Has the Parker solar probe touched the sun? || Why won't the spacecraft melt? || Excellent questions

NASA's Parker Solar Probe Touches The Sun For The First Time

Lift off, of the mighty Delta IV Heavy rocket In August 2018 in Cape Canaveral, Florida, NASA launched Parker Solar Probe to touch the Sun. After spending a few years spiraling closer to our star, the spacecraft has finally arrived. It’s amazing. Parker Solar Probe is touching the Sun. This is Nour Raouafi, the project scientist of the mission. He has been waiting for this moment since the beginning of his career. This is a dream come true. One of the major goals for the Parker Solar Probe mission is to fly through the solar corona and we are doing that now. So, what does it mean to touch the Sun? To answer that, we need to look at the Sun’s structure. Unlike Earth, our Sun doesn’t have a solid surface. It’s a giant ball of hot plasma that’s held together by its own gravity. Solar material flows out from the surface. But around the Sun, it’s bound by the Sun’s gravity and magnetic field. This material forms the Sun’s atmosphere—the corona. Eventually, some of this hot and fast solar material escapes the pull of the Sun and gushes out into space as solar wind. The boundary that marks the edge of the Sun’s atmosphere is known as the Alfvén critical surface. We didn’t know exactly where this boundary was. But for the first time in history, a spacecraft has crossed it. Parker Solar Probe ventured into the corona, touching solar material still bound to the Sun. The wispy corona is too faint to see most of the time, but it’s revealed during total solar eclipses. For centuries, we’ve been studying the Sun’s atmosphere during eclipses because it’s important for understanding how our star influences life in the solar system. But much about the corona remains a mystery. Two of the most challenging scientific mysteries in astrophysics occur in a region that we call solar corona. 

The first mystery is about the temperature. The corona is around 300 times hotter than the photosphere, the visible surface of the Sun below. Secondly, there’s a constant stream of particles flowing from the Sun known as the solar wind. It accelerates up to millions of miles per hour out of the corona and we don’t know how. Solar wind can disrupt our satellites and technology. To better protect them, we need to go where the solar wind starts -- in the corona. So, heading there has been a key goal of NASA’s for a while. We first proposed the idea of sending a spacecraft to the Sun in 1958. We didn’t have the technology to withstand the journey until the 2000s. Since its launch in 2018, Parker has been heading towards our star. Then in April 2021, during Parker’s eighth orbit around the Sun, the spacecraft was about 20 solar radii, or 8 million miles, from the Sun’s surface, when it crossed into the corona. This is a huge milestone. It took us over six decades to come to this point. As Parker entered the corona, its WISPR instrument took these images. Streams of plasma surrounded the spacecraft and Parker’s other instruments detected that the magnetic conditions had changed. Outside the corona, solar wind gushes out, pushing solar material away at high speeds so that it can’t return back to the Sun’s surface. Inside the corona, the Sun’s magnetic field becomes much stronger. Solar material is slower and tethered to the Sun. The bumpy ridges are created by huge flows of plasma traveling out of the corona. Instead of a smooth divide, Parker found that the boundary between these two sides is wrinkly. These bumpy ridges are created by huge flows of plasma traveling out of the corona. Scientists are not sure why this happens, but as Parker gets closer, we’re finding more clues. Before entering the corona, Parker had seen kinks in the solar wind where it would momentarily double-back on itself. Scientists called these features in the solar wind switchbacks. 

But no one knew how or where they formed. In 2021, the spacecraft finally tracked switchbacks to one of their origins. As Parker got even closer to the Sun, it detected bursts of switchbacks. Scientists traced these bursts all the way to the visible surface of the Sun. Here, we see distinct cells. As heat rises beneath, these convection cells churn and create funnels of magnetic energy above the surface. Scientists found that switchbacks form inside these funnels before rising into the corona and beyond. This is only one piece of the switchbacks puzzle though. Exactly how they form is still unknown. Over the next few years, Parker will keep looking for clues as it explores our Sun, the only star we can study up close. The Sun is also the only star known to support life, so understanding it is critical as we search for life beyond our solar system. That will link directly into the question——are we alone in this universe? And that is one of the biggest questions for humanity to answer.

What It’s Like Touching The Sun?

For the first time, a spacecraft has touched the Sun. The NASA spacecraft, Parker Solar Probe, spent more than three years winding its way through planets and progressively approaching our star to learn more about the origin of the solar wind, which propels charged particles across the solar system. The new achievement is a huge step forward for the Parker Solar Probe and a giant leap forward for solar science. Just like landing on the Moon helped scientists understand how it was formed, touching the very stuff the Sun is made of will help scientists unearth crucial facts about our closest star and its influence on the solar system. Parker Solar Probe was launched in 2018 with the goal of exploring the mysteries of the Sun by traveling closer to it than any previous spacecraft. The probe has finally arrived, three years after launch and decades after its conception. 

Observations from Parker’s April 28th flyby, which was the eighth time the spacecraft whizzed by the Sun, revealed that the spacecraft managed to reach inside the Sun’s atmosphere, or corona, for the first time. The Sun, unlike our Earth, is not a solid sphere, but it does have a zone where the star’s immense gravity keeps in the solar material it spews through fusion. However, at a certain distance from the Sun, gravity and magnetic fields are too weak to hold that material together. It’s from that point, known as the Alfvén critical surface, where the solar wind flows away from the Sun, never to return. Solar material with enough energy to pass that point becomes the solar wind, which carries the Sun’s magnetic field with it as it speeds through the solar system to Earth and beyond. Significantly, the solar wind moves so fast beyond the Alfvén critical surface that waves within the wind can never travel fast enough to return to the Sun, severing their connection. Previously, faraway images of the corona revealed that the Alfvén critical surface was between 4.3 and 8.6 million miles (6.9 to 13.8 million kilometers) from the Sun’s surface, which is equivalent to 10 to 20 times the radius of the Sun. 

