The Polarimeter to Unify the Corona and Heliosphere (PUNCH) will investigate the Sun’s outer atmosphere (that is, the corona) and the stream of solar wind it generates. The spacecraft will also track coronal mass ejections, the solar wind tsunamis that can crash around Earth, affecting satellite communications such as GPS, damaging power grids, and creating Northern Lights in the process.

The solar wind is a plasma, whose protons and electrons fly separately along the Sun’s magnetic field lines. Earth’s magnetic field generally protects us from this stream of particles, but when the Sun’s magnetic field touches Earth’s, the two fields can connect, creating openings. When those openings are long-lived, they are called cusps.

“Photographing the sky in polarized light is the secret sauce of the mission,” says PUNCH’s principal investigator Craig DeForest (Southwest Research Institute). Sunlight becomes polarized when it bounces off the plasma’s electrons, he explains. So polarization gives 3D information, showing how features in the solar wind move through space.

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