Spirit rover, as seen by HiRISE on Feb. 15, 2010. Crop and colorization by Stuart Atkinson, image credit: NASA/JPL, U of AZ

JPL issued a press release today with an update that mission controllers have still not heard from the hibernating Spirit rover. Even though the rover is experiencing one of Mars' harshest winters since the rovers arrived, the rover team has begun an active "paging" technique called 'sweep and beep' in an effort to communicate with Spirit instead of just passively listening for any activity from the rover. Based on models of Mars' weather and its effect on available power, mission managers believe that if Spirit responds, it most likely will be in the next few months. But in a 'hope for the best, prepare for the worst' kind of way, the press release added, "However, there is a very distinct possibility Spirit may never respond."

"It will be the miracle from Mars if our beloved rover phones home," said Doug McCuistion, director of NASA's Mars Exploration Program. "It's never faced this type of severe condition before – this is unknown territory."

The Martian winter runs from May through November here on Earth, so there's still a lot of long, dark winter to get through. Spirit has not communicated since March 22, 2010 and is likely in a low-power hibernation mode since the rover was not able to get to a favorable slope for its fourth Martian winter. The low angle of sunlight during these months limits the power generated from the rover's solar panels. During hibernation, the rover shuts down communications and other activities so available energy can be used to recharge and heat batteries, and to keep the mission clock running.

On July 26, rover engineers began the sweep and beep. "Instead of just listening, we send commands to the rover to respond back to us with a communications beep," said John Callas, project manager for the rover. "If the rover is awake and hears us, she will send us that beep."

The earliest date the rover could generate enough power to send a beep to Earth was calculated to be around July 23. However, mission managers don't anticipate the batteries will charge adequately until late September to mid-October.

So, there is still a lot of time to wait things out. While I don't think the rover team is giving up on Spirit at all, it appears they want to prepare the rover faithful for the worst.

But I'm going to make a prediction here: not only will Spirit wake up, but the rover driving team will be able to get her out of the sand trap she is stuck in. Just a hunch, but you heard it here and only time will tell if my prediction comes true.

Based on previous Martian winters, the rover team anticipates the increasing haziness in the sky over Spirit will offset longer daylight for the next two months. The amount of solar energy available to Spirit then will increase until the southern Mars summer solstice in March 2011. JPL says that if we haven't heard from Spirit by March, 2011 it is unlikely that we will ever hear from it.

Leave it to Steve Squyres, however, principal investigator for the rovers, to leave us with a little hope: "This has been a long winter for Spirit, and a long wait for us," he said. "Even if we never heard from Spirit again, I think her scientific legacy would be secure. But we're hopeful we will hear from her, and we're eager to get back to doing science with two rovers again."

Source: JPL

This schematic shows the daytime cycle of hydration, loss and rehydration on the lunar surface. Credit: University of Maryland/McREL.

"Water cycle on the Moon" is a phrase that many people – including lunar scientists – were never expecting to hear. This surprising new finding of ubiquitous water on the surface of the Moon, revealed and confirmed by three different spacecraft last year, has been one of the main topics of recent discussion and study by lunar researchers. But figuring out the cycle of how water appears and disappears over the lunar day remains elusive. As of now, scientists suspect a few different processes that could be delivering water and hydroxyl (OH) to the lunar surface: meteorites or comets hitting the Moon, outgassing from the Moon's interior, or the solar wind interacting with the lunar regolith. But so far, none of the details of any of these processes are adding up.

Dana Hurley from The Johns Hopkins University Applied Physics Laboratory is part of team of scientists attempting to model the lunar water cycle, and she discussed the work at the NASA Lunar Science Institute's third annual Lunar Forum at Ames Research Center, July 20-22, 2010.

"When we do the model, we assume the way that the water is lost is through photodissociation, and so that sets the timescale," Hurley told Universe Today. "And using that timescale the amount that is coming in through the solar wind or micrometeorites can't add up to the amount observed if it is in steady state, so something is not jiving."

Photodissociation involves the breaking up of a substance into simpler components by the radiant energy of sunlight.

It appears the amount of water varies over the course of the lunar day. Two observations a week apart by a spectrometer on the repurposed Deep Impact spacecraft (now called EPOXI) showed the region that was near the Moon's terminator at dawn had a detectable amount of water and hydroxyl, and a week later when it was near noon, those substances were gone. But the new region at dawn then had H2O and OH.

One theory holds that the water and hydroxyl are, in part, formed from hydrogen ions in the solar wind. By local noon, when the moon is at its warmest, some water and hydroxyl are lost. By evening, the surface cools again, and the water and hydroxyl return.

