The Solar-B Brochure

ISAS | PPARC | NASA

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The Dynamic Sun

The Sun is the main source of light and energy for all life on Earth. We seek to understand the origins of solar activity and variability which disrupt our home environment.

"How are the conditions for life on Earth maintained? How does the solar output vary? What knowledge from space can improve the quality of life on Earth?" NASA Strategic Plan, 1994

Figure: Yohkoh soft X-ray image from May 8, 1992.

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The Sun-Earth System

Solar-B will reveal the mechanisms for solar variability and study the origins of space weather and global change.

The Sun and Earth form a tightly coupled system, with solar variability driving effects ranging from space weather to climate change. Global Climate: The Sun's brightness is not constant and its magnetic activity influences the Earth's temperature, contributing both to global warming and little ice ages. Upper Atmosphere: The Sun's magnetic activity causes extreme variations in ultraviolet and X-ray radiation. These radiations control the Earth's ionosphere and the protective ozone layer. Space Weather: The Earth is constantly bombarded by solar material accelerated in the corona. Frequent magnetic disruptions eject massive clouds which cause magnetic storms around the Earth. Energetic particles often create local radiation hazards in space.

Figure: Superposed Skylab coronograph and He 304 Å images; ozone concentration from TOMS; Brueghel painting of skaters during the "Little Ice Age" when solar activity was low; auroral curtain triggered by a solar storm.

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Broader Implications: Our Dynamic Universe

Solar-B will provide detailed information about the dynamic behavior of cosmic magnetic fields.

Astronomical objects from dwarf stars to accretion disks to giant elliptical galaxies have dynamic magnetic fields, the origins of which are not well understood. Pulsars such as the Crab have magnetic fields a billion times stronger than the Sun's, transmitting sufficient energy to power the entire Crab nebula. Magnetic fields in cosmic jets cause massive radio emission by interaction with high-energy particles. Our own Sun has the most intense magnetism in the solar system. The Sun's atmosphere, the million-degree corona, its dynamic nature, and the solar wind extending out to the Earth and beyond, are all direct consequences of the Sun's magnetic activity.

Figure:Galactic radio jets from quasar 3C-175; Yohkoh soft X-ray image from November 12, 1991; the Crab nebula.

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The Solar-B Mission

Solar-B is: An international collaboration building on the highly successful Japan/US/UK Yohkoh (Solar-A) experience. A coordinated set of optical, UV, and X-ray instruments to understand the dynamic Sun. A source of dramatic images of solar activity with a strong education and public outreach component.

Figure: Solar-B satellite; SOHO/EIT Extreme Ultraviolet image; SOHO/MDI Magnetogram image.

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Understanding the Dynamic Sun

Solar-B will provide a new comprehensive view of the dynamic solar atmosphere and engender a unique and timely interaction between theory and observations. Observational Advances: First space based observations of the Sun's vector magnetic fields. Reveals magnetic field's photospheric roots and 3-D linkage to corona. Provides first complete time coverage at high resolution. Theoretical Advances: Numerical techniques for determining vector magnetic fields from spectral data. Comprehensive three-dimensional convection, dynamo, and coronal modeling. Science Objectives: Creation and destruction of the Sun's magnetic field. Modulation of the Sun's Luminosity. Generation of UV and X radiation. Solar wind and eruptions.

Figure: Yohkoh soft X-ray images from February 26, 1992 showing the "Scorpion" filament eruption.

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Objective: Magnetic Field Creation and Destruction

Creation: Processes hidden deep within the Sun generate surface activity in an 11-year cycle. Emerging magnetic field topology reveals the workings of this dynamo process within the sun. Solar-B will observe the emerging magnetic field and, for the first time, its twist in detail over large regions of the Sun. Destruction: The processes by which solar magnetism leaves the Sun to produce a solar cycle are unknown. Solar-B will directly show the magnetic flux removal process and its role in the cycle.

Figure: Solar magnetic field from National Solar Observatory at cycle maximum and minimum; international sunspot numbers from 1749 to 1995.

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Objective: Modulation of the Sun's Luminosity

All life on Earth depends on the Sun's radiation for its existence. Small changes in the solar output can change our climate and weather, with enormous impact on human civilization.

Measurement of the solar "constant" shows the Sun to be less luminous at sunspot cycle minima. An extended period of abnormally low activity coincided with the "Little Ice Age" in the 17th century. Extremely small scale features in the solar photosphere cause the solar cycle changes in the luminosity. Solar-B will make the first observations with resolution, wavelength coverage, and sampling adequate to determine the role of these features in the long-term solar luminosity changes.

Figure: G-band image of the solar photosphere from the Swedish Vacuum Solar Telescope on LaPalma showing bright faculae and dark spots; plot of solar luminosity and the sunspot cycle.

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Objective: Production of UV and X Radiation

The Sun is a powerful and highly variable source of ultraviolet and X radiation, which has major effects on our environment.

The solar UV and X radiation originates in the chromosphere and corona, where temperatures rise to over one million degrees. In flares, energetic particles and even gamma rays are produced, with coronal temperatures exceeding ten million degrees. Solar-B will have the unprecedented spatial resolution and the wavelength and temporal coverage needed to understand the processes which produce the UV and X-ray emission.

Figure: Yohkoh soft X-ray image from November 12, 1991 overlaid on a NSO magnetogram from the same date.

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Objective: Causes of the Solar Wind and Eruptions

Solar Wind: The million-degree corona continually expands outward, becoming a supersonic wind that blows past the Earth, buffeting the geomagnetic field and dumping energy into the upper atmosphere. Eruptions: Large parts of the corona are seen to explode, blast through the solar wind, and cause major magnetic and atmospheric disturbances at the Earth. The solar atmosphere is filled with eruptive events - surges, spicules, X-ray jets - representing release of magnetic energy into the corona.

Solar-B will: Open a new window on the root causes of coronal heating, providing new understanding of solar wind energetics. Provide the first accurate measurements of magnetic fields and electric currents that will reveal the causes of eruptions in the solar atmosphere.

Figure: NIXT soft X-ray image superposed on HAO eclipse image of July 11, 1991; the "Grandaddy" eruptive prominence of June 4, 1946 from HAO.

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Programmatic Benefits to NASA

Highly leveraged participation in a major space science mission. Reliable partner with proven cost and schedule maintenance.

Builds on Yohkoh, SOHO, and TRACE.

Advances goals of the Earth-Solar Connection program. Broad community involvement and outreach.

Figure: Mission schedule and the possible solar cycle behavior.

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Summary

What: Solar-B contains a set of high-resolution solar telescopes and spectrometers. The data will reveal the mechanisms of solar variability that arise in the dynamic structure of the solar atmosphere.

Why: We need such data to understand the variable Sun and its effect on terrestrial climate (global change) and space weather.

Science: Advances in understanding basic plasma astrophysics such as the dynamo and magnetic reconnection processes. Identification of the physics underlying the variations of solar luminosity. Effective interaction between theoretical and observational advances. Identification of the mechanisms of solar variability.

Technology: Solar-B is a cost-effective opportunity to develop specific technologies in remote sensing instrumentation, such as ultra-precise polarimeters and optical and X-ray filters.

Outreach: Solar-B observations will provide a basic tool for education and public understanding of plasma physics at work in nature. Solar-B observations of the Sun, our local star, will substantially influence the public understanding of science and technology.

Figure: Generic sunrise.