No spacecraft has ever flown as close to the Sun as the Parker Solar Probe will. The spacecraft will penetrate the outer solar atmosphere — the corona — where its measurements should help us understand the origin and characteristics of the solar wind. To put this in perspective, consider that Mercury is at 0.39 AU. The Helios-B spacecraft, launched in 1976, closed to within 43 million kilometers of the Sun (0.29 AU), the current record for a close pass. The Parker Solar Probe will fly seven times closer, moving within ten solar radii.
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