Sun shakes Earth's Magnetic Field

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ESA's Cluster Mission helps reveal how the Sun shakes the Earth's magnetic field.

Space is a hostile region for astronauts & satellites. One constituent of this hazardous environment around the Earth are very energetic electrons, able to perturb or permanently damage satellites.

Ultra Low Frequency (ULF) waves, which travel along the Earth's magnetic field lines, are a prime candidate for generating these killer electrons, but the source of these waves remains unclear.
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A recent study using ground based instrumentation and a dozen satellites at a range of altitudes, provides a means to trace the energy source of these waves from the solar wind into the Earth's magnetosphere down to the ground.

Part of this satellite constellation, the four spacecraft of the ESA Cluster mission, was located at the border of the magnetosphere and played a major role in discriminating between the various theoretical ULF wave generation scenarios.

Quasi-sinusoidal oscillations of the magnetic field lines with periods of a few minutes were recorded continuously for several hours,
as if a celestial musician had plucked the magnetic field lines or strings of the Earth's magnetic guitar

Several ways of exciting these waves have been proposed. Most of them involve the solar wind as the external driver. The solar wind is a continuous stream of solar particles impacting and shaping the Earth's magnetic environment. However, understanding the global nature of these geomagnetic pulsations and the tracing of the energy transfer from the solar wind to the ground is a difficult task.

It requires a fortuitous alignment of several satellites, together with ground–based instruments to observe the oscillations simultaneously.

More from ESA releases
A space armada and ground based instruments to track ULF waves
Image & Simulation Credit: Andy Kale, University of Alberta
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'Killer' electrons in orbit explained by Heather Catchpole @ Cosmos Magazine
Killer Electrons In Space Are Now Less Mysterious from Science Daily releases

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The Bullet Cluster

Composite image of the Bullet Cluster.

When individual galaxies collide and spiral into one another, they discard trails of hot gas that stretch across space, providing signposts to the mayhem. Recognising the signs of collisions between whole clusters of galaxies, however, is not as easy.

The orbiting X-ray telescopes XXM-Newton and Chandra have caught a pair of galaxy clusters merging into a giant cluster. The discovery adds to existing evidence that galaxy clusters can collide faster than previously thought.

During the collision the hot gas (shown in pink) in each cluster is slowed and distorted by a drag force, similar to air resistance. A bullet-shaped cloud of gas forms in one of the clusters.

The optical image from the Magellan and the Hubble Space Telescope shows galaxies in orange and white in the background. Hot gas, which contains the bulk of the normal matter in the cluster, is shown by the Chandra X-ray image, which shows the hot intracluster gas in pink. Gravitational lensing and the distortion of background images by mass in the cluster, reveals the mass of the cluster may be dominated by dark matter (blue), an exotic form of matter abundant in the Universe, with very different properties compared to normal matter.

Major cluster-cluster collisions are expected to be rare, with estimates of their frequency ranging from less than one in a thousand clusters to one in a hundred. On collision, their internal gas is thrown out of equilibrium and if unrecognised, causes underestimation of its mass by between 5 and 20 percent.

This is important because the masses of the various galaxy clusters are used to estimate the cosmological parameters that describe how the Universe expands. So, identifying colliding systems is extremely important to our understanding of the Universe.

X-ray satellites discover the biggest collisions in the Universe from ESA
Image Credits: X-ray: NASA/CXC/CfA/M.Markevitch, Optical and lensing map: NASA/STScI, Magellan/U.Arizona/D.Clowe, Lensing map: ESO WFI
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Biggest Collisions in the Universe from Universe Today
A Close Stellar Encounter? debris disk around HD 15115 from Centauri Dreams
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Bow Shocks

Credits: NASA/ESA and The Hubble Heritage Team STScI/AURA


The shock wave that sits above the Earth’s surface is a natural phenomenon. It is located on the side facing the Sun, at approximately one quarter of the distance to the Moon, and is caused by the flow of electrically charged particles from the Sun.

This flow of electrically charged particles known as solar wind is emitted in a gusty manner by the Sun. When it collides with the Earth’s magnetic field, it is abruptly slowed down and this causes a barrier of electrified gas, called the bow shock, to build up. It behaves in the same way as water being pushed out of the way by the front of a ship.

On 24 January 2001, the four Cluster spacecraft were flying at an approximate altitude of 105 000 kilometres, in tetrahedron formation. Each spacecraft was separated from the others by a distance of about 600 kilometres. With such a distance between them, as they approached the bow shock, scientists expected that every spacecraft would record a similar signature of the passage through this region.

Instead, the readings they got were highly contradictory. They showed large fluctuations in the magnetic and electric field surrounding each spacecraft. They also revealed marked variations in the number of solar wind protons that were reflected by the shock and streaming back to Sun.

The detection has implications for the way astronomers investigate larger bow shocks around distant celestial objects. Bow shocks are related to some of the most energetic events in the Universe. Exploding stars and strong stellar winds from young stars cause them. Reforming bow shocks can also accelerate particles to extremely high energies and throw them across space.

Although the conditions that cause the reformation of a shock wave are rare around the Earth, they are common around these other celestial objects.

Cluster makes a shocking discovery ESA Press Release
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New Horizons & Other Starships - Where are they now? from Astroprof
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