Astronomers locate the source of dangerous high-energy particles in the sun

A coronal mass ejection, or CME, that erupted in space on August 31, 2012. Shown here is a combined version of the 171 and 304 angstrom wavelengths taken from the Solar Dynamics Observatory. Note: Earth is not that close to the sun, this image is for scale purposes only. Credit: NASA / Goddard Space Flight Center

The source of potentially dangerous solar particles, released by the Sun at high speed during storms in its outer atmosphere, has been located for the first time by researchers from UCL and George Mason University, Virginia, USA.

These particles are highly charged and, if they reach Earth’s atmosphere, they can potentially disrupt satellites and electronic infrastructure, as well as pose a radiation hazard to astronauts and people on airplanes. In 1859, during what is known as the Carrington Event, a major solar storm caused the failure of telegraph systems in Europe and America. With the modern world so dependent on electronic infrastructure, the potential for harm is much greater.

To minimize the danger, scientists are seeking to understand how these streams of particles are produced so that they can better predict when they might affect Earth.

In the new study, published in Progress of science, the researchers analyzed the composition of solar energetic particles heading toward Earth and found that they had the same “fingerprint” as plasma located low in the Sun’s corona, near the middle region of the Sun’s atmosphere, the chromosphere.

Co-author Dr. Stephanie Yardley (UCL Mullard Space Science Laboratory, MSSL) said: “In our study, we have observed for the first time exactly where energetic solar particles come from on the Sun. Our evidence supports theories that These highly charged particles originate from plasma that has been kept low in the Sun’s atmosphere by strong magnetic fields. These energetic particles, once released, are accelerated by eruptions that travel at a speed of a few thousand kilometers per second.

“Energetic particles can reach Earth very quickly, from several minutes to a few hours, and these events last for days. Currently, we can only provide forecasts of these events as they occur, as it is very difficult to predict these events before they occur. By better understanding the Sun’s processes, we can improve forecasts so that when a major solar storm hits, we have time to act and reduce risks. “

Lead author Dr. David Brooks (George Mason University and Honorary Associate Professor at UCL MSSL) said: “Our observations provide a tantalizing insight into where the material that produces solar energetic particles comes from in some events of the last solar cycle. We are now beginning a new solar cycle, and once it begins, we will use the same techniques to see if our results are generally true or if these events are somehow unusual.

“We are fortunate that our understanding of the mechanisms behind solar storms and solar energetic particles is likely to advance rapidly in the coming years thanks to data to be obtained from two spacecraft: ESA’s Solar Orbiter and the POT Parker Solar Probe, which are closer to the Sun than any other spacecraft. “

For the study, the researchers used measurements from NASA’s Wind satellite, located between the Sun and Earth, to analyze a series of streams of solar energetic particles, each lasting at least one day, in January 2014. They compared this with spectroscopy data from the JAXA-LED Hinode spacecraft. (The EUV imaging spectrometer aboard the spacecraft was built by UCL MSSL and Dr. Brooks is a member of the mission operations team in Japan.)

They found that the solar energy particles measured by the Wind satellite had the same chemical signature, an abundance of silicon compared to sulfur, as the plasma confined near the top of the Sun’s chromosphere. These locations were at the “dots. support “of the hot coronal loops, that is, at the bottom of the magnetic field and plasma loops that extend into the outer atmosphere of the Sun and vice versa.

Using a new technique, the team measured the intensity of the coronal magnetic field at these base points and found it to be very high, in the region of 245 to 550 Gauss, confirming the theory that plasma is trapped in the atmosphere of the Sun by strong magnetic fields. before its launch into space.

Solar energetic particles are released from the Sun and are accelerated by solar flares (large explosions) or coronal mass ejections, ejections of huge plasma clouds and magnetic field. Approximately 100 solar energetic particle events occur every 11-year solar cycle, although this number varies from cycle to cycle.

The latest findings support the idea that some solar energy particles originate from a source other than the slow solar wind (whose origin is still debated), as they are confined under specific conditions in hot coronal loops at the core of the region. from the source. The Sun continuously emits a faster solar wind; its encounter with the Earth’s atmosphere can generate the Northern Lights.

The high-energy particles released in January 2014 came from a volatile region of the Sun that had frequent solar flares and CMEs, and an extremely strong magnetic field. The region, known as 11944, was one of the largest active regions on the Sun at the time and was visible to observers on Earth as a sunspot, a dark spot on the surface of the sun *.

The NOAA / NWS Space Weather Prediction Center issued a strong radiation storm watch at the time, but the solar energetic particle event is not known to have caused any disruption within Earth’s atmosphere, although the computer systems of the Hinode spacecraft recorded several particle impacts. .

A measurement of the magnetic field strength within the 11944 region was taken in a separate study shortly after this time period, and it was one of the highest ever recorded on the Sun: 8.2kG.

Reference: “The Source of the Major Solar Energetic Particle Events of the 11944 Super Active Region” by David H. Brooks and Stephanie L. Yardley, March 3, 2021, Progress of science.
DOI: 10.1126 / sciadv.abf0068

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