Astronomy

Before Voyager 2, what were the highest quality photos of Uranus and Neptune?

Before Voyager 2, what were the highest quality photos of Uranus and Neptune?



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I'm in search of historical knowledge of the outer ice giants, which seems so hard to come by. Right now I would be happy with just a photo of each, the best photo we had of them before Voyager 2. Such a photo from the 60's to early 80's would be great. This will almost surely be from the Hale Telescope at the Palomar Observatory, because it's 5 meter primary mirror was the biggest for a long time.

Note: I'm not entirely sure that Neptune would even be a resolvable disk, but nevertheless I still want to see what our best photo of it (from that time) would be.

After googling this for so long, I've come to the conclusion that the best bet would be old astronomy books, which sadly, I do not have. Maybe someone here can help me out.


As per the books referred to in comments:

Both planets could be resolved as a disk, but no surface features could be observed on either. Spectrograms had been taken, so the general colour of the planets was known. The extreme axial tilt of Uranus was known about. But the relative warmth of Neptune was not.


30 Years Ago -- Voyager 2's Historic Neptune Flyby

Wrapped in teal and cobalt colored bands of clouds, Neptune looks like a blue-hued sibling to Jupiter and Saturn -- the blue indicating the presence of methane. A massive, slate-colored storm was dubbed the "Great Dark Spot," similar to Jupiter's Great Red Spot. Six new moons and four rings were also discovered. This picture of Neptune was produced from the last whole planet images taken through the green and orange filters on the Voyager 2 narrow angle camera. The images were taken at a range of 4.4 million miles from the planet, 4 days and 20 hours before closest approach. The picture shows the Great Dark Spot and its companion bright smudge. On the west limb, the fast moving bright feature called Scooter and the little dark spot are visible. These clouds were seen to persist for as long as Voyager's cameras could resolve them. North of these, a bright cloud band similar to the south polar streak may be seen. (Image Credit: NASA/JPL)

30 Years Ago -- Voyager 2's Historic Neptune Flyby

Thirty years ago, on August 25, 1989, NASA's Voyager 2 spacecraft made a close flyby of Neptune, giving humanity its first close-up look at our Solar System's eighth planet and marking the end of the Voyager mission's Grand Tour of the Solar System's four giant planets - Jupiter, Saturn, Uranus, and Neptune. But that historic first was also a last -- No other spacecraft has visited Neptune since.

Voyager 2 launched on August 20, 1977, about two weeks before its twin spacecraft, Voyager 1. The two spacecraft are today the most distant human-made objects, having recently passed through the Heliosphere &ndash a giant bubble that surrounds the Solar System.

The original goal of the two Voyager spacecraft was to just explore Jupiter and Saturn. However, as part of a mission extension, Voyager 2 also flew by Uranus in 1986 and Neptune in 1989, taking advantage of a once in a 176 year alignment of the planets that enabled it to take a grand tour of the outer planets.

Among its many findings, Voyager 2 discovered Neptune's Great Dark Spot and 450 meter per second (1,000 mph) winds. It also detected geysers erupting from the pinkish-hued nitrogen ice that forms the polar cap of Neptune's moon Triton. Working in concert with Voyager 1, it also helped discover actively erupting volcanoes on Jupiter's moon Io, and waves and kinks in Saturn's icy rings from the tugs of nearby moons.

"The Voyager planetary program really was an opportunity to show the public what science is all about," said Ed Stone, Professor of Physics and Voyager Project Scientist at the California Institute of Technology in Pasadena since 1975. "Every day we learned something new."

"Voyager 2's initial mission was a four-year journey to Saturn, but it is still returning data 33 years later," said Ed Stone in 2010. "It has already given us remarkable views of Uranus and Neptune, planets we had never seen close-up before. We will know soon what it will take for it to continue its epic journey of discovery."

Wrapped in teal and cobalt colored bands of clouds, the planet that Voyager 2 revealed looked like a blue-hued sibling to Jupiter and Saturn -- the blue indicating the presence of methane. A massive, slate-colored storm was dubbed the "Great Dark Spot," similar to Jupiter's Great Red Spot. Six new moons and four rings were discovered.

During the encounter, the engineering team carefully changed the probe's direction and speed so that it could do a close flyby of the planet's largest moon, Triton. The flyby showed evidence of geologically young surfaces and active geysers spewing material skyward. This indicated that Triton was not simply a solid ball of ice, even though it had the lowest surface temperature of any natural body observed by Voyager: minus 391 degrees Fahrenheit (minus 235 degrees Celsius).

The conclusion of the Neptune flyby marked not an end, but a new beginning -- the beginning of the Voyager Interstellar Mission, which continues today, 42 years after launch. Voyager 2 and its twin, Voyager 1 (which had also flown by Jupiter and Saturn), continue to send back dispatches from the outer reaches of our Solar System. At the time of the Neptune encounter, Voyager 2 was about 2.9 billion miles (4.7 billion kilometers) from Earth. Today it is 11 billion miles (18 billion kilometers) from us. The faster-moving Voyager 1 is 13 billion miles (21 billion kilometers) from Earth.

By the time Voyager 2 reached Neptune, the Voyager mission team had completed five planetary encounters. But the big blue planet still posed unique challenges.

At about 30 times farther from the Sun than is the Earth, the icy giant receives only about 0.001 times the amount of sunlight that the Earth does. In such low light, Voyager 2's camera required longer exposures to get quality images. But because the spacecraft would reach a maximum speed of about 60,000 mph (90,000 kph) relative to Earth, a long exposure time would make the image blurry. (Just imagine trying to take a picture of a roadside sign from the window of a speeding car. That gives you an idea of how difficult this was.)

So the team programmed Voyager 2's thrusters to fire gently during the close approach, rotating the spacecraft to keep the camera focused on its target without interrupting the spacecraft's overall speed and direction.

The probe's great distance also meant that by the time radio signals from Voyager 2 reached Earth, they were weaker than those of other flybys. But the spacecraft had the advantage of time -- The Voyagers communicate with Earth via the Deep Space Network, or DSN, which utilizes radio antennas at sites in Madrid, Spain Canberra, Australia and Goldstone, California. During Voyager 2's earlier Uranus encounter in 1986, the three largest DSN antennas were 64 meters (210 feet) wide. To assist with the Neptune encounter, the DSN expanded the dishes to 70 meters (230 feet). They also included nearby non-DSN antennas to collect data, including another 64 meter (210 feet) dish in Parkes, Australia, and multiple 25 meter (82 feet) antennas at the Very Large Array in New Mexico.

The effort ensured that engineers could hear Voyager loud and clear. It also increased how much data could be sent back to Earth in a given period, enabling the spacecraft to send back more pictures from the flyby.

In the week leading up to that August 1989 close encounter, the atmosphere was electric at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, which manages the Voyager mission. As images taken by Voyager 2 during its Neptune approach made the four hour journey to Earth, Voyager team members would crowd around computer monitors around the Lab to see.

"One of the things that made the Voyager planetary encounters different from missions today is that there was no internet that would have allowed the whole team and the whole world to see the pictures at the same time," Stone said. "The images were available in real time at a limited number of locations."

But the team was committed to giving the public updates as quickly as possible, so from August 21 to August 29, they would share their discoveries with the world during daily press conferences. On August 24, a program called "Voyager All Night" broadcast regular updates from the probe's closest encounter with the planet, which took place at 4 AM GMT (9 PM in California on August 24).

The next morning, Vice President Dan Quayle visited the Lab to commend the Voyager team. That night, Chuck Berry, whose song "Johnny B. Goode" was included on the Golden Record that flew with both Voyagers, played at JPL's celebration of the feat.

Of course, the Voyagers' achievements extend far beyond that historic week three decades ago. Both probes have now entered interstellar space after exiting the Heliosphere, a protective bubble around the planets created by the high speed flow of particles and magnetic fields spewed outward by our Sun.

There, they are reporting back to Earth on the "interstellar space weather" and conditions from this region, which is filled with the debris from stars that exploded elsewhere in our galaxy. They have taken humanity's first tenuous step into the cosmic ocean where no other operating probes have flown.

Voyager data also complement other missions, including NASA's Interstellar Boundary Explorer (IBEX), which is remotely sensing that boundary where particles from our Sun collide with material from the rest of the galaxy. And NASA is preparing the Interstellar Mapping and Acceleration Probe (IMAP), due to launch in 2024, to capitalize on Voyager observations.

