April 24, 2007 |
NASA’s twin Solar Terrestrial Relations Observatory (STEREO) spacecraft have made the first three-dimensional images of the sun. The new view will greatly aid scientists’ ability to understand solar physics and thereby improve space weather forecasting.
“The improvement with STEREO’s 3-D view is like going from a regular X-ray to a 3-D CAT scan in the medical field,” said Dr. Michael Kaiser, STEREO Project Scientist at NASA’s Goddard Space Flight Center, Greenbelt, Md.
The STEREO spacecraft were launched October 25, 2006. On January 21 they completed a series of complex maneuvers, including flying by the moon, to position the spacecraft in their mission orbits. The two observatories are now orbiting the sun, one slightly ahead of Earth and one slightly behind, separating from each other by approximately 45 degrees per year. Just as the slight offset between a person’s eyes provides depth perception, the separation of spacecraft allow 3-D images of the sun.
Violent solar weather originates in the sun’s atmosphere, or corona, and can disrupt satellites, radio communication, and power grids on Earth. The corona resembles wispy smoke plumes, which flow outward along the sun’s tangled magnetic fields. It’s difficult for scientists to tell which structures are in front and which are behind.
“In the solar atmosphere, there are no clues to help us judge distance. Everything appears flat in the 2-D plane of the sky. Having a stereo perspective just makes it so much easier,” said Dr. Russell Howard of the Naval Research Laboratory, Washington, the Principal Investigator for the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) suite of telescopes on the spacecraft.
“With STEREO’s 3-D imagery, we’ll be able to discern where matter and energy flows in the solar atmosphere much more precisely than with the 2-D views available before. This will really help us understand the complex physics going on,” said Howard.
STEREO’s depth perception also will help improve space weather forecasts. Of particular concern is a destructive type of solar eruption called a Coronal Mass Ejection (CME). CMEs are eruptions of electrically charged gas, called plasma, from the sun’s atmosphere. A CME cloud can contain billions of tons of plasma and move at a million miles per hour.
The CME cloud is laced with magnetic fields, and CMEs directed toward Earth smash into our planet’s magnetic field. If the CME magnetic fields have the proper orientation, they dump energy and particles into Earth’s magnetic field, causing magnetic storms that can overload power line equipment and radiation storms that disrupt satellites.
Satellite and utility operators can take precautions to minimize CME damage, but they need an accurate forecast of when the CME will arrive. To do this, forecasters need to know the location of the front of the CME cloud. STEREO will allow scientists to accurately locate the CME cloud front. “Knowing where the front of the CME cloud is will improve estimates of the arrival time from within a day or so to just a few hours,” said Howard. “STEREO also will help forecasters estimate how severe the resulting magnetic storm will be.”
“In addition to the STEREO perspective of solar features, STEREO for the first time will allow imaging of the solar disturbances the entire way from the sun to the Earth. Presently, scientists are only able to model this region in the dark, from only one picture of solar disturbances leaving the sun and reaching only a fraction of the sun-Earth distance, said Dr. Madhulika Guhathakurta, STEREO Program Scientist, NASA Headquarters. Washington.
STEREO’s first 3-D images are being provided by NASA’s Jet Propulsion Laboratory, Pasadena, Calif. STEREO is the third mission in NASA’s Solar Terrestrial Probes program within NASA’s Science Mission Directorate, Washington. The Goddard Science and Exploration Directorate manages the mission, instruments, and science center. The Johns Hopkins University Applied Physics Laboratory, Laurel, Md., designed and built the spacecraft and is responsible for mission operations. The STEREO imaging and particle detecting instruments were designed and built by scientific institutions in the U.S., UK, France, Germany, Belgium, Netherlands, and Switzerland.
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