But, Hurley said, the solar wind in steady state does not reproduce the observed surface density of water and hydroxyl.

Additionally, looking at the other possible sources — the known source rate of micrometeoroids and comets — doesn't provide the amount of observed H20 and OH either.

"We'd really like to have a lot more observations to understand how it evolves over the course of the day," Hurley said.

Water in Polar Regions on the Moon Credit: ISRO/NASA/JPL-Caltech/Brown Univ./USGS

She also noted that since there are obviously some unique processes going on, the interaction between the surface and atmosphere needs more study.

"The surface and atmosphere are coupled," Hurley said in an interview with Universe Today. "The atmosphere is produced from the surface; there is no atmosphere that lasts for a long time on the Moon and it is constantly being produced and lost. And so it is coming from the surface, either from something that is coming from the lunar regolith grains or something that is interacting with those grains, whether it is solar wind or something that is impacting. So, the surface is the source of the atmosphere and that atmosphere comes back and interacts with the surface again. And you really have to understand that whole system."

So, what is her best guess as to the source of the water?

Hurley said there has to be some sort of recycling going on within the regolith, and perhaps a complex surface chemistry that allows the H20 and OH to exist for longer periods of time, which would better explain the surface density.

"What I've looked at is what could be happening in the atmosphere and how things hop around from the surface up and then back down to the surface," she said. "The lunar regolith is rather loose, and these small particles and gases can go down within the regolith and be within the top several centimeters and work their way down and back out. So there is an exchange going on in that top layer that is kind of acting as a reservoir. That is my best guess of what is going on."

Caption: Looking down at a plume on Enceladus. Credit: NASA/Space Science Science Institute.

Oh, wow! This is one of the best images yet from the Cassini spacecraft of the "tiger stripes" in the south polar region of Saturn's moon Enceladus. Over the weekend, Cassini flew by Enceladus, and has sent back some incredible new images, such as the one above. The tiger stripes are actually giant fissures that spew jets of water vapor and organic particles hundreds of kilometers, or miles, out into space, and here, Cassini is staring right down into one of the fissures. See more great images of Enceladus below, plus images of the moons Dione and Tethys.

Close-up of the cracked, crevassed surface of Enceladus. Credit: NASA/Space Science Institute.

While the winter is darkening the moon's southern hemisphere, Cassini has its own version of "night vision goggles" — the composite infrared spectrometer instrument – to track heat even when visible light is low. It will take time for scientists to assemble the data into temperature maps of the fissures.

Enceladus against Saturn's limb. Credit: NASA/Space Science Institute.

More plumes on Enceladus. Credit: NASA/Space Science Institute.

Close-up of Tethys. Credit: NASA/Space Science Institute

Dione from 115,370 kilometers away. Credit: NASA/Space Science Institute

A composite image shows a dark matter disk in red. From images in the Two Micron All Sky Survey. Credit: Credit: J. Read & O. Agertz.

Although dark matter is inherently difficult to observe, an understanding of its properties (even if not its nature) allows astronomers to predict where its effects should be felt. The current understanding is that dark matter helped form the first galaxies by providing gravitational scaffolding in the early universe. These galaxies were small and collapsed to form the larger galaxies we see today. As galaxies grew large enough to shred incoming satellites and their dark matter, much of the dark matter should have been deposited in a flat structure in spiral galaxies which would allow such galaxies to form dark components similar to the disk and halo. However, a new study aimed at detecting the Milky Way‘s dark disk have come up empty.

The study concentrated on detecting the dark matter by studying the luminous matter embedded in it in much the same way dark matter was originally discovered. By studying the kinematics of the matter, it would allow astronomers to determine the overall mass present that would dictate the movement. That observed mass could then be compared to the amount of mass predicted of both baryonic matter as well as the dark matter component.

The team, led by C. Moni Bidin used ~300 red giant stars in the Milky Way‘s thick disk to map the mass distribution of the region. To eliminate any contamination from the thin disc component, the team limited their selections to stars over 2 kiloparsecs from the galactic midplane and velocities characteristic of such stars to avoid contamination from halo stars. Once stars were selected, the team analyzed the overall velocity of the stars as a function of distance from the galactic center which would give an understanding of the mass interior to their orbits.

Using estimations on the mass from the visible stars and the interstellar medium, the team compared this visible mass to the solution for mass from the observations of the kinematics to search for a discrepancy indicative of dark matter. When the comparison was made, the team discovered that, “[t]he agreement between the visible mass and our dynamical solution is striking, and there is no need to invoke any dark component.”