The Voyagers send their findings back to DSN antennas with small 13 watt transmitters. (To put this in perspective, 13 watts is just about enough power to run a refrigerator light bulb).

"Every day they travel somewhere that human probes have never been before," said Stone. "Forty two years after launch, and they're still exploring."

Voyager 1 &ndash First to enter the final frontier

In 2012, Voyager 1 spacecraft sensors began to send back readings that the venerable deep-space explorer had encountered a region in space where the intensity of charged particles from beyond our Solar System markedly increased. Voyager scientists looking at this rapid rise drew closer to the inevitable but historic conclusion: Humanity's first emissary to interstellar space was on the edge of our Solar System.

"The laws of physics say that someday Voyager will become the first human-made object to enter interstellar space, but we still do not know exactly when that someday will be," said Ed Stone at the time, Voyager project scientist at the California Institute of Technology in Pasadena. "The latest data indicate that we are clearly in a new region where things are changing more quickly. It is very exciting. We are approaching the Solar System's frontier."

The "frontier" he referred to is the edge of the Heliosphere, a great magnetic bubble that surrounds the Sun and planets. The heliosphere is the Sun's own magnetic field inflated to gargantuan proportions by the Solar wind. Inside lies the Solar System &ndash Our "Home." Outside lies interstellar space, where no spacecraft had gone before.

The data making the 16 hour and 38 minute, 11.1 billion mile (17.8 billion kilometer), journey from Voyager 1 to antennas of NASA's Deep Space Network on Earth detail the number of charged particles measured by the two High Energy telescopes aboard the spacecraft. These energetic particles were generated when stars in our cosmic neighborhood went supernova.

"From January 2009 to January 2012, there had been a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering," said Stone. "More recently, we have seen very rapid escalation in that part of the energy spectrum. Beginning on May 7, 2012, the cosmic ray hits have increased five percent in a week and nine percent in a month."

This marked increase was one of a triad of data sets which needed to make significant swings of the needle to indicate a new era in space exploration. The second important measure from the spacecraft's two telescopes was the intensity of energetic particles generated inside the Heliosphere, the bubble of charged particles the sun blows around itself. While there had been a slow decline in the measurements of these energetic particles, at the time they had not dropped off precipitously, which would be expected when Voyager broke through the Solar boundary.

The final data set that Voyager scientists believed would reveal the major change was the measurement in the direction of the magnetic field lines surrounding the spacecraft. While Voyager was still within the Heliosphere, these field lines run East-West. When it passed into interstellar space, the team expected Voyager would find that the magnetic field lines would orient themselvs in a more North-South direction.

"When the Voyagers launched in 1977, the space age was all of 20 years old," said Stone. "Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be -- or if these two vehicles that we invested so much time and energy in would operate long enough to reach it."

At the time, the two Voyager spacecraft were traveling through a turbulent area known as the Heliosheath. The Heliosheath is the outer shell of a bubble around our solar system created by the solar wind, a stream of ions blowing radially outward from the sun at a million miles per hour. The wind must turn as it approaches the outer edge of the bubble where it makes contact with the interstellar wind, which originates in the region between stars and blows by our solar bubble.

In June 2010, when Voyager 1 was about 11 billion miles away from the sun, data from the Low Energy Charged Particle instrument began to show that the net outward flow of the solar wind was zero.

"Because the direction of the solar wind has changed and its radial speed has dropped to zero, we have to change the orientation of Voyager 1 so the Low Energy Charged Particle instrument can act like a kind of weather vane to see which way the wind is now blowing," said Edward Stone at the time. "Knowing the strength and direction of the wind is critical to understanding the shape of our solar bubble and estimating how much farther it is to the edge of interstellar space."

Voyager engineers performed a test roll and hold on Feb. 2, 2011 for two hours and 15 minutes. When data from Voyager 1 was received on Earth some 16 hours later, the mission team verified the test was successful and the spacecraft had no problem in reorienting itself and locking back onto its guide star, Alpha Centauri.

The Low Energy Charged Particle instrument science team confirmed that the spacecraft had acquired the kind of information it needed, and mission planners gave Voyager 1 the green light to do more rolls and longer holds. There will be five more of these maneuvers over the next seven days, with the longest hold lasting three hours 50 minutes. The Voyager team plans to execute a series of weekly rolls for this purpose every three months.

"We do whatever we can to make sure the scientists get exactly the kinds of data they need, because only the Voyager spacecraft are still active in this exotic region of space," said Jefferson Hall, Voyager mission operations manager at JPL. "We were delighted to see Voyager still has the capability to acquire unique science data in an area that won't likely be traveled by other spacecraft for decades to come."

At one point, budget cuts threatened the program

Back in 2006, when budget cuts threatened the program, The Planetary Society, an influential non-profit space organization, and its members fought successfully with help from NASA scientists to save the Voyagers and maintain communications with these remarkable spacecraft. Were it not for the Society's stand, it may well be that this latest chapter in the Voyager saga would never have been written.

Up until the summer of 2007 Voyager 2, despite being over 7 billion miles from the Sun, was still traveling inside an enormous magnetic bubble around the Sun known as the Heliosphere. The outer envelope of the Heliosphere, where the solar wind collides head-on with the interstellar medium, is known as the Termination Shock.

Significantly, Voyager 2 reached this landmark at a point substantially closer to the Sun than Voyager 1 had been when it crossed the Termination Shock. Back in 2004, the Sun had been near its solar maximum, a peak of activity characterized by strong solar winds that increased the pressure in the Heliosphere and pushed the termination shock outwards. In fact, scientists believe that for a full two years, as Voyager 1 was streaking away from the Sun, the Termination Shock was also moving ahead of it, staying just out of reach of the spacecraft. Finally the Solar activity waned, causing the Heliosphere to slow down its expansion and eventually to contract back towards the Sun. This allowed Voyager 1 to catch up with the Termination Shock, and finally pass through it at a distance of 94.1 Astronomical Units (AU) from the Sun. (Each AU representing the average distance of the Earth and Sun).

Voyager 2, in contrast, was approaching the outer Heliosphere at a time of declining solar activity, and scientists therefore expected that it would cross the Termination Shock much closer to the Sun than its twin. And so it proved to be. The first sign of the approaching crossing came on August 1, 2007 in the form of electron plasma oscillations detected by the Voyager 2's instruments when the spacecraft was 83.4 AU from the Sun. But according to Don Gurnett and Bill Kurth of the University of Iowa, even with this forewarning scientist were surprised when the crossing came a mere 30 days later, when the spacecraft was 83.7 AU from the Sun.

The crossing itself, Gurnett and Kurth explained, is not a single event because the Termination Shock itself keeps shifting its location. As a result Voyager 2 made the passage not once but at least five times, back and forth over the span of two days, before it was finally clear of that turbulent place. The five crossings were marked by sharp spikes registered on the plasma wave instrument and the magnetometer, and on two of the occasions by intense bursts of broadband electric field noise.

One of the most surprising results to come out of Voyager 2's crossing of the Termination Shock relates to the energy levels of the particles at the termination shock. Since the solar wind slows down drastically from a million miles an hour to less and a thousand, scientists expected the excess energy to appear as heat, raising the temperature of the solar wind plasma to around 1 million degrees Kelvin. But Voyager 2's measurements showed that the temperature reached only around 100,000 degrees Kelvin, raising the question of what happened to around 70% of the energy released by the solar wind particles.

The answer came from an unexpected source. Back in 2006 NASA launched twin spacecraft named STEREO A and B into orbits around the Sun to obtain three dimensional pictures of the surface of the Sun and measure Solar magnetic fields and ion fluxes. But for four months, between June and October 2007, STEREO's sensors detected something else: a stream of highly energized neutral atoms flowing from a spot in the outer reaches of the Solar System.

A bit of astronomical sleuthing revealed the nature of this unexpected discovery. The super-energized particles of the Solar wind that arrive at the Termination Shock collide with the cold atoms of the interstellar medium, relinquishing both their charge and their energy. This explains the fate of the missing 70% of the total energy released by the Solar wind -- It goes towards energizing the cold particles of the interstellar medium which form the region beyond the termination shock known as the Heliosheath. Meanwhile the Solar wind atoms, shorn of their energy and no longer inhibited by their charge, flow back towards the Sun where they are captured by STEREO's sensors. Mystery solved.

