January 9, 2013
NASA Cluster Mission Offers New Insights Into Mysteries Of Solar Winds
Brett Smith for redOrbit.com - Your Universe Online
Data collected from the European Space Agency´s (ESA) Cluster Mission showed for the first time how turbulence within solar wind can create a warming effect as the charged particles travel away from the sun.
The solar wind is formed by electrically charged plasma being ejected from the sun´s super hot atmosphere. According to a new report in the new issue of Physical Review Letters based on Cluster data, very small “current sheets” of electrical current separate regions of magnetic fields from within these winds.
“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 the report´s co-author Melvyn Goldstein, project scientist for Cluster at NASA.
The scientists say these small current sheets may play a crucial role in the dissipation of the turbulence. They theorize that as the solar wind turbulence flows from larger disturbances to smaller ones, energy is released from the magnetic fields and dissipates in the surroundings as heat.
A key data-collecting instrument on board each of the four Cluster satellites is the Spatio Temporal Analysis Field Fluctuation (STAFF) magnetometer. The instrument detects rapid variations in magnetic fields, allowing researchers to find very small spatial structures within the plasma.
Two major sets of STAFF observations were used in the study. The first data set was obtained on January 10, 2004, when two Cluster spacecrafts were separated along the solar wind flow by only 12 miles. The other two Cluster satellites orbited further away. At that time, STAFF recorded 450 measurements per second of the solar flow. The second data set was collected by a single Cluster spacecraft 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," said lead author Silvia Perri of the UniversitÃ della Calabria, Italy.
During the 2004 event, the current sheet event lasted only 0.07 seconds for both satellites over a space 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.”
The scientists also noted a phenomenon in their data that indicated that magnetic field lines in the solar wind reconnected and broke, resulting in a transfer of energy to plasma particles. These reconnections are frequent across the universe — including inside the sun as well as within Earth´s own magnetosphere.
While they were able to detect evidence of magnetic reconnections, finding proof of them on a small scale is difficult with current instruments. NASA officials predicted that the upcoming Magnetospheric Multiscale (MMS) mission in 2014 will allow for greater focus on reconnection in the magnetosphere.