Image of Uranus’ crescent taken by a departing Voyager 2 on January 25, 1986 (NASA/JPL)
27 years ago today, January 24, 1986, NASA’s Voyager 2 spacecraft sped past Uranus, becoming simultaneously the first and last spacecraft to visit the blue-tinged gas giant, third largest planet in the Solar System.
The image above shows the crescent-lit Uranus as seen by Voyager 2 from a distance of about 965,000 km (600,000 miles.) At the time the spacecraft had already passed Uranus and was looking back at the planet on its way outwards toward Neptune.
Although composed primarily of hydrogen and helium, trace amounts of methane in Uranus’ uppermost atmosphere absorb most of the red wavelengths of light, making the planet appear a pale blue color.
Image of the 1,500-km-wide Oberon acquired by Voyager 2 on Jan. 24, 1986 (NASA/JPL)
The second of NASA’s twin space explorers (although it launched first) Voyager 2 came within 81,800 kilometers (50,600 miles) of Uranus on January 24, 1986, gathering images of the sideways planet, its rings and several of its moons. Voyager 2 also discovered the presence of a magnetic field around Uranus, as well as 10 new small moons.
Three moons discovered by Voyager 2 in 1986 (NASA/JPL)
Data gathered by Voyager 2 revealed that Uranus’ rate of rotation is 17 hours, 14 minutes.
At the time of this writing, Voyager 2 is 15,184,370,900 km from Earth and steadily moving toward the edge of the Solar System at a speed of about 3.3 AU per year. At that distance, signals from Voyager take just over 14 hours and 4 minutes to reach us.
See images from Voyager 2’s visit of Uranus here, and check out a video of the August 20, 1977 launch below along with more images from the historic Voyager mission’s “Grand Tour” of the outer Solar System.
Artist's concept of NASA's Voyager spacecraft. Image credit: NASA/JPL-Caltech
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Every mechanic loves to tinker with a machine to give it optimum operating efficiency. But this latest engineering feat involving the Voyager 2 spacecraft wins the prize for longest distance tune-up. Akin to servicing an old car to increase gas mileage, engineers at JPL sent commands across 14 billion kilometers (9 billion miles) out to Voyager 2, enabling it to switch to the backup set of thrusters that controls the roll of the spacecraft. This will reduce the amount of power that the 34-year-old probe needs to operate, giving it better “gas mileage” and — hopefully — the power to operate for at least another decade.
The move was a little risky, as these backup roll thrusters were previously unused. It meant trusting equipment which has been idle and out in the harsh environment of space for 32 years to work — and keep working for the remainder of the mission.
“The switchover is pretty permanent – the thrusters are not rated to be reused after being unheated,” said the @NASAVoyager2 Twitter feed.
Voyager 2 will save about 11.8 watts of electric power by turning off the heater that kept the hydrazine fuel to the primary thrusters warm.
Voyager 1 and 2 are each equipped with six sets, or pairs, of thrusters to control the pitch, yaw and roll motions of the spacecraft. With this latest command, both spacecraft are now using all three sets of their backup thrusters.
The primary roll thrusters now turned off fired more than 318,000 times. Voyager 1 changed to the backup for this same component after 353,000 pulses in 2004.
Projected levels of the Voyagers' RTG levels. Credit: @NASAVoyager2 Twitter Feed.
The rate of energy generated by Voyager 2’s Plutonium 238 nuclear power source continues to decline, and is now down to about 270 watts from the 470 watts being produced when the spacecraft launched in 1977. But now, by reducing its power requirements, engineers expect the spacecraft can continue to operate a bit longer.
Still, at the rate of decay, the Voyager spacecraft won’t have sufficient electric power to its instruments sometime by the mid-2020’s.
Using solar power for a spacecraft traveling beyond Jupiter is impractical, (which is why it is important that Congress pass a bill to restore funding for production of Plutonium 238).
Heliocentric distances for Pioneer, Voyager and New Horizons. Credit: NASAVoyager2 Twitter feed.
The Voyagers are on their way toward interstellar space, beyond our solar system, where no human spacecraft has been before. This latest tune-up will hopefully get Voyager 2 a little farther while she’s still able to communicate with Earth.
