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By NASA
Explore This Section Overview Science Science Findings Juno’s Orbits Spacecraft People Stories Multimedia JunoCam Images Jupiter hosts the brightest and most spectacular auroras in the Solar System. Near its poles, these shimmering lights offer a glimpse into how the planet interacts with the solar wind and moons swept by Jupiter’s magnetic field. Unlike Earth’s northern lights, the largest moons of Jupiter create their own auroral signatures in the planet’s atmosphere — a phenomenon that Earth’s Moon does not produce. These moon-induced auroras, known as “satellite footprints,” reveal how each moon interacts with its local space environment.
Juno capturing the marks on Jupiter of all four Galilean moons. The auroras related to each are labeled Io, Eur (for Europa), Gan (for Ganymede), and Cal (for Callisto). NASA/JPL-Caltech/SwRI/UVS team/MSSS/Gill/Jónsson/Perry/Hue/Rabia Before NASA’s Juno mission, three of Jupiter’s four largest moons, known as Galilean moons — Io, Europa, and Ganymede — were shown to produce these distinct auroral signatures. But Callisto, the most distant of the Galilean moons, remained a mystery. Despite multiple attempts using NASA’s Hubble Space Telescope, Callisto’s footprint had proven elusive, both because it is faint and because it most often lies atop the brighter main auroral oval, the region where auroras are displayed.
NASA’s Juno mission, orbiting Jupiter since 2016, offers unprecedented close-up views of these polar light shows. But to image Callisto’s footprint, the main auroral oval needs to move aside while the polar region is being imaged. And to bring to bear Juno’s arsenal of instruments studying fields and particles, the spacecraft’s trajectory must carry it across the magnetic field line linking Callisto and Jupiter.
These two events serendipitously occurred during Juno’s 22nd orbit of the giant planet, in September 2019, revealing Callisto’s auroral footprint and providing a sample of the particle population, electromagnetic waves, and magnetic fields associated with the interaction.
Jupiter’s magnetic field extends far beyond its major moons, carving out a vast region (magnetosphere) enveloped by, and buffeted by, the solar wind streaming from our Sun. Just as solar storms on Earth push the northern lights to more southern latitudes, Jupiter’s auroras are also affected by our Sun’s activity. In September 2019, a massive, high-density solar stream buffeted Jupiter’s magnetosphere, briefly revealing — as the auroral oval moved toward Jupiter’s equator — a faint but distinct signature associated with Callisto. This discovery finally confirms that all four Galilean moons leave their mark on Jupiter’s atmosphere, and that Callisto’s footprints are sustained much like those of its siblings, completing the family portrait of the Galilean moon auroral signatures.
An international team of scientists led by Jonas Rabia of the Institut de Recherche en Astrophysique et Planétologie (IRAP), CNRS, CNES, in Toulouse, France, published their paper on the discovery, “In situ and remote observations of the ultraviolet footprint of the moon Callisto by the Juno spacecraft,” in the journal Nature Communications on Sept. 1, 2025.
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Last Updated Sep 02, 2025 Related Terms
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By NASA
Explore This Section Perseverance Home Mission Overview Rover Components Mars Rock Samples Where is Perseverance? Ingenuity Mars Helicopter Mission Updates Science Overview Objectives Instruments Highlights Exploration Goals News and Features Multimedia Perseverance Raw Images Images Videos Audio More Resources Mars Missions Mars Sample Return Mars Perseverance Rover Mars Curiosity Rover MAVEN Mars Reconnaissance Orbiter Mars Odyssey More Mars Missions Mars Home 3 min read
To See the World in a Grain of Sand: Investigating Megaripples at ‘Kerrlaguna’
NASA’s Mars Perseverance rover acquired this image of inactive megaripples at “Kerrlaguna,” Perseverance’s latest target of exploration, on Aug. 13, 2025. The rover acquired the image using its Right Mastcam-Z camera, one of a pair of cameras located high on the rover’s mast, on Sol 1593 — or, Martian day 1,593 of the Mars 2020 mission — at the local mean solar time of 12:05:13. NASA/JPL-Caltech/ASU Written by Athanasios Klidaras, Ph.D. candidate at Purdue University
On Mars, the past is written in stone — but the present is written in sand. Last week, Perseverance explored inactive megaripples to learn more about the wind-driven processes that are reshaping the Martian landscape every day.
