Alumni Profile • Todd Hoeksema '78
Listening to the Sun

Todd Hoeksema '78When he left Calvin in May 1978, Todd Hoeksema had given up his dream of becoming an astronomer. "There didn't seem to be any jobs," he said. Settling on a more down-to-earth graduate program in Stanford's applied physics department, he received an unexpected phone call from researchers at the school's solar observatory asking if he'd like a summer job. Twenty-eight years later he's still there, and the recipient of NASA's Distinguished Public Service Medal for his leadership of a committee that created a 30-year road map for the space agency's heliophysics research. Heliophysics is the study of that part of the universe dominated by the Sun.

Now a senior scientist in Stanford's Solar Observatories Group, Hoeksema has helped pioneer the new science of helioseismology. An instrument he and his team designed, the Michelson Doppler Imager (MDI), was launched on board the Solar and Heliospheric Observatory (SOHO) in 1995. Floating a million miles sunward from Earth, MDI "listens" to sound waves created by the boiling surface of the Sun.

"The Sun resonates like a bell," Hoeksema said-meaning its surface oscillates in response to trapped sound waves echoing around inside the star. By mapping these seismic oscillations, Hoeksema is trying to understand how changes deep inside cause sunspots to form on its surface. Dark disturbances the size of the Earth and larger, sunspots store magnetic energy in the solar atmosphere. When that energy, for reasons unknown, is suddenly released, solar flares erupt, sending massive shock waves and radiation toward Earth.

One hundred years ago, these episodes of intense "space weather" didn't have much noticeable effect on people, apart from the occasional display of aurora. Now they can cause power failures, like the March 1989 collapse of the HydroQuebec power grid. They disturb the ionosphere and degrade the global positioning system (GPS) navigation used in virtually all forms of transportation-a system relied upon more each year. Hoeksema explains that "as the circuits used in our satellites get smaller and smaller they're more easily thrown off by a small amount of energy from solar radiation."

That means predicting space weather has become critical to determining, for example, whether airline pilots will be able to communicate reliably on any given day. "It's the practical impact it has on our lives that I like about solar physics," Hoeksema said.

Though it has less effect on daily life, another development will make space weather prediction increasingly important. President Bush has charged NASA with sending astronauts back to the Moon and then on to Mars by about 2030. These astronauts, once outside the Earth's magnetosphere, will be subject to dangerous radiation unless they know when to expect solar blasts and take shelter. That new imperative was central to the team of 20 scientists that Hoeksema led from 2004 to 2005 as they laid out a 30-year plan for NASA's solar and space research. The agency's award to Hoeksema for his leadership is the highest honor it confers on nongovernmental employees.

Hoeksema and his colleagues at Stanford and others at Lockheed are now designing a new instrument known as the Helioseismic and Magnetic Imager (HMI) that will help NASA collect the data called for in the research plan. Projected for launch on the Solar Dynamics Observatory in 2008, the HMI, Hoeksema said, "will enable us to look more deeply into the Sun and more closely at its surface and atmosphere. It's everything we've dreamed of."


To see images of the Sun taken by the Michelson Doppler Imager, visit