The Parker Solar Probe has become the first spacecraft to fly through the Sun's upper atmosphere or corona, NASA announced. In April, it passed within 15 solar radii (around 6.5 million miles) from the Sun's surface in a region where magnetic fields dominate solar conditions. "Parker Solar Probe 'touching the Sun' is a monumental moment for solar science and a truly remarkable feat," said NASA associate administrator Thomas Zurbuchen.
The Sun has a superheated atmosphere called the corona (visible from Earth only during a solar eclipse) that's bound to it by gravity and magnetic fields. At a certain limit called the Alfvén critical surface, materials are able to escape those forces and become part of the solar wind, permanently severing their connection to the Sun.
Scientists have estimated that the corona is between 10 to 20 solar radii from the Sun's surface, or around 4.3 to 8.6 million miles. The Parker Solar probe detected the specific magnetic and particle conditions required for the corona at around 18.8 solar radii, or around 8.1 million miles. It passed in and out of the boundary several times, proving that the Alfvén critical surface has spikes and valleys and isn't shaped like a smooth ball.
Inside that region, the probe encountered features called pseudostreamers, or massive structures rising above the Sun's surface visible during solar eclipses. Flying through the objects was like "flying into the eye of the storm" because of the quieter conditions and slowing particles, NASA said.
It also made observations that may helped scientists figure out where "switchbacks," or kinks in the solar wind form. It detected bursts of switchbacks as it passed closer to the sun, and scientists were able to trace those back to the visible surface. Specifically, they found that some types of "fast" switchbacks form in the magnetic funnels created between convection cells on the sun's surface.
The probe has not only made the closest-ever pass by the sun, it's traveling at the greatest speed of any manmade object ever, currently around 430,000 MPH. The next close pass will happen in January 2022, when scientists will try to determine exactly how switchbacks and other solar phenomena form. "Such measurements from the corona will be critical for understanding and forecasting extreme space weather events that can disrupt telecommunications and damage satellites around Earth," NASA wrote.