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Brighter Neptune Suggests a Planetary Change of Seasons
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By NASA
6 Min Read NASA’s Webb Captures Neptune’s Auroras For First Time
At the left, an enhanced-color image of Neptune from NASA’s Hubble Space Telescope. At the right, that image is combined with data from NASA’s James Webb Space Telescope. Credits:
NASA, ESA, CSA, STScI, Heidi Hammel (AURA), Henrik Melin (Northumbria University), Leigh Fletcher (University of Leicester), Stefanie Milam (NASA-GSFC) Long-sought auroral glow finally emerges under Webb’s powerful gaze
For the first time, NASA’s James Webb Space Telescope has captured bright auroral activity on Neptune. Auroras occur when energetic particles, often originating from the Sun, become trapped in a planet’s magnetic field and eventually strike the upper atmosphere. The energy released during these collisions creates the signature glow.
In the past, astronomers have seen tantalizing hints of auroral activity on Neptune, for example, in the flyby of NASA’s Voyager 2 in 1989. However, imaging and confirming the auroras on Neptune has long evaded astronomers despite successful detections on Jupiter, Saturn, and Uranus. Neptune was the missing piece of the puzzle when it came to detecting auroras on the giant planets of our solar system.
“Turns out, actually imaging the auroral activity on Neptune was only possible with Webb’s near-infrared sensitivity,” said lead author Henrik Melin of Northumbria University, who conducted the research while at the University of Leicester. “It was so stunning to not just see the auroras, but the detail and clarity of the signature really shocked me.”
The data was obtained in June 2023 using Webb’s Near-Infrared Spectrograph. In addition to the image of the planet, astronomers obtained a spectrum to characterize the composition and measure the temperature of the planet’s upper atmosphere (the ionosphere). For the first time, they found an extremely prominent emission line signifying the presence of the trihydrogen cation (H3+), which can be created in auroras. In the Webb images of Neptune, the glowing aurora appears as splotches represented in cyan.
Image A:
Neptune’s Auroras – Hubble and Webb
At the left, an enhanced-color image of Neptune from NASA’s Hubble Space Telescope. At the right, that image is combined with data from NASA’s James Webb Space Telescope. The cyan splotches, which represent auroral activity, and white clouds, are data from Webb’s Near-Infrared Spectrograph (NIRSpec), overlayed on top of the full image of the planet from Hubble’s Wide Field Camera 3. NASA, ESA, CSA, STScI, Heidi Hammel (AURA), Henrik Melin (Northumbria University), Leigh Fletcher (University of Leicester), Stefanie Milam (NASA-GSFC) “H3+ has a been a clear signifier on all the gas giants — Jupiter, Saturn, and Uranus — of auroral activity, and we expected to see the same on Neptune as we investigated the planet over the years with the best ground-based facilities available,” explained Heidi Hammel of the Association of Universities for Research in Astronomy, Webb interdisciplinary scientist and leader of the Guaranteed Time Observation program for the Solar System in which the data were obtained. “Only with a machine like Webb have we finally gotten that confirmation.”
The auroral activity seen on Neptune is also noticeably different from what we are accustomed to seeing here on Earth, or even Jupiter or Saturn. Instead of being confined to the planet’s northern and southern poles, Neptune’s auroras are located at the planet’s geographic mid-latitudes — think where South America is located on Earth.
This is due to the strange nature of Neptune’s magnetic field, originally discovered by Voyager 2 in 1989 which is tilted by 47 degrees from the planet’s rotation axis. Since auroral activity is based where the magnetic fields converge into the planet’s atmosphere, Neptune’s auroras are far from its rotational poles.
The ground-breaking detection of Neptune’s auroras will help us understand how Neptune’s magnetic field interacts with particles that stream out from the Sun to the distant reaches of our solar system, a totally new window in ice giant atmospheric science.
From the Webb observations, the team also measured the temperature of the top of Neptune’s atmosphere for the first time since Voyager 2’s flyby. The results hint at why Neptune’s auroras remained hidden from astronomers for so long.
“I was astonished — Neptune’s upper atmosphere has cooled by several hundreds of degrees,” Melin said. “In fact, the temperature in 2023 was just over half of that in 1989.”
Through the years, astronomers have predicted the intensity of Neptune’s auroras based on the temperature recorded by Voyager 2. A substantially colder temperature would result in much fainter auroras. This cold temperature is likely the reason that Neptune’s auroras have remained undetected for so long. The dramatic cooling also suggests that this region of the atmosphere can change greatly even though the planet sits over 30 times farther from the Sun compared to Earth.
Equipped with these new findings, astronomers now hope to study Neptune with Webb over a full solar cycle, an 11-year period of activity driven by the Sun’s magnetic field. Results could provide insights into the origin of Neptune’s bizarre magnetic field, and even explain why it’s so tilted.
“As we look ahead and dream of future missions to Uranus and Neptune, we now know how important it will be to have instruments tuned to the wavelengths of infrared light to continue to study the auroras,” added Leigh Fletcher of Leicester University, co-author on the paper. “This observatory has finally opened the window onto this last, previously hidden ionosphere of the giant planets.”
