SOLAR AND SPACE PHYSICS
A Science for a Technological Society
United States and international programs in solar and space physics seek to improve scientific understanding of the Sun and its variation over time; the relationship between the Sun and Earth’s environment; and the impact of solar activity and space weather events on human activities as well as the Sun’s connections with other bodies in the solar system and to the galaxy beyond. By directly measuring phenomena that occur in our own solar system, solar and space physicists draw connections between experiments in the laboratory and processes observed in remote astrophysical locations. The disciplines that comprise solar and space physics are intellectually rich and vital to a society increasingly dependent on technologies sensitive to the near-Earth space environment.
In 2010, NASA and the National Science Foundation asked the National Research Council to assemble a committee of experts (the “decadal survey committee”) to develop an integrated national strategy that would guide agency investments in solar and space physics (or “heliophysics” in the terminology used by NASA) for the years 2013-2022. That strategy, the result of nearly 2 years of effort by the survey committee, which worked with more than 100 scientists and engineers on eight supporting study panels, is presented in the 2013 publication, Solar and Space Physics: A Science for a Technological Society (http://www.nap.edu/catalog.php?record_id=13060). This booklet, designed to be accessible to a broader audience of policymakers and the interested public, summarizes the content of that report but does not replace, nor should it be construed, as a substitute for the findings and recommendations of the actual report.
View of the aurora from the International Space Station as it crossed over the Southern Indian Ocean on September 17, 2011.
WE LIVE ON A PLANET IMMERSED IN THE TENUOUS OUTER ATMOSPHERE OF A VARIABLE MAGNETIC STAR, THE SUN. AS THE SUN’S OUTER ATMOSPHERE EXPANDS SUPERSONICALLY OUTWARD, IT ENVELOPS EARTH AND SHAPES THE TERRESTRIAL ENVIRONMENT. THIS GUSTY SOLAR WIND FLOWS PAST THE PLANETS, CARVING OUT A CAVITY IN OUR GALAXY THAT EXTENDS SEVERAL TIMES THE DISTANCE FROM PLUTO TO THE SUN. EARTH AND THE OTHER PLANETS OF OUR SOLAR SYSTEM ARE EMBEDDED DEEP WITHIN THIS EXTENDED CAVITY, CALLED THE HELIOSPHERE. THIS IS THE DOMAIN OF HELIOPHYSICS.
The new view of the heliosphere. Illustrated here are the termination shock, the boundary layer where the expanding bubble of solar wind particles abruptly slows down when it begins to press into the interstellar medium; the intermediate zone of slower-moving solar wind particles that forms the heliosheath; and finally the heliopause, the boundary between the solar wind and the interstellar medium.
Although the total energy output of the Sun is remarkably constant, magnetic activity on the Sun causes “space weather”—an analog to the more familiar terrestrial weather—severe space weather events have the potential to disrupt or cause failure in the space- and ground-based technological systems that modern society relies on. The primary drivers of hazardous space weather are the radiation, particles, and fields associated with solar flares—tremendous explosions in the low solar atmosphere—and coronal mass ejections—immense clouds of magnetized plasma launched into space at high speeds.
The heliosphere and planetary environments are elements of a single interconnected system that evolves in response to solar, planetary, and interstellar conditions. For example, Earth’s magnetosphere, the area of space controlled by our planet’s magnetic field, is profoundly affected by disturbances in the solar wind, as well as by changing conditions in the atmosphere below. Interactions in the magnetosphere involving neutral gas, electrically charged particles, and plasma waves occur over a broad range of scales in both space and time. The transport of energy and momentum through this environment exhibits varying degrees of complex feedback, requiring research techniques that treat heliophysics as a coupled system: heliophysics is thus inherently a system science.
Space weather. NOAA Space Weather Prediction Center. http://www.swpc.noaa.gov/info/swx_poster_a.jpg.
At the heart of heliophysics are fundamental questions of basic importance to science and society. Heliophysics research encompasses solar electromagnetic and radiative processes; the generation of solar magnetic fields and acceleration of energetic particles; the storage and violent release of magnetic energy; the origin and evolution of the solar wind and interplanetary magnetic field; and their interactions with planets and moons that have their own magnetospheres and atmospheres. Moreover, as humanity's presence extends farther into space—both by means of robotic probes and human spaceflight—and as society’s technological infrastructure is increasingly linked to space-based assets vulnerable to the effects of space weather, the need to characterize, understand, and predict the dynamics of our environment in space becomes ever more pressing.
HELIOPHYSICS RESEARCH SEEKS TO UNDERSTAND THE HISTORY, EVOLUTION, AND DETAILED WORKINGS OF THE SUN AND SOLAR WIND, TO CHARACTERIZE AND UNDERSTAND EARTH’S SPACE ENVIRONMENT AND UPPER ATMOSPHERE, TO DETERMINE HOW THE HELIOSPHERE INTERACTS WITH THE GALAXY BEYOND, AND TO STUDY RESPONSES AT EARTH AND THROUGHOUT THE HELIOSPHERE TO SOLAR EVENTS AND PERIODIC VARIABILITY.