Millions of Plasma ‘Spicules’ Could Explain the Extreme Heat of the Sun’s Atmosphere

New observations suggest interactions between opposite magnetic fields cause millions of super hot tendrils to erupt from the surface of the sun

The thread-like structures in this image from the Japanese satellite Hinode are spicules, giant plumes of gas that transfer energy through the sun’s various regions. JAXA / NASA

For over a century, astronomers have puzzled over solar spicules, the millions of plasma jets that cover the sun’s surface like whiskers. Researchers are not sure why the grass-like filaments form and what their function is. But new, highly detailed observations of the sun using a specialized solar telescope may have solved the case.

At any given moment, part of the sun's atmosphere, known as the chromosphere, is filled with up to 10 million spicules that usually last under 10 minutes. The threads erupt from the sun’s surface at 60 miles per second, extending up to 6,000 miles before collapsing and being replaced by new spicules.

Christopher Crockett at Science News reports that for years researchers have debated just how the structures form and whether they are the reason the sun’s corona, or outer atmosphere, is hundreds of times hotter than the surface of the sun. But investigating the structures is notoriously difficult. They are small compared to the surface of the sun, appear as thin black streaks in observations, and are short-lived.

In a new paper in the journal Science, astronomers investigated the spicules using the Goode Solar Telescope at the Big Bear Solar Observatory in California, creating some of the highest resolution observations of the tendrils ever produced. According to a press release, the team observed the emergence of spicules while also monitoring nearby magnetic fields. What they found is that spicules emerge a few minutes after the appearance of magnetic fields with reversed polarity compared to other magnetic fields in the area.

The authors believe that when that spot of reverse polarity snaps back to match the polarity of the surrounding region, called magnetic reconnection, it releases a burst of energy that produces the spicules. When two magnetic fields of opposite orientation clash, their magnetic field lines break and reconnect with one another, releasing heat, kinetic energy and particles streaming down the field lines. The process is known to create giant solar flares that sometimes shower earth with particles. According to this new research, the same process could create the much smaller spicules.

The team also took things a step further and analyzed data captured by NASA’s Solar Dynamic Observatory at the same spots where the spicules erupted. The analysis showed glowing, charged iron atoms over the tendrils, an indication that the plasma streams reached 1 million degrees Celsius, transferring heat to the corona, reports Crockett.

“Our new results prove that spicules are formed because of flux cancellation at the lower atmosphere, and they also provide good amount of energy for the heating of the upper atmosphere of the sun,” co-author Dipankar Banerjee of the Indian Institute of Astrophysics tells Brandon Specktor at Live Science.

Solar physicist Juan Martínez-Sykora of the Lockheed Martin Solar & Astrophysics Laboratory is enthusiastic about the new research. “Their observations are amazing,” he says, pointing out that spicules are very small, and capturing the level of detail in the new study is very difficult.

However, he cautions that the magnetic reconnection origin of the spicules is currently just an idea, one that needs to be confirmed with more research and computer simulations. In fact, researchers at his lab released a major model of how the spicules form in 2017. That computer simulation took 10 years of research to build and took an entire year to run, revealing that the plasma making up the spicules is likely a stew of charged and neutral particles.

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