Solar Terrain: Revealing the sun’s complex topography

The sun is no smoothie. The sharpest images of the sun ever taken, released last week, show a rugged surface with gargantuan mesas and valleys formed of scalding gas.

SCORCHING BREW. These beads are vast gaseous granules on the sun’s surface. A granule lasts 6 to 10 minutes. Among the granules are sunspots (dark patches) and faculae (bright areas). Berger/Lockheed Martin Solar and Astrophysics Lab.

The sun’s surface is textured with short-lived structures, known as granules, each as big as Texas. “Up until now, we saw granules as flat pancakes with no apparent height or detailed structure,” says lead researcher Tom Berger of Lockheed Martin in Sunnyvale, Calif. The new images, captured with the Swedish Solar Telescope in La Palma, Spain (SN: 11/16/02, p. 310: Available to subscribers at Something New on the Sun), show some granular structures that are about 300 kilometers high, while the smallest discernible features are 70 kilometers across.

Berger and his colleagues presented the images in Laurel, Md., at the annual meeting of the American Astronomical Society’s Solar Physics Division. By training the telescope on the edge of the sun, the researchers depicted the three-dimensional topographies of the granules, which last 6 to 10 minutes.

Some of these structures are molded by the sun’s powerful magnetic field. By studying the features up close, solar physicists may learn how the magnetic field works and how it boosts or dims the sun’s brightness as observed from Earth, Berger says. This is significant, he adds, because changes in brightness may affect Earth’s long-term climate patterns.

The sun’s magnetic activity waxes and wanes in an 11-year cycle. It’s most frenzied during the so-called solar maximum, when the sun is mottled with dark sunspots–regions of intense magnetic force that lie like vast potholes on the sun’s surface. Until 20 years ago, solar physicists thought sunspots would diminish the sun’s brightness. Instead, they found the opposite situation. They attributed the increase in brightness to an increased abundance of what they call faculae–Latin for “little torches”–small, brilliant structures distributed among the granules.

In the new images, the faculae look like towering walls. This is a surprise, Berger says, because most solar physicists model the faculae as tubes sunken into the solar surface. If the faculae loom above the surface, they could radiate light efficiently, thereby boosting the sun’s overall brightness, especially during the solar maximum.

But Berger says the images aren’t conclusive. For example, the solar atmosphere may be distorting the view, making valleys look like peaks, or vice versa.

As one step toward a clearer image, he plans to use a telescope in orbit around Earth to avoid the distorting effects of the planet’s atmosphere.

“We’re finding that the sun is a fascinating place,” says Craig DeForest, who studies the solar atmosphere at the Southwest Research Institute in Boulder, Colo. “It has a collection of systems that are every bit as complicated as the systems we have on Earth.”


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