many dwarf planets there are in the solar system, but there are likely hundreds, maybe thousands, orbiting the Sun very, very far away - and we know very little about them! Understanding Kuiper belt objects will help scientists understand the formation of the solar system. 

As always, you can learn more about the planets in the solar system, as well as the current night sky in the Dome Planetarium at the Peoria Riverfront Museum.