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By NASA
An unexpectedly strong solar storm rocked our planet on April 23, 2023, sparking auroras as far south as southern Texas in the U.S. and taking the world by surprise.
Two days earlier, the Sun blasted a coronal mass ejection (CME) — a cloud of energetic particles, magnetic fields, and solar material — toward Earth. Space scientists took notice, expecting it could cause disruptions to Earth’s magnetic field, known as a geomagnetic storm. But the CME wasn’t especially fast or massive, and it was preceded by a relatively weak solar flare, suggesting the storm would be minor. But it became severe.
Using NASA heliophysics missions, new studies of this storm and others are helping scientists learn why some CMEs have more intense effects — and better predict the impacts of future solar eruptions on our lives.
During the night of April 23 to 24, 2023, a geomagnetic storm produced auroras that were witnessed as far south as Arizona, Arkansas, and Texas in the U.S. This photo shows green aurora shimmering over Larimore, North Dakota, in the early morning of April 24. Copyright Elan Azriel, used with permission Why Was This Storm So Intense?
A paper published in the Astrophysical Journal on March 31 suggests the CME’s orientation relative to Earth likely caused the April 2023 storm to become surprisingly strong.
The researchers gathered observations from five heliophysics spacecraft across the inner solar system to study the CME in detail as it emerged from the Sun and traveled to Earth.
They noticed a large coronal hole near the CME’s birthplace. Coronal holes are areas where the solar wind — a stream of particles flowing from the Sun — floods outward at higher than normal speeds.
“The fast solar wind coming from this coronal hole acted like an air current, nudging the CME away from its original straight-line path and pushing it closer to Earth’s orbital plane,” said the paper’s lead author, Evangelos Paouris of the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. “In addition to this deflection, the CME also rotated slightly.”
Paouris says this turned the CME’s magnetic fields opposite to Earth’s magnetic field and held them there — allowing more of the Sun’s energy to pour into Earth’s environment and intensifying the storm.
The strength of the April 2023 geomagnetic storm was a surprise in part because the coronal mass ejection (CME) that produced it followed a relatively weak solar flare, seen as the bright area to the lower right of center in this extreme ultraviolet image of the Sun from NASA’s Solar Dynamics Observatory. The CMEs that produce severe geomagnetic storms are typically preceded by stronger flares. However, a team of scientists think fast solar wind from a coronal hole (the dark area below the flare in this image) helped rotate the CME and made it more potent when it struck Earth. NASA/SDO Cool Thermosphere
Meanwhile, NASA’s GOLD (Global-scale Observations of Limb and Disk) mission revealed another unexpected consequence of the April 2023 storm at Earth.
Before, during, and after the storm, GOLD studied the temperature in the middle thermosphere, a part of Earth’s upper atmosphere about 85 to 120 miles overhead. During the storm, temperatures increased throughout GOLD’s wide field of view over the Americas. But surprisingly, after the storm, temperatures dropped about 90 to 198 degrees Fahrenheit lower than they were before the storm (from about 980 to 1,070 degrees Fahrenheit before the storm to 870 to 980 degrees Fahrenheit afterward).
“Our measurement is the first to show widespread cooling in the middle thermosphere after a strong storm,” said Xuguang Cai of the University of Colorado, Boulder, lead author of a paper about GOLD’s observations published in the journal JGR Space Physics on April 15, 2025.
The thermosphere’s temperature is important, because it affects how much drag Earth-orbiting satellites and space debris experience.
“When the thermosphere cools, it contracts and becomes less dense at satellite altitudes, reducing drag,” Cai said. “This can cause satellites and space debris to stay in orbit longer than expected, increasing the risk of collisions. Understanding how geomagnetic storms and solar activity affect Earth’s upper atmosphere helps protect technologies we all rely on — like GPS, satellites, and radio communications.”
Predicting When Storms Strike
To predict when a CME will trigger a geomagnetic storm, or be “geoeffective,” some scientists are combining observations with machine learning. A paper published last November in the journal Solar Physics describes one such approach called GeoCME.
Machine learning is a type of artificial intelligence in which a computer algorithm learns from data to identify patterns, then uses those patterns to make decisions or predictions.
Scientists trained GeoCME by giving it images from the NASA/ESA (European Space Agency) SOHO (Solar and Heliospheric Observatory) spacecraft of different CMEs that reached Earth along with SOHO images of the Sun before, during, and after each CME. They then told the model whether each CME produced a geomagnetic storm.
Then, when it was given images from three different science instruments on SOHO, the model’s predictions were highly accurate. Out of 21 geoeffective CMEs, the model correctly predicted all 21 of them; of 7 non-geoeffective ones, it correctly predicted 5 of them.
