A corona hole observed near the South Pole of the Sun by the Solar Orbiter probe on March 30, 2022. High-energy particles can be seen ejected./ESA
Just as small streams come together to form a huge river, a study has found that small explosions that occur all over the sun create a huge solar wind that can instantly disrupt satellite communications and power grids. The solar wind is a stream of highly energetic particles ejected from the sun into space. Scientists have studied the solar wind for years, but they don’t know where or how it originates.
Dr. Lakshmi Pradeep Chitta of the Max Planck Institute for the Solar System in Germany published an article in the international journal Science on the 25th saying, “European Space Agency (ESA)’s unmanned probe Solar Orbiter has reached the surface of the sun. “We observed small-scale particle ejections occurring in a short period of time.” These small eruptions are the starting point of the gigantic solar wind.
◇Corona hole ejecting high-energy material
The sun’s atmospheric layer, the corona, can reach temperatures of up to 1.5 million degrees Celsius. At extremely high temperatures, matter exists in a plasma state in which the nuclei and electrons are separated. From here, the solar wind, a stream of charged particles, is ejected into space at a speed of 1.6 million kilometers per hour.
Professor Chita’s research team announced that the Solar Orbiter observed a million-degree plasma ejected at a speed of 100 km/sec from the south pole of the sun on March 20, 2022. In the images taken by the probe, black lines ranging in length from 200 to 500 km can be seen in many places. Since it is a negative image in which the contrast appears in reverse, the black line is actually brighter than the other areas. It is the ejection of high-energy particles.
The average speed of the solar wind is 450 km/s, and the fastest one reaches 750 km/s. The eruption time was also short, from 20 to 100 seconds. Still, the energy released at this time is equivalent to the energy used by 3,000 to 4,000 households in the United States for a year, the researchers said.
Picoflares that appear on the surface of the sun and emit high-energy particles at 100 kilometers per second for 20 to 100 seconds. This is the part indicated by the black line. This is a negative film photo, so the black areas are actually hotter than the other surfaces./ESA
Scientists have studied where and how the solar wind originates for decades, but have not been able to find definitive answers. This is because it is difficult to observe the sun up close. However, Solar Orbiter came close to the sun by 45 million km last year. It is closer to the sun than Mercury, which is at the very innermost part of the solar system. After launching in 2020, Solar Orbiter orbits the sun in an elliptical orbit and approaches the sun once every two years.
The researchers said Solar Orbiter’s Extreme Ultraviolet Imaging (EUI) instrument observed a plasma eruption from a so-called “coronal hole” at the south pole of the Sun. The coronal hole is where the temperature is low in the corona and appears dark. Scientists have linked the solar wind to the magnetic field of the coronal hole. Solar Orbiter observations agree with this.
The magnetic field, which is a space that attracts objects from the earth or the sun, extends straight up from the magnetic north and south poles, then bends down again. A coronal hole causes the magnetic field to come out rather than return in. Because of this, the coronal hole ejects particles into space in the solar wind, much like a leaking balloon.
◇Small eruptions gather to form a huge solar wind
Eruptions of high-energy particles from the corona range from X-class solar flares equivalent to the simultaneous exploding of tens of millions of hydrogen bombs, to nanoflares that are one billionth of that size. The eruption observed from the coronal hole discovered by Solar Orbiter last year emitted energy one thousandth smaller than that of a nanoflare, and was named a picoflare. Pico means one trillionth.
Launched in 2020, the European Space Agency (ESA)’s solar probe Solar Orbiter approached the sun in a closer orbit than Mercury./ESA
So far, we have seen that the ultra-high temperature corona naturally expands, and some of it escapes along the magnetic field extending into space. This assumes that the solar wind is generated steadily and continuously. However, this time, it was confirmed that the plasma ejections from the corona hole occur in several places away from each other, and that it proceeds in a very short time and on a small scale.
“One of the findings of this study is that the plasma ejection is not really uniform and occurs in several places,” said co-author Dr Andrei Zhukov of the Royal Observatory of Belgium. It suggests that it can begin,” he said.
Although picoflares are small in energy, they are numerous and can provide enough plasma for a huge solar wind with only about a minute each active. Dr. Cheetah said, “It is like small streams flowing down the mountain and eventually forming a huge river.”
The fact that the coronal hole is the origin of the solar wind was also confirmed in previous studies. In March, Professor Stuart Bale of the University of California, Berkeley, USA, told Nature, “The Parker Solar Probe detected a stream of high-energy particles from the coronal hole on the sun’s surface, which is called ‘high speed’ faster than average. ’ It appears to be the area where the solar wind originates,” he said.
Parker is a solar probe launched by NASA in 2018. It is named after Eugene Parker, a professor at the University of Chicago who first predicted the existence of the solar wind in 1958. Bale’s team said that the Parker probe detected that the solar wind was not uniform in the coronal hole. From here, high-energy particles were emitted like streams of water sprayed from the shower head.
On August 7, 2023, the sun’s surface glowed brightly as it exploded. As a result, communication networks were cut off all over the globe./NASA
◇ Solar wind research to save Earth’s infrastructure
As the solar wind is found to originate from the coronal hole, it is expected to help prevent damage to the Earth during periods of solar activity maximum. When the Sun is at rest, the coronal hole is confined to the poles, so that the fast solar wind from it does not reach the Earth. But every 11 years, when the sun’s magnetic field flips and solar activity increases, coronal holes appear all over the surface. This causes an explosive solar wind that aims directly at the Earth.
When the solar wind with tremendous energy collides with the earth’s atmosphere, the magnetic field is disturbed, causing auroras in the polar regions. At the same time, satellites fail, causing problems with communications and aircraft navigation systems. As the plasma particles build up, induced current is generated, which can destroy power facilities and cause blackouts.
As solar activity is projected to peak next year on an 11-year cycle, large explosions have been frequent in recent years. Three X-class explosions were observed in July and August of this year. Solar eruptions on the 7th caused communication disruptions around the world. Solar wind research is a way to reveal the secrets of the sun and at the same time protect the earth’s infrastructure.
reference material
Science(2023), DOI: https://doi.org/10.1126/science.ade5801
