Parker was gone, but Parker was still heading toward the sun

Source: Science and Technology Daily

Parker Solar Probe NASA

From the perspective of human survival and technological application, the exploration of the nature of the solar wind and the prediction of coronal material ejection are the inevitable needs of human beings to carry out space activities, and they are also an important basis for human beings to understand the origin of life and find extraterrestrial life.

◎ Intern journalist Du Peng

The famous American solar physicist Eugene Parker recently passed away at the age of 94.

Parker was one of the first astronomers to propose and prove the existence of the "solar wind" through mathematical calculations, and played a fundamental role in the study of solar physics.

In August 2018, the solar probe named Parker was launched, and Parker, then 91, was on the launch site to watch the launch, making the Parker solar probe the first probe in NASA history to be named after a living scientist.

Today, Parker is gone, but Parker is still heading for the sun.

The solar wind theory subverts people's understanding of the solar atmosphere

Being able to "name" a solar probe, what is Parker's contribution to the study of the solar field? In the middle of the last century, the theory of static solar atmosphere proposed by the authoritative scholar Chapman became the mainstream view at that time. The theory is that the solar atmosphere is affected by the outward expansion force formed by the sun's ultra-high temperature on the one hand, and by the gravitational force of the sun itself on the other hand, and the two forces are balanced to form a static state of the solar atmosphere.

In 1956, German scientist Ludwig Bielmann pointed out by observing the orientation of the comet's "tail" that the reason why one of the comet's "tails" always turned its back to the sun was because the comet's volatiles were affected by the wind blowing from the sun and were blown in the opposite direction to the sun, thus forming a comet tail.

This doctrine was not widely recognized at the time, and John Simpson, a professor at the University of Chicago in the United States, believed that the doctrine was contrary to the theory of authority, so he gave the task of testing this hypothesis to his student, Eugene Parker.

Parker, who was still a graduate student at the time, based on Chapman's theory of the static solar atmosphere and made mathematical derivations. But the result was a shock to him. The calculations show that if the static solar atmosphere is used as a condition, there is still a huge solar atmospheric pressure at infinity from the sun. This apparently contradictory result made Parker realize that Chapman's theory was not correct. Coupled with the hypothesis previously proposed by Bilman, Parker believes that the sun's atmosphere is not stationary, but is always active and continues to throw particles outward. Through calculations, Parker noted that the Sun's atmospheric particles continue to accelerate after escaping from the Sun's gravity, and their speeds can reach hundreds of kilometers per second near the Earth, which Parker named the solar wind.

Deng Yuanyong, director of the Huairou Solar Observation Base of the National Astronomical Observatory of the Chinese Academy of Sciences, introduced that Parker's solar wind theory subverted people's understanding of the static solar atmosphere when it was first published, which was widely questioned by the scientific community at that time. However, in 1962, the "Mariner 2" probe made observations of the Sun for more than 100 consecutive days during its journey to Venus, continuously observing a stream of charged particles at a speed of up to 400-700 km/s, fully confirming the existence of the solar wind. People finally accepted Parker's previous theory of solar wind, and Parker deservedly became the founder of solar wind research.

Not only that, Deng Yuanyong said that Parker has also made pioneering work in solar magnetic reconnection and solar generator theory. In particular, he and the astronomer Sweet jointly proposed the Sweet-Parker magnetic reconnection model, which gave the first mathematical description of the quantitative magnetic reconnection, which laid the foundation for a more rigorous magnetic reconnection theory. In terms of solar dynamo theory, Parker's coriolis force and convective region turbulence coupling theory broke the previous Thomas Cowlin proposed that the generator process cannot eventually produce an axially symmetrical magnetic field, that is, the magnetic field generated by the generator must be a three-dimensional anti-generator theory model, which promoted the development of the solar dynamo theory; and he also extended and extended the solar dynamo theory to the galactic magnetic field, promoting the development of the galaxy generator theory.

