You may never see Ed Deluca on the 6 o’clock news, flanked by a map of the solar system, delivering the latest forecast on storms in outer space. Still, as this scientist at the Smithsonian Astrophysical Observatory in Cambridge, Mass., explains, his goal is to “forecast space weather in ways similar to the forecasts meteorologists provide on Earth.

A solar astronomer, Deluca is using a powerful space telescope to keep a close eye on the surface of the sun, where violent explosions can blast potentially damaging “storms” of radiation at the Earth.

Just such a forecast was needed on March 10, 1989, when a massive eruption on the sun belched a huge cloud of hot plasma toward Earth. Three days later, the plasma cloud slammed into Earth’s upper atmosphere. Electrical currents generated by the collision at ground level overloaded power grids across North America and Europe. In Canada, the Quebec power grid collapsed in the middle of the night, leaving millions without electricity.

Advance warning of solar storms may someday give power utilities, satellite operators, radio stations, global positioning systems and others who own and operate sensitive, high-tech electronic systems time enough to protect their valuable equipment.

X-ray Telescope
The newest tool Deluca and his colleagues are using to spy on the sun was launched last year aboard the Japanese Hinode (hee-no-day) mission. Hinode is carrying three instruments to probe the sun, one of which is a special X-ray Telescope developed by scientists at the Smithsonian Astrophysical Observatory.

Although the sun emits most of its energy as visible light, it also is constantly generating powerful X-rays. Earth’s atmosphere shields it from these solar X-rays so, to study them, astronomers must use telescopes that can see X-ray radiation and which orbit outside Earth’s atmosphere.

Solar X-rays originate in the sun’s corona, a tenuous layer of gases that lies above the sun’s photosphere, or visible surface. The corona is seen as a ghostly, milk-white glow during a total solar eclipse. During such an eclipse, the moon blocks light from the sun’s photosphere, allowing the fainter light from the corona to be seen.

Although the sun’s surface is only 10,000 degrees Fahrenheit, its corona is more than 100 times as hot. Hydrogen, helium and other gases in the corona reach temperatures of millions of degrees. They form a plasma—the fourth state of matter—in which atoms are ionized because their electrons have been ripped away.

Just what process generates the energy that heats the corona, and fuels the sun’s massive eruptions, remains one of the more persistent and puzzling questions in solar physics. Hinode has been specifically designed to try to answer this question.

Magnetic twists
Astronomers believe the sun’s magnetic field holds the key to this mystery. The sun has a magnetic field just as the Earth does, but 100 times stronger. Because the sun is a ball of plasma and not solid rock, its magnetic field is unstable and can become twisted.

Hinode’s X-ray Telescope has provided the first clear view of the sun’s tangled magnetic fields, which store huge amounts of energy. When the magnetic field twists, it builds up more and more energy, like a rubber band being stretched tighter and tighter.

When this magnetic field snaps back into place, a process known to astrophysicists as magnetic reconnection, it releases massive amounts of energy, causing solar flares—the rapid brightening of the corona in X-rays—and coronal mass ejections, which are the release of solar plasma and magnetic fields into interplanetary space.

For many years, solar theorists have suggested the existence of twisted, tangled magnetic fields generated by the sun, Smithsonian Astrophysical Observatory Senior Astrophysicist Leon Golub says. “With the X-ray Telescope, we can see them clearly for the first time.”

Unlike Earth’s magnetic field, which is roughly constant in every location, the sun is dotted with “active regions” where the local magnetic field is thousands of times stronger than Earth’s. Those active regions tend to have sunspots at their centers and are the sources of solar flares.

The Hinode X-ray Telescope has uncovered new details in these active regions, including gigantic arcing magnetic structures that dwarf the underlying sunspots. Whereas the largest sunspots are about the size of Earth, the active regions above them extend across one-third of the sun’s face, spanning an area the size of 30 Earths or more.

The X-ray Telescope also has shown intricate details of smaller explosive events called X-ray jets. These streams of plasma squirt from the sun’s surface like water jets in a Jacuzzi. By studying the jets in detail, astronomers are learning more about the physical processes that, on a larger scale, power solar eruptions.

Magnetic field mapping
Hinode, together with ground-based telescopes, is now mapping the sun’s magnetic field in great detail. The X-ray Telescope is unveiling the form of the magnetic fields in the sun’s corona.

Another instrument being carried by Hinode, the Solar Optical Telescope, is working with ground-based telescopes to measure the magnetic fields on the surface of the sun. This data is used to run complex computer models that predict the coronal magnetic structure. The results are compared with actual X-ray observations. Computer models can be adjusted when reality strays from the prediction.

Once solar astronomers have a map of the sun’s magnetic field, “we can compare it to the model and ask such questions as: Does this region look like it will produce a flare? How soon might it go off? How strong might the flare be?” DeLuca says. “If the models are accurate, and we are working to improve them all the time, then we may be able to answer these questions”—and perhaps forecast solar storms headed toward Earth.

“Everything we thought we knew about X-ray images of the sun is out of date,” Golub says. “We’ve seen many new and unexpected things. For that reason alone, the Hinode mission is already a success.”

Presently, the sun is relatively quiet, with few active regions or sunspots. Astronomers call this the solar minimum. However, the sun’s level of activity varies in an 11-year cycle. Five years from now, the solar surface will be covered with seething active regions ripe for explosions. When the next solar maximum comes, Hinode and a fleet of other sun-spying instruments will be watching.