These observations, led by Fletcher, were taken as part of Hammel’s Guaranteed Time Observation program 1249. The team’s results have been published in Nature Astronomy.
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
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Space Telescope Science Institute, Baltimore, Maryland
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Space Telescope Science Institute, Baltimore, Md.
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Henrik Melin (Northumbria University)
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Last Updated Mar 25, 2025 Editor Stephen Sabia Contact Laura Betz laura.e.betz@nasa.gov Related Terms
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By NASA
Rotor Optimization for the Advancement of Mars eXploration (ROAMX) team members and test stand at NASA Ames Research Center.NASA During 2024-2025, helicopter blades optimized for Mars were tested in the Planetary Aeolian Laboratory (PAL) at NASA Ames Research Center as part of the Rotor Optimization for the Advancement of Mars eXploration (ROAMX) project. The experimental test-chamber of the PAL can be depressurized to create atmospheric air pressures of different planetary bodies such as Mars. The full-scale ROAMX blades were spun in hover configuration up to 4000 RPM at an atmospheric density of Mars (approximately 0.015 kilograms per cubic meter). The Ingenuity blades were also tested in the PAL to compare the performance of the optimized blades against the Ingenuity Mars Helicopter Technology Demonstrator. The test was conducted to validate computational models of the performance of the optimized blades. Simulations show that the optimized ROAMX blades perform significantly better than the Ingenuity blades, allowing helicopters on Mars to fly farther, faster, and carry a science payload. The next phase of testing will occur with higher RPMs and additional collective angles.
Rotor Optimization for the Advancement of Mars eXploration (ROAMX) hover test stand with ROAMX blades installed in the Planetary Aeolian Laboratory (PAL) low-pressure chamber at NASA Ames Research Center.NASAView the full article
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By NASA
Credit: NASA NASA has selected SpaceX of Starbase, Texas, to provide launch services for the Near-Earth Object (NEO) Surveyor mission, which will detect and observe asteroids and comets that could potentially pose an impact threat to Earth.
The firm fixed price launch service task order is being awarded under the indefinite delivery/indefinite quantity NASA Launch Services II contract. The total cost to NASA for the launch service is approximately $100 million, which includes the launch service and other mission related costs. The NEO Surveyor mission is targeted to launch no earlier than September 2027 on a SpaceX Falcon 9 rocket from Florida.
The NEO Surveyor mission consists of a single scientific instrument: an almost 20-inch (50-centimeter) diameter telescope that will operate in two heat-sensing infrared wavelengths. It will be capable of detecting both bright and dark asteroids, the latter being the most difficult type to find with existing assets. The space telescope is designed to help advance NASA’s planetary defense efforts to discover and characterize most of the potentially hazardous asteroids and comets that come within 30 million miles of Earth’s orbit. These are collectively known as near-Earth objects, or NEOs.
The mission will carry out a five-year baseline survey to find at least two-thirds of the unknown NEOs larger than 140 meters (460 feet). These are the objects large enough to cause major regional damage in the event of an Earth impact. By using two heat-sensitive infrared imaging channels, the telescope can also make more accurate measurements of the sizes of NEOs and gain information about their composition, shapes, rotational states, and orbits.
The mission is tasked by NASA’s Planetary Science Division within the agency’s Science Mission Directorate at NASA Headquarters in Washington. Program oversight is provided by NASA’s Planetary Defense Coordination Office, which was established in 2016 to manage the agency’s ongoing efforts in planetary defense. NASA’s Planetary Missions Program Office at the agency’s Marshall Space Flight Center in Huntsville, Alabama, provides program management for NEO Surveyor. The project is being developed by NASA’s Jet Propulsion Laboratory in Southern California.
Multiple aerospace and engineering companies are contracted to build the spacecraft and its instrumentation, including BAE Systems SMS (Space & Mission Systems), Space Dynamics Laboratory, and Teledyne. The Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, will support operations, and the Infrared Processing and Analysis Center at the California Institute of Technology (Caltech) in Pasadena, California, is responsible for processing survey data and producing the mission’s data products. Caltech manages JPL for NASA. Mission team leadership includes the University of California, Los Angeles. NASA’s Launch Services Program at the agency’s Kennedy Space Center in Florida is responsible for managing the launch service.
For more information about NEO Surveyor, visit:
https://science.nasa.gov/mission/neo-surveyor/
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Last Updated Feb 21, 2025 LocationNASA Headquarters Related Terms
Kennedy Space Center Launch Services Office Launch Services Program NEO Surveyor (Near-Earth Object Surveyor Space Telescope) Planetary Defense Coordination Office Planetary Science Division Science Mission Directorate Space Operations Mission Directorate View the full article
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By European Space Agency
The European Space Agency (ESA) has endorsed the United Nations' (UN) designation of 2029 as the International Year of Asteroid Awareness and Planetary Defence.
The initiative will foster international collaboration in the field of planetary defence and educate the public on the risks and opportunities associated with near-Earth asteroids.