The study of the sun is an inevitable requirement for space activities

Parker was the father of the solar wind, and Parker was tasked with studying the solar wind, especially solar storms. If the solar wind in normal conditions can still be called "gentle breeze", then a solar storm with much greater energy can be regarded as a "wild storm". In early February, a geomagnetic storm triggered by a solar storm could be one of the reasons spaceX's 40 Starchain satellites failed to ascend to their intended orbit and were scrapped.

The sun's "temper" is uncertain and elusive, but it is not entirely unpredictable. Deng Yuanyong said that it takes at least a few hours for the sun's high-energy particles to reach the earth, and it takes at least two or three days for the plasma cloud to reach the earth, so humans can already make certain forecasts for solar storms. But he also pointed out that the current ground installation alone can not carry out a more in-depth study of the solar wind, "the actual observed solar wind speed is much greater than the theoretical value, how is it accelerated?" How is the temperature of particles anisotropic in the solar wind formed? None of these important questions are yet to be determined. ”

Compared with ground facilities, the parker solar probe's most unique advantage is its unprecedented proximity to the sun. "It's only about 9 solar radii when it's closest to the sun, a 96 percent shorter distance than ground-based observations." Song Yongliang, an associate researcher at the Huairou Solar Observation Base of the National Astronomical Observatory of the Chinese Academy of Sciences, said that with this unparalleled advantage, Parker can detect the nature of the initial solar wind and study the coupling of the solar local coronal magnetic field and particle motion, which is unmatched by ground and Earth orbiters.

Song Yongliang believes that from the perspective of human survival and technological application, the exploration of the nature of the solar wind and the prediction of coronal mass ejection are the inevitable needs of human beings to carry out space activities, and are also an important basis for human beings to understand the origin of life and find extraterrestrial life. The Parker Solar Probe will also conduct in-depth research on the sun's magnetic field, plasma, high-energy particles, and the nature of the solar wind to help scientists deepen their understanding of solar activity.

Solar exploration has entered the era of "touch"

In December 2021, NASA announced that the Parker Solar Probe had successfully passed through the sun's outer atmosphere in April 2021 and sampled its particles and magnetic fields, which was also the first time that a human probe had successfully entered the solar atmosphere.

Scientists generally believe that there is an alfine interface in the outermost layer of the solar atmosphere, which marks the end of the solar atmosphere and the beginning of the solar wind. According to previous studies, this proximal interface is between 10 and 20 solar radii from the surface of the Sun. Passing through this proximity interface means truly entering the solar atmosphere.

During this crossing, the Parker Solar Probe adopted a step-by-step strategy, first "circling" around the sun and gradually approaching the outer layer of the solar atmosphere; subsequently, Timing to fly at an ultra-high speed of 692,000 kilometers per hour to 18.8 solar radii from the surface of the Sun; here, Parker detected specific magnetic fields and particle conditions, which means that Parker officially entered the solar atmosphere; and then Parker repeatedly entered the solar atmosphere like a needle lead, in the process, Parker found that the Alfin Pro interface is not smooth spherical, its surface has undulating peaks and valleys, and these peaks and valleys linked to the activity of the sun's surface can help scientists understand how solar activity affects the solar atmosphere and solar wind.

Before Parker entered the solar atmosphere, the closest man-made probe to the sun was Helios 2, which reached 42.73 million kilometers from the sun in 1976. The reason why parker was able to have an unprecedented "intimate contact" with the sun was mainly due to its "sandwich biscuit" structure of the heat shield. The heat shield, which is mounted on the sun-facing side of the probe, is made of carbon composite material with a thickness of about 12 centimeters, and the specific structure is sandwiched between two carbon fiber panels with a carbon composite foam material of about 11.4 centimeters thick. With the protection of this "sandwich cookie", the temperature of the sun-facing side of the heat shield is as high as about 1371 degrees Celsius, while the other side of the heat shield is only 29 degrees Celsius.

Parker is scheduled to approach about 6.16 million kilometers from the sun's surface in December 2024, hoping to break the limit of its own artificial probe's approach to the sun again.

In the words of Deng Yuanyong, the Parker solar probe is truly pushing human research on the sun into the "touch" era.