The Parker Solar Probe will come nearer to the Sun than any spacecraft in history. Jane Green looks at how it will solve one of our star’s biggest mysteries in the process
On 12 August 2018, NASA’s Parker Solar Probe (PSP) blasted off from Cape Canaveral Air Force Station into the pre-dawn Florida sky on a mission to become the first-ever spacecraft to ‘touch the Sun’. Later this year, on 24 December 2024, Parker will come seven times closer to the Sun than any spacecraft before it, diving through its outermost atmosphere, the corona, and in the process smashing its own speed record to become the fastest human-made spacecraft ever launched.
In yet another first, NASA named the probe for a living individual: visionary astrophysicist Professor Eugene Parker who, in the mid-1950s, proposed theories about how stars emit energy. He called this flow of energy the solar wind, and described the complex system of plasmas, magnetic fields and energetic particles comprising the phenomenon. He also posited a controversial theory for why the corona was so much hotter than the Sun’s ‘surface’ – a theory for which the Probe is delivering evidence. Prof Parker witnessed the launch but sadly passed in March 2022, aged 94.
The goals of this modern-day Icarus are to trace the flow of energy heating the Sun’s outer atmosphere, to shed light on the birthplaces of the solar wind and to explore how the wind’s energetic particles are transported and accelerated. By getting up close and personal with our nearest star, it’s hoped PSP will resolve another long-standing question: why the corona is so much hotter than the Sun’s ‘surface’, a paradox known as the coronal heating problem (see page 63).
It took six decades before advances in thermal engineering enabled the building of spacecraft that can survive the scorching temperatures, high-energy radiation and magnetic fields filling the Sun’s upper atmosphere, or corona. Invisible due to the overpowering brilliance of the photosphere, the corona is most readily seen when the Moon covers the Sun during a total eclipse, or when a circular coronagraph blocks our star’s disc.
Temperatures in the corona exceed a colossal 1,000,000°C (1,800,000°F), hot enough to rip electrons from atoms to form plasma – where negatively charged electrons have separated from positively charged ions, creating a sea of free-floating particles with individual elect
