A NASA probe ‘touches’ the sun

For the first time, a spacecraft has managed to ‘touch’ the Sun: the probe Parker Solar Probe NASA flew through the upper atmosphere of our stars, as announced by the US space agency, “a giant step in solar science.”

Just as landing on the Moon allowed scientists to understand how it formed, touching the matter the Sun is made of will help scientists uncover critical information about our nearest star and its influence on the solar system.

“This is a monumental moment for solar science and a truly remarkable achievement,” he said. Thomas Zurbuchen, Associate Administrator of NASA’s Science Mission Directory in Washington, USA. “This milestone not only gives us more detailed information about the evolution of the Sun and its impacts on our solar system, but everything we’ve learned about our own star also teaches us more about stars in the rest of the universe.”

Touching the stuff the Sun is made of will help scientists uncover critical information about our nearest star and its influence on the solar system.

As you drive closer to the solar surface, Parker makes new discoveries, even from within the solar wind. In 2019, this space probe found that magnetic structures zigzag in the solar wind, called curves (zigzags, in English), abound near the Sun. But how and where they form remains a mystery. Now, the Parker Solar spacecraft has passed close enough to identify a place from which they originated: the solar surface.

This first pass through the corona, as well as future overflights in this area, will provide data on phenomena impossible to study from a distance. “By flying so close to the Sun, Parker Solar now detects conditions in the magnetically dominated layer of the solar atmosphere – the crown– like we’ve never been able to before,” he explains nour raouafi, Scientist at the Parker project at Johns Hopkins Applied Physics Laboratory (USA).

“We see evidence of being at the corona in magnetic field data, solar wind data and visually in images. In fact, we can see the spacecraft flying through coronal structures that can be observed during a total solar eclipse,” he adds.

closer than ever

The Parker Solar space probe was launched in 2018 to explore the mysteries of the Sun, traveling closer to it than any other spacecraft before. Three years after release and decades after the first conception, Parker has finally arrived.

Unlike Earth, the Sun does not have a solid surface, but a overheated atmosphere, made of solar material connected to the Sun by gravity and magnetic forces. As increased heat and pressure push this material away from the Sun, it reaches a point where gravity and magnetic fields are too weak to contain it.

This point, known as the Alfvén’s critical surface, marks the end of the solar atmosphere and the beginning of the solar wind. The solar material with the energy to cross this boundary becomes the solar wind, which carries the Sun’s magnetic field with it as it travels through the solar system, to Earth and beyond. Importantly, beyond the critical surface of Alfvén, the solar wind moves so fast that waves within the wind can never travel fast enough to return to the Sun, interrupting their connection.

Until now, researchers weren’t sure exactly where Alfvén’s critical surface was located. According to remote images of the corona, estimates place it between 10 and 20 solar rays from the Sun’s surface: between 4.3 and 8.6 million miles (that is, between 6.9 ​​ and 13.8 million of kilometers). Parker’s spiral path slowly brings it closer to the Sun, and during later approaches, the spacecraft was consistently below 20 solar rays (91% of the distance from Earth to Sun), putting it in a position to cross. The limit, if the estimates were correct.

On April 28, 2021, during his eighth flyover of the Sun, Parker Solar found specific magnetic and particle conditions at 18.8 solar rays (about 13 million kilometers) above the solar surface, telling scientists that he had crossed the sun. critical surface of Alfvén for the first time time and finally entered the solar atmosphere.

“We had the expectation that, sooner or later, we would find the crown for at least a short period of time,” he says. Justin Kasper, lead author of a new article about the milestone published in Physical Review Letters and teacher of Michigan University (USA). “But it’s very exciting that we’ve already achieved it.”

in the eye of the storm

During the flyover, Parker Solar entered and exited the crown several times. This was to be expected, as some researchers predicted that Alfvén’s critical surface was not shaped like a smooth ball, but rather peaks and valleys that crease the surface. Find out where these bumps line up with the solar activity coming from the surface can help scientists learn how events on the Sun affect the atmosphere and the solar wind.

When Parker Solar dove just below 15 solar rays (about 10.4 million kilometers) from the Sun’s surface, it transited through a feature in the corona called pseudostreamer. Pseudostreamers are massive structures that rise above the Sun’s surface and can be seen from Earth during the solar eclipses.