After wrapping up its investigation at the contact between clay and olivine-bearing rocks at “Westport,” Perseverance is journeying south once more. Previously, attempts were made to drive uphill to visit a new rock exposure called “Midtoya.” However, a combination of the steep slope and rubbly, rock-strewn soil made drive progress difficult, and after several attempts, the decision was made to return to smoother terrain. Thankfully, the effort wasn’t fruitless, as the rover was able to gather data on new spherule-rich rocks thought to have rolled downhill from “Midtoya,” including the witch hat or helmet-shaped rock “Horneflya,” which has attracted much online interest.
More recently, Perseverance explored a site called “Kerrlaguna” where the steep slopes give way to a field of megaripples: large windblown sand formations up to 1 meter (about 3 feet) tall. The science team chose to perform a mini-campaign to make a detailed study of these features. Why such interest? While often the rover’s attention is focused on studying processes in Mars’ distant past that are recorded in ancient rocks, we still have much to learn about the modern Martian environment.
Almost a decade ago, Perseverance’s forerunner Curiosity studied an active sand dune at “Namib Dune” on the floor of Gale crater, where it took a memorable selfie. However the smaller megaripples — and especially dusty, apparently no longer active ones like at “Kerrlaguna” — are also common across the surface of Mars. These older immobile features could teach us new insights about the role that wind and water play on the modern Martian surface.
After arriving near several of these inactive megaripples, Perseverance performed a series of measurements using its SuperCam, Mastcam-Z, and MEDA science instruments in order to characterize the surrounding environment, the size and chemistry of the sand grains, and any salty crusts that may have developed over time.
Besides furthering our understanding of the Martian environment, documenting these potential resources could help us prepare for the day when astronauts explore the Red Planet and need resources held within Martian soils to help them survive. It is hoped that this investigation at “Kerrlaguna” can provide a practice run for a more comprehensive campaign located at a more extensive field of larger bedforms at “Lac de Charmes,” further along the rover traverse.
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Last Updated Aug 21, 2025 Related Terms
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By European Space Agency
The exoplanet TRAPPIST-1 d intrigues astronomers looking for possibly habitable worlds beyond our solar system because it is similar in size to Earth, rocky, and resides in an area around its star where liquid water on its surface is theoretically possible. But according to a new study using data from the NASA/ESA/CSA James Webb Space Telescope, it does not have an Earth-like atmosphere.
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By NASA
4 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Ocean currents swirl around North America (center left) and Greenland (upper right) in this data visualization created using NASA’s ECCO model. Advanced computing is helping oceanographers decipher hot spots of phytoplankton growth.NASA’s Scientific Visualization Studio As Greenland’s ice retreats, it’s fueling tiny ocean organisms. To test why, scientists turned to a computer model out of JPL and MIT that’s been called a laboratory in itself.
Runoff from Greenland’s ice sheet is kicking nutrients up from the ocean depths and boosting phytoplankton growth, a new NASA-supported study has found. Reporting in Nature Communications: Earth & Environment, the scientists used state-of-the art-computing to simulate marine life and physics colliding in one turbulent fjord. Oceanographers are keen to understand what drives the tiny plantlike organisms, which take up carbon dioxide and power the world’s fisheries.
Greenland’s mile-thick ice sheet is shedding some 293 billion tons (266 billion metric tons) of ice per year. During peak summer melt, more than 300,000 gallons (1,200 cubic meters) of fresh water drain into the sea every second from beneath Jakobshavn Glacier, also known as Sermeq Kujalleq,the most active glacier on the ice sheet. The waters meet and tumble hundreds of feet below the surface.
Teal-colored phytoplankton bloom off the Greenland coast in this satellite image captured in June 2024 by NASA’s PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) mission.NASA The meltwater plume is fresh and more buoyant than the surrounding saltwater. As it rises, scientists have hypothesized, it may be delivering nutrients like iron and nitrate — a key ingredient in fertilizer — to phytoplankton floating at the surface.
