Solar Probe Plus will be an extraordinary and 
historic mission, exploring what is arguably the last region of the solar system to be visited by a spacecraft, the Sun’s outer atmosphere or corona as it extends out into space. Approaching as close as 9.5 solar radii* (8.5 solar radii above the Sun’s surface), Solar Probe Plus will repeatedly sample the near-Sun environment, revolutionizing our knowledge and understanding of coronal heating and of the origin and evolution of the solar wind and answering critical questions in heliophysics that have been ranked as top priorities for decades. Moreover, by making direct, in-situ measurements of the region where some of the most hazardous solar energetic particles are energized, Solar Probe+ will make a fundamental contribution to our ability to characterize and forecast the radiation environment in which future space explorers will work and live. [Source: NASA]
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SPP at University of California, Berkeley