South Atlantic Anomaly Magnetic Field NASA – Key Facts 2025

High above the South Atlantic Ocean, Earth’s magnetic shield is behaving oddly. NASA’s latest tracking, based on data running through 2025, confirms that a region of weakened magnetic field known as the South Atlantic Anomaly (SAA) is not only persisting but growing and potentially splitting into two distinct cells. The phenomenon has drawn attention from space agencies and engineers alike, though its practical effects are largely confined to satellites and astronauts in low Earth orbit.

For people on the ground, the SAA remains an invisible, harmless feature of the planet’s natural magnetic variation. Yet for spacecraft passing overhead, it presents a genuine operational risk. Understanding what the anomaly is, why it exists, and how it is changing helps separate fact from the occasional rumour.

What Is the South Atlantic Anomaly and Where Is It?

The South Atlantic Anomaly is a large region stretching from South America across the southern Atlantic Ocean toward Africa. At that location, Earth’s magnetic field dips to its weakest intensity, allowing charged particles from the Sun and the Van Allen radiation belts to penetrate much closer to the planet than elsewhere.

Key insights from recent observations include:

• The SAA is a natural, ongoing phenomenon caused by Earth’s dynamic core, not a sign of immediate pole reversal.
• NASA and ESA have observed an 8% increase in the anomaly’s area since 1970, with a possible split into two low-intensity regions.
• While harmless to life on Earth, the SAA forces satellite operators to power down sensitive instruments and increases astronaut radiation exposure.
• Latest 2025 data confirms the western lobe is weakening faster, but the anomaly is not expanding uniformly.

A Dent in Earth’s Magnetic Field

Scientists often describe the SAA as a “dent” or “pothole” in the magnetic field. Unlike the rest of the planet, where the field acts as a protective bubble, this region lets energetic particles dip as low as 200 kilometres above the surface. The NASA 2015–2025 visualization maps the feature both at Earth’s surface and at the core-mantle boundary, illustrating the deep connection between surface weakness and processes taking place thousands of kilometres below.

Geographic Extent: Over South America and Africa

The anomaly is not a uniform patch. Researchers have observed that it behaves differently toward Africa and South America, which helps explain its irregular growth and split structure. ESA-linked reporting based on 2014–2025 satellite measurements says the anomaly expanded by roughly half the size of continental Europe and that weakening has accelerated since 2020.

Visualizing the SAA: NASA Maps and Simulations

The NASA OSDR RadLab knowledge base provides maps and technical diagrams of the SAA. Users can explore the anomaly’s shape and intensity, though real-time tracking requires dedicated satellite data.

Is the South Atlantic Anomaly Dangerous? Effects on Satellites, Astronauts, and You

Questions about the SAA’s danger are among the most common. The answer depends on where you are.

Why Satellites Power Down Over the SAA

The practical danger is to spacecraft electronics. Particle radiation in the SAA can knock out onboard computers, interfere with satellite data collection, and cause technical glitches or blackouts. Operators often shut down sensitive systems before the spacecraft enters the region to reduce the risk of damage. The International Space Station and other low Earth orbit missions regularly pass through the anomaly.

Astronaut Radiation Exposure Risk

For astronauts, the region increases exposure to ionizing radiation. The source material emphasises operational risk to spacecraft more than acute danger to crew, but the environment is monitored closely, and extra shielding or scheduling adjustments are made.

No Danger to People on Earth – Here’s Why

NASA’s own framing is clear: the SAA causes no visible impacts on daily life at the surface and remains within what scientists consider normal magnetic variation. The atmosphere provides complete protection from the energetic particles that dip lower over the region.

Can the SAA Cause Electronics to Fail?

Yes, but only for electronics in space. Satellites and spacecraft components can suffer bit flips, data corruption, or even permanent damage if not properly shielded. On the ground, mobile phones, GPS receivers, and computers are unaffected.

Myth vs. Fact: The SAA and the Bermuda Triangle

There is no scientific evidence linking the SAA to any disappearance or event in the Bermuda Triangle. The SAA is a magnetic field phenomenon, not a vortex or energy portal. The idea remains a persistent myth without support from research.

What Causes the South Atlantic Anomaly and Why Is It Growing?

The dominant explanation ties the SAA to Earth’s magnetic field generation in the molten outer core, where flow patterns are changing.

Earth’s Core: Tilted Magnetic Axis and Molten Metal Flows

NASA notes that the magnetic field is not perfectly centred on Earth. The dipole is offset and tilted, which helps produce the weak region. A major hypothesis is that the African Large Low Shear Velocity Province—a massive dense rock region deep beneath Africa—disturbs the geomagnetic field generation and contributes to the weakening over the South Atlantic.

