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From Nature: Although the Sun is quite near to us compared with other stars, it has always kept intriguing and fundamental scientific secrets from us.

For instance, we still don’t know how the solar corona — the Sun’s outermost atmosphere — maintains temperatures in excess of one million kelvin, whereas the visible surface has temperatures of just below 6,000 K1. The corona produces the solar wind, an outflow of plasma particles (free ions and electrons) that expands into the space between the planets. In 2018, NASA launched the Parker Solar Probe2 (PSP) with the aim of identifying the mechanisms behind the heating of the corona and the acceleration of the solar wind.