NASA: 'Dent' in Earth's Magnetic Field Could Spell Trouble for Satellites
A small but evolving dent in Earth’s magnetic field can cause big headaches for satellites.
Earth’s magnetic field acts like a protective shield around the planet, repelling and trapping charged particles from the Sun. But over South America and the southern Atlantic Ocean, an unusually weak spot in the field – called the South Atlantic Anomaly, or SAA – allows these particles to dip closer to the surface than normal. Particle radiation in this region can knock out onboard computers and interfere with the data collection of satellites that pass through it – a key reason why NASA scientists want to track and study the anomaly.
The South Atlantic Anomaly is also of interest to NASA’s Earth scientists who monitor the changes in magnetic field strength there, both for how such changes affect Earth's atmosphere and as an indicator of what's happening to Earth's magnetic fields, deep inside the globe.
Currently, the SAA creates no visible impacts on daily life on the surface. However, recent observations and forecasts show that the region is expanding westward and continuing to weaken in intensity. It is also splitting – recent data shows the anomaly’s valley, or region of minimum field strength, has 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 help prepare for future challenges to satellites and humans in space.
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. Earth is a bit like a bar magnet, with north and south poles that represent opposing magnetic polarities and invisible magnetic field lines encircling the planet between them. But unlike a bar magnet, the core magnetic field is not perfectly aligned through the globe, nor is it perfectly stable.
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Although the South Atlantic Anomaly arises from processes inside Earth, it has effects that reach far beyond Earth’s surface. The region can be hazardous for low-Earth orbit satellites that travel through it. If a satellite is hit by a high-energy proton, it can short-circuit and cause an event called single event upset or SEU. This can cause the satellite’s function to glitch temporarily or can cause permanent damage if a key component is hit. In order to avoid losing instruments or an entire satellite, operators commonly shut down non-essential components as they pass through the SAA. Indeed, NASA's Ionospheric Connection Explorer regularly travels 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 passes through the SAA. It is well protected, and astronauts are safe from harm while inside. However, the ISS has other passengers affected by the higher radiation levels: Instruments like the Global Ecosystem Dynamics Investigation mission, or GEDI, collect data from various positions on the outside of the ISS. The SAA causes “blips” on GEDI’s detectors and resets the instrument’s power boards about once a month, according Bryan Blair, the mission’s deputy principal investigator and instrument scientist, and a lidar instrument scientist at Goddard.
“These events cause no harm to GEDI. 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 couple of hours of lost data, but it only happens every month or so.”
Bryan Blair, the mission’s deputy principal investigator and instrument scientist.
“These events cause no 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 couple of hours of lost data, but it only happens every month or so.”
In order to understand how the SAA is changing and to prepare for future threats to satellites and instruments, Sabaka, Kuang and their colleagues use observations and physics to contribute to global models of Earth’s magnetic field.
The team assesses the current state of the magnetic field using data from the European Space Agency’s Swarm constellation, previous missions from agencies around the world, and ground measurements. Sabaka’s team teases apart the observational data to separate out its source before passing it on to Kuang’s team. They combine the sorted data from Sabaka’s team with their core dynamics model to forecast geomagnetic secular variation (rapid changes in the magnetic field) into the future.
The geodynamo models are unique in their ability to use core physics to create near-future forecasts, said Andrew Tangborn, a mathematician in Goddard’s Planetary Geodynamics Laboratory.
“This is similar to how weather forecasts are produced, but we are working with much longer time scales,” he said. “This is the fundamental difference between what we do at Goddard and most other research groups modeling changes in Earth’s magnetic field.”
One such application that Sabaka and Kuang have contributed to 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 made by worldwide research teams that describe Earth’s magnetic field and track how it changes in time.
“Even though the SAA is slow-moving, it is going through some change in morphology, so it’s also important that we keep observing it by having continued missions,” Sabaka said. “Because that’s what helps us make models and predictions.”
The changing SAA provides researchers new opportunities to understand Earth’s core, and how its dynamics influence other aspects of the Earth system, said Kuang. By tracking this slowly evolving “dent” in the magnetic field, researchers can better understand the way our planet is changing and help prepare for a safer future for satellites.
(Source: NASA. Image and video provided)