Is the SAA a Sign of an Impending Pole Reversal?

While the SAA is associated with core dynamics that could theoretically lead to a reversal over millions of years, current research indicates no imminent reversal. The field behaviour seen today is within the range of normal geomagnetic variation.

The 2025 Update: Splitting and Expansion

NASA’s 2015–2025 visualization maps show the SAA as a changing feature at both the Earth’s surface and the core-mantle boundary. The western lobe is weakening faster, and the anomaly’s area has grown by about 8% since 1970.

How Is NASA Tracking the South Atlantic Anomaly in 2025?

Multiple satellite missions contribute to monitoring the SAA. The NASA ICON mission and the ESA Swarm constellation provide high-resolution magnetic field data.

NASA’s ICON and Swarm Missions

ICON, launched in 2019, studies the ionosphere and how it responds to space weather. Swarm, a trio of ESA satellites, has been mapping the geomagnetic field in unprecedented detail since 2013. Together, they supply the data that revealed the split and the accelerated weakening after 2020.

The Growing Dent: Expansion by 8% Since 1970

Area calculations show the SAA has grown by approximately 8% over the past five decades. The weakening has not been uniform: the western cell has deepened more than the eastern part.

Split or Not? Understanding the Two Low-Intensity Regions

Observations from 2015–2020 indicated the weak region had begun to split from one valley into two cells. NASA’s models projected that split to continue out to 2025. Current data confirms the split is more pronounced, though whether it will remain permanent is uncertain.

South Atlantic Anomaly Tracker and Map: How to See It Live

NASA’s RadLab SAA Knowledge Base and Visualizer

The NASA OSDR RadLab provides a knowledge base with maps and detailed explanations. It is not a real-time tracker, but it offers the most authoritative reference for the anomaly’s current shape and intensity.

Using the OSDR Visualization Tool

The RadLab interface allows users to view the SAA at different altitudes and time periods. Researchers and space enthusiasts can examine the split structure and the evolution since 2015.

Other Sources: ESA Swarm Data Viewer

The ESA Swarm website offers public access to magnetic field measurements, including products that show the SAA. These tools are designed for specialist use, but provide the raw data behind the news reports.

When Was the South Atlantic Anomaly Discovered and How Has It Evolved?

A timeline of key milestones helps contextualise the current changes.

1. 1958 – Discovery of the SAA by particles trapped in radiation belts (Van Allen probes).
2. 1970s–2010s – Gradual mapping; recognition of expansion.
3. 2013–2020 – ESA Swarm mission provides high-resolution data; NASA ICON launched 2019.
4. 2020 – NASA publishes article “Slowly Splitting Dent” – reveals western lobe deepening.
5. 2024–2025 – ScienceAlert reports continued growth; SAA area now ~8% larger than 1970; split more pronounced.
6. 2025 (Nov) – Latest observations: anomaly continues evolving; no immediate pole reversal expected.

What Do Scientists Know for Sure About the SAA and What Remains Uncertain?

What Does the South Atlantic Anomaly Tell Us About Earth’s Magnetic Field?

The SAA is a symptom of a living geomagnetic field, not a crisis. It is a natural laboratory for understanding how Earth’s magnetic field evolves over time. Understanding the anomaly helps improve satellite design and astronaut safety protocols. The anomaly’s growth highlights the dynamic nature of Earth’s core – not a cause for alarm.

Unlike a “hole” in the ozone layer, the SAA does not allow harmful solar radiation directly to the surface; it only weakens the field at satellite altitudes. This distinction is crucial for interpreting the seriousness of the phenomenon.

For a broader look at how measurements and data collection work, see How Many Seconds in a Year – Full Breakdown for Every Type.

What Are the Key Sources of Information on the South Atlantic Anomaly?

The South Atlantic Anomaly arises from two features of Earth’s core: The tilt of its magnetic axis, and the flow of molten metals within its outer core.

NASA (2020 press release)

Likened by NASA to a ‘dent’ in Earth’s magnetic field, or a kind of ‘pothole in space’, the South Atlantic Anomaly has expanded by around 8% since 1970.

ScienceAlert (2025)

The SAA is the near-Earth region where Earth’s magnetic field is weakest relative to an idealized Earth-centered dipole field.

Wikipedia

What Is the Bottom Line on the South Atlantic Anomaly in 2025?

The South Atlantic Anomaly is a real, well-documented region of magnetic weakness that continues to evolve. It poses no danger to life on the ground, but remains a significant operational concern for satellites and astronauts. NASA and ESA will keep monitoring it through 2026 and beyond. For a deeper understanding of how scientists verify such phenomena, see What Is Primary Research – Definition, Methods and Examples.

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