Milestone! NASA probe touches the sun for the first time

According to the latest news from foreign media, Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate, announced at the 2021 American Geophysical Union Fall Meeting on the 14th that three years after its launch, the Parker Solar Probe reached the outermost layer of the sun's atmosphere (corona) at 9:33 a.m. Eastern Time on April 28 this year, and stayed there for 5 hours, becoming the first spacecraft to "touch the sun." The relevant research results were also published in the American journal Physical Review Letters.

An artist's conception of the Parker Solar Probe approaching the sun. Image source: Physicists' Organization website

The mission is led by the Applied Physics Laboratory of Johns Hopkins University in the United States. Researchers said that the Parker Solar Probe passed through the corona during its eighth close approach to the sun in April. It took them several months to recover the data, and then several more months to confirm it. According to NASA, this is a milestone in the study of solar science, which not only allows people to have a deeper understanding of the evolution of the sun and its impact on the solar system, but also helps people learn more about other stars in the universe.

In 2018, NASA launched the Parker Solar Probe, with the ultimate goal of reaching the solar corona and achieving humanity's first close "contact" with this star.

The outer edge of the Sun begins at the Alfvén critical surface, below which the Sun's gravity and magnetism directly control the solar wind. In April, Parker spent five hours below the Alfvén critical surface, in direct contact with the Sun's plasma. Below this surface, the pressure and energy of the Sun's magnetic field are stronger than those of the particles.

The probe made the first direct observations of material within the solar atmosphere, revealing discoveries about the Sun.

The Parker Solar Probe reaches the sun's outer atmosphere (corona). Image source: CNN website

The Sun's corona is much hotter than its actual surface. The corona has a maximum temperature of 1 million Kelvin (1.8 million degrees Fahrenheit), while the surface has a temperature of about 6,000 Kelvin (10,340 degrees Fahrenheit).

Parker's many trips in and out of the corona have helped researchers understand that the Alfvén critical surface is not a smooth circle around the sun, but a jagged, uneven surface with peaks and valleys, where many scientists believe the sun's magnetic field reversal occurs. When Parker arrived here, it was about 8 million miles (13 million kilometers) from the center of the sun.

The researchers noticed that the Alfvén critical surface was concave at a much lower rate than it was convex. This finding could mean that solar magnetic field reversals do not form in the corona. Alternatively, the magnetic reconnection rate in the sun's lower atmosphere could cause fewer reversals.

During the flyby of the solar corona, when Parker passed 6.5 million miles (10.46 million kilometers) from the solar surface, it passed through a region called a pseudocoronal streamer, a large magnetic structure protruding from the solar surface that can be observed from Earth during a solar eclipse. The data showed that the largest and most distant fluctuations in the Alfvén critical surface are produced by pseudocoronal streamers. It is not yet clear why pseudocoronal streamers push the Alfvén critical surface away from the Sun.

Artist's conception of the Parker Solar Probe approaching the sun. Image source: NASA

Scientists have also observed that the sun's magnetic field pulls the solar wind in the same direction as its rotation at great distances, not just at close range, which increases the speed of the solar wind as it moves away from the sun.

The probes also recorded evidence for a potential boost in energy within the corona, which could affect heating and dissipation.

The Parker Solar Probe will reportedly fly through the corona again during its next flyby in January. It will make 21 close approaches to the sun over seven years before its mission is complete. In 2024, the probe will come within 3.9 million miles of the sun's surface, which is closer to the sun than Mercury, the closest planet to the sun.

Researchers say that as the Parker Solar Probe flies into the solar corona, people will have a deeper understanding of the inner workings of this mysterious region.

◎ Zhang Jiaxin, intern reporter of Science and Technology Daily

Source: Science and Technology Daily

Editor: Wang Yu

Review: Yue Liang

Final review: Liu Haiying