How Close Can We Get to the Sun?

About 4 million miles (6.4 million kilometers) is quite a distance. It’s the equivalent of driving around Earth’s widest point, the equator, 160 times in a row.

Well that’s about as close to the sun that NASA has gotten the Parker Solar Probe, so far anyway. The spacecraft, which launched Aug. 12, 2018, has set several major milestones since then, including becoming the first craft ever in history to touch the sun.

Such proximity to our massive star is completely new. NASA’s Helios 2 probe came within 27 million miles (43.5 million kilometers) of the surface of the sun in 1976. That was closer than any other spacecraft at that point.

Ah, but records invite challengers. Earth and the sun are 93 million miles (150 million kilometers) apart. One NASA scientist said that if the two bodies stood on opposite ends of an American football field, the Parker Solar Probe’s mission would bring it all the way to the sun’s 4-yard line.

Solar exploration technology has come a long way. Yet still need to keep a few engineers limitations in mind — and it doesn’t look like we’ll be sending astronauts on a journey toward the sun anytime soon. So how did the Parker Solar Probe touch the sun and what is it up to next?

High Heat and the Corona Mystery

Extreme heat is the most obvious concern. The sun’s surface temperature is a stifling 10,340 degrees Fahrenheit (5,726 degrees Celsius). Curiously though, the area that surrounds the sun is even hotter.

You know that halo of light that creeps out from behind the moon during a solar eclipse? That’s the corona. A layer of blistering plasma, it represents the uppermost portion of the sun’s atmosphere. The corona begins roughly 1,300 miles (2,100 kilometers) above the surface and extends far into space.

Parts of it get hot. Very hot. In some places, the corona is liable to be 300 times hotter than the surface. No one knows why this is; NASA hopes that the Parker Solar Probe will find some clues.

That’s where the Parker Solar Probe passed through on its eighth flyby of the sun April 28, 2021. The spacecraft dipped to just 14.97 solar radii (6.4 million miles) from the sun’s surface through an area in the corona known as a pseudostreamer. These are massive structures that rise from the sun like ribbons. You can see them during a solar eclipse. The first flyby lasted about four hours and the Parker Solar Probe got as close as 3.83 million miles from the sun’s surface.

“Flying so close to the sun, Parker Solar Probe now senses conditions in the corona that we never could before,” Nour Raouafi, the Parker Solar Probe project scientist at John Hopkins University Applied Physics Laboratory, said in a press statement. “We see evidence of being in the corona from magnetic field data, solar wind data and visually in white-light images. We can actually see the spacecraft flying through coronal structures that can be observed from Earth during a total solar eclipse.”

So Much Radiation

The sun emits a huge amount of radiation, including some forms that we perceive as visible light. Dangerous types of radiation intensify as you get closer to the sun. High radioactivity levels in deep space may be linked to cardiovascular problems. A 2016 survey found that astronauts who’d flown outside of low-Earth orbit were more likely to die of heart attacks or strokes than their peers who stayed closer to the home planet.

If you were sent adrift in nothing but an average NASA spacesuit, solar radiation would claim your life before you’d so much as reached the halfway point between Earth and the sun.

Clearly, you’d fare better inside a spaceship. NASA research scientist Eric Christian has said that it might someday be possible to design a vessel that could safely take human astronauts within 4 million miles (6.4 million kilometers) of the sun. But before we can even think about such a high-risk mission, we’ll need to see how the Parker Solar Probe fares. So far, it’s faring well.

How It Keeps Its Cool

To protect most of its data-collecting instruments, the Parker Solar Probe was fitted with a custom-made heat shield, consisting of two carbon-composite lightweight boards, an outer layer of reflective paint and a foam core. The shield looks more like a snail’s shell than a turtle’s: Instead of enveloping the entire probe, it sits on one side of it. When facing the sun, this “thermal protection system” safeguards the instruments behind it from heat radiation that’s 475 times more powerful than anything Earth-orbiting satellites experience.

For the Parker Solar Probe to do its job, the thermal protection system continually faces the sun. Thrusters always orient the shields into the right position. Those thrusters need fuel, and eventually the spacecraft will run out of juice. The Parker Solar Probe was designed to orbit the sun at least 24 times. Feb. 25, 2022, was its 11th successful approach, and it put the spacecraft in Earth’s view. Most of the passes occur when the sun is between the spacecraft and Earth leaving no direct line of sight. However, this 11th pass gave more than 40 observatories and a dozen spacecraft the opportunity to train their telescopes on the probe to gather valuable data.

Included in the data that will stream back to scientists through May 1, 2022, is a massive solar prominence that hit the probe directly in February 2022. It was the largest flare the Parker Solar Probe has witnessed since its launch.

“The shock from the event hit Parker Solar Probe head-on, but the spacecraft was built to withstand activity just like this — to get data in the most extreme conditions,” project scientist Nour Raouafi said in a press statement. “And with the sun getting more and more active, we can’t wait to see the data that Parker Solar Probe gathers as it gets closer and closer.”

After its mission ends in 2025, there won’t be enough fuel to keep the thrusters working much longer. Unprotected parts of the Parker Solar Probe will then shift toward the sun and disintegrate, transforming the probe into to space dust.

Dust in the (Solar) Wind

The Parker Solar Probe can trace its roots back to NASA’s beginnings. On Oct. 24, 1958, less than three months after the administration was established, one of its committees made an ambitious proposal: Send a man-made probe beyond the planet Mercury to look at the sun up close.

Mercury is usually between 29 and 43 million miles (46 and 70 million kilometers) away from the sun. The Parker Solar Probe will go far inside the planet’s orbit to gather information on solar wind. This phenomenon is still poorly understood but can destroy satellites and really screw up our GPS signals and radio communications here on Earth. If the probe can help us figure out a way to predict these winds, it could end up saving the world trillions of dollars. What can we say? Curiosity pays, and so does exploration.

Originally Posted: Aug 9, 2018

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