NASA's Parker Solar Probe just flew through the Sun's outer layer known as the corona on April 28 this year, but the findings were published in the Physical Review Letters yesterday on December 14.

The Parker Solar Probe collected particles and measured the Sun’s magnetic field.

"Parker Solar Probe 'touching the Sun' is a monumental moment for solar science and a truly remarkable feat," said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington, DC.

"Not only does this milestone provide us with deeper insights into our Sun's evolution and its impacts on our solar system, but everything we learn about our own star also teaches us more about stars in the rest of the universe.”

The Sun isn’t just a solid ball floating in space. It’s a densely packed soup of plasma with a thin outer layer known as the corona. Think of the corona like an atmosphere. The corona is the ‘stuff’ blowing off of the Sun but will not actually blow away into space because it’s still within the Sun’s magnetic pull.

However, portions of the corona that escape the Sun’s magnetic pull are known as solar winds. Solar winds cause Auroras. Auroras are dynamic patterns of brilliant lights that resemble curtains, rays, and spirals that cover the entire sky. They can be seen from high northern latitudes like Norway and Sweden or high southern latitudes like South Africa and Chile. 

Solar winds don’t just make the sky pretty though, they can also disrupt satellite and communication systems. 

The dividing line between corona and solar wind isn't crystal clear, the actual boundary of the corona is called the Alfvén Critical Surface (ACS), and until now, it wasn't entirely clear where the ACS actually lay. 

By taking remote images of the corona (the bright, somewhat spikey bits around the moon that you can see during a solar eclipse) and analyzing other data, scientists have estimated that the ACS stretches anywhere from 10 to 20 solar radii above the surface of the Sun, which is approximately 7 to 14 million kilometers.

The Parker Solar Probe has been on a tightening spiral trajectory around the Sun since it first launched in 2018, and on its eighth revolution, it observed key magnetic and particle conditions that signaled it had crossed the ACS and entered the Sun's atmosphere.

The probe's first passage though the corona only lasted a few hours but will have more opportunities to fly through the corona again, the next one is scheduled for January 2022. 

During the solar flyby, the Parker Solar Probe recorded that the ACS isn't merely smooth shell, but is actually filled with spikes, ripples, and valleys. 

“Flying so close to the Sun, the Parker Solar Probe now senses conditions in the magnetically dominated layer of the solar atmosphere – the corona – that we never could before,” said Nour Raouafi, Parker project scientist at Johns Hopkins Applied Physics Laboratory in Maryland. “We see evidence of being in the corona in magnetic field data, solar wind data, and visually in images. We can actually see the spacecraft flying through coronal structures that can be observed during a total solar eclipse.”

The Parker Solar Probe was launched to study the Sun from closer than any probe before by orbiting very close to its surface. The Parker Solar Probe can endure the Sun’s heat thanks to a thermal shield made of an advanced carbon-composite material that can withstand temperatures up to 1,377 degrees Celsius.

The thermal shield cuts through the Sun's heat like a race car breaks up air in front of it, therefore a draft is created behind it. 

In the space behind the race car, if there is another car behind it, that other car actually encounters less wind resistance and can actually accelerate faster than the car in the front.

The Parker Solar Probe’s thermal shield does the same thing. It bears the brunt of the Sun’s heat, so that the delicate instruments behind it don’t melt. And it is these instruments that gather essential data about the Sun.

Tags : Sun