Stanford scientist recognized for his contribution to solar physics

By Emily Saarman

NASA awarded a Stanford solar physicist its highest honor for nongovernmental employees. J. Todd Hoeksema, a senior scientist at the Hansen Experimental Physics Laboratory, won a distinguished public service medal for his leadership in "sun-solar system connection science" and in particular for his leadership of NASA's committee to create a 30-year "roadmap" for heliophysics research.

"This was the first roadmap that had to fit what we want to do scientifically with what the agency needs to do practically to send people outside of the Earth's protective magnetosphere," Hoeksema said. The 30-year plan laid out research questions that will help scientists learn more about the fundamental physics of the sun, the effects of solar events on Earth and ways to protect astronauts and spacecraft from the harms of solar wind.

To accomplish these goals, Hoeksema says it's important to measure many different parameters at the same time. "You can't spend your whole career studying just the sun or just the Earth anymore," he said. "You really have to understand the system as a whole and how everything interacts."

Although the Bush administration has charged NASA with sending astronauts to Mars by 2030, Hoeksema said NASA has received no additional funding to meet this goal. "All of a sudden we have less money and more to do, just like everyone else," he said. The heliophysics research budget, which was projected to grow significantly over the next five years, will now be held at $700 million annually, which "sounds like a lot until you break it up into missions that cost almost $1 billion each [over the life of the projects]," Hoeksema explained.

Understanding the Sun-Earth connection

It is easy to think of the sun as benign and unchanging, but in reality the sun is a dynamic ball of boiling gases that scientists are only beginning to understand. "The sun does things that affect the Earth," Hoeksema said. "It affects radio communication pretty severely. It affects the way satellites are operated. People even reroute airliners because of solar activity."

Global positioning system (GPS) navigation, used in ships, planes and cars, is vulnerable to changes in space weather. Explosions on the sun, known as solar flares, blast high-energy gamma rays and X-rays toward Earth. Within minutes, these rays ionize gases in our upper atmosphere, which can disrupt signals from GPS satellites and make performance of navigation systems uncertain.

"If you're landing an airplane and suddenly you're not as sure about your position as you were a few minutes ago, you could have problems," Hoeksema said. Improved prediction of these radio blackouts is one of NASA's new research priorities.

To predict space weather, physicists need to understand the source of the solar flaresthe sun's magnetic field. Unlike the Earth, which has a stable north-south field, the sun's magnetic field is complex and constantly changing. Small magnetic disruptions pop up on the surface of the sun every day and the north-south polarity of the entire field swaps approximately every 11 years. Scientists aren't sure exactly what causes the sun's magnetic field or its erratic behavior, but the 30-year roadmap provides for new instruments that will help scientists look deeply into the sun for clues.

Large magnetic field disturbances on the surface of the sun form active regions known as sunspots. Sunspots are the source of solar flares and another type of solar eruption called a coronal mass ejection. Although the development of sunspots is still largely a mystery, scientists do know that the sun's activity varies in roughly 11-year cycles and is most intense during the "solar maximum." The next maximum is expected in 2012 and Stanford's solar group plans to observe every minute of it.

"I'm interested in understanding how the active regions interact with small-scale features to make that 11-year solar cycle happen," Hoeksema said. A technique called helioseismology is key to his work and that of the about 20 other scientists in the Stanford Solar Observatory Group. Helioseismic instruments "listen" to the sound waves created by the boiling surface of the sun.

"The sun resonates like a bell," Hoeksema said. "From the characteristics of those resonances you can tell how fast it's rotating, the temperature and the density. You can sense the magnetic fields a little bit too. We're trying to put all those pieces of information together to build up a better picture of what's inside the sun."

Although helioseismology has been developing since the late 1970s, past instruments have been forced to choose either a low-resolution map of the entire sun or a high-resolution map of a fraction of the sun. The Stanford solar group is working on an instrument known as the Helioseismic and Magnetic Imager, or HMI, that should solve this problem by taking high-resolution images of the entire sun every 50 seconds. The HMI instrument will be launched on NASA's Solar Dynamics Observatory satellite in 2008.

"HMI is going to do the helioseismology just perfectlyit's everything we've dreamed of," Hoeksema said. "Finally we'll be able to characterize the inside of the sun as well as we know how."

Emily Saarman is a science-writing intern at Stanford News Service.