While this finding doesn’t rule out the presence of dark matter, it does place constraints on it distribution and, if confirmed in other galaxies, may challenge the understanding of how dark matter serves to form galaxies. If dark matter is still present, this study has demonstrated that it is more diffuse than previously recognized or perhaps the disc component is flatter than previously expected and limited to the thin disc. Further observations and modeling will undoubtedly be necessary.

Yet while the research may show a lack of our understanding of dark matter, the team also notes that it is even more devastating for dark matter’s largest rival. While dark matter may yet hide within the error bars in this study, the findings directly contradict the predictions of Modified Newtonian Dynamics (MOND). This hypothesis predicts the apparent gain of mass due to a scaling effect on gravity itself and would have required that the supposed mass at the scales observed be 60% higher than indicated by this study.

This image shows a three and a half hour (0000 - 0330 UT) time lapse movie of the flare and filament event. Credit: NASA/SDO

An active sunspot (1123) erupted early this morning (Nov. 12th), producing a C4-class solar flare and apparently hurling a filament of material in the general direction of Earth. Coronagraph images from the Solar and Heliospheric Observatory (SOHO) and NASA’s twin STEREO spacecraft show a faint coronal mass ejection emerging from the blast site and heading off in a direction just south of the sun-Earth line. The cloud could deliver a glancing blow to Earth’s magnetic field sometime on Nov. 14th or 15th. High latitude sky watchers could see auroras on those dates.

New sunspot 1123 in the Sun's southern hemisphere is crackling with C-class solar flares. Credit: SDO/HMI.

Here’s a look at the two sunspots currently visible on the Sun.

Speaking of sunspots, there’s a great video from Oct. 25-27, 2010, showing two sunspots merging:

 some of the best images taken by Opportunity during her 7 Year Martian Trek

Martian Moon Phobos eclipsing the sun on Sol 45

Ready to Enter Endurance.

This view looking was taken by the navigation camera on June 6, 2004. That was two sols before Opportunity entered the crater, taking the route nearly straight ahead in this image. This view is a cylindrical projection with geometric seam correction. Credit: NASA/JPL

Wopmay in False Color .

NASA's Mars Exploration Rover Opportunity examined a boulder called Wopmay before heading further east inside Endurance Crater. The frames combined into this false-color view were taken by Opportunity's panoramic camera during the rover's 251st martian day (Oct. 7, 2004). The coloring accentuates iron-rich spherical concretions as bluish dots embedded in the rock and on the ground around it. The rock is about one meter (3 feet) across. Credit: NASA/JPL/Cornell

Burns Cliff.

Opportunity captured this view of Burns Cliff after driving right to the base of this southeastern portion of the inner wall of Endurance Crater. The view combines frames taken by Opportunity's panoramic camera between the rover's 287th and 294th martian days (Nov. 13 to 20, 2004). The mosaic spans more than 180 degrees side to side. Because of this wide-angle view, the cliff walls appear to bulge out toward the camera. In reality the walls form a gently curving, continuous surface. Image credit: NASA/JPL/Cornell

Opportunity's Heat Shield in Color, Sol 335.

This image from the panoramic camera on NASA's Mars Exploration Rover Opportunity features the remains of the heat shield that protected the rover from temperatures of up to 2,000 degrees Fahrenheit as it made its way through the martian atmosphere. This two-frame mosaic was taken on Sol 335 (Jan. 2, 2005). The view is of the main heat shield debris seen from approximately 10 meters (about 33 feet) away from it. Many rover-team engineers were taken aback when they realized the heat shield had inverted, or turned itself inside out. The height of the pictured debris is about 1.3 meters (about 4.3 feet). The original diameter was 2.65 meters (8.7 feet), though it has obviously been deformed. The Sun reflecting off of the aluminum structure accounts for the vertical blurs in the picture.

Iron Meteorite on Mars.

Opportunity finds an iron meteorite on Mars, the first meteorite of any type ever identified on another planet. The pitted, basketball-size object is mostly made of iron and nickel. Opportunity used its panoramic camera to take the images used in this approximately true-color composite on the Sol 339 (Jan. 6, 2005). Credit: NASA/JPL/Cornell

Opportunity at Crater's Cape Verde in October 2006.

This image from the High Resolution Imaging Science Experiment on NASA's Mars Reconnaissance Orbiter shows the Mars Exploration Rover Opportunity near the rim of Victoria Crater. Victoria is an impact crater about 800 meters (half a mile) in diameter at Meridiani Planum near the equator of Mars. Five days before this image was taken, Opportunity arrived at the rim of Victoria, after a drive of more than 9 kilometers (over 5 miles). It then drove to the position where it is seen in this image. This view is a portion of an image taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on Oct. 3, 2006. Credit: NASA/JPL/UA

Victoria’s Secret Revealed in Color.

