Authors: Samuel T. Badman (Center for Astophysics | Harvard & Smithsonian), Yeimy J. Rivera (Center for Astophysics | Harvard & Smithsonian), Stuart D. Bale (University of California, Berkeley), Michael L. Stevens (Center for Astophysics | Harvard & Smithsonian)

The global structure of the Sun’s extended corona is governed by the physical processes which represent some of the biggest outstanding questions in heliophysics. These include the nature of coronal heating and solar wind acceleration. NASA’s Parker Solar Probe (Parker) offers unique new opportunities to probe this structure directly through its unprecedented orbit which takes it closer to the Sun than any prior spacecraft. As of Spring 2023, Parker has achieved perihelia of 13.3 Rs, but will continue to dive deeper to an eventual closest approach of 9.8Rs at the end of 2024. Already Parker is starting to offer tantalizing glimpses into the sub-alfvenic corona. The most recent orbits exhibit hints of an imminent global plasma regime change on multiple fronts: As well as unambiguous crossings of the Alfven critical surface, Parker sees significant solar wind deceleration, possible global magnetic field reorganization, and proton core temperatures hot enough to be comparable to isothermal solar wind models. In this talk, we will discuss how these exciting initial measurements may become decisive constraints in the latter orbits of the Parker mission. We trace the implications of making such direct measurements of the corona-solar wind transition to the science questions of coronal heating and solar wind acceleration. This poster may be viewed at https://docs.google.com/drawings/d/1J1RSGbmQrdFnovZbPwvXu5MJZRZpgX_NmaII5CZbvQk.