Spaceflight Now: Breaking News

International team building next explorer to study Sun
Posted: January 20, 2001

Our Sun is a violent star and is capable of producing explosive flares and hurling clouds of matter toward Earth -- activities that in the past have interfered with satellite communications and electric power transmission grids on Earth.

To learn more about the forces that create these disruptions on the Sun, scientists from Japan, the United States and the United Kingdom are working together to build instruments to fly in 2005 on the Solar-B mission, a satellite being developed by Japan's Institute of Space and Astronautical Science (ISAS).

An artist's concept of the Solar-B satellite. Photo: NASA/MSFC
"NASA is working with scientists across the country to design and build the major elements of the three instruments for Solar-B," said Lawrence Hill, project manager for Solar-B at NASA's Marshall Space Flight Center in Huntsville, Ala. "NASA has just completed the design phase, and we'll soon begin building the instruments that will help us understand the star closest to home."

The Solar-B spacecraft will be placed into a Sun-synchronous orbit around the Earth. This is a polar rather than an equatorial orbit and allows the instruments to remain in continuous sunlight for nine months of each year. The Solar-B instruments will observe how magnetic fields on the Sun's surface, called the photosphere, interact with the Sun's outer atmosphere, the corona, that extends millions of miles out into space.

"This high-temperature outer solar atmosphere is the only place in the universe where scientists can make very detailed observations of how magnetic fields interact with the hot ionized gases, or plasmas, that make up all stars," said Dr. John Davis, Solar-B project scientist at the Marshall Center. "The instruments will work together to show how changes in magnetic fields deep inside the Sun erupt through the different layers of the Sun's atmosphere, creating the violent disturbances that sometimes affect us on Earth."

The origin of the Sun's violent behavior lies with its magnetic field, which is generated deep in the star's interior. The magnetic field is buoyant and rises to the surface where it is often visible as sunspots, which are large concentrations of magnetic flux. Energy is stored in the magnetic field.

As the field rises into and through the solar atmosphere, energy can be released either gradually to heat the outer atmosphere to temperatures in excess of a million degrees or explosively in solar flares or coronal mass ejections (CMEs). Solar-B's scientific mission is to observe the distribution of the magnetic field at the photosphere where it first becomes visible and to study how it releases its energy to the surrounding atmosphere.

"By studying, in detail, how the character of the field changes with time over a solar cycle, we hope to learn how the field is generated and if and how the field affects solar luminosity," said Davis.

Recent measurements of the energy flowing from the Sun, the solar "constant", shows the Sun to be less luminous at the minimum of the sunspot cycle when Solar-B will be launched. The records of sunspot observations from 400 years ago indicate an extended period when sunspots were extremely rare, and the sunspot cycle even disappeared. This period coincided with a series of very harsh winters in Europe known as the "Little Ice Age."

Solar scientists have found suggestions that extremely small magnetic features in the solar photosphere are responsible for the changes in the luminosity. Solar-B will enable the first comprehensive set of observations to determine the role of these features in long-term solar luminosity changes and provide better answers to this provocative question of how the Sun impacts Earth's climate.

Solar-B is an international mission sponsored by ISAS based in Sagamihara, a suburb of Tokyo, Japan, with its partners -- NASA and the Particle Physics and Astronomy Research Council based in Swindon, United Kingdom. The heart of the Solar-B mission is a large solar optical telescope that is being developed by the Japanese Institute. To measure the magnetic fields, structures and flow patterns in the photosphere, NASA will provide a set of instruments for the telescope's focal plane. X-Ray and Extreme Ultraviolet Telescopes, each of which contain major components supplied by the three international partners, will record how the energy stored in and released by the magnetic field propagates through the Sun's outer atmosphere.

The Marshall Center is managing the development of the NASA-provided components for the Solar-B Focal Plane Package, the X-ray Telescope and the Extreme Ultraviolet Imaging Spectrometer.

When Solar-B instrument fabrication and testing is completed by the investigators and accepted by NASA, the instruments will be shipped to Japan for further testing and integration with the rest of the Solar-B satellite.

Solar-B is scheduled for launch from Kagoshima, Japan, in August or early September 2005. Once the satellite is in orbit, NASA and the science teams will support instrument operations and data collection from the operations center located at ISAS in Sagamihara.

Solar-B is part of the Sun Earth Connection science theme, managed by NASA's Office of Space Science, Washington, DC, and the Solar Terrestrial Probes Program at NASA's Goddard Space Flight Center in Greenbelt, Md.