<\/p>\n The new findings<\/a>, published Dec. 11 in The Astrophysical Journal Letters, could help improve space weather<\/a> models of how solar activity affects Earth and sharpen predictions of atmospheric behavior around other stars, scientists say.<\/p>\n You may like<\/p>\n “Before, we could only estimate the sun’s boundary from far away without a way to test if we got the right answer,” study lead author Sam Badman, an astrophysicist at the Center for Astrophysics \u2223 Harvard & Smithsonian (CfA) in Massachusetts, said in a statement<\/a>. “But now we have an accurate map that we can use to navigate it as we study it.”<\/p>\n “And, importantly, we also are able to watch it as it changes and match those changes with close-up data,” he added. “That gives us a much clearer idea of what’s really happening around the sun<\/a>.”<\/p>\n The boundary, known as the Alfv\u00e9n surface, marks the point where the outward flow of the solar wind<\/a> becomes faster than magnetic waves that would otherwise carry material back toward the sun. Beyond this “point of no return,” solar particles can no longer fall back and instead stream permanently into interplanetary space.<\/p>\n Scientists knew that this boundary shifts with the sun’s roughly 11-year activity cycle<\/a> \u2014 expanding and becoming more complex during solar maximum, and shrinking during quieter solar minimum periods. Until now, however, they lacked direct confirmation of what those changes actually looked like.<\/p>\n “That’s actually what we predicted in the past, but now we can confirm it directly,” Badman said in the statement.<\/p>\n To build the new maps, the researchers combined close-up measurements from the Parker Solar Probe, which repeatedly plunged through the sun’s outer atmosphere during record-breaking close passes<\/a> as the solar cycle ramped up toward its peak, with data from the European Space Agency<\/a>‘s Solar Orbiter and NASA’s Wind mission, both of which reside about 1 million miles (1.5 million kilometers) from Earth.<\/p>\n Using an instrument onboard Parker called the Solar Wind Electrons Alphas and Protons (SWEAP), the team directly sampled the region beneath the Alfv\u00e9n surface, confirming that the maps correctly show where the sun’s magnetic influence fades and the solar wind escapes, according to the statement.<\/p>\n You may like<\/p>\n “This work shows without a doubt that Parker Solar Probe is diving deep with every orbit into the region where the solar wind is born,” study co-author Michael Stevens, an astronomer at the CfA and the principal investigator of the SWEAP instrument, said in the statement.<\/p>\n \n An artist’s illustration of NASA’s Parker Solar Probe spacecraft during one of its close flybys of the sun. (Image credit: NASA\/Johns Hopkins APL\/Steve Gribben)<\/p>\n Pinpointing where and how the solar wind escapes the sun is essential to answering some of the biggest open questions in solar physics, including why the sun’s corona gets hotter the farther it extends away<\/a> from the solar surface.<\/p>\n![\"An](\"https:\/\/www.newsbeep.com\/il\/wp-content\/uploads\/2025\/10\/dod7VJw7EK2QwiGPQWWrg7.jpg\")
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