Parker Solar Probe Data Refines Boundary of Sun's Atmosphere

New scientific analysis utilizing data from NASA's Parker Solar Probe is providing a more precise map of the outer boundary of the Sun's atmosphere, the corona. This demarcation line is crucial as it governs the transition point where solar particles begin to flow outward as the solar wind, escaping the star's magnetic and gravitational influence. The corona itself is characterized by an extreme temperature, often surpassing one million degrees Fahrenheit, despite its very low plasma density, extending millions of kilometers from the solar surface.

Researchers, including Sam Badman from the Center for Astrophysics | Harvard & Smithsonian, have been processing data collected during the probe’s closest approaches, or perihelia, to the Sun. This enhanced clarity regarding the atmospheric edge is vital for improving space weather forecasting, which directly affects terrestrial infrastructure and assets in orbit. The ability to accurately locate this boundary aids in predicting the arrival and intensity of solar wind gusts capable of disrupting power grids and satellite communications.

The Parker Solar Probe executed a record-breaking pass on December 24, 2024, traveling to within 3.8 million miles, or approximately 6.1 million kilometers, of the Sun’s surface, making it the fastest human-made object at a speed of 430,000 miles per hour. Subsequent perihelia in 2025, specifically on March 22 and June 19, yielded in-situ measurements of the solar environment as the probe navigated dynamic phenomena like Coronal Mass Ejections (CMEs) and magnetic field structures known as 'switchbacks.'

Further observations included the heliospheric current sheet, the expansive magnetic boundary where the Sun's magnetic polarity reverses, which significantly modulates space weather intensity near Earth. The complex data set processing has led researchers, publishing in journals such as the Astrophysical Journal Letters, to confirm the existence of two distinct classes of slow solar wind, addressing a long-standing question in heliophysics. Evidence also suggests that magnetic switchbacks are essential for closing the energy budget required to accelerate the fast solar wind.

The historical theory of the corona’s extreme heat was first proposed by Eugene Parker in 1958, which led to the prediction of the solar wind, later confirmed by missions like Luna 1 and Mariner 2. As the Sun currently moves through the declining phase of its 11-year solar cycle, the outer atmospheric boundary is known to exhibit increased irregularity. The Parker Solar Probe, managed by the Johns Hopkins Applied Physics Laboratory for NASA, is positioned to observe these evolving structures as the Sun nears its next minimum, providing a unique perspective.

This fundamental scientific clarification concerning the corona's edge is directly relevant to societal needs, as improved solar wind modeling enables more robust protection for critical electrical systems and communication satellites. The mission continues to provide firsthand accounts from within the solar atmosphere, a vantage point Kelly Korreck, a heliophysicist at NASA Headquarters, noted is essential for understanding solar processes. The probe's instruments, shielded by a heat shield rated to withstand temperatures up to 2,600 degrees Fahrenheit, continue to operate following the late 2024 encounter.