Going through the pseudotreamer was like flying to the bottom of a storm. Inside, conditions calmed down, particles slowed down, and the number of turns decreased, a dramatic change from the particle barrage that the spacecraft normally encounters in the solar wind.

For the first time, the spacecraft found itself in a region where the magnetic fields they were strong enough to dominate the movement of particles. These conditions were definitive proof that the spacecraft had passed the critical surface of Alfvén and entered the solar atmosphere, where magnetic fields shape the movement of everything in the region.

“I’m excited to see what Parker will discover by repeatedly passing the crown over the next few years,” he says. Nicola Fox, director of NASA Heliophysics Division. “The opportunity for new discoveries is limitless.”

The size of the crown also depends on solar activity. As the Sun’s 11-year cycle of activity increases, the solar cycle, the outer edge of the crown will expand, giving Parker Solar a greater chance of staying inside the crown for longer periods.

“It’s a very important region to go into because we think all kinds of physics are potentially activated,” notes Kasper. “And now we’re entering this region and we’re hoping to start seeing some of these physics and behaviors.”

When the Parker Solar spacecraft passed through the solar corona, it passed through structures called coronal coils. These structures can be seen as bright features moving up in the upper images and down in the lower row. / NASA | Johns Hopkins APL | Naval Research Laboratory

The origins of zigzag structures

In recent solar encounters, Parker Solar has collected data pointing to the origin of zigzag-shaped structures in the solar wind. The data showed that one point where the curves originate is on the visible surface of the Sun: o photosphere.

In the mid-1990s, the Ulysses Mission NASA and the European Space Agency flew over the sun’s poles and discovered a handful of weird twists S-shaped lines in the solar wind’s magnetic field, which deflected charged particles in a zigzag path as they escaped the Sun. For decades, scientists thought these occasional changes were oddities confined to the polar regions of our star .

In 2019, 34 solar rays from the Sun, Parker discovered that flashbacks were not rare but common in the solar wind. This renewed interest in features raised new questions: Where do they come from? Were they forged on the surface of the Sun or shaped by some process that distorts the magnetic fields in the solar atmosphere?

Understanding where and how the components of the fast solar wind emerge, and whether they are linked to the curves, can help scientists answer an ancient solar mystery: how the corona heats to millions of degrees.

The new findings finally confirm that an origin point is close to the solar surface.

The clues came as Parker orbited closer to the star in its sixth flyover, less than 25 solar rays. The data showed that the changes occur in spots and have a higher percentage of helium, which is known to come from the photosphere, than other elements. The origins of the changes were further narrowed when scientists found spots lined with magnetic funnels emerging from the photosphere between convective cell structures called super granules.

In addition to being the cradle of curves, scientists believe that magnetic funnels may be the birthplace of a component of the solar wind. It comes in two different varieties, fast and slow, and funnels may be where some of the particles in the fast solar wind come from.

“The structure of the inverted regions coincides with a small magnetic funnel structure at the base of the crown,” he says. stuart’s burden, teacher of University of California (USA). “This is what we expect from some theories, and this points to a source for the solar wind itself.”

This image represents the distances from the Parker Solar spacecraft to the Sun for some of these landmarks and discoveries. / ASA’s Goddard Space Flight Center | Mary P. Hrybyk-Keith

Understanding where and how the components of the fast solar wind arise, and whether they are linked to curves, can help scientists answer an ancient solar mystery: as the crown heats up to millions of degrees, much hotter than the solar surface below.

While the new findings point to where the changes are made, scientists still can’t confirm how they form. One theory suggests that they can be created by plasma waves that sweep over the region like ocean waves. Another maintains that they are produced by an explosive process known as magnetic reconnection, believed to occur at the boundaries where the magnetic funnels meet.

“My instinct is that as we enter the mission and get closer and closer to the Sun, we’ll learn more about how magnetic funnels are connected to curves,” explains Bale. “And hopefully that resolves the question of which process converts them.”

Now that researchers know what to look for, passes closer to Parker may reveal even more clues about U-turns and other solar phenomena.

“It’s really exciting to see our advanced technologies succeed in bringing Parker Solar closer to the Sun than ever before, and be able to bring back incredible science,” he concludes. Joseph Smith, executive director of NASA’s Parker program. “We are looking forward to seeing what more the mission will discover as it moves forward in the coming years.”


Kasper et al. (2021) “Parker Solar Probe Enters the Magnetically Dominated Solar Corona”. Physical Review Letters


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