After 33 years, NASA’s twin Voyager spacecraft are still actively working – gathering information, communicating with Earth, (and Tweeting!), and they are about to go where no space probe has gone before: into interstellar space. Because of the unfamiliar nature of the heliosphere, and especially its outermost layer, the heliosheath, it is not known exactly when the Voyagers will actually reach the “great beyond.”
“The heliosheath is 3 to 4 billion miles (4.8 to 6 billion km) in thickness,” said Voyager Project Scientist, Ed Stone. “That means we’ll be out within five years or so.” The V’ger’s Plutonium 238 heat source will keep the critical subsystems running through at least 2020, but after that, Stone says, “Voyager will become our silent ambassador to the stars.”
This video features highlights of the Voyager journeys to the outer planets and the discoveries they have made, and shows where they are now and where they are headed.
These two pictures of Uranus -- one in true color (left) and the other in false color -- were compiled from images returned Jan. 17, 1986, by the narrow-angle camera of Voyager 2. Credit: NASA/JPL
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Voyager 2 is the only spacecraft that has flown close by one of the more enigmatic planets in our solar system (and the butt of many one-liners): Uranus. It was 25 years ago today (Jan. 24) that Voyager made the close pass, and scientists from JPL have been reminiscing about how they pored over the data being returned by the Grand-Touring Voyagers.
“Voyager 2’s visit to Uranus expanded our knowledge of the unexpected diversity of bodies that share the solar system with Earth,” said Project Scientist Ed Stone, who is now based at the California Institute of Technology in Pasadena. “Even though similar in many ways, the worlds we encounter can still surprise us.”
Voyager 2 has discovered two "shepherd" satellites associated with the rings of Uranus. Image Credit: NASA/JPL
From the flyby, we saw for the first time Uranus’ small group of tenuous rings, and the tiny shepherding moons that sculpted them. Unlike Saturn’s icy rings, they found Uranus’ rings to be dark gray, reflecting only a few percent of the incident sunlight.
Miranda, innermost of Uranus' large satellites, is seen at close range in this Voyager 2 image, taken Jan. 24, 1986, as part of a high-resolution mosaicing sequence. Image credit: NASA/JPL
The images also showed the small, icy Uranus moon Miranda that had a grooved terrain with linear valleys and ridges cutting through the older terrain and sometimes coming together in chevron shapes. They also saw dramatic fault scarps, or cliffs. All of this indicated that periods of tectonic and thermal activity had rocked Miranda’s surface in the past.
The scientists were also shocked by data showing that Uranus’ magnetic north and south poles were not closely aligned with the north-south axis of the planet’s rotation. Instead, the planet’s magnetic field poles were closer to the Uranian equator. This suggested that the material flows in the planet’s interior that are generating the magnetic field are closer to the surface of Uranus than the flows inside Earth, Jupiter and Saturn are to their respective surfaces.
Voyager 2 was launched on Aug. 20, 1977, 16 days before its twin, Voyager 1. After completing its prime mission of flying by Jupiter and Saturn, Voyager 2 was sent on the right flight path to visit Uranus, which is about 3 billion kilometers (2 billion miles) away from the sun. Voyager 2 made its closest approach – within 81,500 kilometers (50,600 miles) of the Uranian cloud tops – on Jan. 24, 1986.
By the end of the Uranus encounter and science analysis, data from Voyager 2 enabled the discovery of 11 new moons and two new rings, and generated dozens of science papers about the quirky seventh planet.
Voyager 2 moved on to explore Neptune, the last planetary target, in August 1989. It is now hurtling toward interstellar space, which is the space between stars. It is about 14 billion kilometers (9 billion miles) away from the sun. Voyager 1, which explored only Jupiter and Saturn before heading on a faster track toward interstellar space, is about 17 billion kilometers (11 billion miles) away from the sun.
“The Uranus encounter was one of a kind,” said Suzanne Dodd, Voyager project manager, based at JPL. “Voyager 2 was healthy and durable enough to make it to Uranus and then to Neptune. Currently both Voyager spacecraft are on the cusp of leaving the sun’s sphere of influence and once again blazing a trail of scientific discovery.”