This Opportunity panorama reveals 2,500 ft-wide, 230 ft-deep Victoria Crater from the lip at Duck Bay alcove. Geologic layers reveal the history of Martian water here. The panorama was taken about 8 feet from the crater rim on Sol 952 (28 Sept 2006) as the rover sat between two steep promontories, Cape Verde and Cabo Frio. This vista exposes a thick stack of geologic layers which revealed the hidden watery secrets of the Martian environment farther back in time than any other location visited previously by the rovers. One can see a ½ mile to the distant cliff walls of the crater, above a windswept dune field in the center. This mosaic was assembled from navcam images and featured in Aviation Week & Space Technology magazine and on the Astronomy Picture of the Day (APOD) on 2 Oct. 2006 in high resolution. Credit: NASA/JPL/Cornell, Bernhard Braun, Marco Di Lorenzo, Kenneth Kremer. http://antwrp.gsfc.nasa.gov/apod/ap061002.html

Check out this spherical projection panorama of Opportunity descending inside Victoria Crater on Sol 1332. Credit: NASA/JPL/Cornell/Nasatech.net

Layers of Cape Verde in Victoria Crater.

This view of Victoria crater is looking north from Duck Bay towards the dramatic promontory called Cape Verde. The dramatic cliff of layered rocks is about 50 meters (about 165 feet) away from the rover and is about 6 meters (about 20 feet) tall. The taller promontory beyond that is about 100 meters (about 325 feet) away, and the vista beyond that extends away for more than 400 meters (about 1300 feet) into the distance. This is an approximately true color rendering of images taken by the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity during Sol 952 (Sept. 28, 2006) using the camera's 750-nanometer, 530-nanometer and 430-nanometer filters. Credit: NASA/JPL/Cornell

Opportunity Traverse Map, Eagle to Victoria.

NASA's Mars Exploration Rover Opportunity reached the rim of Victoria Crater on Sept. 28, 2006, Sol 952. Opportunity drove 9.28 kilometers (5.77 miles) in the explorations that took it from Eagle Crater, where it landed in January 2004, eastward to Endurance Crater, which it investigated for about half of 2004, then southward to Victoria.

Lyell Panorama inside Victoria Crater.

During four months prior to the fourth anniversary of its landing on Mars, Opportunity examined rocks inside an alcove called Duck Bay in the western portion of Victoria Crater. The main body of the crater appears in the upper right of this panorama, with the far side of the crater lying about 800 meters (half a mile) away. Bracketing that part of the view are two promontories on the crater's rim at either side of Duck Bay. They are Cape Verde, about 6 meters (20 feet) tall, on the left, and Cabo Frio, about 15 meters (50 feet) tall, on the right. This view combines many images taken by Opportunity's panoramic camera (Pancam) from the Sol 1,332 through 1,379. (Oct. 23 to Dec. 11, 2007).

The Real News about Ophiuchus: There’s a Runaway Star Plowing Through It

by Nancy Atkinson on January 24, 2011

The blue star near the center of this image is Zeta Ophiuchi, a runaway star plowing through the constellation Ophiuchus. Credit: NASA/JPL-Caltech/UCLA

Lots of folks seem to be up in arms about the “new” sign in the zodiac, Ophiuchus, and the news that all the star signs are no longer in sync with the actual constellations. Of course, *most* of us already knew that news is centuries old, and that the zodiac has no effect whatsoever on our lives and it never has (most readers of Universe Today, anyway!) Now for some real news about Ophiuchus: NASA’s Wide-field Infrared Survey Explorer, or WISE has found a massive, runaway star, called Zeta Ophiuchi that is plowing through a cloud of space dust in Ophiuchus. The result is a brilliant bow shock, seen here as a yellow arc in this stunning new image.

Zeta Ophiuchi is a big mama, with a mass of about 20 times that of our sun. In this image, in which infrared light has been translated into visible colors we see with our eyes, the star appears as the blue dot inside the bow shock.

Zeta Ophiuchi once orbited around an even heftier star. But it was a fatal attraction. When that star exploded in a supernova, Zeta Ophiuchi shot away like a bullet. It’s traveling at a whopping 24 kilometers per second (54,000 miles per hour), and heading toward the upper left area of the picture.

As the star tears through space, its powerful winds push gas and dust out of its way and into what is called a bow shock. The material in the bow shock is so compressed that it glows with infrared light that WISE can see. The effect is similar to what happens when a boat speeds through water, pushing a wave in front of it.

