Not too hot to handle

NASA’s Parker Solar Probe is one of the most daring missions in the Solar System.

Led by the Applied Physics Laboratory at Johns Hopkins University, the mission made history in 2021 when it became the first spacecraft to touch part of the Sun. It flew 13 million kilometers (8.1 million miles) above the Sun’s surface, passing through and sampling the outer atmosphere, called the corona. In September 2022, it passed through one of the most powerful coronal mass ejections ever recorded, becoming the first spacecraft ever to do so. And in December 2024, the probe went even closer to the Sun, flying 6.1 million kilometers (3.8 million miles) above the surface, nearly 10 times closer than Mercury’s orbit.

This close to the Sun, temperatures can reach nearly a million degrees Celsius (over a million degrees Fahrenheit), even hotter than the Sun’s surface. 

The question that naturally arises is: How can anything survive temperatures that high?

“People started thinking about building a probe to fly close to the Sun back in the late ’50s,” said the mission’s project scientist Nour Rawafi in an interview with Planetary Radio host Sarah Al-Ahmed. “But it took us over six decades to get to the point technologically where we could build a spacecraft robust enough to withstand the harsh environment around the star. It’s probably one of the harshest environments you can ever fly through.”

One crucial component of Parker Solar Probe’s death-defying stunt is its heat shield. It is about 11.5 centimeters (4.5 inches) thick and made of carbon composite foam sandwiched between two carbon plates, painted white to reflect as much heat as possible. As it passes the Sun, the spacecraft’s autonomous systems keep it oriented so that the heat shield is always between the probe and the Sun.

Another factor that helps make the mission possible is the nature of how heat is transferred in the vacuum of space. The Sun’s corona has very low density, meaning that there aren’t a lot of particles that can transfer heat. So although the overall temperature in the corona is around a million degrees, Parker Solar Probe’s heat shield is predicted to only get heated to a maximum of about 1,400 degrees Celsius (about 2,500 degrees Fahrenheit) during its closest passes.

When Parker Solar Probe made its close pass in December 2024, it broke another record. As it whizzed past the Sun, it was traveling at over 190 kilometers per second (about 120 miles per second) — the fastest that any human-made object has ever moved.

Before flight, the heat shield was tested to withstand temperatures up to 1,650 degrees Celsius (3,000 degrees Fahrenheit). Although this might seem paltry if you’d been imagining a shield capable of handling million-degree temperatures, it is still an extraordinary feat. Parker Solar Probe’s heat shield would even survive direct contact with the hottest lava on Earth. 

“The heat shield is the key technology that enabled the whole mission,” said Rawafi. “But, wherever you look on this spacecraft, there is cutting-edge technology.” And nearly seven years after launching, that technology is still performing well. 

“The spacecraft is very healthy, knock on wood. We launched in 2018 when the Sun was very quiet, and we’ll end the prime mission [in 2025] at solar maximum. Hopefully, we’ll extend it to cover the whole solar cycle and go beyond that.”

As Parker Solar Probe continues its mission to get up close and personal with the Sun, we can surely expect some more astounding feats of exploration.