Voyager 2 is easily the most famous spacecraft sent from Earth to explore other planets. Launched on August 20, 1977, Voyager visited Jupiter and Saturn, and is the only spacecraft to have ever made a flyby of the outer planets Uranus and Neptune. It flew past Neptune in 1989, but it’s still functioning and communicating with Earth.
Voyager 2 and its twin spacecraft Voyager 1 were built at NASA’s Jet Propulsion Lab in Pasadena, California. The two spacecraft were built with identical components, but launched on slightly different trajectories. Voyager 2 took advantage of a rare alignment of the planets so that it could use a gravity assisting boost as it flew past each one. The increased velocity from Jupiter would help it reach Saturn, Saturn helped it get to Uranus and then to Neptune.
It made its closest approach to Jupiter on July 9, 1979, passing within 570,000 km of the planet’s cloud tops. It captured some of the first, highest resolution images of Jupiter’s moons, showing volcanism on Io, and cracks in the icy surface of Europa. Astronomers now suspect that Europa’s surface hides a vast ocean of water ice.
Voyager 2 then went on to visit Saturn on August 26, 1981, and then onto Uranus on January 24, 1986. This was the first time a spacecraft had ever encountered Uranus, and captured images of the planet close up. Voyager studied Uranus’ rings, and discovered several new moons orbiting the planet. Voyager 2 made its final planetary visit with Neptune on August 25, 1989. Here the spacecraft discovered the planet’s “Great Dark Spot”, and discovered more new moons.
Voyager 2 is now considered an interstellar mission. This means that it has enough velocity to escape the Solar System and travel to another star. Of course, at its current speed, it would take hundreds of thousands of years to reach even the closest star. Scientists think that the spacecraft will continue transmitting radio signals until at least 2025, almost 50 years after it was launched.
We have written many articles about Voyager 2 for Universe Today. Here’s an article about NASA’s diagnosed problems with Voyager 2, and here are some Voyager 2 pictures.
This artist's rendering depicts NASAs Voyager 2 spacecraft as it studies the outer limits of the heliosphere - a magnetic 'bubble' around the solar system that is created by the solar wind. Image credit: NASA/JPL-Caltech
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What could be happening out near the edge of the solar system? The 33-year-old Voyager 2 spacecraft has experienced an anomaly where the data it sends back is unreadable. To try and understand the problem, engineers at JPL have shifted the spacecraft into a mode where it transmits only spacecraft health and status data. Preliminary engineering data received on May 1 show the spacecraft is basically healthy, and that the source of the issue is the flight data system, which is responsible for formatting the data to send back to Earth.
Voyager team members first noticed changes in the return of data packets from Voyager 2 on April 22, and have been working since then to troubleshoot the problem and resume the regular flow of science data. Because of a planned roll maneuver and moratorium on sending commands, engineers got their first chance to send commands to the spacecraft on April 30. It takes nearly 13 hours for signals to reach the spacecraft and nearly 13 hours for signals to come down to NASA’s Deep Space Network on Earth.
Voyager 2 is about 13.8 billion kilometers, or 8.6 billion miles, from Earth, and launched on August 20, 1977. Its twin, Voyager 1 is about 16.9 billion kilometers (10.5 billion miles) away from Earth, and launched almost two weeks after Voyager 2.
The original mission was a four-year journey to Saturn, and later the flybys of Uranus and Neptune were added to give us a “Grand Tour” of the outer solar system. If all goes well, Voyager 2 should leave the solar system and enter interstellar space in about five years.
Artist’s impression of how Triton, Neptune’s largest moon, might look from high above its surface. Credit: ESO/L. Calçada
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If you’re planning a trip to Neptune’s moon Triton, you’ll want to head to the southern hemisphere where it’s now just past mid-summer. Yes, distant Triton actually does have seasons, astronomers at ESO’s Very Large Telescope recently determined. “We have found real evidence that the Sun still makes its presence felt on Triton, even from so far away,” said astronomer Emmanuel Lellouch in an ESO press release. “This icy moon actually has seasons just as we do on Earth, but they change far more slowly.” According to the first ever infrared analysis of Triton’s atmosphere, the seasons last about 40 Earth years. But while summer is in full swing in Triton’s southern hemisphere, there’s no need to pack your bikini. The average surface temperature is about minus 235 degrees Celsius.