“The algorithm shows promise,” said heliophysicist Jack Ireland of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in the study. “Understanding if a CME will be geoeffective or not can help us protect infrastructure in space and technological systems on Earth. This paper shows machine learning approaches to predicting geoeffective CMEs are feasible.”
The white cloud expanding outward in this image sequence is a coronal mass ejection (CME) that erupted from the Sun on April 21, 2023. Two days later, the CME struck Earth and produced a surprisingly strong geomagnetic storm. The images in this sequence are from a coronagraph on the NASA/ESA (European Space Agency) SOHO (Solar and Heliospheric Observatory) spacecraft. The coronagraph uses a disk to cover the Sun and reveal fainter details around it. The Sun’s location and size are indicated by a small white circle. The planet Jupiter appears as a bright dot on the far right. NASA/ESA/SOHO Earlier Warnings
During a severe geomagnetic storm in May 2024 — the strongest to rattle Earth in over 20 years — NASA’s STEREO (Solar Terrestrial Relations Observatory) measured the magnetic field structure of CMEs as they passed by.
When a CME headed for Earth hits a spacecraft first, that spacecraft can often measure the CME and its magnetic field directly, helping scientists determine how strong the geomagnetic storm will be at Earth. Typically, the first spacecraft to get hit are one million miles from Earth toward the Sun at a place called Lagrange Point 1 (L1), giving us only 10 to 60 minutes advanced warning.
By chance, during the May 2024 storm, when several CMEs erupted from the Sun and merged on their way to Earth, NASA’s STEREO-A spacecraft happened to be between us and the Sun, about 4 million miles closer to the Sun than L1.
A paper published March 17, 2025, in the journal Space Weather reports that if STEREO-A had served as a CME sentinel, it could have provided an accurate prediction of the resulting storm’s strength 2 hours and 34 minutes earlier than a spacecraft could at L1.
According to the paper’s lead author, Eva Weiler of the Austrian Space Weather Office in Graz, “No other Earth-directed superstorm has ever been observed by a spacecraft positioned closer to the Sun than L1.”
Earth’s Lagrange points are places in space where the gravitational pull between the Sun and Earth balance, making them relatively stable locations to put spacecraft. NASA By Vanessa Thomas
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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By NASA
6 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
NASA Ames research scientist Kristina Pistone monitors instrument data while onboard the Twin Otter aircraft, flying over Monterey Bay during the October 2024 deployment of the AirSHARP campaign. NASA/Samuel Leblanc In autumn 2024, California’s Monterey Bay experienced an outsized phytoplankton bloom that attracted fish, dolphins, whales, seabirds, and – for a few weeks in October – scientists. A team from NASA’s Ames Research Center in Silicon Valley, with partners at the University of California, Santa Cruz (UCSC), and the Naval Postgraduate School, spent two weeks on the California coast gathering data on the atmosphere and the ocean to verify what satellites see from above. In spring 2025, the team returned to gather data under different environmental conditions.
Scientists call this process validation.
Setting up the Campaign
The PACE mission, which stands for Plankton, Aerosol, Cloud, ocean Ecosystem, was launched in February 2024 and designed to transform our understanding of ocean and atmospheric environments. Specifically, the satellite will give scientists a finely detailed look at life near the ocean surface and the composition and abundance of aerosol particles in the atmosphere.
Whenever NASA launches a new satellite, it sends validation science teams around the world to confirm that the data from instruments in space match what traditional instruments can see at the surface. AirSHARP (Airborne aSsessment of Hyperspectral Aerosol optical depth and water-leaving Reflectance Product Performance for PACE) is one of these teams, specifically deployed to validate products from the satellite’s Ocean Color Instrument (OCI).
The OCI spectrometer works by measuring reflected sunlight. As sunlight bounces off of the ocean’s surface, it creates specific shades of color that researchers use to determine what is in the water column below. To validate the OCI data, research teams need to confirm that measurements directly at the surface match those from the satellite. They also need to understand how the atmosphere is changing the color of the ocean as the reflected light is traveling back to the satellite.
In October 2024 and May 2025, the AirSHARP team ran simultaneous airborne and seaborne campaigns. Going into the field during different seasons allows the team to collect data under different environmental conditions, validating as much of the instrument’s range as possible.
Over 13 days of flights on a Twin Otter aircraft, the NASA-led team used instruments called 4STAR-B (Spectrometer for sky-scanning sun Tracking Atmospheric Research B), and the C-AIR (Coastal Airborne In-situ Radiometer) to gather data from the air. At the same time, partners from UCSC used a host of matching instruments onboard the research vessel R/V Shana Rae to gather data from the water’s surface.
Ocean Color and Water Leaving Reflectance
The Ocean Color Instrument measures something called water leaving reflectance, which provides information on the microscopic composition of the water column, including water molecules, phytoplankton, and particulates like sand, inorganic materials, and even bubbles. Ocean color varies based on how these materials absorb and scatter sunlight. This is especially useful for determining the abundance and types of phytoplankton.