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By NASA
5 Min Read Planetary Alignments and Planet Parades
A sky chart showing Mars, Jupiter, Saturn, and Venus in a “planet parade.” Credits:
NASA/JPL-Caltech On most nights, weather permitting, you can spot at least one bright planet in the night sky. While two or three planets are commonly visible in the hours around sunset, occasionally four or five bright planets can be seen simultaneously with the naked eye. These events, often called “planet parades” or “planetary alignments,” can generate significant public interest. Though not exceedingly rare, they’re worth observing since they don’t happen every year.
Why Planets Appear Along a Line in The Sky
“Planet parade” isn’t a technical term in astronomy, and “planetary alignment” can refer to several different phenomena. As the planets of our solar system orbit the Sun, they occasionally line up in space in events called oppositions and conjunctions. A planetary alignment can also refer to apparent lineups in our sky with other planets, the Moon, or bright stars.
The planets of our solar system always appear along a line on the sky. This line, referred to as the ecliptic, represents the plane in which the planets orbit, seen from our position within the plane itself. NASA/Preston Dyches When it comes to this second type of planetary alignment, it’s important to understand that planets always appear along a line or arc across the sky. This occurs because the planets orbit our Sun in a relatively flat, disc-shaped plane. From Earth, we’re looking into that solar system plane from within. We see the racetrack of the planets from the perspective of one of the racers ourselves. When viewed edge-on, this disc appears as a line, which we call the ecliptic or ecliptic plane.
So, while planet alignment itself isn’t unusual, what makes these events special is the opportunity to observe multiple planets simultaneously with the naked eye.
Will the Planets Actually be Visible?
Before preparing to observe a planet parade, we have to consider how high the planets will appear above the horizon. For most observers to see a planet with the naked eye, it needs to be at least a few degrees above the horizon, and10 degrees or higher is best. This is crucial because Earth’s atmosphere near the ground dims celestial objects as they rise or set. Even bright planets become difficult or impossible to spot when they’re too low, as their light gets scattered and absorbed on its path to your eye. Buildings, trees, and other obstructions often block the view near the horizon as well.
This visibility challenge is particularly notable after sunset or before sunrise, where the sky is still glowing. If a planet appears very low within the sunset glow, it is very difficult to observe.
The Planets You Can See, and Those You Can’t
Five planets are visible without optical aid: Mercury, Venus, Mars, Jupiter, and Saturn. Ancient civilizations recognized these worlds as bright lights that wandered across the starscape, while the background stars remained fixed in place. In fact, the word “planet” comes to us from the Greek word for “wanderer.”
The solar system includes two additional major planets, Uranus and Neptune, plus numerous dwarf planets like Pluto and Ceres. Uranus and Neptune orbit in the dim, cold depths of the outer solar system. Neptune absolutely requires a telescope to observe. While Uranus is technically bright enough to detect with good eyesight, it’s quite faint and requires dark skies and precise knowledge of its location among similarly faint stars, so a telescope is recommended. As we’ll discuss in the next section, planet parades necessarily must be observed in twilight before dawn or after sunset, and this is not a good time to try observing extremely faint objects like Uranus and Neptune.
Thus, claims about rare six- or seven-planet alignments which include Uranus and Neptune should be viewed with the understanding that these two distant planets will not be visible to the unaided eye.
What Makes Multi-Planet Lineups Special
Lineups of four or five planet naked-eye planets with optimal visibility typically occur every few years. Mars, Jupiter, and Saturn are frequently seen in the night sky, but the addition of Venus and Mercury make four- and five-planet lineups particularly noteworthy. Both orbit closer to the Sun than Earth, with smaller, faster orbits than the other planets. Venus is visible for only a couple of months at a time when it reaches its greatest separation from the Sun (called elongation), appearing just after sunset or before sunrise. Mercury, completing its orbit in just 88 days, is visible for only a couple of weeks (or even a few days) at a time just after sunset or just before sunrise.
Planet parades aren’t single-day events, as the planets move too slowly for that. Generally, multi-planet viewing opportunities last for weeks to a month or more. Even five-planet events last for several days as Mercury briefly emerges from and returns to the Sun’s glare.
In summary, while they aren’t once-in-a-lifetime events, planetary parades afford an uncommon opportunity to look up and appreciate our place in our solar system, with diverse worlds arrayed across the sky before our very eyes.
Other Planet Lineups
Other recent and near-future multi-planet viewing opportunities:
January 2016 – Four planets visible at once before sunrise Late April to Late August 2022 – Four planets visible at once before sunrise Mid-June to Early July 2022 – Five planets visible at once before sunrise January to mid-February 2025 – Four planets visible at once after sunset Late August 2025 – Four planets visible at once before sunrise Late October 2028 – Five planets visible at once before sunrise Late February 2034 – Five planets visible at once after sunset (Venus and Mercury challenging to observe) About the January/February 2025 Planet Parade
The current four-planet lineup concludes by mid-February, as Saturn sinks increasingly lower in the sky each night after sunset. By mid-to-late February, Saturn appears less than 10 degrees above the horizon as sunset fades, making it difficult to observe for most people. While Mercury briefly joins Saturn in the post-sunset glow at the end of February, both planets will be too low and faint for most observers to spot.
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