NASA's Mission to Touch the Sun - Latest Global News

NASA’s Mission to Touch the Sun

The original version from this story appeared in Quanta Magazine.

Our sun is the most observed star in the entire universe.

We see His light every day. For centuries, scientists have tracked the dark spots on its radiant surface, while in recent decades telescopes in space and on Earth have studied solar rays at wavelengths that span the electromagnetic spectrum. Experiments have also sniffed the Sun’s atmosphere, captured gusts of solar wind, collected solar neutrinos and high-energy particles, and mapped our star’s magnetic field—or attempted to, since we haven’t yet really observed the polar regions crucial for learning about the Sun’s internal magnetic structure.

Through all this scrutiny, however, one crucial question remained embarrassingly unresolved. On its surface the sun is at a pleasant 6,000 degrees Celsius. But the outer layers of its atmosphere, called the corona, can be a blistering – and mind-boggling – 1 million degrees hotter.

You can see this scorching shell of gas during a total solar eclipse, like the one that occurred over part of North America on April 8. If you were in the path of totality, you could see the corona as a glowing halo around the sun shadowed by the moon.

This year, this halo looked different than the one that appeared during the last solar eclipse in North America in 2017. Not only is the Sun more active now, but you also saw a structure that we – the scientists who study our home star – finally understand. Observing the Sun from a distance was not enough to understand what warms the corona. To solve this and other mysteries, we needed a space probe that grazes the sun.

That spacecraft – NASA’s Parker Solar Probe – was launched in 2018. As it orbits the sun and dips in and out of the solar corona, it has collected data that shows us how small-scale magnetic activity within the sun’s atmosphere makes the solar corona appear almost unimaginably hot.

From the surface to the shell

To understand the roasting corona, we need to consider magnetic fields.

The sun’s magnetic motor, the so-called solar dynamo, is located about 200,000 kilometers below the sun’s surface. As it rotates, this engine drives solar activity, which waxes and wanes over periods of about 11 years. When the Sun is more active, solar flares, sunspots, and outbursts increase in intensity and frequency (as is the case now, near solar maximum).

On the Sun’s surface, magnetic fields collect at the boundaries of swirling convection cells called supergranules, which look like bubbles in a pan of boiling oil on the stove. The constantly boiling surface of the sun concentrates and amplifies the magnetic fields at the cell edges. These enhanced fields then trigger transient jets and nanoflares as they interact with the solar plasma.

Courtesy of NSO/NSF/AURA/Quanta Magazine

CAPTION: These churning convection cells on the Sun’s surface, each about the size of the state of Texas, are closely linked to the magnetic activity that heats the Sun’s corona.
IMAGE CREDIT: NSO/NSF/AURA

Magnetic fields can also penetrate the sun’s surface and cause larger phenomena. In regions with strong fields you can see dark sunspots and huge magnetic loops. In most places, particularly in the lower solar corona and near sunspots, these magnetic arcs are “closed,” with both ends connected to the Sun. These closed loops come in a variety of sizes, from tiny to the dramatic, glowing arcs seen during solar eclipses.

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