From ‘macro’ to ‘micro’ – turbulence seen by Cluster

Such small-scale vortex turbulence, whose existence was predicted through mathematical models, has not been observed before in space. The results are not only relevant for space physics, but also for other applications like research on nuclear fusion.

On 9 March 2002, the four Cluster satellites, flying in tetrahedral formation at 100 kilometres distance from each other, were crossing the northern ‘magnetic cusp’ when they made their discovery. Magnetic cusps are the regions over the magnetic poles where the magnetic field lines surrounding Earth form a magnetic funnel.

The magnetic cusps are the two important regions in Earth’s magnetosphere where the ‘solar wind’ - a constant flow of charged particles generated by the Sun that crosses the whole Solar System - can directly access the upper layer of Earth’s atmosphere (the ionosphere).

Large amounts of plasma (a gas of charged particles) and energy are transported through these and other ‘accessible’ regions, to penetrate the magnetosphere - Earth’s natural protective shield. Only less than one percent of all the energy carried by the solar wind and hitting the Earth’s magnetosphere actually manages to sneak through, but it still can have a significant impact on earthly systems, like telecommunication networks and power lines.

The solar material sneaking in generates turbulence in the plasma surrounding Earth, similar to that in fluids but with more complex forces involved. Such turbulence is generated for instance in the areas of transition between layers of plasma of different density and temperature, but its formation mechanisms are not completely clear yet.

The turbulence exists at different scales, from few thousand to few kilometres across. With in situ ‘multi-point’ measurements, the four Cluster satellites reported in the year 2004 the existence of large scale turbulence - vortices up to 40 000 kilometres wide, at the flank of the ‘magnetopause’ (a boundary layer separating the magnetosphere from free space). The new discovery of ‘micro’ turbulence, with vortices of only 100 kilometres across, is a first in the study of the plasma surrounding Earth.

Cluster: an unprecedented diagnostic tool
Such a discovery is very relevant. For example, it allows scientists to start linking small and large-scale turbulence, and start questioning how it is actually formed and what are the connections. For instance, what are the basic mechanisms driving and shaping the turbulence? How much do vortices contribute to the transport of mass and energy through boundary layers? Are small vortices needed to generate large ones? Or, on the other hand, do large vortices dissipate their energy and create a cascade of smaller ones?

In trying to answer these questions, Cluster is an unprecedented diagnostic tool for the first three-dimensional map of the near-Earth environment, its exceptionality being given by its multi-spacecraft simultaneous observations. Cluster is revolutionising our understanding of the ways and the mechanisms by which solar activity affects Earth.

Besides, Cluster’s study of the turbulence in Earth’s plasma, with the dynamics and the energies involved, is contributing to the advancement of fundamental theories on plasma. This is not only important in astrophysics, but also as far as the understanding and the handling of plasma in laboratories is concerned, given the high energies involved. This is particularly relevant for research on nuclear fusion.

For example, Cluster’s data are complementing research on plasma physics in the international ITER project, an experimental step involving several research institutes around the world for tomorrow’s electricity-producing power plants. In this respect, by probing into the magnetosphere, Cluster has free access to the only open ‘natural laboratory’ for the study of plasma physics.

Cluster sees tsunamis in space
Cluster is providing new insights into the working of a ‘space tsunami’ that plays a role in disrupting the calm and beautiful aurora, or northern lights, creating patterns of auroral dances in the sky.
Magnetic fields get reconnected in turbulent plasma too
Using measurements of the four ESA's Cluster satellites, a study published this week in Nature Physics shows pioneering experimental evidence of magnetic reconnection also in turbulent 'plasma' around Earth.
Cluster Spacecraft Catch Crashing Waves in Earth's Magnetic Bubble
A bevy of satellites buzzing around in the Earth's magnetosphere has found at least part of the answer to a long-standing puzzle about the source of the charged particles that feed the aurora.

The charged particles come from explosions on the sun and smash into the Earth's magnetic field, which repels the bulk of them. But many slip through, often via a physical process called magnetic reconnection, where the magnetic field traveling with the particles breaks and reconnects with the Earth's field, opening a window for the particles to surge through. Once inside, these excited particles can spiral down toward the poles and create brilliant auroras when they hit the atmosphere.
'Impressionist' Spacecraft to View Solar System's Invisible Frontier
(PhysOrg.com) -- At the edge of our solar system in December 2004, the Voyager 1 spacecraft encountered something never before experienced during its then 26-year cruise through the solar system — an invisible shock formed as the solar wind piles up against the gas in interstellar space. This boundary, called the termination shock, marks the beginning of our solar system's final frontier, a vast expanse of turbulent gas and twisting magnetic fields.
MIT tests unique approach to fusion power
An MIT and Columbia University team has successfully tested a novel reactor that could chart a new path toward nuclear fusion, which could become a safe, reliable and nearly limitless source of energy.
Solar telescope reaches 120,000 feet on jumbo-jet-sized balloon
In a landmark test flight, the National Center for Atmospheric Research (NCAR) and a team of research partners this month successfully launched a solar telescope to an altitude of 120,000 feet, borne by a balloon larger than a Boeing 747 jumbo jet. The test clears the way for long-duration polar balloon flights beginning in 2009 that will capture unprecedented details of the Sun's surface.
In Search of Interstellar Dragon Fire
Ancient explorers set sail expecting to encounter dragons on the world's unknown oceans. NASA's twin Voyager spacecraft are searching for dragons of a different sort as they enter the boundary of our solar system – cosmic "dragons" that breathe a strange fire of high-speed atomic fragments called cosmic rays.
Researchers Produce Images of Gases Escaping from Jupiter's Moon Io
Boston University researchers published today the first clear evidence of how gases from Jupiter’s tiny moon’s volcanoes can lead to the largest visible gas cloud in the solar system. Jupiter, the largest planet in the solar system, has a moon named Io that is just 100 km larger in radius than Earth’s Moon.

From ‘macro’ to ‘micro’ – turbulence seen by Cluster

Related stories:

News discussion: