This stereoscopic visualization shows a simple model of the earth’s magnetic field. The magnetic field partially protects the Earth from harmful charging particles coming from the sun. Credit: NASA’s Goddard Space Flight Center
A small but evolving area in the Earth’s magnetic field can cause major headaches for satellites.
The Earth’s magnetic field acts as a protective shield around the planet, repelling and trapping charged particles from the sun. But across South America and the South Atlantic, an unusually weak spot in the field – the South Atlantic Anomaly, or SAA – causes these particles to dip closer to the surface than normal. Particular radiation in this region can strike on board computers and interfere with the data collection of satellites passing through it – an important reason why NASA scientists want to track and study the anomaly.
The South Atlantic Anomaly is also of interest to NASA Earth scientists who monitor the changes in magnetic field strength, both for how such changes affect the Earth’s atmosphere and as an indicator of what is happening. magnetic fields of the earth, deep in the world.
At present, the SAA does not create any visible impact on daily life on the surface. Recent observations and forecasts, however, show that the region is expanding to the west and continues to weaken in intensity. It is also split – recent data shows the fall of the anomaly, as region of minimum field strength, is split into two lobes, creating additional challenges for satellite missions.
A host of NASA scientists in geomagnetic, geophysics and heliophysics research groups observe and model the SAA, to monitor and predict future changes – and to help prepare for future challenges for satellites and humans in space.
The Earth’s magnetic field acts as a protective shield around the planet, repelling and trapping charged particles from the sun. But across South America and the South Atlantic, an unusually weak spot in the field – the South Atlantic Anomaly, or SAA – causes these particles to dip closer to the surface than normal. At present, the SAA does not create any visible impact on daily life on the surface. Recent observations and forecasts, however, show that the region is expanding to the west and continues to weaken in intensity. The South Atlantic Anomaly is also of interest to NASA Earth scientists who monitor the changes in magnetic strength, both for how such changes affect the Earth’s atmosphere and as an indicator of what is happening. the magnetic fields of the earth, deep in the world. Credit: NASA’s Goddard Space Flight Center
It’s what counts inside
The South Atlantic Anomaly arises from two functions of the Earth’s core: the tilt of its magnetic axis, and the flow of molten metals within the outer core.
Earth is a bit like a bar magnet, with north and south poles representing opposite magnetic polarities and invisible magnetic field lines that surround the planet between them. But unlike a bar magnet, the nuclear magnetic field is not perfectly tuned by the world, nor is it perfectly stable. This is because the field originates from the outer core of the earth: molten, iron-rich and in violent motion 1800 miles below the surface. These coarse metals act as a massive generator, called the geodynamo, and produce electric currents that produce the magnetic field.
As the nuclear motion changes over time, the magnetic field fluctuates in complex geodynamic conditions within the nucleus and at the boundary with the fixed mantle above in space and time. These dynamic processes in the nucleus ripple outward to the magnetic field around the planet, generating the SAA and other functions in the Earth’s orbit – including tilt and drift of the magnetic pulse, which over time move. These evolutions in the field, which occur on a similar time scale as the convection of metals in the outer core, give scientists new clues to help them discover the nuclear dynamics that drive the geodynamo.
“The magnetic field is actually a superposition of fields from many current sources,” said Terry Sabaka, a geophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Regions outside the Earth also contribute to the observed magnetic field. He said, however, most of the field comes from the core.
The forces at the core and the tilt of the magnetic axis together produce the anomaly, the area of weaker magnetism – allowing charged particles in the earth’s magnetic field to dive closer to the surface.
As streams of solar material strike the Earth’s magnetosphere, it can be caught and held in two donut-shaped belts around the planet, called the Van Allen Belts. The belts restrict the particles to travel across the earth’s magnetic field lines, jumping continuously back and forth from pole to pole. Credit: NASA Goddard / Tom Bridgman
The Sun expels a constant outflow of particles and magnetic fields, known as the solar wind and large clouds of heat plasma and radiation called ejections from coronal mass. As this solar material flows across space and strikes the Earth’s magnetosphere, the space occupied by the Earth’s magnetic field, it can be trapped and held in two donut-shaped belts around the planet called the Van Allen Belts. The belts restrict the particles to travel across the earth’s magnetic field lines, jumping continuously back and forth from pole to pole. The inner belt begins about 400 miles from the Earth’s surface, which keeps its particle radiation a healthy distance from the Earth and its surrounding satellites.
However, if a particularly strong storm of particles from the Sun reaches Earth, the Van Allen belts can strongly attack and the magnetic field can be deformed, allowing the charged particles to penetrate the atmosphere.
“The observed SAA can also be interpreted as a result of the weakening of dipole field dominance in the region,” said Weijia Kuang, a geophysicist and mathematician at Goddard’s Geodesy and Geophysics Laboratory. “More specifically, a localized field with reverse polarity grows strongly in the SAA region, making the field intensity very weak, weaker than that of the surrounding regions.”
