Scientists solve a puzzle concerning the sun’s burning atmosphere

Our brilliant heat-giving star is still, at best, a mystery in many respects, despite widespread solar-centric projects having sprung up in recent years such as NASA’s Parker Solar Probe and NASA / ESA’s Solar Orbiter investigating winds. of the Sun and the temperatures of the corona. and heliosphere.

One of the biggest questions that has been pondered over the past few decades is why the Sun’s solar atmosphere is literally millions of degrees warmer than the surface. Now a recorded solar wind anomaly could help solve this conundrum, and it took a 7-year orbiting instrument to indicate the ways in which stored magnetic energy heats the solar atmosphere.

Using imaging spectrograph images of the Earth Orbiting Interface Region (IRIS) and the Atmospheric Imaging Assembly (AIA), scientists from Rice University, the University of Colorado Boulder, and NASA’s Marshall Space Flight Center have discovered evidence that low magnetic rings are heated to millions of degrees Kelvin.

The study researchers said heavier ions such as silicon receive preferential treatment and are roasted in both the solar wind and the threshold region between the chromosphere and the sun’s corona.

Within these zones, dense rings of magnetized plasma are in a constant arc state. Although these energized vortices are smaller and harder to analyze, astrophysicists have long theorized that they have protected the magnetically driven mechanism that emits bursts of energy like nanoflars.

Since it was first launched in 2013, IRIS has functioned as a high-end spectrometer created specifically to observe this dark transition region. The main goal of the little explorer is to try to understand how the solar atmosphere is energized.

In a new NASA-funded research paper published last week in the online journal Nature Astronomy, researchers detail the “clearing” in these reconnected circuits that host strong spectral signatures of oxygen and heavier silicon ions.

Rice solar physicist Stephen Bradshaw, lead author Shah Mohammad Bahauddin of the Laboratory for Atmospheric and Space Physics in Colorado, and NASA astrophysics Amy Winebarger examined the IRIS images that resolved the details of those transition circuits and detected pockets. of superheated plasma.

These shots helped the team analyze ionic motions and temperatures within the circuits using the light they emit, which appear as spectral lines that act as telltale chemical “fingerprints”.

“It’s in the emission lines where all the physics is imprinted,” Bradshaw said. “The idea was to learn how these tiny structures are heated and hope to say something about how the corona itself is heated. This could be an omnipresent mechanism operating throughout the solar atmosphere. “

In the hot spots, jets containing silicon ions were reconnecting and moving towards (shifted towards blue) and away (shifted towards red) the observer (IRIS) at speeds of up to 100 kilometers per second. This distinct Doppler shift was not detected for the lighter oxygen ions.

“The transition region is only about 10,000 degrees Fahrenheit, but convection on the surface of the sun affects the rings, twisting and intertwining the thin magnetic wires that make them up and adding energy to the magnetic fields that eventually heat the plasma,” he explained. Bradshaw. “The IRIS observations showed that the process is underway and we are reasonably sure that at least one response to the first part is through magnetic reconnection, of which the jets are a key signature.”

Within that mechanism, the magnetic fields of the plasma wires break and reconnect at intertwined points in lower energy states, releasing their stored magnetic energy. The intersection of this dynamic process is where the plasma overheats.

“We looked at the regions in these small ring structures where reconnection was taking place and measured the emission lines of the ions, mainly silicon and oxygen,” he noted. “We found that the spectral lines of silicon ions were much wider than oxygen. We had to explain it. We examined and pondered and found that there is a kinetic process called ion cyclotron heating which favors heating of heavy ions over lighter ones.

“In the solar wind, the heavier ions are significantly hotter than the lighter ions. This has been definitively measured. Our study shows for the first time that this is also a property of the transition region and could therefore persist throughout the atmosphere due to the mechanism we have identified, including the heating of the solar corona, particularly because the solar wind is a manifestation of the corona expanding into interplanetary space “.

Bradshaw, Bahauddin and Winebarger are delighted to have solved a vital part of the chromospheric puzzle and hope that more IRIS data will provide a more complete overview of the mysterious solar forces at work, allowing them to come up with a concise global theory regarding the complex atmosphere of the sun.