Researchers track these microscopic organisms because, though smaller by far than a pinhead, they’re titans of the ocean food web. Inhabiting every ocean from the tropics to the polar regions, they nourish krill and other grazers that, in turn, support larger animals, including fish and whales.
Previous work using NASA satellite data found that the rate of phytoplankton growth in Arctic waters surged 57% between 1998 and 2018 alone. An infusion of nitrate from the depths would be especially pivotal to Greenland’s phytoplankton in summer, after most nutrients been consumed by prior spring blooms. But the hypothesis has been hard to test along the coast, where the remote terrain and icebergs as big as city blocks complicate long-term observations.
“We were faced with this classic problem of trying to understand a system that is so remote and buried beneath ice,” said Dustin Carroll, an oceanographer at San José State University who is also affiliated with NASA’s Jet Propulsion Laboratory in Southern California. “We needed a gem of a computer model to help.”
Sea of Data
To re-create what was happening in the waters around Greenland’s most active glacier, the team harnessed a model of the ocean developed at JPL and the Massachusetts Institute of Technology in Cambridge. The model ingests nearly all available ocean measurements collected by sea- and satellite-based instruments over the past three decades. That amounts to billions of data points, from water temperature and salinity to pressure at the seafloor. The model is called Estimating the Circulation and Climate of the Ocean-Darwin (ECCO-Darwin for short).
Simulating “biology, chemistry, and physics coming together” in even one pocket along Greenland’s 27,000 miles (43,000 kilometers) of coastline is a massive math problem, noted lead author Michael Wood, a computational oceanographer at San José State University. To break it down, he said the team built a “model within a model within a model” to zoom in on the details of the fjord at the foot of the glacier.
Using supercomputers at NASA’s Ames Research Center in Silicon Valley, they calculated that deepwater nutrients buoyed upward by glacial runoff would be sufficient to boost summertime phytoplankton growth by 15 to 40% in the study area.
More Changes in Store
Could increased phytoplankton be a boon for Greenland’s marine animals and fisheries? Carroll said that untangling impacts to the ecosystem will take time. Melt on the Greenland ice sheet is projected to accelerate in coming decades, affecting everything from sea level and land vegetation to the saltiness of coastal waters.
“We reconstructed what’s happening in one key system, but there’s more than 250 such glaciers around Greenland,” Carroll said. He noted that the team plans to extend their simulations to the whole Greenland coast and beyond.
Some changes appear to be impacting the carbon cycle both positively and negatively: The team calculated how runoff from the glacier alters the temperature and chemistry of seawater in the fjord, making it less able to dissolve carbon dioxide. That loss is canceled out, however, by the bigger blooms of phytoplankton taking up more carbon dioxide from the air as they photosynthesize.
Wood added: “We didn’t build these tools for one specific application. Our approach is applicable to any region, from the Texas Gulf to Alaska. Like a Swiss Army knife, we can apply it to lots of different scenarios.”
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Jane J. Lee / Andrew Wang
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Written by Sally Younger
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Last Updated Aug 06, 2025 Related Terms
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By NASA
5 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
The north polar region of Jupiter’s volcanic moon Io was captured by the JunoCam imager aboard NASA’s Juno during the spacecraft’s 57th close pass of the gas giant on Dec. 30, 2023. A technique called annealing was used to help repair radiation damage to the camera in time to capture this image. Image data: NASA/JPL-Caltech/SwRI/MSSS Image processing by Gerald Eichstädt An experimental technique rescued a camera aboard the agency’s Juno spacecraft, offering lessons that will benefit other space systems that experience high radiation.
The mission team of NASA’s Jupiter-orbiting Juno spacecraft executed a deep-space move in December 2023 to repair its JunoCam imager to capture photos of the Jovian moon Io. Results from the long-distance save were presented during a technical session on July 16 at the Institute of Electrical and Electronics Engineers Nuclear & Space Radiation Effects Conference in Nashville.