A pothole in space
Although the South Atlantic Anomaly arises from processes within the Earth, it has effects that reach far above the Earth’s surface. The region can be dangerous for low-Earth satellites as they travel through. When a satellite is hit by a high energy proton, it can short circuit and cause an event called a single event transmission as SEU. This may temporarily glitch the satellite’s function or may cause permanent damage if a key component is hit. To prevent instruments from being lost as a whole satellite, operators often shut down non-essential components as they pass through the SAA. Indeed, NASA’s Ionospheric Connection Explorer travels regularly through the region and so the mission keeps constant tabs on the SAA’s position.
The International Space Station, which is in low-Earth orbit, also runs through the SAA. It is well protected, and astronauts are safe from damage when inside. However, the ISS has affected other passengers due to the higher radiation levels: Instruments such as the Global Ecosystem Dynamics Investigation mission, like GEDI, collect data from various positions on the outside of the ISS. The SAA causes “blips” on GEDI’s detectors and reinserts the instrument’s power boards about once a month, said Bryan Blair, the mission’s deputy researcher and instrument scientist, and a scientist lidar instrument at Goddard’s. .
The Sun expels a constant outflow of particles and magnetic fields, known as the solar wind and immense clouds of hot plasma and radiation called ejections coronal mass. This solar material flows across space and strikes the earth’s magnetosphere, the space occupied by the earth’s magnetic field, which acts as a protective shield around the planet. Credit: NASA Goddard / Bailee DesRocher
“These events do not cause any harm to GEDI,” Blair said. “The detector blips are rare compared to the number of laser shots – about one blip in a million shots – and the reset line event causes a few hours of lost data, but it only happens every month or so.”
In addition to measuring the strength of the SAA’s magnetic field, NASA scientists have also studied particle radiation in the region using the Solar, Anomalous, and Magnetospheric Particle Explorer, as SAMPEX – the first of NASA’s Small Explorer mission, launched in 1992 and providing observations until 2012. One study, led by NASA heliophysicist Ashley Greeley as part of her doctoral dissertation, used two decades of data from SAMPEX to show that the SAA is slowly but surely moving into a northwestern direction drives. The results helped confirm models made by geomagnetic measurements and showed how the location of the SAA changes as the geomagnetic field evolves.
“These particles are actually connected to the magnetic field, which leads their motions,” said Shri Kanekal, a researcher in the Heliospheric Physics Laboratory at NASA Goddard. “Therefore, any knowledge of particles also gives you information about the geomagnetic field.”
Greeley’s results, published in the journal Space Weather, were also able to provide a clear picture of the type and amount of particulate radiation that satellites receive when conducting the SAA, which eliminates the need for continuous monitoring. in the region stressed.
The information Greeley and her collaborators gather from SAMPEX’s in-situ measurements has also been useful for satellite design. Low-Earth Orbit engineers, like LEO, used the results to design systems that prevent a latch-up event from failing or causing the spacecraft to lose.
Models of a more secure future for satellites
To understand how the SAA is changing and preparing itself for future threats to satellites and instruments, Sabaka, Kuang and her colleagues use observations and physics to contribute to global models of the Earth’s magnetic field.
The team assesses the current state of the magnetic field with data from the European Space Agency’s Swarm constellation, previous missions of agencies around the world, and ground measurements. Sabaka’s team places the observation data separately to separate its source before passing it on to Kuang’s team. They combine the sorted data of the Sabaka team with their nuclear dynamics model to predict geomagnetic secular variation (rapid changes in the magnetic field) in the future.
The geodynamo models are unique in their ability to use nuclear physics to make near-future forecasts, said Andrew Tangborn, a mathematician at Goddard’s Planetarium Geodynamics Laboratory.
“This is similar to how weather forecasts are produced, but we are working with much longer scaling up,” he said. “This is the fundamental difference between what we do at Goddard and most other research groups that model changes in the Earth’s magnetic field.”
One such application to which Sabaka and Kuang have contributed is the International Geomagnetic Reference Field, or IGRF. Used for a variety of research from the core to the boundaries of the atmosphere, the IGRF is a collection of candidate models created by global research teams that describe the Earth’s magnetic field and track how it changes over time. .
“Even though the SAA is moving slowly, it is going through some change in morphology, so it is also important that we continue to observe it,” Sabaka said. “Because this is what helps us make models and predictions.”
The changing SAA offers researchers new opportunities to understand the core of the Earth, and how its dynamics affect other aspects of the Earth’s system, Kuang said. By gradually changing this ‘dent’ in the magnetic field, scientists can better understand the way our planet is changing and help prepare for a safer future for satellites.
