Parker Solar Probe’s spiral trajectory gradually brings it closer to the Sun, and during the last few passes, the spacecraft was consistently within 20 solar radii (93% of Earth’s distance from the Sun), theoretically putting it in the position to cross the boundary.įor the first time in history, a spacecraft has touched the Sun. Estimates based on remote images of the corona had put it somewhere between 10 and 20 solar radii from the surface of the Sun - 4.3 to 8.6 million miles. Until now, researchers were unsure exactly where the Alfvén critical surface lies. Beyond the Alfvén critical surface, the solar wind moves so fast that waves within the wind cannot travel back to the Sun. Solar material with enough energy to make it past that boundary drags the magnetic field of the Sun along with it as it races across the solar system. That point, known as the Alfvén critical surface, marks the end of the solar atmosphere and beginning of the solar wind. As that material gets pushed away from the Sun by rising heat and pressure, it reaches a point where the gravitational forces and magnetic fields are too weak to contain it. Unlike Earth, the Sun doesn’t have a solid surface, but it does have a superheated atmosphere made of material bound to the Sun by gravity and magnetic forces. Plasma within the corona (circle at left), is still connected to the Sun, and waves in the plasma travel back and forth between the surface and upper corona. Beyond the Alfvén critical surface, the solar wind moves so fast that waves within the wind cannot ever travel fast enough to make it back to the Sun - severing their connection. Solar material with the energy to make it across that boundary (circle at right) becomes the solar wind, which drags the magnetic field of the Sun with it as it races across the solar system, to Earth and beyond. The Alfvén critical surface marks the end of the solar atmosphere and the beginning of the solar wind - and by crossing into it, NASA’s Parker Solar Probe has “touched the Sun” for the first time. We can actually see the spacecraft flying through coronal structures that can be observed from Earth during a total solar eclipse.” Closer Than Ever Beforeįortified to withstand some of the most extreme conditions in the solar system, Parker Solar Probe launched in 2018 to explore the mysteries of the Sun by traveling closer to it than any spacecraft before. “We see evidence of being in the corona from magnetic field data, solar wind data, and visually in white-light images. “Flying so close to the Sun, Parker Solar Probe now senses conditions in the corona that we never could before,” said Nour Raouafi, the Parker Solar Probe project scientist at APL. The first passage through the corona - as well as more flybys to come - will provide data on phenomena that are impossible to study from afar. Having halved its distance to the Sun since then, Parker Solar Probe has now identified one place where those features originate: the solar surface. In 2019, Parker Solar Probe discovered that striking magnetic zig-zag structures in the solar wind, called switchbacks, are plentiful close to the Sun. “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.”Īs it circles closer to the solar surface, Parker Solar Probe - built and operated by the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland - is making discoveries that other spacecraft were too far away to see, including from within the solar wind, the flow of particles speeding from the Sun that can influence us at Earth. “Parker Solar Probe ‘touching the Sun’ is a monumental moment for solar science and a truly remarkable feat,” said Thomas Zurbuchen, the associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. Just as landing on the Moon allowed scientists to understand how it was formed, touching the Sun is helping scientists uncover critical information about our closest star and its influence on the solar system. The new milestone marks one major step for Parker Solar Probe and one giant leap for solar science. NASA’s Parker Solar Probe has now flown through the Sun’s upper atmosphere - called the corona - sampling particles and characterizing magnetic fields in this dynamic environment. The results have been accepted for publication in Physical Review Letters and the Astrophysical Journal.įor the first time in history, a spacecraft has touched the Sun. A major milestone and new results from NASA’s Parker Solar Probe were announced Dec. 14 in a press conference at the 2021 American Geophysical Union Fall Meeting in New Orleans.
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