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Seven ESA satellites team up to explore Earth's magnetic field

(1 July 2015) For the first time ever, two of ESA’s flagship space missions – Cluster and Swarm – have joined forces to simultaneously measure the properties of Earth’s magnetic field at two different altitudes.

This is the first time that multiple spacecraft have simultaneously and directly measured the current density of the magnetic field surrounding our planet at each location. Their results not only explore and characterise the magnetic behaviour in the space around our planet, but also directly show a clear link between field-aligned currents flowing at different altitudes around the Earth.

One of the key aims of ESA’s Swarm mission, consisting of three satellites launched in November 2013 into low Earth orbit, is to probe and explore the strength, properties, and dynamics of Earth’s internal magnetic field in greater detail than ever before.

However, the satellites’ delicate sensors also pick up the natural and powerful electric currents flowing throughout our planet’s ionosphere and magnetosphere, driven by the wind of charged particles streaming from the Sun. The ionosphere is an ionised region of Earth’s upper atmosphere extending upwards to about 1000 km, with the magnetosphere, the region in which Earth’s magnetic field dominates, sitting above it and stretching much further out into space.

Ionospheric currents are thought to be connected to those in the magnetosphere via FACs. Understanding and separating the various magnetic sources and streams is vital so that missions like Swarm can isolate Earth’s more subtle interior dynamics – FACs in particular are known to disturb such measurements in the planet’s polar regions.

“Swarm and Cluster took readings at altitudes of 500 and 15 000 kilometres respectively,” explained Malcolm Dunlop, lead author of the new study. Dunlop is a professor at Beihang University in Beijing, China, a visiting professor at Imperial College London, UK, the PI institute for Cluster’s magnetometer, and a space environment scientist at RAL (STFC), UK.

“The Swarm spacecraft are orbiting just within the ionosphere, whereas Cluster is in the magnetosphere, so they’re in very different regions of space,” he added. “The data sent back by both missions show that large-scale FACs in the measured regions have clearly matching behaviour and structure – the first time this has been seen directly from local magnetic gradients.”