Oh, and you’ll also want to bring along a little breathable air. The ESO team also – unexpectedly – discovered carbon monoxide in Triton’s thin atmosphere, mixed in with methane and nitrogen.
The astronomer’s observations revealed that Triton’s thin atmosphere varies seasonally, thickening when warmed. When the distant sun’s rays hits Triton at their best summer angle, a thin layer of frozen nitrogen, methane, and carbon monoxide on Triton’s surface sublimates into gas, thickening the icy atmosphere as the season progresses during Neptune’s 165-year orbit around the Sun. Triton passed the southern summer solstice in 2000. Voyager 2's view of Triton. Credit: NASA
So, while this action increases the thickness of the atmosphere, thus increasing the atmospheric pressure, you’ll still need a pressure suit as well for your visit. Based on the amount of gas measured, Lellouch and his colleagues estimate that Triton’s atmospheric pressure may have risen by a factor of four compared to the measurements made by Voyager 2 in 1989, when it was still spring on the giant moon. The Voyager data indicated the atmosphere of nitrogen and methane had a pressure of 14 microbars, 70,000 times less dense than the atmosphere on Earth. The data from ESO shows the atmospheric pressure is now between 40 and 65 microbars — 20,000 times less than on Earth.
Carbon monoxide was known to be present as ice on the surface, but Lellouch and his team discovered that Triton’s upper surface layer is enriched with carbon monoxide ice by about a factor of ten compared to the deeper layers, and that it is this upper “film” that feeds the atmosphere. While the majority of Triton’s atmosphere is nitrogen (much like on Earth), the methane in the atmosphere, first detected by Voyager 2, and only now confirmed in this study from Earth, plays an important role as well.
“Climate and atmospheric models of Triton have to be revisited now, now that we have found carbon monoxide and re-measured the methane,” said co-author Catherine de Bergh. The team’s results are published in Astronomy & Astrophysics
If we could actually visit Triton, it would likely be a very interesting destination as we know it has geologic activity and a changing surface – plus its unique retrograde motion would offer a unique view of the solar system.
While Triton is the seventh largest moon in our solar system, its distance and position from Earth makes it difficult to observe, and ground-based observations since Voyager 2 have been limited. Observations of stellar occultations (a phenomenon that occurs when a Solar System body passes in front of a star and blocks its light) indicated that Triton’s surface pressure was increasing in the 1990’s. But a new instrument on the VLT, the Cryogenic High-Resolution Infrared Echelle Spectrograph (CRIRES) has provided the chance to perform a more detailed study of Triton’s atmosphere. “We needed the sensitivity and capability of CRIRES to take very detailed spectra to look at the very tenuous atmosphere,” said co-author Ulli Käufl.
These observations are just the beginning for the CRIRES instrument, which will be extremely helpful in studying other distant bodies in our solar system, such as Pluto and other Kuiper Belt Objects. Pluto is often considered a cousin of Triton with similar conditions, and in the light of the carbon monoxide discovery on Triton, astronomers are racing to find this chemical on the even more distant Pluto.
Uranus as seen through the automated eyes of Voyager 2 in 1986. (Credit: NASA/JPL).
The gas (and ice) giant known as Uranus is a fascinating place. The seventh planet from out Sun, Uranus is the third-largest in terms of size, the fourth-largest in terms of mass, and one of the least dense objects in our Solar System. And interestingly enough, it is the only planet in the Solar System that takes it name from Greek (rather than Roman) mythology.
But these basic facts really only begin to scratch the surface. When you get right down to it, Uranus is chock full of interesting and surprising details – from its many moons, to its ring system, and the composition of its aqua atmosphere. Here are just ten things about this gas/ice giant, and we guarantee that at least one of them will surprise you.
