Humanity has officially touched the Sun (or, at least, one of its probes has)

Parker solar probe partly determines where Sol ends and begins

NASA's Parker solar probe has become the first spacecraft to reach the Sun, after solar boffins announced the feat at a meeting of the American Geophysical Union.

The event actually happened way back on April 28, but it took months before the data made its way back to Earth and a few more before scientists could confirm the event. But now NASA has said, yep, that definitely happened – one of humanity's instruments has touched our local star.

The Parker probe has been hurtling towards – and looping around – the Sun since its launch in August 2018. When the spacecraft entered the star's corona in April, it was its eighth close approach to Sol.

The mission was launched with three main goals: to trace the flow of energy that heats the corona and accelerates solar wind, to learn about the structure and forces of the magnetic fields that create solar wind, and to determine what accelerates and transports energetic particles. To boldly go where no-one has gone before counts for extra credit.

Understanding solar winds is useful because occasional gouts of star stuff can disrupt satellites and other electronic technology. But determining how solar winds are created is hard, because the Sun doesn't have a solid surface – it's mostly hot plasma held together by its own gravity, and boundaries are hard to pin down.

Boffins have defined the "Alfvén Critical Surface" as the point separating the end of the solar atmosphere, or the corona, and the beginning of solar wind.

The corona is essentially the visible part in an eclipse. By dipping into it for over five hours, Parker taught scientists that the Sun's magnetic field changes there.

During the flyby, the spacecraft crossed the Alfvén Critical Surface several times. In doing so, it confirmed a prediction: the boundary isn't perfectly round. It has spikes and waves and wrinkles – no doubt these features have some secrets to tell about how Sun-related events affect the atmosphere.

The spacecraft has a special heat shield made of reinforced carbon composite foam that allows it to withstand the blasting heat and energy produced by our star. The inner plate that faces the Sun has a white ceramic paint that reflects heat. Amazingly, the instruments onboard stay at a mere 27° Celsius (81°F).

It takes eight minutes for radio communication to travel between Earth and the probe – more if it is actively making observations, as the probe is cut off from communication at that time. Also, having the heat shield continuously pointed at the sun sometimes means that it just can't be in a position that allows transmission to Earth.

All this means Parker must protect itself autonomously, which it does using light-direction-detecting sensors and reaction wheels that reposition it into shadows.

It's very likely that the eighth orbit is not the only one where Parker entered the corona during perihelion – the point in the orbit where the spacecraft is closest to the Sun – but scientists are not quite ready to confirm whether its ninth and tenth passes, which occurred just last month, qualify. They want to look more at the data.

The next flyby will occur in January 2022. Parker will continue to fly ever closer to the Sun until it goes down in a blaze of glory in 2025.

In a video posted by NASA, astrophysicist and senior scientist at Johns Hopkins University Applied Physics Laboratory Dr Nour Raouafi said the mission is important because our Sun is the only one known to harbor life. According to Dr Raouafi, Parker "will link directly into the question – are we alone in this universe?"

Well, so far we're the only ones who've built a thing just to launch it into the Sun, so we've got that. ®

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