ESA- SPACE IMAGEN - The solar wind is swirly

Tiny turbulent swirls in the solar wind.

Using ESA’s Cluster quartet of satellites as a space plasma microscope, scientists have zoomed in on the solar wind to reveal the finest detail yet, finding tiny turbulent swirls that could play a big role in heating it.

Turbulence is highly complex and all around us, evident in water flowing from a tap, around an aircraft wing, in experimental fusion reactors on Earth, and also in space.

In the stream of charged particles emitted by the Sun – the solar wind – turbulence is thought to play a key part in maintaining its heat as it streams away and races across the Solar System.

As the solar wind expands, it cools down, but to a much smaller extent than would be expected if the flow were smooth.

Turbulence arises from irregularities in the flow of particles and magnetic field lines, but understanding how this energy is transferred from the large scales where it originates, to the small scales where it is dissipated, is like trying to trace energy as it is transferred from the smooth, laminar flow of a river down to the small turbulent eddies formed at the bottom of a waterfall.

In a new study, two of the four Cluster satellites have made extremely detailed observations of plasma turbulence in the solar wind.

They were separated by just 20 km along the direction of the plasma flow and operated in ‘burst mode’ to take 450 measurements per second.

By comparing the results with computer simulations, scientists confirmed the existence of sheets of electric current just 20 km across, on the borders of turbulent swirls.

“This shows for the first time that the solar wind plasma is extremely structured at this high resolution,” says Silvia Perri of the Universita della Calabria, Italy, and lead author of the paper reporting the result.

Cluster previously detected current sheets on much larger scales of 100 km in the magnetosheath, the region sandwiched between Earth’s magnetic bubble – the magnetosphere – and the bow shock that is created as it meets the solar wind.

At the borders of these turbulent eddies the process of ‘magnetic reconnection’ was detected, whereby oppositely directed field lines spontaneously break and reconnect with other nearby field lines, thus releasing their energy.

“Although we haven’t yet detected reconnection occurring at these new, smaller scales, it is clear that we are seeing a cascade of energy which may contribute to the overall heating of the solar wind,” said Dr Perri.  

Future missions such as ESA’s Solar Orbiter and NASA’s Solar Probe Plus will be able to determine whether similar processes are also in play closer to the Sun, while NASA’s Magnetospheric Multiscale mission will specifically probe the small-scale regions where reconnection can occur.

“This Cluster result demonstrates the mission’s unique capability to probe universal physical phenomena, in this case pushing the mission’s instrument measurement capabilities to their limit to unlock features at small scales,” comments Matt Taylor, ESA’s Cluster Project Scientist.

“Future multi-spacecraft missions will make very detailed studies of these small-scale plasma phenomena and provide further context to our Cluster measurements.”

 ESA

Guillermo Gonzalo Sánchez Achutegui

ayabaca@gmail.com

ayabaca@hotmail.com

ayabaca@yahoo.com

 

Astronomy: Earth’s magnetic field provides vital protection

Hi My Friends: AL VUELO DE UN QUINDE EL BLOG., A chance alignment of planets during a passing gust of the solar wind has allowed scientists to compare the protective effects of Earth’s magnetic field with that of Mars’ naked atmosphere. The result is clear: Earth’s magnetic field is vital for keeping our atmosphere in place.

This animation shows how a particular stream of the solar wind sweeps through space, interacting with both Earth and Mars.

Credits: ESA

A chance alignment of planets during a passing gust of the solar wind has allowed scientists to compare the protective effects of Earth’s magnetic field with that of Mars’ naked atmosphere. The result is clear: Earth’s magnetic field is vital for keeping our atmosphere in place.

The alignment took place on 6 January 2008. Using ESA’s Cluster and Mars Express missions to provide data from Earth and Mars, respectively, scientists compared the loss of oxygen from the two planets’ atmospheres as the same stream of solar wind hit them. This allowed a direct evaluation of the effectiveness of Earth’s magnetic field in protecting our atmosphere.
They found that while the pressure of the solar wind increased at each planet by similar amounts, the increase in the rate of loss of martian oxygen was ten times that of Earth’s increase.
Such a difference would have a dramatic impact over billions of years, leading to large losses of the martian atmosphere, perhaps explaining or at least contributing to its current tenuous state. This artist's impression shows the magnetosphere of Mars. Unlike Earth, which has an internal magnetic field, Mars lacks a planet-wide magnetic field so the martian magnetosphere is smaller than the terrestrial one.

Credits: ESA
The result proves the efficacy of Earth’s magnetic field in deflecting the solar wind and protecting our atmosphere.
“The shielding effect of the magnetic field is easy to understand and to prove in computer simulations, thus it has become the default explanation,” says Yong Wei from the Max-Planck-Institut für Sonnensystemforschung, Germany, who led the study.
Now, by making measurements during a planetary alignment when the two planets were being hit by exactly the same part of the solar wind, the team have proved it in reality.
They now hope to extend their work by incorporating data from ESA’s Venus Express spacecraft, which also carries a sensor that can measure the loss of its atmosphere.
Venus will provide an important new perspective on the issue because like Mars, it has no global magnetic field, yet it is similar in size to Earth and has a much thicker atmosphere.
It will therefore provide unique data to help place the Earth and Mars results in context.

This artist's impression shows how the solar wind shapes the magnetospheres of Venus (top), Earth (middle) and Mars (bottom). Unlike Venus and Mars, Earth has an internal magnetic field which makes its magnetosphere bigger. The lines coming out of the Sun symbolise the outward propagation of the solar wind. The planet’s distances are not shown to scale.

Credits: ESA
http://www.esa.int/esaCP/SEMXWW7YBZG_index_1.html#subhead2
There are a number of upcoming planetary alignments that will provide good opportunities for such studies.
“For the next few months there is a good alignment between the Sun, Earth, Venus and Mars, and observations made by many spacecraft, including Mars Express, Venus Express and NASA’s STEREO solar observatory, will be analysed together,” says Olivier Witasse, ESA Mars Express Project Scientist.
Cluster will continue to play an important role in these studies, too. It is the only mission in near-Earth space capable of taking such measurements.
In addition, scientists are keen to observe how the increase in solar activity associated with the current solar cycle may affect the loss of atmospheric particles from all three planets.
“The European family of Solar System missions, with their unique observational capabilities, will play a vital role in studying this behaviour during the approaching maximum in solar activity,” says Matt Taylor, ESA Cluster Project Scientist. ESA
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com