"This is the first mapping of energetic neutral particles from the edge of the Heliosphere" said Robert P. Lin of the University of California. "You can't get a global picture of this region through normal telescopes" Lin said, and hence the importance of STEREO's discovery. In fact, Lin said, the unexpected detection "heralds a new kind of astronomy using neutral atoms," which can be used where more traditional methods fail.

Today, Voyager 2 is about 18.2 billion kilometers, or 11.3 billion miles, from Earth. Voyager 1 is about 22.0 billion kilometers (13.7 billion miles) away from Earth. Judging by their unmatched track record, it seems likely that Voyager 2 and its twin, Voyager 1, will continue to be humanity's eyes and ears into the realm of the stars for years to come. As the Space Age hits the 62-year mark, there is little doubt -- The Voyagers are going the distance.


30 Years Ago: Voyager 2's Historic Neptune Flyby

Humanity's first and (so far) last visit to the outermost giant planet in our solar system was a monumental event for scientists and the public alike.

Thirty years ago, on Aug. 25, 1989, NASA's Voyager 2 spacecraft made a close flyby of Neptune, giving humanity its first close-up of our solar system's eighth planet. Marking the end of the Voyager mission's Grand Tour of the solar system's four giant planets - Jupiter, Saturn, Uranus and Neptune - that first was also a last: No other spacecraft has visited Neptune since.

"The Voyager planetary program really was an opportunity to show the public what science is all about," said Ed Stone, a professor of physics at Caltech and Voyager's project scientist since 1975. "Every day we learned something new."

Wrapped in teal- and cobalt-colored bands of clouds, the planet that Voyager 2 revealed looked like a blue-hued sibling to Jupiter and Saturn, the blue indicating the presence of methane. A massive, slate-colored storm was dubbed the "Great Dark Spot," similar to Jupiter's Great Red Spot. Six new moons and four rings were discovered.


Voyager 2 took these two images of the rings of Neptune on Aug. 26, 1989, just after the probe's closest approach to the planet. Neptune's two main rings are clearly visible two fainter rings are visible with the help of long exposure times and backlighting from the Sun.
Credit: NASA/JPL-Caltech
Full image and caption

During the encounter, the engineering team carefully changed the probe's direction and speed so that it could do a close flyby of the planet's largest moon, Triton. The flyby showed evidence of geologically young surfaces and active geysers spewing material skyward. This indicated that Triton was not simply a solid ball of ice, even though it had the lowest surface temperature of any natural body observed by Voyager: minus 391 degrees Fahrenheit (minus 235 degrees Celsius).

The conclusion of the Neptune flyby marked the beginning of the Voyager Interstellar Mission, which continues today, 42 years after launch. Voyager 2 and its twin, Voyager 1 (which had also flown by Jupiter and Saturn), continue to send back dispatches from the outer reaches of our solar system. At the time of the Neptune encounter, Voyager 2 was about 2.9 billion miles (4.7 billion kilometers) from Earth today it is 11 billion miles (18 billion kilometers) from us. The faster-moving Voyager 1 is 13 billion miles (21 billion kilometers) from Earth.

Getting There

By the time Voyager 2 reached Neptune, the Voyager mission team had completed five planetary encounters. But the big blue planet still posed unique challenges.

About 30 times farther from the Sun than Earth is, the icy giant receives only about 0.001 times the amount of sunlight that Earth does. In such low light, Voyager 2's camera required longer exposures to get quality images. But because the spacecraft would reach a maximum speed of about 60,000 mph (90,000 kph) relative to Earth, a long exposure time would make the image blurry. (Imagine trying to take a picture of a roadside sign from the window of a speeding car.)

So the team programmed Voyager 2's thrusters to fire gently during the close approach, rotating the spacecraft to keep the camera focused on its target without interrupting the spacecraft's overall speed and direction.

The probe's great distance also meant that by the time radio signals from Voyager 2 reached Earth, they were weaker than those of other flybys. But the spacecraft had the advantage of time: The Voyagers communicate with Earth via the Deep Space Network, or DSN, which utilizes radio antennas at sites in Madrid, Spain Canberra, Australia and Goldstone, California. During Voyager 2's Uranus encounter in 1986, the three largest DSN antennas were 64-meters (210 feet) wide. To assist with the Neptune encounter, the DSN expanded the dishes to 70 meters (230 feet). They also included nearby non-DSN antennas to collect data, including another 64-meter (210 feet) dish in Parkes, Australia, and multiple 25-meter (82 feet) antennas at the Very Large Array in New Mexico.

The effort ensured that engineers could hear Voyager loud and clear. It also increased how much data could be sent back to Earth in a given period, enabling the spacecraft to send back more pictures from the flyby.

Being There

In the week leading up to that August 1989 close encounter, the atmosphere was electric at NASA's Jet Propulsion Laboratory in Pasadena, California, which manages the Voyager mission. As images taken by Voyager 2 during its Neptune approach made the four-hour journey to Earth, Voyager team members would crowd around computer monitors around the Lab to see.

"One of the things that made the Voyager planetary encounters different from missions today is that there was no internet that would have allowed the whole team and the whole world to see the pictures at the same time," Stone said. "The images were available in real time at a limited number of locations."

But the team was committed to giving the public updates as quickly as possible, so from Aug. 21 to Aug. 29, they would share their discoveries with the world during daily press conferences. On Aug. 24, a program called "Voyager All Night" broadcast regular updates from the probe's closest encounter with the planet, which took place at 4 a.m. GMT (9 p.m. in California on Aug. 24).

The next morning, Vice President Dan Quayle visited the Lab to commend the Voyager team. That night, Chuck Berry, whose song "Johnny B. Goode" was included on the Golden Record that flew with both Voyagers, played at JPL's celebration of the feat.


Chuck Berry (left) and Carl Sagan (right) at a Voyager 2 Neptune flyby celebration in August 1989.
Credit: NASA/JPL-Caltech
Full image and caption

Of course, the Voyagers' achievements extend far beyond that historic week three decades ago. Both probes have now entered interstellar space after exiting the heliosphere - the protective bubble around the planets created by a high-speed flow of particles and magnetic fields spewed outward by our Sun.

They are reporting back to Earth on the "weather" and conditions from this region filled with the debris from stars that exploded elsewhere in our galaxy. They have taken humanity's first tenuous step into the cosmic ocean where no other operating probes have flown.

Voyager data also complement other missions, including NASA's Interstellar Boundary Explorer (IBEX), which is remotely sensing that boundary where particles from our Sun collide with material from the rest of the galaxy. And NASA is preparing the Interstellar Mapping and Acceleration Probe (IMAP), due to launch in 2024, to capitalize on Voyager observations.

The Voyagers send their findings back to DSN antennas with 13-watt transmitters - about enough power to run a refrigerator light bulb.

"Every day they travel somewhere that human probes have never been before," said Stone. "Forty-two years after launch, and they're still exploring."


Today in science: Voyager 2 met Uranus

January 24, 1986. On this date, the Voyager 2 spacecraft came within 50,640 miles (81,500 km) of the cloud tops of the planet Uranus. It was the closest – and only – visit by a human-made craft to this planet. During its closest approach, and in the weeks before and after, Voyager 2 transmitted a treasure trove of scientific data that indelibly changed our view of this enigmatic, distant world.

Many remarkable discoveries came from this mission. Data from Voyager 2 revealed that a Uranian day is just 17 hours and 14 minutes long. It showed that Uranus’ atmosphere is very similar to that of the other gas giants, composed mainly of hydrogen and helium. Below it lay water, ammonia and methane ices.

The mostly featureless light green-blue disk of Uranus was imaged by Voyager 2 on January 14, 1986, when it was about 7.8 million miles (12.6 million km) from the planet. Image via NASA/ JPL.

Scientists knew, from telescopic observations made from Earth, that Uranus’ rotation axis was tilted at 98 degrees. In other words, the planet’s equator lies almost perpendicular to the plane of its orbit! Scientists think the planet was tipped on its side by a collision with a planet-sized object, early in the solar system’s history.

As a result, Uranus has, perhaps, the most interesting seasonal patterns in the solar system. Read more: What are the seasons like on Uranus?

Voyager 2 revealed that Uranus has a bizarre magnetic field. The planet’s magnetic field is also tilted, at 59 degrees from Uranus’ axis of rotation. This arrangement creates a non-uniform magnetic field for Uranus that can vary by up to 10 times!

A diagram of Uranus’ magnetic field based on data from Voyager 2. It’s tilted, at 59 degrees, from the axis of rotation. S and N are magnetic south and north poles. Image via Ruslik0/ Wikimedia Commons.

