Swarm : Why magnetism matters

Built by Astrium, the European Space Agency (ESA) Swarm mission will measure the Earth’s magnetic field with unprecedented levels of accuracy. The three Swarm satellites will fly in a triangular formation to build up a complete picture of the Earth’s magnetic field and how it’s changing. The satellites will study everything from the core to the crust, and from the surface of the planet out into space to examine the magnetic ‘bubble’ surrounding the Earth known as the magnetosphere. There are also instruments on board to measure the drag and density of the atmosphere.
The fourth of ESA’s Earth Explorer missions (after GOCE, SMOS and CryoSat), the Swarm mission is not only of great interest to scientists but is also directly relevant to all of us on the planet. A better understanding of the Earth’s magnetic field will help improve navigation for ships and aircraft and be used to predict the effects of solar activity. We also need to know how the magnetic field is changing and what would happen if it went into reverse.
“Swarm will be like looking at the Earth with new eyes,” says Astrium UK’s Head of Science & Exploration, Ralph Cordey. “It’s a means of sensing processes, which we simply haven’t been able to do on a global scale before at the resolution that Swarm will provide.”
“It’s going to produce new information on the properties of our core and the generation of the magnetic field on our planet and link those to the properties of the magnetosphere around the Earth,” Ralph adds. “So it’s doing a whole bunch of jobs in one that we’ve simply not been able to do before.”
Bar magnet
The Earth is essentially an enormous bar magnet floating in space. Seafarers have used compasses to exploit these properties for hundreds of years – there is even some evidence that Chinese sailors were using compasses 3,000 years ago. What’s perhaps surprising is that, despite the advent of GPS, we are still using compasses today. Ships and aircraft rely on a compass as one of their primary means of navigation, particularly in bad weather when GPS signals can sometimes be lost.
However, unlike a bar magnet, the Earth’s magnetic field is constantly shifting and changing. The magnetic north is in a different place to the North Pole, and it changes position all the time. These fluctuations are not fully understood but result from the generation of the magnetic field in the Earth’s core.
Most geologists now agree that the core is made up of two parts: an inner solid iron core and an outer liquid iron core. This outer ocean of iron is in constant motion and it is believed that this turbulent movement generates and is responsible for altering the Earth’s magnetic field.
The result of these changes in magnetic field mean that maps showing the Earth’s magnetic field – and the maps and charts that are produced for ships and aircraft – have to be officially adjusted every five years. Information from Swarm will be used to improve computer simulations of the Earth’s magnetic field and how, and why, it is changing.
The magnetic field also has areas of particular weakness or strength. There is one area in the southern hemisphere, known as the South Atlantic Anomaly, where the field is especially weak. In the last hundred and fifty years the entire field magnetic field of the Earth has weakened by some 10%. Eventually, but only probably in a couple of thousand years, the Earth’s magnetic field might even go into reverse.

The Swarm satellites will also give an insight into the structure of the Earth. The magnetic field has to pass from the planet’s core through the mantle to the surface. The mantle has rocks with electrical conductivity and these distort the magnetic signal. So understanding what effect this distortion has on the magnetic signal will give scientists information on the structure of the lower mantle.
Space weather
The sun is continuously bombarding the Earth with a stream of charged particles, known as the solar wind, and the occasional more violent eruptions such as solar flares. We sometimes see this activity as spectacular aurora – the so-called Northern and Southern Lights, the aurora borealis and aurora australis. This interaction between the sun and the Earth is known as space weather and we are protected from the worst effects by the magnetosphere. This magnetosphere makes life on our planet possible – without it our atmosphere could be ripped away.
Solar storms can cause electrical disturbances in the magnetosphere, with potentially damaging effects for orbiting satellites, communications and even power grids on the ground. Being able to predict space weather is becoming increasingly important and scientists across Europe intend to use Swarm to build up a more accurate model of solar activity and its influence on the Earth. There are also plans to coordinate Swarm with earlier missions such as the Cluster satellite quartet, built by Astrium for the European Space Agency, which is already studying the Earth’s magnetosphere, and NASA’s STEREO (Sun TErrestrial RElations Observatory) duo, which is investigating the sun.
In the short term, scientists hope to be able to use the combination of these satellites to track large space weather events – the sort which might pose dangers to Earth-based power and satellite systems. In the longer term, they plan to build up much better computer models of the space environment to help predict future space weather effects. Any products developed from this would have potential benefits for satellite operators as well as power and communications companies.

Source / Author: Astrium