The Mysteries of the Solar Plasma

How new experiments in plasma physics, and the Parker Solar Probe, might unlock the Sun’s secret source of power.

Beautiful arcs above the solar surface called coronal loops that emit in the extreme ultraviolet (EUV).

Much of the luminous universe — not counting ‘dark’ stuff — is hydrogen, at millions of degrees, and billions of atmospheres, crushed inside stars. Electrons are splitting off atoms and emitting light in the process. This state of matter is called a plasma.

In August of last year, NASA launched the Parker Solar Probe. In a series of ellipsoidal passes, it will fly through the solar corona — the sun’s atmosphere — capturing data. Like a child sticking his finger into a jar, poking something is usually the first step toward unraveling a scientific mystery.

I had the joy of getting a good look at the corona in 2017. The corona is what you see when an eclipse reaches totality, the beautiful luminous arms of light that reach out in all directions; the result of a cloud of fast-moving electrons scattering light as it diffuses out into space.

The Parker probe will fly through these arms, and scientists hope that it will begin to address the huge gaps in our understanding of the sun.

The corona is observed to be hot. This might not surprise you. But it actually rises in temperature from six thousand degrees at the surface to millions of degrees in the corona. That’s weird. We would expect the atmosphere to fall in temperature as you get farther from the heat source, and the pressure drops, and heat is radiated out to space.

The energy needed to supply this missing heat is only .01% of the total solar power output, but scientists have not completely explained how the energy gets from point A to B. Energy typically flows from hot to cold; not from cold to hot.

The best theories suggest that powerful electric and magnetic fields transport energy from the interior to the far reaches of the atmosphere. Exactly how this works is not fully clear.

For the purpose of aiding in the resolution of this mystery, Stuart Bale from UC Berkeley has equipped the probe with a series of magnometers and sensors to directly read the magnetic fields inside the corona.

There are also instruments to detect the particles whizzing by as the probe plummets through the corona. The probe will be able to identify electrons, protons, various ions, and isotopes of helium. These particles start off in the corona, but end up as a solar wind, expanding into space.

Eugene Parker, for whom the probe was named, first suggested that the corona must be undergoing constant supersonic expansion into the vacuum of space. Scientists confirmed this, but found fast particles traveling more quickly than expected. Something is accelerating them; and whatever it is seems to have something to do with solar activity.

Galileo was the first to observe the sun and notice spots on the surface. We now know the Sun is a tumultuous place, with incredibly strong magnetic field lines laced among explosions, giant arcs (coronal loops), dark spots (coronal holes), mass ejections, and flares that emit everything from radio waves to gamma rays while sending shocks that ripple across the entire solar disk. ‘Fast’ solar wind is often correlated with these events, but little is known about what causes the events themselves.

These are some of the mysteries the Parker probe hopes to answer.