Voyager 2 found that Uranus has radiation belts similar in intensity to those of Saturn. Earth also has radiation belts, with the two main ones known as the Van Allen belts.

Initially, 10 new moons were discovered in the data sent back by Voyager 2, for a total of 15 moons known at the time. In 1999, additional analysis of Voyager 2 data revealed an 11th moon. Today, we know of 27 moons orbiting Uranus.

Among the newly discovered moons was Puck, just 100 miles (160 km) in diameter, with a gray heavily cratered surface.

Voyager 2 also imaged the Uranian moons we already knew, revealing their amazing geology.

The last Uranian moon discovered before Voyager 2’s arrival was Miranda, found by Gerard Kuiper at McDonald Observatory in Texas in 1948. Thanks to Voyager 2, we saw Miranda much more clearly. In fact, it picked up the nickname of Frankenstein moon because its strange haphazard appearance.

Puck, one of the moons of Uranus discovered by Voyager 2. This image was taken on January 24, 1986, at a distance of about 306,300 miles (500,000 km). Image via NASA/ JPL. Observe Miranda’s sharp and diverse features, which gave it the nickname Frankenstein moon. Image via NASA/ JPL.

By the time of Voyager 2’s visit, it had already been discovered from Earth that Uranus has rings. Voyager 2 surveyed Uranus’ rings and discovered two new ones, bringing the total number of rings to 11. Today, there are 13 known rings.

A backlit view of the Uranian ring system shows fine particles distributed through the rings. This image was taken just 147,000 miles (240,000 km) away from the planet. Image via NASA/ JPL.

And so Voyager 2 vastly increased our knowledge of Uranus – and then left this world behind for one final rendezvous, with Neptune in August 1989, before heading out of the solar system. In December 2018, NASA announced that Voyager 2 had entered interstellar space. Forty-three years after it launched from Cape Canaveral in 1977, the spacecraft is almost 11.5 billion miles (18.5 billion km) from home.

By the way, it was the famous astronomer William Herschel who discovered Uranus. It was the first planet to be discovered with a telescope, the first to be added to the group of bright planets – Mercury, Venus, Mars, Jupiter, Saturn – known since antiquity.

Uranus is the third-largest planet in our solar system. It could contain 63 Earths. But it isn’t a bright planet because it’s very far away, about 1.9 billion miles (3 billion km) from the sun, or 20 times the Earth-sun distance.

Bottom line: Voyager 2’s closest encounter with Uranus happened on January 24, 1986. It’s the only spacecraft to have ever visited this frigid world in the outer solar system, leaving a rich legacy of information that has forever changed our view of that pale green-blue planet.


Accidental discovery

In the late winter of 1781, British astronomer Sir William Herschel had just finished building a new 6.3-inch (16 centimeters) reflecting telescope and began to study the stars through it. On the night of March 13, he had his telescope turned on the constellation of Gemini, the twins. There, to his great surprise, he came across an extra star that was not plotted on any of his star charts. An accomplished astronomer, Herschel was quick to realize that what he found could not possibly be a star, for it appeared in his telescope as a glowing disk as opposed to a twinkling speck of light.

Continuing his observations of this unusual object night after night, Herschel soon perceived movement it was slowly shifting its position among the background stars of Gemini. Finally, he decided that he had discovered a new comet and he wrote up a detailed report of his observations, which were published on April 26.

The report of a new comet excited astronomers all over Europe, and they all eagerly trained their telescopes on Herschel's discovery. King George III, who loved the sciences, had the astronomer brought to him and presented him with a life pension and a residence at Slough, in the neighborhood of Windsor Castle.


Jupiter

“Jupiter governs a combination of feeling and thought. It includes humanity, benevolence, compassion, honour, candour, good humour, and the higher moral and social qualities.”

“The planet Jupiter is especially related to the magnetic aura that surrounds every living creature.”

“Jupiter may be said to represent the aspect of power, of harmoniously balanced expansion, growth that which urges evolution.”

Holst echoes Leo’s image of Jupiter as governing “benevolence,” “good humour,” and “harmonious balanced expansion” with his majestic and uplifting movement. Looking at what we’ve learned from Jupiter over the years it seems that they weren’t too wide of the mark.

Gas giant Jupiter is certainly majestic and powerful — it’s the largest planet in our Solar System. Over 1300 planet Earths could fit inside it.

It’s notable that Leo described Jupiter’s relation to the “magnetic aura that surrounds every living creature” as Jupiter has a magnetic field that’s fourteen times as strong as Earth’s. Just like on Earth, this magnetic field is a big factor in the existence of beautiful lights in the vicinity of the northern and southern poles — the aurorae. On Earth these aurorae are caused by charged particles from the Sun interacting with Earth’s magnetic field. On Jupiter the aurorae are believed to be caused by other factors — for example, the plasma produced by the volcanic moon, Io and the transport of this plasma within the planet’s magnetic field — as well as by charged particles from the Sun. When presenting the show I can display Jupiter’s aurorae in all their glory.

Jupiter could also be seen as the “benevolent” host of 79 known moons, although “harmoniously balanced” might not be an accurate description of their wonky orbits. Eight of Jupiter’s moons are regular moons that move in the same direction as the planet’s rotation and roughly along its equatorial plane. But the rest are irregular moons that are much more distant from Jupiter. Many of them move in the opposite direction to Jupiter’s rotation and at different angles to its equator. The regular moons most likely formed long ago from a ring of gas and solid debris around Jupiter, while the irregular moons probably once orbited the Sun but were snatched into orbit around Jupiter by the planet’s gravity. The orbital paths of Jupiter’s moons can also be displayed during the show.

These moons aren’t the only thing orbiting Jupiter. In 2016, after a journey of 2.8 billion kilometres that lasted five years, the NASA space probe Juno reached Jupiter. Since then Juno has been swooping close to the planet every 53 days, investigating its gravity and magnetic fields, and searching for clues about how the planet formed. Among Juno’s scientific instruments is a colour camera called JunoCam. Over the past four years it’s sent back some stunning images. It’s given us a closer look at Jupiter’s swirling storms, including the Great Red Spot, a gigantic storm, more than twice the size of Earth! Many of the images captured by Juno can be displayed during the show.


30 years ago: Voyager 2's historic Neptune flyby

This picture of Neptune was taken by Voyager 2 less than five days before the probe's closest approach of the planet on Aug. 25, 1989. The picture shows the "Great Dark Spot"—a storm in Neptune's atmosphere—and the bright, light-blue smudge of clouds that accompanies the storm. Credit: NASA/JPL-Caltech

Thirty years ago, on Aug. 25, 1989, NASA's Voyager 2 spacecraft made a close flyby of Neptune, giving humanity its first close-up of our solar system's eighth planet. Marking the end of the Voyager mission's Grand Tour of the solar system's four giant planets—Jupiter, Saturn, Uranus and Neptune—that first was also a last: No other spacecraft has visited Neptune since.

"The Voyager planetary program really was an opportunity to show the public what science is all about," said Ed Stone, Voyager's project scientist since 1975. "Every day we learned something new."

Wrapped in teal- and cobalt-colored bands of clouds, the planet that Voyager 2 revealed looked like a blue-hued sibling to Jupiter and Saturn, the blue indicating the presence of methane. A massive, slate-colored storm was dubbed the "Great Dark Spot," similar to Jupiter's Great Red Spot. Six new moons and four rings were discovered.

During the encounter, the engineering team carefully changed the probe's direction and speed so that it could do a close flyby of the planet's largest moon, Triton. The flyby showed evidence of geologically young surfaces and active geysers spewing material skyward. This indicated that Triton was not simply a solid ball of ice, even though it had the lowest surface temperature of any natural body observed by Voyager: minus 391 degrees Fahrenheit (minus 235 degrees Celsius).

The conclusion of the Neptune flyby marked the beginning of the Voyager Interstellar Mission, which continues today, 42 years after launch. Voyager 2 and its twin, Voyager 1 (which had also flown by Jupiter and Saturn), continue to send back dispatches from the outer reaches of our solar system. At the time of the Neptune encounter, Voyager 2 was about 2.9 billion miles (4.7 billion kilometers) from Earth today it is 11 billion miles (18 billion kilometers) from us. The faster-moving Voyager 1 is 13 billion miles (21 billion kilometers) from Earth.

By the time Voyager 2 reached Neptune, the Voyager mission team had completed five planetary encounters. But the big blue planet still posed unique challenges.

