Up close and personal with the Sun

During the launch of NASA’s Parker Solar Probe in 2018, headlines would have had you believe that the spacecraft was on a mission to touch the Sun. It will get close, very close in astronomical terms, but no probe could handle a temperature of 5,500 °C and radiation spewing from the Sun’s fiery surface.

Speeding ever faster and ever nearer to our home star, with the assistance of seven gravity kicks from Venus, the Parker Solar Probe’s 24 looping orbits over its seven-year mission will end in a dramatic 700,000 km/h flyby. It will be the first spacecraft to graze the edge of the Sun’s atmosphere – just 6.9 million km from the surface.

This may still sound far away, but beats all past efforts hands-down: the previous record of 43 million km was set by Helios 2 in 1976 (which the Parker Solar Probe smashed in January this year when it swept past 13.5 million km from the Sun).

Even 6.9 million km away, the spacecraft requires an 11 cm-thick carbon-composite shield to protect its instruments from 1,400 °C temperatures and deadly radiation. Its computer system also circulates water around the spacecraft and tucks solar panels behind the shield when necessary, allowing the instruments to stay at a cool 26 °C.

Why NASA wants to send a probe so close to the Sun is simple: the Sun’s atmosphere, called the solar corona (the jagged ring you can only see during a total eclipse) still holds many mysteries that can only be solved close-up.

For decades, scientists have been stumped as to why the corona is so hot. Why does this thin atmosphere reach temperatures in excess of 1 million °C when the surface is so much cooler? They also want to know how the Sun produces space weather closer to home. The Sun drives a stream of highenergy particles, known as solar wind, in all directions across the Solar System. These particles jet past Earth at speeds up to 800 km per second, shaking Earth’s magnetic field and scrambling satellites. Can we predict when the solar wind gets stormy so we can protect satellites?

To solve these mysteries, the small car-sized spacecraft is packed with four instrument suites that study magnetic fields, plasma and energetic particles, and image the solar wind.

Data from these instruments are already helping scientists learn more about the corona and high-energy solar particles. And it is hoped that by the mission’s conclusion in 2025, before the spacecraft meets its fiery end in the heart of the Sun, the Parker Solar Probe will have finally exposed some of the Sun’s most elusive secrets

Dr Benjamin Skuse is a freelance science writer

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