The solar wind is made of an electrically-charged gas called plasma. One theory about the wind's puzzling high temperatures is that irregularities in the flow of charged particles and magnetic fields in the plasma create turbulence, which, in turn, dissipates and adds heat to its surroundings.
A 2-dimensional vision of the solar wind turbulence at the smallest scale seen yet, thanks to observations by Cluster satellites. The approximate location of the measurements is indicated on a graphic illustrating features of Earth’s magnetic environment. The inset shows conditions as would be seen facing the solar wind, with current sheets forming at the border of turbulent eddies. The trajectory of the Cluster spacecraft is marked on the inset by the black line and the color gradients represent the magnetic field strength intensity.
Background graphic: ESA/ATG Medialab
Inset: NASA/J. Dorelli
Using two separate sets of data sent back by Cluster, an international team of scientists has probed the spatial characteristics of this turbulence in more detail and at smaller scales than ever before. They saw evidence that the turbulence evolved to form very small “current sheets” -- thin sheets of electrical current that separate regions of rotated magnetic field.
“For the first time, we were able to obtain direct evidence for the existence of current sheets at these very small scales, where dissipation of magnetic energy into heat is thought to occur,” said Melvyn Goldstein, project scientist for Cluster at NASA’s Goddard Space Flight Center in Greenbelt, Md. Goldstein is a co-author of a paper on these results that appeared in the Nov. 9, 2012, issue of Physical Review Letters.
This solar wind is a non-stop gale of plasma, mainly protons and electrons, which originates in the sun’s searingly hot lower atmosphere. It blasts outward in all directions at an average speed of about 250 miles per second. The outflow is so energetic that it pulls along the sun’s magnetic field. The solar wind travels across the entire solar system, until it reaches the boundary with interstellar space. The plasma cools as it expands during its outward journey. However, the amount of cooling is much less than would be expected in a constant, smooth flow of solar particles since the density is so low that the particles cannot be receiving extra heat from the most common method on Earth: collisions.
By providing the first observations of these small current sheets, the Cluster data help confirm that such sheets may play an important role in the dissipation of the turbulence – meaning that as the turbulence cascades from larger disturbances to smaller ones, energy is taken out of the magnetic field and added to its surroundings as heat. The current sheets are more or less two-dimensional. They may are also be sites where the magnetic field lines reconnect and break, resulting in a transfer of energy to both particle heating and particle flows. Such magnetic reconnection occurs in many regions in the universe including in the solar wind, inside the sun and other stars, and in Earth’s magnetic environment, the magnetosphere. Finding direct evidence for magnetic reconnection at these scales is difficult with the present instrumentation, however, and resolution of that question may have to await the launch of NASA’s Magnetospheric Multiscale (MMS) mission in 2014, a mission that will focus on reconnection in the magnetosphere.
The team’s study made use of the high time resolution of the Spatio Temporal Analysis Field Fluctuation (STAFF) magnetometer, which is carried on each of the four Cluster spacecraft. STAFF is capable of detecting rapid variations in magnetic fields, which means that very small spatial structures can be recognized within the plasma.
The scientists examined two sets of STAFF observations. The first data were obtained on Jan. 10, 2004, when two Cluster spacecraft (C2 and C4) were separated along the solar wind flow direction by only 12 miles apart, while the two other spacecraft were much further away. At that time, STAFF was operating in rapid burst mode, during which it recorded 450 measurements of the magnetic field per second. Additional data were obtained by a single spacecraft (Cluster 2) on March 19, 2006.
"During the 2004 observation, both spacecraft were so close that they observed almost simultaneously the same structure in the solar wind as it passed them by. The magnetic field data showed the typical signature of a current sheet crossing," says Silvia Perri of the Università della Calabria, Italy, who is the lead author of the paper. At that time, the solar wind was flowing at about 350 miles per second. The current sheet event lasted only 0.07 seconds for both satellites and this corresponds to a spatial size of about 25 miles.
“This shows for the first time that the solar wind plasma is extremely structured at these very small scales,” says Perri. “It is clear that we are seeing a release of energy approaching smaller and smaller scales, which may contribute to the overall heating of the solar wind.”For more information about NASA's MMS Mission, visit:
Visualizing how radiation bombardment boosts superconductivity
26.05.2015 | DOE/Brookhaven National Laboratory
Hubble observes one-of-a-kind star nicknamed 'Nasty'
22.05.2015 | NASA/Goddard Space Flight Center
Physicists have developed an innovative method that could enable the efficient use of nanocomponents in electronic circuits. To achieve this, they have developed a layout in which a nanocomponent is connected to two electrical conductors, which uncouple the electrical signal in a highly efficient manner. The scientists at the Department of Physics and the Swiss Nanoscience Institute at the University of Basel have published their results in the scientific journal “Nature Communications” together with their colleagues from ETH Zurich.
Electronic components are becoming smaller and smaller. Components measuring just a few nanometers – the size of around ten atoms – are already being produced...
Development and implementation of an advanced automobile parking navigation platform for parking services
To fulfill the requirements of the industry, PolyU researchers developed the Advanced Automobile Parking Navigation Platform, which includes smart devices,...
The world's first electrical car and passenger ferry powered by batteries has entered service in Norway. The ferry only uses 150 kWh per route, which...
On Tuesday, 19 May 2015 the research icebreaker Polarstern will leave its home port in Bremerhaven, setting a course for the Arctic. Led by Dr Ilka Peeken from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) a team of 53 researchers from 11 countries will investigate the effects of climate change in the Arctic, from the surface ice floes down to the seafloor.
RV Polarstern will enter the sea-ice zone north of Spitsbergen. Covering two shallow regions on their way to deeper waters, the scientists on board will focus...
Nanoengineers at the University of California, San Diego developed a gel filled with toxin-absorbing nanosponges that could lead to an effective treatment for skin and wound infections caused by MRSA (methicillin-resistant Staphylococcus aureus), an antibiotic-resistant bacteria. This "nanosponge-hydrogel" minimized the growth of skin lesions on mice infected with MRSA - without the use of antibiotics. The researchers recently published their findings online in Advanced Materials.
To make the nanosponge-hydrogel, the team mixed nanosponges, which are nanoparticles that absorb dangerous toxins produced by MRSA, E. coli and other...
20.05.2015 | Event News
18.05.2015 | Event News
12.05.2015 | Event News
26.05.2015 | Ecology, The Environment and Conservation
26.05.2015 | Life Sciences
26.05.2015 | Power and Electrical Engineering