Photographs taken out the window of the Twin Otter aircraft during the October 2024 AirSHARP deployment showcase the variation in ocean color, which indicates different molecular composition of the water column beneath. The red color in several of these photos is due to a phytoplankton bloom – in this case a growth of red algae. NASA/Samuel Leblanc
The AirSHARP team used radiometers with matching technology – C-AIR from the air and C-OPS (Compact Optical Profiling System) from the water – to gather water leaving reflectance data.
“The C-AIR instrument is modified from an instrument that goes on research vessels and takes measurements of the water’s surface from very close range,” said NASA Ames research scientist Samuel LeBlanc. “The issue there is that you’re very local to one area at a time. What our team has done successfully is put it on an aircraft, which enables us to span the entire Monterey Bay.”
The larger PACE validation team will compare OCI measurements with observations made by the sensors much closer to the ocean to ensure that they match, and make adjustments when they don’t.
Aerosol Interference
One factor that can impact OCI data is the presence of manmade and natural aerosols, which interact with sunlight as it moves through the atmosphere. An aerosol refers to any solid or liquid suspended in the air, such as smoke from fires, salt from sea spray, particulates from fossil fuel emissions, desert dust, and pollen.
Imagine a 420 mile-long tube, with the PACE satellite at one end and the ocean at the other. Everything inside the tube is what scientists refer to as the atmospheric column, and it is full of tiny particulates that interact with sunlight. Scientists quantify this aerosol interaction with a measurement called aerosol optical depth.
“During AirSHARP, we were essentially measuring, at different wavelengths, how light is changed by the particles present in the atmosphere,” said NASA Ames research scientist Kristina Pistone. “The aerosol optical depth is a measure of light extinction, or how much light is either scattered away or absorbed by aerosol particulates.”
The team measured aerosol optical depth using the 4STAR-B spectrometer, which was engineered at NASA Ames and enables scientists to identify which aerosols are present and how they interact with sunlight.
Twin Otter Aircraft
AirSHARP principal investigator Liane Guild walks towards a Twin Otter aircraft owned and operated by the Naval Postgraduate School. The aircraft’s ability to perform complex, low-altitude flights made it the ideal platform to fly multiple instruments over Monterey Bay during the AirSHARP campaign. NASA/Samuel Leblanc
Flying these instruments required use of a Twin Otter plane, operated by the Naval Postgraduate School (NPS). The Twin Otter is unique for its ability to perform extremely low-altitude flights, making passes down to 100 feet above the water in clear conditions.
“It’s an intense way to fly. At that low height, the pilots continually watch for and avoid birds, tall ships, and even wildlife like breaching whales,” said Anthony Bucholtz, director of the Airborne Research Facility at NPS.
With the phytoplankton bloom attracting so much wildlife in a bay already full of ships, this is no small feat. “The pilots keep a close eye on the radar, and fly by hand,” Bucholtz said, “all while following careful flight plans crisscrossing Monterey Bay and performing tight spirals over the Research Vessel Shana Rae.”
Campaign Data
Data gathered from the 2024 phase of this campaign is available on two data archive systems. Data from the 4STAR instrument is available in the PACE data archive and data from C-AIR is housed in the SeaBASS data archive.
Other data from the NASA PACE Validation Science Team is available through the PACE website: https://pace.oceansciences.org/pvstdoi.htm#
Samuel LeBlanc and Kristina Pistone are funded via the Bay Area Environmental Research Institute (BAERI), which is a scientist-founded nonprofit focused on supporting Earth and space sciences.
About the Author
Milan Loiacono
Science Communication SpecialistMilan Loiacono is a science communication specialist for the Earth Science Division at NASA Ames Research Center.
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Last Updated Jun 26, 2025 Related Terms
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Preparations for Next Moonwalk Simulations Underway (and Underwater)
With Voyager 2 in the background, John Casani holds a small U.S. flag that was sewn into the spacecraft’s thermal blankets before its 1977 launch. Then Voyager’s project manager, Casani was first to envision the mission’s Golden Record, which lies before him with its cover at right. NASA/JPL-Caltech During his work on several historic missions, Casani rose through a series of technical and management positions, making an indelible mark on the nation’s space program.
John R. Casani, a visionary engineer who served a central role in many of NASA’s historic deep space missions, died on Thursday, June 19, 2025, at the age of 92. He was preceded in death by his wife of 39 years, Lynn Casani, in 2008 and is survived by five sons and their families.
Casani started at the Jet Propulsion Laboratory in Southern California in 1956 and went on to work as an electronics engineer on some of the nation’s earliest spacecraft after NASA’s formation in 1958. Along with leading the design teams for both the Ranger and Mariner series of spacecraft, he held senior project positions on many of the Mariner missions to Mars and Venus, and was project manager for three trailblazing space missions: Voyager, Galileo, and Cassini.
His work helped advance NASA spacecraft in areas including mechanical technology, system design and integration, software, and deep space communications. No less demanding were the management challenges of these multifaceted missions, which led to innovations still in use today.
JPL’s John Casani receives the National Air & Space Museum’s Lifetime Achievement Award.Carolyn Russo/NASM, National Air and Space Museum, Smithsonian Institution “John had a major influence on the development of spacecraft that visited almost every planet in our solar system, as well as the people who helped build them,” said JPL director Dave Gallagher. “He played an essential role in America’s first attempts to reach space and then the Moon, and he was just as crucial to the Voyager spacecraft that marked humanity’s first foray into interplanetary — and later, interstellar — space. That Voyager is still exploring after nearly 50 years is a testament to John’s remarkable engineering talent and his leadership that enabled others to push the boundaries of possibility.”
Born in Philadelphia in 1932, Casani studied electrical engineering at the University of Pennsylvania. After a short stint at an Air Force research lab, he moved to California in 1956 and was hired to work at JPL, a division of Caltech, on the guidance system for the U.S. Army Ballistic Missile Agency’s Jupiter-C and Sergeant missile programs.
In 1957, the Soviet Union launched Sputnik 1, the first human-made Earth satellite, alarming America and changing the trajectory of both JPL and Casani’s career. With the 1958 launch of Explorer 1, America’s first satellite, the lab transitioned to concentrating on robotic space explorers, and Casani segued from missiles to spacecraft.
One of his jobs as payload engineer on Pioneer 3 and 4, NASA’s first missions to the Moon, was to carry each of the 20-inch-long (51-cm-long) probes in a suitcase from JPL to the launch site at Cape Canaveral, Florida, where he installed them in the rocket’s nose cone.
At the dawn of the 1960s, Casani served as spacecraft systems engineer for the agency’s first two Ranger missions to the Moon, then joined the Mariner project in 1965, earning a reputation for being meticulous. Four years later, he was Mariner project manager.
Asked to share some of his wisdom in a 2009 NASA presentation, Casani said, “The thing that makes any of this work … is toughness. Toughness because this is a tough business, and it’s a very unforgiving business. You can do 1,000 things right, but if you don’t do everything right, it’ll come back and bite you.”
Casani’s next role: project manager for NASA’s high-profile flagship mission to the outer planets and beyond — Voyager. He not only led the mission from clean room to space, he was first to envision attaching a message representing humanity to any alien civilization that might encounter humanity’s first interstellar emissaries.
“I approached Carl Sagan,” he said in a 2007 radio interview, “and asked him if he could come up with something that would be appropriate that we could put on our spacecraft in a way of sending a message to whoever might receive it.” Sagan took up the challenge, and what resulted was the Golden Record, a 12-inch gold-plated copper disk containing sounds and images selected to portray the diversity of life and culture on Earth.
Once Voyager 1 and 2 and their Golden Records launched in 1977, JPL wasted no time in pointing their “engineer’s engineer” toward Galileo, which would become the first mission to orbit a gas giant planet. As the mission’s initial project manager, Casani led the effort from inception to assembly. Along the way, he had to navigate several congressional attempts to end the project, necessitating multiple visits to Washington. The 1986 loss of Space Shuttle Challenger, from which Galileo was to launch atop a Centaur upper-stage booster, led to mission redesign efforts before its 1989 launch.
After 11 years leading Galileo, Casani became deputy assistant laboratory director for flight projects in 1988, received a promotion just over a year later and then, from 1990 to 1991, served as project manager of Cassini, NASA’s first flagship mission to orbit Saturn.
Casani became JPL’s first chief engineer in 1994, retiring in 1999 and serving on several nationally prominent committees, including leading the investigation boards of both the Mars Climate Orbiter and the Mars Polar Lander failures, and also leading the James Webb Space Telescope Independent Comprehensive Review Panel.
In early 2003, Casani returned to JPL to serve as project manager for NASA’s Project Prometheus, which would have been the nation’s first nuclear-powered, electric-propulsion spacecraft. In 2005, he became manager of the Institutional Special Projects Office at JPL, a position he held until retiring again in 2012.
“Throughout his career, John reflected the true spirit of JPL: bold, innovative, visionary, and welcoming,” said Charles Elachi, JPL’s director from 2001 to 2016. “He was an undisputed leader with an upbeat, fun attitude and left an indelible mark on the laboratory and NASA. I am proud to have called him a friend.”
Casani received many awards over his lifetime, including NASA’s Exceptional Achievement Medal, the Management Improvement Award from the President of the United States for the Mariner Venus Mercury mission, and the Air and Space Museum Trophy for Lifetime Achievement.
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Last Updated Jun 25, 2025 Related Terms
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