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The Sun is covered with moss, though not the kind you’re thinking

Have you ever wondered what secrets lie hidden in the Sun’s atmosphere? Scientists have been puzzled by a peculiar structure on the Sun that they’ve dubbed “moss” due to its resemblance to the earthly plants.

This bright, patchy plasma formation has been a mystery for decades, but recent research is shedding light on its superheating mechanism.

Discovering the Sun’s moss

Souvik Bose, a research scientist at Lockheed Martin Solar and Astrophysics Laboratory and Bay Area Environmental Institute, NASA’s Ames Research Center in California’s Silicon Valley, and his team have made significant progress in understanding the “moss” on the Sun.

First identified in 1999 by NASA’s TRACE mission, this structure is found around the center of sunspot groups, where magnetic conditions are strong. It spans two atmospheric layers, the chromosphere and corona, and lies beneath the feathery ropes of plasma known as coronal loops.

Sunspot groups: Dark regions on the Sun’s surface

Sunspot groups are areas on the Sun’s surface that appear darker than their surroundings due to their lower temperatures. These fascinating features have captivated astronomers for centuries and play a crucial role in our understanding of solar activity and its impact on Earth.

Formation and structure

Sunspots form when intense magnetic fields emerge from the Sun’s interior and pierce through its surface. These magnetic fields inhibit the upward flow of hot gases from below, causing the affected areas to cool down and appear darker. Sunspots typically develop in pairs or groups, with each spot having opposite magnetic polarities.

Within a sunspot group, the largest and most dominant spot is called the “leader,” while the smaller spots are known as “followers.” The leader spot usually appears first and is located closer to the Sun’s equator, while the followers trail behind and are positioned at higher latitudes.

Sun moss and the sunspot cycle

Sunspot groups are not static features; they evolve and change over time. The number and size of sunspot groups on the Sun’s surface vary in a periodic manner known as the sunspot cycle, which lasts approximately 11 years.

During the peak of the cycle, known as the solar maximum, the Sun exhibits a higher number of sunspot groups and increased solar activity. Conversely, during the solar minimum, sunspot groups are less frequent, and the Sun is relatively calm.

Impact on solar activity

Sunspot groups are often associated with intense solar activity, such as solar flares and coronal mass ejections (CMEs). These events occur when the magnetic fields in and around sunspots become entangled and release a tremendous amount of energy.

Solar flares and CMEs can have significant impacts on Earth, including disrupting satellite communications, affecting power grids, and triggering beautiful auroral displays.

Astronomers monitor sunspot groups using various ground-based and space-based observatories. The Solar and Heliospheric Observatory (SOHO), a joint mission between NASA and ESA, provides continuous observations of the Sun and helps scientists track the development and evolution of sunspot groups.

Ground-based solar telescopes, such as the McMath-Pierce Solar Telescope in Arizona and the Swedish Solar Telescope in La Palma, offer detailed views of sunspot groups and their intricate structures.

Sun moss heating enigma

One of the biggest challenges scientists have faced is understanding how the mossy region is connected to the Sun’s lower atmospheric layers.

In addition, how is the material there heated from 10,000 degrees Fahrenheit to nearly 1 million degrees Fahrenheit — a staggering 100 times hotter than the bright surface below? This heating mechanism has been a puzzle for the past quarter of a century.

Thanks to observations from NASA’s High Resolution Coronal Imager (Hi-C) sounding rocket and the Interface Region Imaging Spectrograph (IRIS) mission, combined with complex 3D simulations, scientists have gained new insights into the superheating mechanism at play in the moss.

“Thanks to the high-resolution observations and our advanced numerical simulations, we’re able to figure out part of this mystery that’s stumped us for the past quarter of a century,” said Bose. “However, this is just a piece of the puzzle; it doesn’t solve the whole problem.”

Role of electrical currents

The research team discovered that electrical currents may contribute to heating the moss. Throughout this region, there is a tangle of magnetic field lines, like invisible spaghetti.

This mess of magnetic spaghetti creates electrical currents that can help heat material to a wide range of temperatures, from 10,000 to 1 million degrees Fahrenheit.

The local heating in the moss appears to occur in addition to heat flowing from the hot, multi-million-degree overlying corona.

Implications for understanding the Sun’s corona

The findings, published in the journal Nature Astronomy, can help scientists understand the larger question of why the Sun’s entire corona is so much hotter than the surface. However, to fully address how the corona and moss are heated, more observations are needed.

Hi-C is scheduled to launch again this month to capture a solar flare and possibly another moss region together with IRIS.

Scientists and engineers are also working on developing new instruments onboard the future MUlti-slit Solar Explorer (MUSE) mission to further investigate this fascinating phenomenon.

Sun moss and the future of solar research

In summary, as scientists continue to unravel the mysteries of the Sun’s atmosphere, the discovery of electrical currents contributing to the superheating of solar moss marks a significant milestone.

This breakthrough, made possible by advanced observations and complex simulations, brings us one step closer to understanding the perplexing heating mechanism of the Sun’s corona.

With upcoming missions like Hi-C and MUSE, researchers are poised to delve deeper into the secrets of the solar moss and its role in the larger puzzle of the Sun’s atmospheric heating.

As we eagerly await further revelations, this fascinating cosmic garden reminds us that even the most familiar celestial object still holds countless mysteries waiting to be explored.

The full study was published in the journal Nature Astronomy.


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