Mission scientists are particularly interested in solving two long-standing puzzles: how the stream of particles flowing continuously from the sun, known as the solar wind, is accelerated to its tremendous velocities; and why the sun's outer atmosphere, or corona, is so much hotter than its surface. (Corona temperatures can top 2 million degrees Fahrenheit, or 1.1 million degrees Celsius. The solar surface is downright temperate by comparison, at 11,000 F, or 6,000 C.)

The PSP is tackling these questions by brazenly barreling into the corona itself. Once every five months or so, the probe zooms through the sun's sizzling atmosphere, getting unprecedented up-close looks at our star.