• Science We have a good star: the Sun is very rare

Solar flares are the most powerful explosions in the Solar System. By releasing large amounts of magnetic energy in a few minutes, they heat plasma to tens of millions of degrees and accelerate particles to high speeds. They are thus the origin of a wave of radiation and solar wind that causes so-called solar storms, a phenomenon capable of creating serious disturbances in satellites and communications, both in outer space and on Earth. This is why these phenomena have been studied for decades, looking for reliable methods to predict them.

The development of a physical model capable of anticipating these great solar flares occupies this Thursday the cover of the magazine Science . Called the kappa-scheme and created by researchers at the University of Nagoya (Japan), this new model has been based on magnetic observations to identify critical thresholds of instability on the solar surface. In this way, it predicts when a large surface eruption is imminent, in addition to identifying where it will occur and how much energy it can release. "Large flares can cause solar storms; one of the main goals is to predict such storms and protect our society from their effects," says Kanya Kusano, director of the Institute for Environmental Research Space-Earth at Nagoya University and responsible for the article. .

The novelty of this system is that it chooses a unique approach, based on magnetohydrodynamics (MHD), a discipline that studies the dynamics of conductive fluids and their relationship with electric and magnetic fields. The authors tested the effectiveness of their model by comparing it with data from the NASA Solar Dynamics Observatory (SDO): k-scheme was able to identify the appearance, location and size of most of the large flares with up to 20 hours of advance. "The reliability of our prediction is greater than the current ones" stresses Kusano. "Right now, the hit rate for class X eruptions by space agencies around the world is less than 50%; our approach can predict seven out of nine class X2 or larger eruptions."

Protect missions

The radiation risk posed by solar flares is a major concern in the design of manned missions. The energetic protons can pass through the human body, causing biochemical damage, so you need to find ways to protect astronauts. A solar flare on January 20, 2005 released the highest concentration of protons ever measured directly, launching a high-speed shower of particles around Earth and the Moon. According to NASA, a team of astronauts would have had just 15 minutes to take cover.

That is why many observatories regularly monitor these phenomena and make periodic measurements of the magnetic field and the solar photosphere, considered to be the surface of the Sun. But predicting solar flares is a difficult task. "The physics for this is complex and covers a wide range of spatial scales, we also lack key observable elements such as the magnetic field of the sun's corona", writes the professor at the University of Graz (Austria) Astrid Veronig in the same number from Science. "In fact, the possibility that eruptions are inherently stochastic processes [a succession of random variables that evolve as a function of another variable] is not ruled out."

Kusano and his team will continue to refine their method. "Now, I am collaborating with the National Institute of Information and Communication Technology (NICT), which is responsible for forecasting space weather in Japan, to implement our forecasting scheme and make it operational in a couple of years, "says the researcher. In this regard, observations from Hawaii's Daniel K. Inouye Solar Telescope (DKIST), which will begin this year, will provide better resolution of the structure of the solar magnetic field and its dynamics.

Precisely last May, the sun experienced the greatest glare in recent years. Although it is too early to say for sure, NASA believes that this new activity could indicate that the sun is waking up from its cyclical sleep: it goes through an 11-year cycle in which its magnetic poles are reversed - as if the north and south poles from the Earth they will exchange places - and during this time their activity accelerates. When the activity is low, it is known as the solar minimum, and when it is high, the solar maximum. As the sun approaches solar maximum and its activity cycle accelerates, its surface is covered in spots, ephemeral dark marks created by this strong magnetic activity.

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