This global color mosaic shows Neptune's largest moon, Triton. Pink-hued methane ice may compose a massive polar cap on the moon's surface, while dark streaks overlaying this ice is thought to be dust deposited from huge geyser-like plumes that erupt from Triton's surface. Credit: NASA/JPL-Caltech

About 30 times farther from the Sun than Earth is, the icy giant receives only about 0.001 times the amount of sunlight that Earth does. In such low light, Voyager 2's camera required longer exposures to get quality images. But because the spacecraft would reach a maximum speed of about 60,000 mph (90,000 kph) relative to Earth, a long exposure time would make the image blurry. (Imagine trying to take a picture of a roadside sign from the window of a speeding car.)

So the team programmed Voyager 2's thrusters to fire gently during the close approach, rotating the spacecraft to keep the camera focused on its target without interrupting the spacecraft's overall speed and direction.

The probe's great distance also meant that by the time radio signals from Voyager 2 reached Earth, they were weaker than those of other flybys. But the spacecraft had the advantage of time: The Voyagers communicate with Earth via the Deep Space Network, or DSN, which utilizes radio antennas at sites in Madrid, Spain Canberra, Australia and Goldstone, California. During Voyager 2's Uranus encounter in 1986, the three largest DSN antennas were 64-meters (210 feet) wide. To assist with the Neptune encounter, the DSN expanded the dishes to 70 meters (230 feet). They also included nearby non-DSN antennas to collect data, including another 64-meter (210 feet) dish in Parkes, Australia, and multiple 25-meter (82 feet) antennas at the Very Large Array in New Mexico.

The effort ensured that engineers could hear Voyager loud and clear. It also increased how much data could be sent back to Earth in a given period, enabling the spacecraft to send back more pictures from the flyby.

In the week leading up to that August 1989 close encounter, the atmosphere was electric at NASA's Jet Propulsion Laboratory in Pasadena, California, which manages the Voyager mission. As images taken by Voyager 2 during its Neptune approach made the four-hour journey to Earth, Voyager team members would crowd around computer monitors around the Lab to see.

"One of the things that made the Voyager planetary encounters different from missions today is that there was no internet that would have allowed the whole team and the whole world to see the pictures at the same time," Stone said. "The images were available in real time at a limited number of locations."

Voyager 2 took these two images of the rings of Neptune on Aug. 26, 1989, just after the probe's closest approach to the planet. Neptune's two main rings are clearly visible two fainter rings are visible with the help of long exposure times and backlighting from the sun. Credit: NASA/JPL-Caltech

But the team was committed to giving the public updates as quickly as possible, so from Aug. 21 to Aug. 29, they would share their discoveries with the world during daily press conferences. On Aug. 24, a program called "Voyager All Night" broadcast regular updates from the probe's closest encounter with the planet, which took place at 4 a.m. GMT (9 p.m. in California on Aug. 24).

The next morning, Vice President Dan Quayle visited the Lab to commend the Voyager team. That night, Chuck Berry, whose song "Johnny B. Goode" was included on the Golden Record that flew with both Voyagers, played at JPL's celebration of the feat.

Of course, the Voyagers' achievements extend far beyond that historic week three decades ago. Both probes have now entered interstellar space after exiting the heliosphere—the protective bubble around the planets created by a high-speed flow of particles and magnetic fields spewed outward by our Sun.

They are reporting back to Earth on the "weather" and conditions from this region filled with the debris from stars that exploded elsewhere in our galaxy. They have taken humanity's first tenuous step into the cosmic ocean where no other operating probes have flown.

Voyager data also complement other missions, including NASA's Interstellar Boundary Explorer (IBEX), which is remotely sensing that boundary where particles from our Sun collide with material from the rest of the galaxy. And NASA is preparing the Interstellar Mapping and Acceleration Probe (IMAP), due to launch in 2024, to capitalize on Voyager observations.

The Voyagers send their findings back to DSN antennas with 13-watt transmitters—about enough power to run a refrigerator light bulb.

"Every day they travel somewhere that human probes have never been before," said Stone. "Forty-two years after launch, and they're still exploring."


Fifteenth Anniversary of Voyager 2 Flyby of Uranus in 1986

The first unmanned space probe flyby in history of the planet Uranus by Voyager 2 on January 24, 1986 should have been an exciting one in the history of planetary exploration:

  • Uranus was the first planet discovered by humans not thousands of years before written history and civilization, but in relatively moderns times - on March 13, 1781 by German musician turned English astronomer William Herschel, to be exact. I know others may have viewed Uranus telescopically before Herschel, be he was the first one to figure out that it was a planet and not a comet or star. Theoretically one could see Uranus with unaided vision from Earth, but it would have been too dim for our ancestors to really notice it, even in their non-light polluted night skies (at least none ever said they did that made it to our time).
  • Uranus was later found to be a world tipped on its side compared to the rest of the known planets in the Sol system. Only later did astronomers learn that Pluto was tipped even moreso on its side and Venus was knocked all the way around from our perspective. With an axial tilt of almost 98 degrees (compare this to Earth's 23.5 degree tilt), Uranus' poles spend roughly half their time in the planet's 84-year solar orbit either in constant darkness or light.
  • The discovery of a ring system around Uranus in 1977 gave the first real evidence that, rather than being unique to Saturn, ring systems around Jovian worlds are probably common. Indeed, the next few years - thanks to the Voyager probes - would show that these rings were indeed standard features for all of the gas giant planets of our Sol system.
  • The five known moons of Uranus were virtually unknown little worlds, but after the Voyager probes' experiences with the exciting satellites of Jupiter and Saturn from 1979 through 1981, it was assumed they too would hold exciting new surprises for us.
  • Voyager 2 was not meant to visit Uranus after Saturn, having already come from a scaled-down version of the Grand Tour of the outer planets. However, since Voyager 1 did make it to Saturn and perform a close examination of its largest moon Titan, Voyager 2 was given the go-ahead to Uranus and eventually Neptune in 1989 (it should be noted that Voyager 2 also survived being shut off in 1981 to allegedly save some bucks by the Reagan Administration, I kid you not). So with this rare bonus in hand, scientists were most eager to get their first close-up views of this bizarre alien world way out in the outer Sol system. But fate likes to play games with human expectations, and the Universe itself certainly does not cater to our wants and desires. The Voyager 2 mission to Uranus did go off as planned, but its two main problems had nothing to do with the space probe itself:
  • Uranus itself did not turn out to be as "exciting" as the other two previously explored Jovian worlds, Jupiter and Saturn. The clouds were a bland and featureless shade of blue. The rings were dark and thin. The moons did not look much different from the other icy satellites of Jupiter and especially Saturn. Miranda was the only real exception, looking like a world that had been literally torn apart and smashed back together, complete with 20-kilometer high sheer ice cliffs.

One would think that exploring any new world for the first time in what was (and still is) the early days of our testing the waters of deep space would be exciting enough, but somehow the public and press had gotten spoiled by the amazing wonders at Jupiter and Saturn (not to mention many space-based science fiction flicks), and Uranus was just not cutting the bill, even if it was tipped on its side.

  • The other deflecting event took place just four days after Voyager 2's closest flyby: The Space Shuttle Challenger 51-L mission ended tragically before it could even get into Earth orbit, where a leak in a solid rocket booster acted like a torch on the external fuel tank and caused it to explode, turning the shuttle into scrap metal and killing the seven astronauts on board - one of whom was going to be the first teacher in space.

This flight alone killed more astronauts than all previous manned space tragedies combined: The lone cosmonaut of Soyuz 1 in 1967 and the three cosmonauts of Soyuz 11 who had just returned from a thirty-day stay on the Soviet Salyut 1 space station in June of 1971 (the three astronauts of the Apollo 1 crew were killed in a fire during a ground test in 1967).

Needless to say, the press attention almost immediately evaporated from the lone space robot and the dull world it had been monitoring over two billion kilometers away to Cape Canaveral and NASA and did not come back.

Despite all this negativity from the general human perspective towards the Voyager 2 Uranus encounter, many new and important items were learned about this new world. Among them was the discovery of ten new moons circling the planet, a powerful magnetic field tipped sixty degrees to the planet's axis, and strong evidence that the outer Sol system went through a very violent period of collisions with other celestial bodies in the early days of our system's creation, judging by what happened to Uranus' moons and the planet itself, having been knocked completely on its side.

