A spacecraft ‘touched’ the sun. Here’s how it survived.

A NASA probe has become the first spacecraft to “touch” the sun, traveling into a region where the temperature is a spicy 2 million degrees-Fahrenheit.

The Parker Solar Probe flew into the star’s corona, which is its outermost atmosphere, in April. At 6.5 million miles from the sun’s surface, though, that’s the closest anything has come to the fiery orb, according to NASA.

Building instruments that could withstand the scorching heat without disintegrating — and continue taking measurements — was an engineering feat. So how did they do it without turning Parker into Icarus?

Scientists at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., made and monitored one of the two exposed tools on the spacecraft. Called the Solar Probe Cup, the equipment sits outside the heat shield and catches some of the sun's plasma.

Parker entered the corona three times on April 28, at one point for five hours, and sampled particles and magnetic fields. Findings from the event were published last week in Physical Review Letters.

The cup got so hot, it glowed red-orange like a fireplace poker at 1,800 degrees, said Anthony Case, the center’s instrument scientist. That’s a temperature on par with volcanic lava. But it never reached the millions of degrees of its environment.

The key here is understanding the difference between temperature and heat, Case said. Temperature measures how fast particles are moving, while heat is the amount of energy they transfer. 

A 100-degree day feels hot on people’s skin because lots of molecules in the air are quickly hitting their bodies, transferring heat.

“You can feel how hot, how fast they're moving. That's how we sense temperature,” he said. “But in space, there are just very, very few particles. So even though it's a million degrees, there's billions of times, or probably billions of billions of times, less particles than there are in the air on Earth.”

Empty space means fewer particles around to transfer energy and thus heat. What really increases the cup’s temperature is that it faces the sunlight, which can heat it up. 

In determining what the cup should be made of, scientists narrowed their options to a small sliver of the periodic table. The device is made of tungsten, niobium, molybdenum and sapphire — materials with high melting points. Tungsten, for example, can tolerate up to 6,192 degrees.

For eight years, the team worked on the cup's design. At one facility in the Pyrenees Mountains of France, scientists used thousands of mirrors to reflect sunlight and focus it into a tiny area to test the materials under superheated conditions.

Case recalled one failed test during that period involving an oven. A metal coiled around some objects was completely gone after baking.

“All we could see was a shadow of this twisted wire where it had evaporated away and left sort of a deposit on the metal that it was next to,” he said. “Needless to say, we didn't use that material anymore.”

Scientists say if the cup gets too hot during the mission, it wouldn’t melt. Just as dry ice can go from a solid to steam, the device would vaporize when exposed to the vacuum of space. That natural process is called “sublimating.”

“It actually just basically disappears,” Case said.

A 4.5-inch thick heat shield protects other instruments and electronics by keeping the spacecraft in shadow at about 85 degrees, according to NASA. The solar panels powering the probe have a simple cooling system: about a gallon of pumped deionized water that has a higher boiling point than normal. 

Parker’s mission, which launched in August 2018, is to learn how the sun and corona work. Scientists have been studying solar wind, gases flowing off the sun. So far the probe has revealed that at least some magnetic zigzags in the wind, known as "switchbacks," come from the sun's surface. Understanding the origins of the switchbacks and other aspects of solar wind could help keep astronauts, spacecrafts, and satellites safer. 

Right now, scientists don’t know how to forecast “space weather,” something that can disrupt power grids, telecommunications and GPS systems. These events don’t happen often, but a solar flare in March 1989 caused all of Quebec, Canada, to experience a 12-hour power outage. It also jammed radio signals for Radio Free Europe.

During the April flyby, Parker reached 90 to 95% of the distance from Earth to the star, and it’s expected to get a heck of a lot closer. The plan is to come within 3.9 million miles of the surface.

Michael Stevens, an astrophysicist who helps monitor the cup, compared the spring encounter to driving to Disney World, stopping in the parking lot, and then getting back on the highway: The brief visit didn’t give scientists much insight into the rides.

But as the probe ventures closer, Stevens, who gets the first look at the cup’s data, considers himself the guy standing at the front of the line for Space Mountain.

“I want to go the rest of the way into Disney World, and I want to go meet Mickey Mouse,” he said. “We really were just on the doorstep of it."