These estimates were not too far off. According to Parker’s data, it crossed the Alfvén critical surface on April 28th at 18.8 solar radii (8.1 million miles) above the Sun’s surface and finally crossed the solar atmosphere. Parker Solar Probe flew into and out of the corona many times during the flyby. It discovered that the Alfvén critical surface is not shaped like a smooth ball. It has “spikes and valleys” (as NASA termed it), where the surface protrudes higher or lower from the Sun’s center. The surface also likely varies with solar wind activity, which is dependent on the Sun’s 11-year solar cycle. Parker was only able to spend a few hours in the corona due to the intense conditions, but it did manage to go as low as 15 solar radii (around 6.5 million miles) from the Sun’s surface. In that zone, it found a pseudostreamer, one of the huge structures that rise above the Sun’s surface and can be seen from Earth during total solar eclipses. Passing through the pseudostreamer was like flying into the eye of a storm. Inside the pseudostreamer, the conditions quieted, particles slowed, and the number of switchbacks decreased. This is a stark contrast to the bustling barrage of particles the spacecraft ordinarily faces in the solar wind. Parker is expected to get considerably closer to the Sun in future flybys, coming as low as 8.86 solar radii (3.83 million miles) from the Sun’s photosphere, its visible surface. Some surprising physics surfaced even before the first trips into the corona. During recent solar encounters, Parker Solar Probe collected data on the source of zig-zag-shaped structures in the solar wind known as switchbacks. The data showed one spot that switchbacks originate is at the visible surface of the Sun, the photosphere. The switchbacks have been known for a long time, but they were initially identified in the 1990s by the NASA-European Space Agency mission Ulysses, which orbited the Sun’s poles. While scientists first thought the switchbacks were only found in solar areas, Parker discovered in 2019 that they were common in the solar wind. According to new discoveries by the mission, switchbacks occur in patches and have a higher percentage of helium, known to come from the photosphere, than other elements. 

Scientists also found that the patches line up with magnetic funnels emerging from the photosphere, called supergranules. This is useful for understanding solar physics because the funnels may be where fast solar wind particles originate. The structure of the switchback regions corresponds to a small magnetic funnel structure at the base of the corona. Some theories predict this, and this identifies a source for the solar wind itself. If scientists could better understand the physics of switchbacks, they may be able to explain why the corona is millions of degrees Fahrenheit or Celsius hotter than the Sun’s surface. The next solar flyby for the Parker Solar Probe is set for late February 2022, though the spacecraft will collect data for weeks before and after the closest approach. The “touching of the Sun” by the Parker Solar Probe is a watershed moment in solar science and indeed an extraordinary achievement. Not only does this achievement give scientists a better understanding of the Sun’s evolution and its effects on the solar system, but everything they learn about the Sun also educates them about other stars through out the universe.

Why won't the spacecraft melt?

NASA's Parker Solar Probe is a mission to explore the Sun. How can it do that? Why won’t the spacecraft melt? Excellent questions. 

Reason #1

The heat shield

You can’t face off with the sun without packing the right gear. This is why Solar Probe is equipped with a white shield that reflects heat off the front and keeps things cool in the back.  The heat shield is made of a couple of different materials. One is of carbon carbon which is a lot like the graphite epoxy you might see in your golf clubs or tennis rackets, but it’s been super heated. The inside is a carbon foam which is another form of carbon which is about 97% air. It's a very light weight way of making a very strong structure.  

Reason #2

IT's smart

Nobody likes a needy explorer. Solar Probe can take care of itself, thank you very much, and that’s because it has autonomy software that will keep its instruments safe and cool behind the heat shield. We are too far away to joystick it into place, so it basically has to always be sensing whether or not the heat shield is in the right position and correct itself if it isn’t. There are these things called solar limb sensors, just poking out at the very edge of the shadow. If those get illuminated, the spacecraft knows, “Oh, I’m going the wrong direction,” and can actually right itself. 

Reason #3

The cooling system

It’s important to stay hydrated in the Sun, even for a spacecraft! Solar Probe circulates water to keep the solar cells from overheating. It stays cool and keeps power. Basically water flows behind the solar arrays and into the radiators, so the water warms up behind the solar cells and then cools down at the radiator that heat transfer is happening a lot like the veins in your body 

Reason #4

Heat is not a temperature

Yes, you read right: Heat is not the same as temperature. Temperature is a measurement, but heat is an energy transfer. This matters because Solar Probe will be visiting the sun’s outer layer, the corona. Like all stars, the Sun is made of plasma. How tightly packed that plasma is depends on the layer. While the Sun’s corona has a very high temperature the plasma particles are fairly spread out, so even though the temperature in the corona is 2- to 3-million degrees Fahrenheit, the heat around the spacecraft is manageable.  

The corona and where we are going is actually not that dense at all, there’s only a couple particles. Those are very hot, but we aren’t touching a lot of them. So, it’s kind of like when you put your hand into an oven. The oven might be at 400 degrees Fahrenheit, but your hand isn’t going to be at 400 degrees Fahrenheit.

Thanks for reading: Has the Parker solar probe touched the sun? || Why won't the spacecraft melt? || Excellent questions, Sorry, my English is bad:)