While Voyager 2 certainly did give us more information on Uranus than all previous Earth-based studies combined, no quick flyby can do what an orbiting probe can, as Galileo has certainly shown with Jupiter since 1995 and Cassini will with Saturn starting in 2004.

Though I would certainly like to be proven wrong here, there are no serious plans to orbit or even visit Uranus again any time soon.

For more on the Voyager 2 mission to Uranus, read here:

For more on the Voyager probes, go here and scroll down a bit for the Uranus encounter information:


Worlds of Creation: Uranus

The ancient world knew of planets – the five wandering stars that moved with respect to the background stars. The invention of the telescope allowed Galileo to discover that Jupiter had moons – proving that not everything orbits Earth. This led to the realization that Earth is also a planet, and that the six planets orbit the sun. It didn’t seem to occur to most astronomers that the solar system might have other planets – those too distant and too faint to be detected be the unaided eye. This changed in the year 1781 with the discovery of the planet Uranus.

The Discovery

William Herschel (1738-1822) was an astronomer and music composer. He was also masterful at building mirrors for reflecting telescopes, which he sold for profit, sometimes also building and selling the entire telescope.[1] He had constructed his own 6.2-inch Newtonian, a very high-quality telescope for the time. (Today you can purchase a similarly-sized telescope for around $300 on the internet). He used his telescope to explore the heavens, and began keeping a journal of his observations in 1774. Herschel specialized in observations of double stars – stars which appear very close together even when viewed in a telescope.[2] He catalogued hundreds of binary stars, as well as nebulae and star clusters. But his greatest discovery was serendipitous. In March, 1781, he spotted in his telescope a very small, light-blue disk.

Since no one was thinking that there could possibly be other planets besides the six that were already known, Herschel did not realize the nature of his discovery at first. He knew that this object was unusual. It didn’t look like a typical star. In a telescope, stars appear as points of light with no apparent size except for the glare surrounding them. This new object was clearly a disk very small, but still noticeably larger than a point. Herschel suspected he might be seeing the actual disk of a particularly large or nearby star – either that, or a comet.

Herschel’s follow-up observations revealed that this object slowly changed its position relative to the background stars from night to night. So it couldn’t be a star. Yet, the object did not have a visible coma – the cloud that typically surrounds a comet. Nor did it have a tail. Further observations revealed that this object did not move the way comets typically do. Comets tend to have elliptical orbits with high eccentricity and inclinations. But this new disk was moving in a nearly circular path and in the same plane as the planets. It was clearly a planet – one far beyond Saturn and unknown to the ancient world.

But what to name it? The other five planets (not including Earth) had been known from antiquity and were named after Roman deities. Herschel decided that this new planet should reflect the times. He wanted to name it Georgium Sidus (George’s Star) after King George III who was in power at the time. Herschel reasoned that this would reflect the time that the planet was discovered. Understandably, this pleased the king, but the suggested name was not favored outside of Britain. The French, in particular, refused the suggestion and opted to call the new planet Herschel after its discoverer. Several other names were suggested, including Neptune.

But tradition prevailed and the planet was named after the pagan god Uranus. But there is a twist: Uranus is the (Latinized) name of a Greek god, whereas all the other planets are named after Roman gods. The name seemed fitting in a number of ways. In Greek mythology, Uranus was the god of the sky, which fits the lovely sky-blue color of this new planet. Furthermore, Uranus was the father of Cronos (the Greek equivalent of Saturn) who was the father of Zeus (the Greek equivalent of Jupiter). And the name avoided any political implications. It took several decades for this name to become universally accepted.

Orbital and Physical Properties

Uranus orbits the sun at a distance of 1.79 billion miles – that’s over twice the distance of Saturn, and nineteen times the distance between the sun and Earth. It takes 84 years to complete an orbit. Like all planets, it orbits the sun prograde (counter-clockwise as viewed from over the sun’s north pole), and in approximately the same plane as the other planets. Uranus is four times the size of Earth in diameter. And so even at its great distance, it is large enough to reflect sufficient sunlight to be easily seen in a small telescope, and even in binoculars. In fact, the brightness of Uranus is near the limit of naked-eye visibility. So, at the right time of year, Uranus can be seen (barely) with the unaided eye under extremely dark skies.

Even a modest backyard telescope will reveal the sky-blue color of Uranus. With a six-inch (diameter mirror) or larger telescope, at 200x or greater magnification, you can distinctly see that Uranus has size. It really does appear as a little blue disk and not like a star. You can even see limb-darkening the circumference of the disk appears darker than the center due to the way sunlight reflects. With larger telescopes, white weather patterns can often be seen on the planet.

Uranus is sometimes classified as a Jovian or gas-giant planet. But more commonly in recent literature it (along with Neptune) is classified as an ice giant. This is because the interior of Uranus is thought to be comprised of icy materials like methane and ammonia, which exist in a liquid state in the mantle of Uranus. Its outer atmosphere consists of hydrogen and helium gasses, just like Jupiter and Saturn. However, Uranus has far more methane, which gives rise to its blue color. Its atmospheric wind speeds can exceed 500 miles per hour. Like Jupiter and Saturn, Uranus has no solid surface.

Just as Venus (the second planet from the sun) is the hottest, so Uranus (the second most distant planet from the sun) is the coldest. Its surface atmospheric temperature hovers around 323 degrees below zero on the Fahrenheit scale, which is colder than the more distant planet Neptune. We would expect Uranus to be cold because it is 20 times farther from the sun than Earth, and the sun would appear 400 times fainter. But why is it colder than Neptune? Neptune, like Jupiter and Saturn, has internal heat which far exceeds the energy it receives from the sun. But Uranus doesn’t. This is quite a perplexing puzzle for secular models. Why does Uranus lack internal heat if it supposedly formed the same way as the other giant planets?

Uranus rotates once every 17 hours, 14 minutes – the slowest of the outer four planets. But the orientation of its rotation is strange. The axis of rotation is tilted 98 degrees relative to the axis of its orbit around the sun. So, Uranus rotates on its side. It has its poles where other planets have their equators, and vice-versa. This causes extreme seasons. At the time of Uranus’s (northern) summer solstice, its north pole is pointed almost directly at the sun. So, there would be no day/night cycle. The entire northern hemisphere would see the sun at all times, and the entire southern hemisphere would be in darkness. Forty-two years later, the situation is reversed. Of course, in between these extremes, when Uranus passes its vernal or autumnal equinox, its equator is aligned with the sun – resulting in a “normal” day and night cycle. This last occurred in 2007. At this time we were treated to an edge-on view of Uranus.

The tilt of Uranus is very challenging for secular models of solar system formation. Such models propose that the solar system formed from a collapsing nebula. As the nebula contracts, any initial rotation becomes much faster due to conservation of angular momentum. Consequently, all the planets should be rotating the same way and with an axis identical to their orbital axis. We’ve already seen that Venus rotates exactly backwards. And now we see that Uranus rotates at just over 90 degrees from the secular prediction. I often wonder if the Lord gives such unique properties to His creations just to frustrate secular thinking.

The extreme tilt of Uranus leads to some challenges with terminology. In particular, which pole of Uranus should be considered the north pole? We could use the magnetic field as a guide, but the magnetic field of Uranus was unknown before 1986, and some planets like Mars do not have a global magnetic field. Two conventions are common, and they yield opposite answers for the planet Uranus.

One common convention is to define the north pole as that which points above the invariable plane of the solar system, where “above” means the same celestial hemisphere in which Earth’s North pole points. By this definition, the axial tilt of a planet can never exceed ninety degrees, because then it would no longer be pointing above the plane. Using this convention, Uranus is tilted 82 degrees, and rotates retrograde (backwards) because it rotates clockwise as viewed from the north pole – the opposite of Earth. However, this definition fails if we ever discover a planet that is tilted exactly 90 degrees relative to the plane of the solar system because neither pole would point above this plane.

The pole designated “north” depends on the convention.

The other convention is to define the north pole by the right-hand rule. Namely, the north pole is the one about which the planet rotates counter-clockwise. If you curl the fingers of your right hand in the direction the planet is rotating, then your thumb defines the direction of the north pole. By this definition all planets rotate prograde, but some are tipped more than 90 degrees such that their north pole points below the plane of the solar system. For example, under this definition, Venus rotates prograde, but is tilted 177 degrees – its north pole is at the bottom. We will use this definition in this article.[3]

Before Voyager

The extreme distance to Uranus makes the study of this world rather challenging. Before the Voyager 2 flyby, all observations of Uranus were done from Earth, 1.79 billion miles away. Nonetheless, ground-based telescopes have revealed that Uranus has five moons. In order of increasing distance from the planet, they are Miranda, Ariel, Umbriel, Titania, and Oberon. The first two (Oberon and Titania) were discovered by William Herschel in 1787. Understandably, these are the brightest of the five. They can be seen with a moderate backyard telescope, but require very dark skies and considerable skill. Umbriel and Ariel are more challenging, but they too can be spotted. Miranda is the faintest of the five.[4]

The orbits of the five major moons of Uranus as viewed from above the north pole. This is approximately the way the system looked as viewed from Earth in January 1986.

