By Cheryl Pellerin
USINFO Staff Writer

Washington - An international mission to study the sun has returned new, detailed images of the solar atmosphere that scientists say will change the way they understand Earth's nearest star.

NASA released images March 21 that show the sun's magnetic field is much more turbulent and dynamic than previously known. Instruments aboard the international spacecraft Hinode, originally called Solar B, captured the images.

"For the first time," said Richard Fisher, director of NASA's Heliophysics Division, at a March 21 briefing at NASA headquarters, "we are able to make out tiny granules of hot gas that rise and fall in the sun's magnetized atmosphere. These images will open a new era of study on some of the sun's processes that affect Earth, astronauts, orbiting satellites and the solar system."

The spacecraft Hinode (pronounced hin-oh-day), which means "sunrise" in Japanese, is carrying out a collaborative mission led by the Japan Aerospace Exploration Agency (JAXA) and includes the European Space Agency and Britain's Particle Physics Astronomy Research Council. NASA and other U.S. and international scientists helped develop the spacecraft's three main instruments.

"What happens when we see things for the first time in any scientific endeavor is that we get this new vision, we get new insights, and the insights lead to progress on some of the outstanding issues in the field," said Judith Karpen, a research astrophysicist at the U.S. Naval Research Laboratory in Washington.

Hinode's discoveries, she added, "may lead to our ability to predict some of the eruptive events that have such impact on life on Earth and also on our space program."

THE SUN

The sun is the closest star to Earth and the most closely studied. Scientists can observe directly only the outer layers of the solar atmosphere - the photosphere, chromosphere and corona. The layers are all different, with regions of gradual transition between them.

The sun has the same chemical elements as Earth but is so hot that the elements exist as gases, and the sun has no real surface. The sun is a ball of gas that gets denser near the solar core. The photosphere is the depth at which scientists can see no deeper toward the core.

When scientists refer to the sun's size, they usually mean the size of the region surrounded by the photosphere. The photosphere's temperature is 4,226 to 5,726 degrees Celsius.

The gases that extend away from the photosphere make up the chromosphere, which is about 2,500 kilometers thick. From the bottom to the top of the chromosphere, the average temperature rises from 4,226 to 9,726 degrees Celsius, an increase that scientists still do not understand. Throughout the rest of the sun, temperatures drop as gases move away from the core.

The chromosphere merges into the corona, the outermost region of the atmosphere. The corona extends millions of miles into space above the photosphere and is very hot - millions of degrees Celsius. Because of this heat, most radiation is emitted at ultraviolet and X-ray wavelengths.

Magnetic fields on the sun seem to play an important part in heating the corona to such high temperatures, but scientists do not yet understand how this happens.

ANSWERING QUESTIONS

Three main instruments on Hinode are helping answer questions about the sun: the solar optical telescope, developed by the National Astronomical Observatory of Japan, scientists from NASA and JAXA, Lockheed Martin, Mitsubishi Electric Corporation and the National Center for Atmospheric Research; the X-ray telescope, developed by the National Astronomical Observatory and the Smithsonian Astrophysical Observatory in Massachusetts; and the extreme ultraviolet imaging spectrometer, designed and developed by scientists from Japan, the United Kingdom, NASA in the United States, and Norway.

The solar optical telescope, the largest ever flown, provided the fine-scale structure views of the sun's lower atmosphere, Fisher said. The imaging spectrograph is used to diagnose physical characteristics and properties of the sun's atmosphere, and the X-ray telescope collects X-rays emitted from the sun's corona.

"The X-ray eruption starts with a large magnetic loop that collapses downward, and then everything erupts upward after that," said Leon Golub, senior astrophysicist at the Smithsonian Astrophysical Observatory, describing one of the images. "This hasn't been seen before, it's totally unexpected and as far as I'm concerned it's impossible," he added, "but it's happening, so we're going to have to explain it. And there are many, many things coming down in the data that have that character."

The X-ray telescope has provided the first clear view of the possible energy source for the corona, according to a March 21 statement by the Harvard-Smithsonian Center for Astrophysics, involving twisted and tangled magnetic fields that store huge amounts of energy that, when released, heats the corona and powers solar eruptions like flares and coronal mass ejections.

More information about Hinode and its mission is available on the NASA Web site.