The corona at the outermost layer of the Sun’s atmosphere is thousands of times hotter than the surface of the star, possibly due to weak yet stable waves that help transmit energy.
The solar corona is the outermost layer of the Sun’s atmosphere. (Image: Popular Science)
The surface of the Sun, known as the photosphere, has a temperature of about 5,500 degrees Celsius. However, even farther from the core, the outermost layer of the Sun’s atmosphere, called the corona, is much hotter, often reaching temperatures of up to 40 million degrees Celsius, according to NASA. The corona is composed of hot ionized gas known as plasma and is the source of extreme space weather events such as solar flares. However, researchers have not definitively understood why the corona is so hot.
In a study published on September 12 in the journal Nature Communications, scientists investigated a common oscillation associated with the Sun known as low-amplitude non-dispersive torsional oscillations. This oscillation occurs within the arc of the Sun’s magnetic field, which is a dome-shaped structure made of plasma, extending from the photosphere to the corona. These waves are relatively weak but do not lose strength over multiple oscillation cycles. Therefore, they can provide a significant amount of energy to the corona over time.
The research team focused on how these waves propagate upward and downward, left and right, or at any angle, a characteristic known as polarization. The ability to analyze the 3D geometric features of the waves could reveal their origins and the energy available to them. However, previously, scientists lacked the methodology to examine wave patterns from multiple viewpoints, thereby detecting polarization.
Valery Nakariakov, a solar physicist at the University of Warwick in Coventry, England, and his colleagues used data from the Solar Orbiter of the European Space Agency (ESA) and NASA’s Solar Dynamics Observatory to analyze the corona from various positions. They found that almost all waves oscillate in the same direction. This discovery demonstrates that energy from the Sun’s surface can be transmitted to the corona, heating it up. According to Nakariakov, the study’s results provide important information to answer the persistent question of what heats the Sun’s corona.