This bow shock is completely hidden in visible light. Infrared images like this one from WISE are therefore important for shedding new light on the region.

And that’s the real news from Ophiuchus.

But if you want to know the “real” dates of astrological signs according to astronomers, (not astrologers) here they are (courtesy of Live Science, via Discovery Space — see those two links if you missed all the excitement about star signs changing…):

Capricorn: Jan. 20-Feb. 16.
Aquarius: Feb. 16-March 11.
Pisces: March 11-April 18.
Aries: April 18-May 13.
Taurus: May 13-June 21.
Gemini: June 21-July 20.
Cancer: July 20-Aug. 10.
Leo: Aug. 10-Sept. 16.
Virgo: Sept. 16-Oct. 30.
Libra: Oct. 30-Nov. 23.
Scorpio: Nov. 23-29.
Ophiuchus: Nov. 29-Dec. 17.
Sagittarius: Dec. 17-Jan. 20.

Mars Exploration Rover Mission Status Report

PASADENA, Calif. -- The team operating NASA's Mars rover Opportunity will temporarily suspend commanding for 16 days after the rover's seventh anniversary next week, but the rover will stay busy.

For the fourth time since Opportunity landed on Mars on Jan. 25, 2004, Universal Time (Jan. 24, Pacific Time), the planets' orbits will put Mars almost directly behind the sun from Earth's perspective.

During the days surrounding such an alignment, called a solar conjunction, the sun can disrupt radio transmissions between Earth and Mars. To avoid the chance of a command being corrupted by the sun and harming a spacecraft, NASA temporarily refrains from sending commands from Earth to Mars spacecraft in orbit and on the surface. This year, the commanding moratorium will be Jan. 27 to Feb. 11 for Opportunity, with similar periods for the Mars Reconnaissance Orbiter and Mars Odyssey orbiter.

Downlinks from Mars spacecraft will continue during the conjunction period, though at a much reduced rate. Mars-to-Earth communication does not present risk to spacecraft safety, even if transmissions are corrupted by the sun.

NASA's Mars Reconnaissance Orbiter will scale back its observations of Mars during the conjunction period due to reduced capability to download data to Earth and a limit on how much can be stored onboard.

Opportunity will continue sending data daily to the Odyssey orbiter for relay to Earth. "Overall, we expect to receive a smaller volume of daily data from Opportunity and none at all during the deepest four days of conjunction," said Alfonso Herrera, a rover mission manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The rover team has developed a set of commands to be sent to Opportunity in advance so that the rover can continue science activities during the command moratorium.

"The goal is to characterize the materials in an area that shows up with a mineralogical signal, as seen from orbit, that's different from anywhere else Opportunity has been," said JPL's Bruce Banerdt, project scientist for Opportunity and its rover twin, Spirit. The area is at the southeastern edge of a crater called "Santa Maria," which Opportunity approached from the west last month.

Drives last week brought Opportunity to the position where it will spend the conjunction period. From that position, the rover's robotic arm can reach an outcrop target called "Luis de Torres." The rover's Moessbauer spectrometer will be placed onto the target for several days during the conjunction to assess the types of minerals present. The instrument uses a small amount of radioactive cobalt-57 to elicit information from the target. With a half-life of less than a year, the cobalt has substantially depleted during Opportunity's seven years on Mars, so readings lasting several days are necessary now to be equivalent to much shorter readings when the mission was newer.

Opportunity will also make atmospheric measurements during the conjunction period. After conjunction, it will spend several more days investigating Santa Maria crater before resuming a long-term trek toward Endurance crater, which is about 22 kilometers (14 miles) in diameter and, at its closest edge, about 6 kilometers (4 miles) from Santa Maria.

Opportunity's drives to the southeastern edge of Santa Maria brought the total distance driven by the rover during its seventh year on Mars to 7.4 kilometers (4.6 miles), which is more than in any previous year. The rover's total odometry for its seventh anniversary is 26.7 kilometers (16.6 miles).

Opportunity and Spirit, which landed three weeks apart, successfully completed their three-month prime missions in April 2004, then began years of bonus extended missions. Both have made important discoveries about wet environments on ancient Mars that may have been favorable for supporting microbial life. Spirit's most recent communication was on March 22, 2010. On the possibility that Spirit may yet awaken from a low-power hibernation status, NASA engineers continue to listen for a signal from that rover.

Voyager 2 at Uranus, 25 Years Ago Today

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. Image credit: NASA/JPL

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

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.”