The five moons orbit around their planet’s equator. This is true for all large moons in the solar system except for Triton and Earth’s moon. But since Uranus is tilted 98 degrees, so are its moons. They orbit in the same direction that Uranus rotates, and in the same rotation plane, which is often at nearly 90 degrees relative to our line of sight on Earth. It is enjoyable to watch these moons orbit around Uranus night after night because we can often see them from almost directly “above” in contrast to Jupiter’s moons which always appear nearly edge-on. Of course, as Uranus orbits the sun, it too appears edge-on from our perspective twice every 84 years.

Another remarkable discovery was made using earth-based telescopes: Uranus has rings. Before 1977, Saturn was the only planet known to have rings. The rings or Uranus evaded detection until 1977 because they are far less dense and also darker than Saturn’s rings, making them very difficult to see. Even in 1977 they were not directly visible in our best telescopes. So how were they discovered? The answer involved an occultation of Uranus.

An occultation is the event of a planet crossing directly in front of a star, thereby blocking the star’s light. With modern technology, we can predict well in advance when these events are going to happen. As the planet Uranus drifts in front of a background star, the star does not wink out instantly because Uranus is not a solid sphere – it has a thick atmosphere. And so the outer, thinner atmosphere first crosses in front of the star, absorbing only some of its light. The star dims. Next the thicker atmosphere moves in front, and eventually the starlight is completely blocked. So, by watching the way in which the star fades, astronomers were hoping to learn something about the atmosphere of Uranus.

But strangely, before the disk of Uranus passed in front of the star, the star appeared to dim five times in succession. Then Uranus occulted the star, and when the star re-emerged from the other side, it again faded five times. Clearly, there were five obstacles both on the left and right side of Uranus and at equal distances, which were blocking the starlight. The observers recognized that a system of rings would produce such an effect.[5] Repeated observations confirmed this, and revealed the existence of four additional rings, for a total of nine. So, rather than a broad sheet of rings like Saturn’s A,B, and C rings, Uranus apparently has (at least) nine, thin, rope-like rings, much like Saturn’s F-ring.

Hubble Space Telescope image of Uranus and its main rings

We now know that Uranus has a total of thirteen rings. The additional four rings are somewhat broader than the ropelike nine. The Voyager 2 spacecraft discovered two of these, completing the eleven rings of the inner group. The Hubble Space Telescope later discovered two rings at greater distance, which constitute the outer group: the ν (nu) and μ (mu) rings. The inner of these two (nu) is red in color, whereas the outer ring (mu) is blue. The inner 13 rings of Uranus are all a very dark and slightly reddish grey. The naming of these rings seems haphazard they are assigned either a number or a Greek letter. In order of increasing distance from Uranus, the rings are ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν and μ.

Illustration of the rings of Uranus Hubble images of the outer faint rings of Uranus

Our knowledge of Uranus grew by volumes in January, 1986, thanks to the data collected by the Voyager 2 spacecraft. Recall, Voyager 1 and Voyager 2 were launched in the late 1970s and visited both Jupiter and Saturn. But only Voyager 2 had the proper trajectory to go on to visit Uranus.

On January 24, 1986, Voyager 2 flew by the planet Uranus revealing the planet in unprecedented detail. For the first time, we had direct images of the rings. And Voyager discovered two additional rings bringing the total up to eleven. We obtained the first (and only) closeup views of the five known moons. And Voyager 2 discovered ten more moons, never before seen from Earth.

This image from Voyager 2 shows the nine main inner rings of Uranus. The outer bright ring is the epsilon ring.

Although we know from Earth-based telescopes that Uranus often develops white clouds in its atmosphere, the planet was almost completely cloud-free during the Voyager 2 flyby. Unlike Jupiter and Saturn, no obvious belts or zones are apparent in visible light images of Uranus, however infrared images show that Uranus does have them.

Voyager 2 was also equipped with a device to measure magnetic fields. This confirmed that Uranus indeed has a strong magnetic field. This was quite surprising to many secularists magnetic fields naturally decay over time and cannot persist for billions of years. However, the creation physicist Russ Humphreys predicted the strength of the magnetic field of Uranus back in 1984, based on the biblical age of about 6000 years. The Voyager 2 measurements confirmed Dr. Humphreys’ prediction.[6] In science, if you want to get the right answer, you need to take the Bible seriously.

Secular scientists often attempt to explain the existence of strong magnetic fields after (in their mind) billions of years by appealing to a magnetic dynamo model. The idea is that movement within a planet due to its rotation can somehow recharge a magnetic field over time. However, this model requires that the rotation axis is closely aligned with the magnetic poles which is approximately true for Earth. But Voyager 2 found that the magnetic field of Uranus was not even remotely aligned with its rotation axis. In fact, a line connecting the magnetic poles does not pass through the center of Uranus. So as Uranus rotates, its magnetic field wobbles drastically, producing a corkscrew shape in space.

It was such a great start to the new year. We finally had images of Uranus in detail. Textbook writers eagerly began to replace the low-quality, blurry, Earth-based photographs, with these new stunning space-based images. Seven of the planets had now been visited by manmade spacecraft – a triumph of technology. Scientists would spend years studying the data from that brief flyby, and learn many new wonderful truths about God’s creation. To this day, Voyager 2 is the only spacecraft to have visited Uranus.

Yet, only four days after Voyager 2’s historic flyby, the space program was struck with a disastrous setback. The Space Shuttle Challenger exploded shortly after launch, and the lives of seven astronauts were tragically ended. The many previous successful space missions may have given people the impression that space travel is routine and safe. In reality, it is a very complicated feat of engineering in which thousands of systems must function properly and work together or the system fails. The destruction of Challenger dominated the news headlines for weeks, and largely overshadowed the new discoveries obtained by Voyager 2.

Only One Hemisphere

Thanks to the Voyager 2 flyby, we now have very high-resolution images of Uranus. These are still the sharpest images available, and are found in virtually all astronomy textbooks produced after the 1986 flyby. But technically, these images show only half of Uranus – its northern hemisphere (as defined by the right-hand rule). This is because Uranus was very near its northern summer solstice during the 1986 flyby. Hence, its north pole was pointed almost directly at the sun, and the southern hemisphere was in complete darkness. Of course, this isn’t a problem for mapping Uranus since it is essentially a featureless blue sphere we expect the south pole to look about the same as the north pole. And recent Hubble images have confirmed this expectation.[7]

These Hubble images show the changing perspective of Uranus as viewed from Earth. The system appeared edge-on in 2007, and will again in 2049.

But it is an issue for the moons. Voyager 2 provided wonderful images of the five major moons of Uranus. These moons are tidally locked and rotate around Uranus’s equator. Hence, they also had only their northern hemispheres exposed to sunlight during the flyby. To this day, we only have images of the northern hemispheres of any of the moons of Uranus. To make a complete map of these moons, we could send another craft past Uranus during its (northern) winter solstice. This will occur in the year 2028 at which time the southern hemisphere of Uranus and its moons will be illuminated while the northern hemisphere is in total darkness. Alternatively, an orbiter could arrive up to 20 years later and still provide complete maps by imaging the moons over time. But keep in mind that it took Voyager 2 over eight years to get to Uranus, and that was with two gravitational assists (one from Jupiter, and one from Saturn). If we miss the upcoming window, it will be 84 years before another such opportunity arises. Currently, there are no plans in progress to send another spacecraft to Uranus.

Voyager 2 image of the northern hemisphere of Titania: Uranus’s largest moon.

Fortunately, the Hubble Space Telescope can now provide Earth-based images of Uranus that allow us to see features in its atmosphere, albeit with less resolution than Voyager 2. This has allowed astronomers to watch the effects of seasonal changes on Uranus. Such images reveal storms and clouds, often on gargantuan scales, in contrast to the nearly featureless Voyager images. Ground-based observational technology has also improved drastically in the last three decades. However, neither ground-based observations nor Hubble can match the detailed images of the moons of Uranus provided by Voyager 2.

