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Earth from outer space

February 21, 2012

Three German-built satellites will examine the Earth's little-known magnetic field. The research should deliver precise data that will help in predicting space weather, and tell us whether the poles are shifting.

Swarm satellite
Carbon fiber satellites of the Swarm mission are reminiscent of a broomstick shapeImage: Credits: ESA–R. Bock/IABG

The European Space Agency's (ESA) Swarm mission will soon launch three satellites into space. Built in Germany, the satellites will research the earth's magnetic field, which acts as an invisible shield that repels energized particles from the sun and deep space.

The ESA's Swarm mission, with a launch date in mid-2012, is intended to observe the Earth's geomagnetic field by measuring processes in the molten core, as well as on the mantle and crust of the planet.

Information delivered can be used to determine whether the poles are shifting, and help predict space weather.

satellites in orbit around Earth
From their orbit, the satellites will look deep into the EarthImage: ESA–P. Carril

Space mission into the depths of Earth

Albert Zaglauer, a project director with the company Astrium in Friedrichshafen, explained the importance of the geomagnetic field.

"Without the Earth's magnetic field, we wouldn't exist, as we'd be fully exposed to cosmic radiation," Zaglauer told DW.

The Earth's magnetic field comes from movement of molten lava in the planet's core. And as measurements over the last 150 years show, the strength of the magnetic field has been steadily decreasing.

Researchers also know that the magnetic poles of the Earth move, completely reversing about every half a million years. It may even be the case that the Earth's poles will soon be due to swap.

The three satellites of the Swarm mission will, from their orbits of 460 to 530 kilometers (286 to 329 miles) above the Earth, measure the current state and ongoing development of the Earth's magnetic field to a more precise degree than ever before.

Sensitive instruments on the satellites will investigate regional differences in magnetic characteristics of the Earth's crust, as well as how the magnetic field influences ocean currents.

The mysterious processes occurring in the Earth's interior originate in outer space: The sun continuously beams charged particles of differing intensity to Earth.

Sometimes these particles punch right through the Earth's magnetic field above the poles, causing the colorful phenomenon known as aurora borealis.

graphic of magnetic forces running through Earth
A magnetic field courses through each pole and Earth's molten coreImage: GFZ

Air guitars of a different sort

Three satellites are necessary for making simultaneous measurements from different locations in order to follow quick changes in the magnetic field during solar storms.

Nils Olsen, who is involved in planning the Swarm mission from the Danish National Space Center in Copenhagen, spoke enthusiastically about the project.

"It's really astounding, all the things we can learn about the Earth and the sun through these quite small satellites," Olsen told DW.

Each satellite weighs about 500 kilograms (1,102 lbs.) and measures about nine meters (30 feet) long. To keep drag to a minimum, the satellites have a streamlined form, and the sensitive measuring instruments lie at the end of a long arm that is extended once the satellites are in space.

With a long neck and slim body, the satellites almost look like guitars, or flying broomsticks.

At a cost of about 90 million euros ($117 million), technicians and engineers had to build the satellites such that the electronic devices onboard would minimally disturb the sensitive measuring instruments.

That's why the main body of the satellites is made of carbon fiber, which doesn't influence the measurements of magnetic fields.

Blast-off with an atomic rocket

After some final tests in Germany, the satellites will be transported to Russia. Around the middle of July, the satellites will be put into orbit from the Plesetsk Cosmodrome, a space center some distance north of Moscow.

Toward the end of the mission, the physicists will take measurements from only 300 km (186 miles) above the Earth. At this elevation, the magnetic field is far stronger and thus, easier to measure.

The Swarm satellites will stay in orbit about four years. Due to friction in the extremely thin atmosphere, the satellite trio will gradually fall back to Earth, burning up upon re-entry.

graphic showing satellites in orbit from space
The satellites will burn up upon re-entry, after about four yearsImage: ESA

Researchers are happy with a timely increase in sun activity before the start of the Swarm mission. In the coming years, the sun will produce many explosions and outbursts of radiation, stressing the Earth's magnetic field.

"We'll be able to follow the changes in the upper atmosphere quite exactly. This will improve space weather forecasts," clarified Eigil Friis-Christensen of the Technical University of Denmark, and a scientist for the Swarm mission.

Predicting space weather includes collecting data from the sun, solar wind, magnetosphere and ionosphere.

Data instead of pictures

In the long run, researchers want to use data from Swarm and other sun satellites to create precise space weather reports, like those for Earth.

Although the sun storms present no danger to people on the Earth's surface, they can destroy satellites, disrupt GPS signals and lead to short circuits in electrical grids.

Swarm is the fourth mission of the ESA's "Earth Explorer" program, which has the goal of investigating the most important Earth phenomena.

The satellites Cryosat, Goce und Smos have already been placed into orbit, to observe the Earth's icy regions, gravitational field, soil moisture and salt content of its oceans.

With further missions in the coming years, European countries will consolidate their position as global leaders in earth observation.

But the Swarm team, with its unspectacular sets of data, will have a hard time competing with many other satellite missions, which excite the public with colorful images.

The Swarm satellites won't be delivering pictures - since they don't have any cameras - Zaglauer said.

"Unfortunately, data measurements won't really be comprehended outside the world of experts. But they are unbelievably important for our lives!"

Author: Dirk Lorenzen / sad
Editor: Neil King