Earth is commonly bombarded by solar winds coming from the Sun, but the problem with this is that the solar winds that reach our planet are hotter than they should be. This phenomenon defies the laws of physics that the wind should cool down as it expands through space.

Scientists have finally unraveled the mystery behind this as they published their peer-reviewed study "Electron Temperature of the Solar Wind" in the Proceedings of the National Academy of Sciences (PNAS). 

Unraveling the mystery of hotter solar winds hitting on Earth

As the Sun's heliosphere expels plasma, the laws of physics demand it to cool down after it expands through space. However, it seems like it is taking its sweet time in doing so, which means that the temperature is cooling down at a slower rate than the models predict.

Since its discovery in 1959, people have already been studying the solar wind. But according to physicist Stas Boldyrev from the University of Wisconsin-Madison, some parts of the Sun's plasma is not well understood by scientists.

Boldrev, together with his colleagues, physics professor Cary Forest and Jan Edgal from the University of Wisconsin-Madison, have explained this discrepancy in solar wind temperature. They sought the answer in the related field of plasma physics.

Using laboratory equipment to study moving plasma, the researchers were able to discover what keeps the solar wind from cooling down before hitting Earth. Turns out, the problem lies in a trapped sea of electrons that just can't seem to escape from the Sun's grip.

At first it was thought that the process itself follows the adiabatic laws of physics, which means that the heat energy remains constant; it neither increased nor decreased. The journey of the electron is not simple as it is shoved around at the vast magnetic fields of space and leaves plenty of opportunity for heat to be passed back and forth.

Furthermore, due to its tiny mass, the electrons get a good head start over heavier ions as they shoot forth from the Sun's atmosphere. This leaves a largely positive cloud of particles in their wake.

In time, the growing attraction between these opposite charges takes over the inertia of those flying electrons. It then results in pulling the particles back to where magnetic fields once again play havoc with their paths.

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Mirror Machines

Boldyrev and his team likened this phenomenon to an electron ping-pong playing out inside their laboratory which is commonly used to study plasma. It is called a mirror machine, in which although the name suggests it to have mirrors, it is not the shiny type but a different kind.

Also known as magnetic mirrors or magnetic traps, these linear fusion devices are long tubes with a bottle-neck at either end which has a reflective nature that is created as streams of plasma passing through a bottle pinch at either end.  It alters its surrounding fields in a way that the particles within the stream reflect inside again.

Boldyrev said that some particles can go outside the bottle and they stream along expanding magnetic field lines outside the bottle. The researchers wanted to know how the temperature of the electrons that escaped decreases outside this opening to keep the plasma warm.

The researchers suggest that the population of trapped electrons that turns back and forth plays a major role in how electrons distribute their heat energy. It changes the typical distributions of particle velocities and temperatures in predictable ways.

This model can be used to further understand the mystery of the solar wind. Finding out that mysteries in space can also be studied using this model suggests that there could be more solar phenomena worth studying this way.

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