This Hubble Space Telescope image of Uranus shows a massive weather pattern blanketing the south pole. The image was taken in September, 2018.

The Moons of Uranus

Of the four giant planets, Uranus has the least massive system of moons. Indeed, the largest moon of Uranus (Titania) is less than half the diameter of Earth’s moon. The five major moons of Uranus are large enough to be spherical, but still very small compared to the largest moons of Jupiter and Saturn. The major five moons are composed of roughly equal portions of rock and ice, except for Miranda which has more ice. The surface of Miranda is astonishing. It almost appears as if this little moon has been broken apart and reassembled incorrectly. It is amazing to see such detail on these little worlds which appear only as faint points in the largest Earth-based telescopes.

Miranda The five major moons of Uranus compared to Earth’s moon

Voyager 2 discovered 10 additional moons – all of them closer to Uranus than Miranda. The innermost two moons are Cordelia and Ophelia. Cordelia orbits just inside Uranus’s epsilon ring, whereas Ophelia orbits just outside. They are shepherd satellites that keep particles constrained within the epsilon ring, just as Prometheus and Pandora patrol Saturn’s F-ring.[8] The epsilon ring is the brightest, most visible ring of Uranus.

The remaining eight moons discovered by Voyager 2 in increasing distance from Uranus are: Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, and Puck. Of these, Puck is the largest with a diameter of about 100 miles. Three additional inner moons have been discovered in the years after the Voyager encounter. Cupid orbits in between Rosalind and Belinda, Perdita orbits in between Belinda and Puck, and Mab orbits within Uranus’s mu-ring, in between Puck and Miranda.

Orbits of the inner moons of Uranus

Students of literature will find the names of these moons familiar. Most of the moons of Uranus are named after characters from the plays of William Shakespeare. The remaining ones are named after characters from Alexander Pope’s humorous poem, “The Rape of the Lock.” This naming scheme is unique to Uranus, and honors the English heritage of William Herschel. Uranus was the first planet discovered by an Englishmen, so why not name its moons after characters from the greatest English playwright?

Amazingly, all of these 18 moons are regular – having nearly circular, prograde orbits in the plane of their planet’s equator.[9] Until 1997, Uranus was the only giant planet without any known irregular satellites. But astronomers have found nine additional moons from Earth-based observatories, bringing the current total up to 27. All nine additional moons orbit at a much greater distance than any of the inner or major moons. And all nine are irregular. Their orbits have higher eccentricities and inclinations than the inner moons. All but one of these nine orbit Uranus retrograde the moon Margaret is the exception, and has one of the most eccentric orbits of the moons of our solar system. So we again see the pattern that is so prominent in the moon systems of the giant planets inner moons orbit prograde and in the same plane thereby avoiding collision in the limited space, and outer moons do whatever they want.

Orbits of the irregular outer moons of Uranus as viewed from above Uranus’s north pole.

What a wonderful time to be a Christian! We can explore planets that were completely unknown to the ancient world. And we have even sent spacecraft to image them. These discoveries continue to confirm biblical creation.

The table below lists the moons of Uranus in order of increasing distance from the planet. Blue indicates inner moons, yellow for the major five, green for retrograde irregular moons, and orange for the prograde irregular moon Margaret.


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New Hubble images show storms on Uranus and Neptune

Bright and dark clouds and storms on Uranus (left) and Neptune (right) as seen by the Hubble Space Telescope in September 2018. Image via NASA/ ESA/ A. Simon (NASA Goddard Space Flight Center) and M.H. Wong/A. Hsu (University of California, Berkeley)/HubbleSite.

In recent years, the gas giant planets Jupiter and Saturn, along with Pluto, have captured most of the attention in the outer solar system – which is understandable, given the epic missions of Juno, Cassini and New Horizons to these worlds. But the two ice giants – Uranus and Neptune – are still there, too, just waiting to be explored again.

Now the Hubble Space Telescope has taken some beautiful new images of these distant worlds, which were released on February 7, 2019. The images are from the Outer Planet Atmospheres Legacy (OPAL) program, which annually captures global maps of the outer planets when they are closest to Earth in their orbits.

Uranus and Neptune each have been visited only once so far by a spacecraft from Earth – Voyager 2 – in 1986 and 1989 respectively. Voyager 2 sent back some stunning images of both planets and some of their moons, but there’s so much still to learn. No new space missions to these worlds are being planned, although some have been proposed. Until a new future mission can be launched, Hubble is the best resource we have for studying these distant planets.

Larger view of the bright cloud cap over the north pole of Uranus. Image acquired by Hubble in September 2018, via HubbleSite.

The new image of Uranus shows a bright cloud cap across the north pole. Near the edge of that cloud cap is another large, compact methane-ice cloud – sometimes bright enough to be photographed even by amateur astronomers. Another narrow cloud band encircles the planet north of the equator it is still not known how bands like these are confined to such narrow widths, since both Uranus and Neptune have very broad westward-blowing wind jets.

The northern cloud cap is thought to result from Uranus’ odd rotational axis – the planet rotates “on its side” compared to other planets in the solar system. Seasonal changes in atmospheric flow may create such clouds right now, Uranus is nearing the middle of the summer season at the north pole, when the sun shines directly on the pole and never sets. In winter seasons, the planet tends to have its typical blander appearance.

The new views of Neptune are also very impressive, showing a huge dark storm – about 6,800 miles (10,943 km) across – near the top of the planet, reminiscent of storms on Jupiter and Saturn. Unlike those storm formations, however, the dark ones on Neptune tend to form and then dissipate fairly quickly after about two years. By comparison, storms on Jupiter, including the Great Red Spot, have been observed to last up to hundreds of years. A previous study led by University of California, Berkeley undergraduate student Andrew Hsu estimated that these storms appear every four to six years at different latitudes.

Larger view of the huge dark storm system on Neptune, seen by Hubble in September 2018. Image via HubbleSite.

This new storm on Neptune is only the fourth such one seen by Hubble since 1993, but others were also photographed by the Voyager 2 spacecraft in 1989. As noted in Gizmodo by Amy Simon, a scientist at NASA’s Goddard Space Flight Center:

The Neptune dark spot is much larger than the one we saw a few years ago, and is comparable in size to the Voyager Great Dark Spot seen in 1989. This is also the first time we could see the region before a storm of that size formed, so that will help us in modeling the formation process.

As on Jupiter, the dark storm vortices swirl in an anti-cyclonic direction, dredging up material from deeper levels in the planet’s atmosphere. This is similar to lenticular or “pancake-shaped” clouds on Earth, which form as air is pushed over the tops of mountains. One cool example is the one that often hangs over the top of Lítla Dímun island, the smallest of the Faroe Islands, a self-governing archipelago, part of the Kingdom of Denmark.

A closer view of one of Neptune’s dark storms, the Great Dark Spot, as seen by Voyager 2 in 1989. Image via NASA/JPL.

There are other storms on Neptune as well – bright white “companion clouds.” These form when the flow of ambient air is disturbed and diverted upward over the darker storm vortices, which causes gases in the atmosphere to freeze into methane ice crystals.

The new dark storm on Neptune was first seen by Hubble in September 2018, but was preceded by other cloud activity as early as 2016. This is possible evidence that such storms first develop deeper in the atmosphere, only becoming visible when the tops of the storms reach a high enough altitude.

The new images are part of a scrapbook of images used by planetary scientists with OPAL to track weather phenomena on these distant worlds just like on Earth, repeated observations are needed to do this. According to Simon:

The yearly observations are helping us to understand the frequency of storms, as well as their longevity.

An ethereal crescent Uranus as seen by Voyager 2 in 1986, just after the flyby. Image via NASA/JPL.

Uranus and Neptune are both ice giants, with no solid surfaces beneath their atmospheres. Instead, they have mantles of hydrogen and helium surrounding a water-rich interior (the water being in the form of supercritical fluid), which itself is thought to surround a rocky core. Each planet has a bluish hue due to atmospheric methane that absorbs red light but allows blue-green light to be scattered back into space.

Bottom line: Uranus and Neptune are both active, dynamic planets, much like Jupiter and Saturn, with massive storms and other clouds churning in their atmospheres. Although no spacecraft have been able to visit these distant worlds since the late 1980s, the Hubble Space Telescope is still busy observing them, tracking the unique weather phenomena of these icy giants.