First spacecraft to fly through Sun's corona

On 14/12/2021, NASA announced that the Parker Solar Probe had become the first spacecraft to fly through the Sun’s upper atmosphere, known as the corona. The milestone was revealed during the American Geophysical Union Fall Meeting, although the actual crossing occurred earlier on 28/04/2021 during the spacecraft’s eighth close flyby of the Sun. During this encounter, Parker Solar Probe crossed the Alfvén critical surface, the boundary where solar wind plasma transitions from being magnetically bound to the Sun to flowing freely into space. This crossing marked the first direct sampling of the solar atmosphere by a human made spacecraft. During the April 2021 pass, the spacecraft moved in and out of the corona several times and spent a total of roughly five hours within the solar atmosphere. At the time of the crossing, the probe was approximately 13 million kilometers from the Sun’s center. Instruments onboard measured particles and magnetic fields directly, confirming that the boundary of the corona is irregular rather than smooth. Observations identified structures described as wrinkles and valleys in the Alfvén surface, indicating that the corona’s extent varies depending on solar activity and magnetic conditions. The Parker Solar Probe is protected by a 4.5 inch thick carbon composite heat shield designed to withstand external temperatures of about 1,377 degrees Celsius while maintaining near room temperature conditions for onboard instruments. This thermal protection system enabled the spacecraft to safely operate while immersed in the Sun’s outer atmosphere. Data collected during the crossing also helped scientists trace the origin of magnetic switchbacks, sudden reversals in the solar wind’s magnetic field, linking them to processes occurring near the solar surface. The findings from the 28/04/2021 encounter provided the first in situ measurements of the corona and improved understanding of how the solar wind forms and accelerates. The Parker Solar Probe continues to perform progressively closer flybys of the Sun, with later orbits designed to move deeper into the corona and gather additional measurements of plasma behavior, magnetic structures, and energy transfer near the Sun.