Why is the Sun’s atmosphere so hot?

If you were to sit on the Sun’s surface, you’d note something interesting before being entirely vaporised.

The surface of the Sun is a toasty 6,000 degrees Celsius, but the atmosphere of the Sun – known as the corona – is estimated to be about a million degrees Celsius. That’s unusual because normally heat gets cooler as it moves away from its energy source – in this case the core at the middle of the Sun.

A new paper published in the Astrophysical Journal Letters has looked into this phenomenon using two satellites which are currently headed towards the Sun.

The two satellites – Europe’s Solar Orbiter and NASA’s Parker Solar Probe – were used to produce a simultaneous measurement of the solar corona and microphysical properties of the plasma.

Plasma is one of the four fundamental states of matter, but is mostly located in hot stars. It’s similar to gas but is filled with charged particles.

Although we still don’t know for sure why the surface is so much cooler than the corona, the new research suggests that turbulence -which was long suspected as the cause – could be on the money.

Turbulence doesn’t just affect people on airplanes. While normally gas or fluid sits in distinct layers, turbulence is when that fluid or gas is tossed about.

The theory is that turbulence in the atmosphere of the Sun could be heating the plasma inside the corona because all that tossing releases energy into heat.

While more work is needed, the two probes will hopefully be able to provide more information before long.

The Solar Orbiter is only three years into its seven-year mission, while the Parker Solar Probe is still two years off its completed mission, all of which will get the two spacecraft closer and closer to the Sun’s corona.

“This is a scientific first. This work represents a significant step forward in solving the coronal heating problem,” says Daniel Müller, Project Scientist.

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