A Spacecraft Has 'Touched' The Sun For The First Time in History

 

A human-built spacecraft has swooped in and made contact with the Sun, marking a historic milestone.

NASA's Parker Solar Probe passed into and through the solar corona, the Sun's upper atmosphere, on April 28, 2021. Not only did it survive – showing the effectiveness of Parker's high-tech heat shielding – but it also took in situ measurements, providing us with a trove of never-before-seen data on our Solar System's core.

"The Parker Solar Probe 'touching the Sun' is a watershed moment for solar science and a really extraordinary achievement," said astrophysicist Thomas Zurbuchen, associate administrator for NASA Headquarters' Science Mission Directorate.

"Not only does this achievement provide us a better understanding of our Sun's evolution and its effects on our Solar System, but everything we learn about our own star tells us more about stars throughout the Universe."

The Parker Solar Probe was launched in 2018 with the primary goal of studying the solar corona. It should make a total of 26 close approaches, or perihelions, to the Sun over the course of its seven-year mission, employing a total of seven gravity assist manoeuvres from Venus to bring it closer. The perihelion in April was the seventh and first to penetrate the corona.

Parker recorded variations in the Sun's magnetic field and sampled particles during his nearly five-hour stay inside the solar atmosphere. Previously, we depended on external data to estimate these qualities.

"Flying so near to the Sun, the Parker Solar Probe now detects circumstances in the magnetically dominated layer of the solar atmosphere - the corona – that we've never been able to detect before," said astronomer Nour Raouafi of the Johns Hopkins Applied Physics Laboratory.

"Magnetic field measurements, solar wind data, and photos all provide evidence of being in the corona. The spacecraft can be seen travelling through coronal structures that can be seen during a total solar eclipse."

Above: Coronal streamers, which can only be viewed from Earth during an eclipse, are the brilliant features shown in these images. The Parker probe captured these images during the ninth perihelion in August of this year.

There is no solid surface on the Sun. Instead, the Alfvén critical surface, where gravity and the Sun's magnetic fields are too weak to hold the solar plasma, defines its border.

Above this point, the solar wind appears, sweeping powerfully through the Solar System and breaking away from the Sun in waves. The photosphere, which is made up of churning convection cells and plasma, is much below what we call the Sun's'surface.'

Parker's purpose was to learn more about the Alfvén critical surface, such as where it is and what its topography is like, because we didn't know anything about it. The Alfvén critical surface was estimated to be between 10 and 20 solar radii from the Sun's centre. Parker reached the corona at a distance of 19.7 solar radii and sank as low as 18.4 solar radii throughout its corona journey.

Surprisingly, the probe only encountered the corona's magnetic conditions on a sporadic basis, implying that the Alfvén critical surface is wrinkled. Parker came across a magnetic structure known as a pseudostreamer at a lower depth, which we can see arcing out from the Sun during solar eclipses. Parker's findings show that these structures are to blame for the Alfvén critical surface's deformation, albeit we don't know why.

Conditions were quieter inside the pseudostreamer than in the surrounding solar environment. Particles were no longer as chaotically buffeting the spaceship, and the magnetic field was more ordered.

Parker also looked on the occurrence of solar switchbacks. These are Z-shaped kinks in the solar wind's magnetic field, and it's unclear where or how they develop. Switchbacks have been around since the 1990s, but it wasn't until Parker examined them in 2019 that we discovered how ubiquitous they are. The data from the probe's sixth flyover revealed that switchbacks are caused by patches.

Parker has now discovered them within the solar atmosphere, indicating that at least some of the switchbacks originate in the lower corona.

"The structure of the switchback zones lines up with a small magnetic funnel structure at the base of the corona," astronomer Stuart Bale of the University of California, Berkeley, stated. "This is what some theories predict, and it identifies a source for the solar wind itself."

We still don't know how these strange structures came to be, but with dozens more perihelions on the way, some as close as 9.86 solar radii from the Sun's centre, we're sure to find out.

"

We've been studying the Sun and its corona for decades, and we know there's some fascinating physics at work to heat and accelerate the solar wind plasma. We still don't know exactly what that physics is "Raouafi explained.

"With the Parker Solar Probe now travelling towards the magnetically dominated corona, we will finally gain some answers about how this mysterious region works."