Our sun's 5 biggest remaining mysteries

Our sun’s 5 biggest remaining mysteries

When we enjoy the long summer days of the northern hemisphere, few realize that there is still much we do not understand about the sun. For billions of years, our star has offered the kind of stable energy production that not only enabled the evolution of life as we know it, but also the evolution of civilization as we know it. Still, the fine points of astrophysics that guide our deceptively simple yellow dwarf star remain a puzzle.

We know the basics of how the sun’s energy comes from its fusion of hydrogen to helium and that the sun’s complex chemical composition is largely derived from previous generations of stars that sowed its elemental composition. But there are significant gaps in our understanding of the sun’s internal mechanics and chemical composition.

To learn more about what we do not know about the physics of the sun, I contacted astronomer and solar physicist Jason Jackiewicz, at New Mexico State University in Las Cruces, for his views on five of the most important solar mysteries below.

—- The mystery of why the sun’s outermost atmosphere (or corona) is so much warmer than its surface.

The corona is above the surface of the sun, therefore above the heat source, but is still 1000 times warmer, Jackiewicz said. The sun’s surface provides enough energy to flow away from it to keep the corona warm, he says. Still, that type of heating would require that the energy be deposited there in some way.

But because this outer corona is so weak, Jackiewicz and colleagues cannot understand why this energy does not just go on to outer space. Solar physicists are still puzzled by how the corona hangs on this amount of heat.

—- How and where the sun generates its magnetic fields

Magnetic fields are observed at the surface (like sunspots) and in the solar atmosphere (like coronal loops), but they are likely to be generated in the interior, says Jackiewicz. Such processes require plasma (charged gas) and movement (likely rotation), he says.

Many researchers believe that this occurs most strongly at about 70 percent of the solar radius, which may be where the fields are “wound up” and strengthened, says Jackiewicz. And because magnetic fields are liquid, they then rise to the surface and appear as sunspots, he says.

But because the sun is a gaseous body, it does not rotate at the same fixed speed as an earthly mass body. For example, at the surface, its poles rotate more slowly than its equator.

The equator rotates once in about 25 days, and the polar regions about 30-32 days, says Jackiewicz. This is absolutely not happening on earth, otherwise the planet would cut itself into pieces, he states.

Different layers under the sun also rotate at different speeds.

So if you go into the sun from the surface about 50,000 km, you would be in an area that rotates faster than the surface, says Jackiewicz. Then you go a little deeper than that and it slows down again, he says.

At a depth of about 200 million km, we find that the sun rotates like a solid body, more like the earth, says Jackiewicz, and we know all this from studying solar earthquakes that examine the interior.

—- What sets and regulates our sun’s 11-year solar cycles?

Sunspots and magnetism generally grow and subside in the sun for 11 years, says Jackiewicz.

Sunspots manifest as darker areas on the solar surface due to strong magnetic fields emerging through the solar surface. This causes a slight area cooling, which causes what appear to be dark spots when placed next to the sun’s surrounding very bright photosphere (or surface).

At the beginning of the solar cycle, sunspots tend to be at average latitudes, around plus or minus 30 degrees latitude on each hemisphere, says Jackiewicz. As the cycle continues, they come closer and closer to the equator, he says. When the next cycle begins, they then return to appear at average latitudes, even though the polarity has reversed in the northern and southern hemispheres from the previous cycle, says Jackiewicz.

What about the 11-year cycle?

Surface properties of the sun come and go every day or so, says Jackiewicz; this is a strange time scale.

—- What do the sun’s super eruptions and superflares generate?

They are linked to magnetic fields, which occur when magnetic energy needs to be released due to rotation and stretching of the fields, says Jackiewicz. The biggest difference between flare and coronal mass ejections (CMEs) is that flares mainly emit X-rays and ultraviolet radiation, but CMEs actually lift mass from the sun, he says.

Major solar events cause billions in damage annually, via power outages, communication disruptions and damage to electrical systems, says Jackiewicz. If we return to a more human-centered space exploration program, with humans on the Moon or Mars, then the consequences of such space weather will be even more important, he says.

—- The mystery of the sun’s chemical composition

In the beginning, there was only hydrogen and helium, says Jackiewicz, with all the other elements in the periodic table synthesized in the stars’ nuclei. Our sun was formed when the universe was about two-thirds of its current age and is thus more enriched on these other elements than the early stars, he says.

“The sun is the reference star for all the hundreds of billions of other stars in our galaxy, and the trillions and trillions of stars in other galaxies,” Jackiewicz said.

We know all the elements that make up the sun, but we do not know their relative abundance, says Jackiewicz. So the chemical composition of the sun is still under debate, he says. It is a difficult thing to measure, even for our nearest star, says Jackiewicz. Observations and models must work together to give consistent results, and they do not always do that, he says.

What confuses you most about the sun?

It is fair to say that we understand the mass, age, size and total radiation of the sun quite well, says Jackiewicz. We know how it has evolved, and how it will evolve billions of years into the future, in a general way, he says. But it is the things of the higher order that are so puzzling; its deep inner structure, magnetic fields, solar cycle variations and eruptive events, says Jackiewicz.

What about his own personal quest to understand the sun?

I want to know what the interior looks like, says Jackiewicz. As a sonogram that shows a fetus inside the mother, we try to make pictures of the sun’s underside, but can only probe a bit in, he says.

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