JunoCam is a color, visible-light camera. The optical unit for the camera is located outside a titanium-walled radiation vault, which protects sensitive electronic components for many of Juno’s engineering and science instruments.
This is a challenging location because Juno’s travels carry it through the most intense planetary radiation fields in the solar system. While mission designers were confident JunoCam could operate through the first eight orbits of Jupiter, no one knew how long the instrument would last after that.
Throughout Juno’s first 34 orbits (its prime mission), JunoCam operated normally, returning images the team routinely incorporated into the mission’s science papers. Then, during its 47th orbit, the imager began showing hints of radiation damage. By orbit 56, nearly all the images were corrupted.
The graininess and horizontal lines seen in this JunoCam image show evidence that the camera aboard NASA’s Juno mission suffered radiation damage. The image, which captures one of the circumpolar cyclones on Jupiter’s north pole, was taken Nov. 22, 2023. NASA/JPL-Caltech/SwRI/MSSS Long Distance Microscopic Repair
While the team knew the issue may be tied to radiation, pinpointing what, specifically, was damaged within JunoCam was difficult from hundreds of millions of miles away. Clues pointed to a damaged voltage regulator that is vital to JunoCam’s power supply. With few options for recovery, the team turned to a process called annealing, where a material is heated for a specified period before slowly cooling. Although the process is not well understood, the idea is that the heating can reduce defects in the material.
“We knew annealing can sometimes alter a material like silicon at a microscopic level but didn’t know if this would fix the damage,” said JunoCam imaging engineer Jacob Schaffner of Malin Space Science Systems in San Diego, which designed and developed JunoCam and is part of the team that operates it. “We commanded JunoCam’s one heater to raise the camera’s temperature to 77 degrees Fahrenheit — much warmer than typical for JunoCam — and waited with bated breath to see the results.”
Soon after the annealing process finished, JunoCam began cranking out crisp images for the next several orbits. But Juno was flying deeper and deeper into the heart of Jupiter’s radiation fields with each pass. By orbit 55, the imagery had again begun showing problems.
“After orbit 55, our images were full of streaks and noise,” said JunoCam instrument lead Michael Ravine of Malin Space Science Systems. “We tried different schemes for processing the images to improve the quality, but nothing worked. With the close encounter of Io bearing down on us in a few weeks, it was Hail Mary time: The only thing left we hadn’t tried was to crank JunoCam’s heater all the way up and see if more extreme annealing would save us.”
Test images sent back to Earth during the annealing showed little improvement the first week. Then, with the close approach of Io only days away, the images began to improve dramatically. By the time Juno came within 930 miles (1,500 kilometers) of the volcanic moon’s surface on Dec. 30, 2023, the images were almost as good as the day the camera launched, capturing detailed views of Io’s north polar region that revealed mountain blocks covered in sulfur dioxide frosts rising sharply from the plains and previously uncharted volcanos with extensive flow fields of lava.
Testing Limits
To date, the solar-powered spacecraft has orbited Jupiter 74 times. Recently, the image noise returned during Juno’s 74th orbit.
Since first experimenting with JunoCam, the Juno team has applied derivations of this annealing technique on several Juno instruments and engineering subsystems.
“Juno is teaching us how to create and maintain spacecraft tolerant to radiation, providing insights that will benefit satellites in orbit around Earth,” said Scott Bolton, Juno’s principal investigator from the Southwest Research Institute in San Antonio. “I expect the lessons learned from Juno will be applicable to both defense and commercial satellites as well as other NASA missions.”
More About Juno
NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. The Italian Space Agency, Agenzia Spaziale Italiana, funded the Jovian InfraRed Auroral Mapper. Lockheed Martin Space in Denver built and operates the spacecraft. Various other institutions around the U.S. provided several of the other scientific instruments on Juno.
More information about Juno is at:
https://www.nasa.gov/juno
News Media Contact
DC Agle
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Karen Fox / Molly Wasser
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Deb Schmid
Southwest Research Institute, San Antonio
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Last Updated Jul 21, 2025 Related Terms
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