Some of the sun’s coronal loops (bright yellowy structures in this image) might be optical illusions caused by “wrinkles” in the solar atmosphere, a new study suggests.

Solar Dynamics Observatory/GSFC/NASA

Hot strands of plasma arch out from the sun’s surface. These iconic features are known as coronal loops. But many of the loops we see might not actually be there, scientists now report.  

Some, they say, might be an illusion created by dense “wrinkles” in a curtain of plasma known as the coronal veil. They base this idea on unexpected structures that emerged in computer models. Those computer programs were designed to simulate the sun’s atmosphere — including its outermost region, the corona.

Researchers proposed these phantom loops March 2 in The Astrophysical Journal. If true, these ghostly loops may change how scientists go about measuring some properties of our star.

“It’s kind of inspiring to see these detailed structures,” says Markus Aschwanden. These loops, he says, “are so different than what we anticipated.” Aschwanden was not involved in the study. This astrophysicist works at Lockheed Martin’s Solar & Astrophysics Lab in Palo Alto, Calif.

Only in the past few years have cientists begun to develop a better understanding of the sun’s complex corona. Its loops have been used to measure many of the corona’s traits, including its temperature and density. In fact, coronal loops may be key to figuring out why the sun’s atmosphere is so much hotter than its surface. Astronomers also have puzzled over why the loops appear to be so orderly when they rise from the sun’s turbulent surface.     

Solar physicist Anna Malanushenko works at the National Center for Atmospheric Research in Boulder, Colo. She’s part of a team that tried to isolate individual coronal loops in 3-D computer simulations. That computer program had been developed to model the life cycle of a solar flare — powerful magnetic outbursts that shoot bright spurts of radiation into space. Coronal loops appear to align themselves to the sun’s magnetic field, like metal shavings around a bar magnet. So the researchers expected to see neatly oriented strands of plasma.

But they didn’t. The plasma instead formed a curtainlike structure winding out from the sun’s surface. Parts of it folded in on itself like a wrinkled sheet. The computer model suggested that many of the supposed coronal loops weren’t real. Plasma structures formed along the magnetic fields. But these were neither thin nor as compact as had been expected. They more closely resembled clouds of smoke.

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The team changed the point of view by which the computer visualized these wrinkles in the modeled veil. This changed the plasma’s shape. From certain viewing angles, what had been wrinkles now instead looked like coronal loops.

The observations were mind-blowing, says Malanushenko. “The traditional thought was that if we see this arching coronal loop that there is a garden hose–like strand of plasma.” But the computer analysis now suggests the plasma’s structure is much more complex. It has complicated boundaries and a ragged structure.

Still, not all coronal loops are necessarily ghosts within a coronal veil. “We don’t know which ones are real and which ones are not,” Malanushenko says. “And we absolutely need to,” she says, to understand the sun’s atmosphere.

It’s also not clear how the apparent coronal veil might impact previous analyses of the sun’s atmosphere. “On one hand, this is depressing,” Malanushenko says. Why? Her team’s new findings cast doubt on what solar scientists had thought they understood. On the other hand, she finds this new uncertainty exciting. Astronomers will need to develop a way to observe the veil and confirm its existence, she says. And, she adds, “Whenever we develop new methods, we open the door for new knowledge.”

3-D: Short for three-dimensional. This term is an adjective for something that has features that can be described in three dimensions — height, width and length. 

align: (noun: alignment) To place or organize things in a patterned order, following an apparent line.

angle: The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.

astronomer: A scientist who works in the field of research that deals with celestial objects, space and the physical universe.

astrophysics: An area of astronomy that deals with understanding the physical nature of stars and other objects in space. People who work in this field are known as astrophysicists.

atmosphere: The envelope of gases surrounding Earth, another planet or a moon.

computer model: A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

computer program: A set of instructions that a computer uses to perform some analysis or computation. The writing of these instructions is known as computer programming.

corona: (in astronomy) The outermost layer of the atmosphere surrounding the sun (and other stars). The sun’s corona is normally visible only during a total solar eclipse, when it is seen as an irregularly shaped, pearly glow surrounding the darkened disk of the moon.

density: The measure of how condensed some object is, found by dividing its mass by its volume.

develop: To emerge or to make come into being, either naturally or through human intervention, such as by manufacturing.

illusion: A thing that is or is likely to be wrongly perceived or interpreted by the senses.

journal: (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. Peer-reviewed journals are the gold standard: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or work that is not novel or convincingly demonstrated.

life cycle: The succession of stages that occur as an organism grows, develops, reproduces — and then eventually ages and dies. Or the sum of all processes involved in creating a product, starting with the extraction of raw materials and ending with the disposal of the product when it's no longer useful. Indeed, engineers describe this as the cradle-to-grave life of a product.

magnet: A material that usually contains iron and whose atoms are arranged so they attract certain metals.

magnetic field: An area of influence created by certain materials, called magnets, or by the movement of electric charges.

model: A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. 

physicist: A scientist who studies the nature and properties of matter and energy.

plasma: (in chemistry and physics) A gaseous state of matter in which electrons separate from the atom. A plasma includes both positively and negatively charged particles.

simulate: To deceive in some way by imitating the form or function of something. A simulated sense of touch may fool the brain into thinking a finger has touched something even though a hand may no longer exists and has been replaced by a synthetic limb. (in computing) To try and imitate the conditions, functions or appearance of something. Computer programs that do this are referred to as simulations.

simulation: (v. simulate) An analysis, often made using a computer, of some conditions, functions or appearance of a physical system. A computer program would do this by using mathematical operations that can describe the system and how it might change over time or in response to different anticipated situations.

solar: Having to do with the sun or the radiation it emits. It comes from sol, Latin for sun.

solar flare: An explosive event that takes place on the sun when energy that has built up in 'twisted' magnetic fields (usually above sunspots) becomes suddenly released. The energy can in minutes heat to many millions of degrees, emitting a burst of energy. That energy consists of radiation across the electromagnetic spectrum, from gamma rays to radio waves.

star: The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become hot enough, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

trait: A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

turbulent: (n. turbulence)  An adjective for the unpredictable fluctuation of a fluid (including air) in which its velocity varies irregularly instead of maintaining a steady or calm flow.

Journal:​ A. Malanushenko et al. The coronal veil. Astrophysical Journal. Published online March 2, 2022. doi: 10.3847/1538-4357/ac3df9.

Journal:​ C. DeForest et al. Mapping the territory: What current remote sensing tells us to expect for PSP. American Geophysical Union meeting, New Orleans, December 12, 2017.

Journal:​ J. Klimchuk. Key aspects of coronal heating. Philosophical Transactions of the Royal Society A. April 20, 2015. doi: 10.1098.rsta.2014.0256.

Journal:​ C.E. Parnell and I. De Moortel. A contemporary view of coronal heating. Philosophical Transactions of the Royal Society A. June 4, 2012. doi: 10.1098/rsta.2012.0013.

Journal:​ D.B. Jess et al. Alfvén waves in the lower solar atmosphere. Science. Vol. 323, March 20, 2009, p. 1582. doi: 10.1126/science.1168680.

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