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PROBING THE SUN:

High above Antarctica, a balloon-borne telescope will gather unprecedented images of solar magnetic fields

NCAR scientists and engineers, working with colleagues in Germany and Spain, are building a unique telescope that will capture images of the Sun from a perch high in the atmosphere.

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Scientists are gradually unraveling the mysteries of the Sun. (Photo by Caspar Ammann, UCAR Digital Image Library.)

At the heart of what’s known as the Sunrise project is a lightweight, 1-meter telescope. Borne by a balloon, it will circle Antarctica for about two weeks at an altitude of approximately 40,000 meters (130,000 feet). Its advanced instrumentation will provide high-resolution images of the Sun’s outer surface, or photosphere, enabling scientists to get unprecedented views of small-scale magnetic fields that drive solar variability and profoundly affect Earth’s atmosphere.

The international team expects to launch the telescope in late 2008. If the instrument can be recovered intact and funding is available, it will be launched again the following year to obtain additional images.

“This project will allow us to view features of the Sun that we’ve never seen before,” says NCAR scientist Bruce Lites, a principal investigator on the Sunrise project.

Learning about magnetic fields

The Sun is the source of light and energy for life on Earth and the principal driver of atmospheric motion. Solar disruptions, such as coronal mass ejections, have profound impacts on our upper atmosphere, touching off geomagnetic storms that affect sensitive communications and other systems on Earth. But scientists remain uncertain about the causes of solar variability and disruptions. They need specialized instruments to examine the Sun in detail.

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NCAR scientists Bruce Lites (left) and Kim Streander, who are working on the Sunrise project, examine a telescope that will be used to capture ultraviolet images during a test flight. (Photo by Carlye Calvin, ©UCAR.)

“The Sunrise telescope will allow us to carry out novel research programs,” says Wolfgang Schmidt of the University of Freiburg in Germany, a collaborator on the project.

The primary goal of the Sunrise project is to investigate the structure and dynamics of the Sun’s magnetic field. The magnetic field fuels solar activity and causes variations in radiation, which may be a significant factor in long-term changes in our climate.

The project also may help scientists glean insights into magnetic fields in general. The universe contains numerous classes of objects, such as stars, that are dominated by magnetohydrodynamic and plasma processes, but only the Sun is close enough to examine in any detail.

“Sunrise will broaden our understanding of the really fundamental physical processes of the outer atmospheres of stars and the forces that drive stellar winds,” Lites explains.

Working with international collaborators is vital on such a major project, Lites adds. “The solar community is not large, so solar physicists around the world need to work with each other,” he says. “In times of limited funding, it’s especially important to pool our resources and move forward on really big projects.”

International contributions

NCAR staffers, using NSF funding and a grant from NASA, are designing the gondola and telescope pointing system. They are also working on the data system and cameras for one of the key instruments, a polarimetric spectrograph that measures wavelengths in the Sun’s electromagnetic spectrum and enables scientists to make inferences about its magnetic field.

Researchers at Germany's Max Planck Institute for Solar System Research are building the telescope, providing optics and mechanisms for the polarimetric spectrograph, and designing a filtergraph for high-resolution images in the visible and ultraviolet spectral ranges. Their colleagues at the Kiepenheuer Institute for Solar Physics are creating a fine-pointing system to achieve very high precision image stability. Spanish researchers at the Astrophysics Institute of the Canary Islands are designing an imaging magnetograph experiment, which will provide two-dimensional magnetic field maps.

The telescope is being developed at a time when an array of sophisticated new solar instruments is coming on line. Images from the 1-meter Swedish Solar Telescope in the Canary Islands, for example, have been dazzling the scientific community by showing, for the first time, the three-dimensional structure of the Sun’s photosphere, as well as small sunspots that traverse what appear to be raised ridges.

As detailed as these images are, Sunrise will provide far more information, including measurements of the magnetic fields, in part because the telescope will reach an altitude at which it will not have to contend with distortions caused by Earth’s atmosphere.

The balloon-mounted telescope is expected to capture images as small as 40 kilometers (25 miles), compared to 90 kilometers (56 miles) for the Swedish telescope. In addition, Sunrise will train its instruments on the same small area of the Sun for two weeks, thereby allowing researchers to witness dynamic changes in magnetic fields.

Only in the last few years have scientists discovered planets orbiting other stars. NCAR’s Timothy Brown, one of the pioneers in this field, was part of the research team that, in 2001, made the first detection of a planetary atmosphere in another solar system. The breakthrough observation pointed the way toward finding atmospheres hundreds of light years away and possibly locating planets with similar characteristics to Earth.

planets

TrES-1, the first extrasolar planet found by a new small-telescope network, orbits its bright star in this artist’s rendition. (Illustration by David A. Aguilar, Harvard-Smithsonian Center for Astrophysics.)

Now Brown is working with scientists in the United States and Spain in a systematic effort to find other planets in the Milky Way. The project, called Transatlantic Exoplanet Survey (TrES), utilizes small telescopes in the Canary Islands, Arizona, and California to scan promising regions of the galaxy that are crowded with stars. Researchers at NCAR, the Lowell Observatory, the California Institute of Technology, and Spain’s Astrophysics Institute of the Canary Islands look for the telltale dimming of starlight that could indicate an orbiting planet passing between its star and Earth.

Using telescopes on two continents allows the scientists to focus on the same region for about twice as much time each night as they could using just one telescope. The effort began paying dividends in 2004 when the team found a dense, Jupiter-sized planet about 500 light years from Earth. They called it TrES-1.

Such research can provide insights into the nature of the galaxy, the physics of stars (including the Sun), and, perhaps most intriguingly, whether Earth is an anomaly. “People like to know how they fit into the universe,” Brown says. “Is Earth typical, or is it rare or even unique?”

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