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Solar and Space Physics: A Science for a Technological Society
15
1
Enabling Discovery in Solar
and Space Physics
EARTH’S DYNAMIC SPACE ENVIRONMENT
We live on a planet whose orbit traverses the tenuous outer atmosphere of a variable magnetic star, the
Sun. This stellar atmosphere is a rapidly flowing plasma—the solar wind—that envelops Earth as it rushes
outward, creating a cavity in the galaxy that extends to some 140 astronomical units (AU). 1 There, the
inward pressure from the interstellar medium balances the outward pressure of the solar plasma, forming
the heliopause, the boundary of our home in the universe. Earth and the other planets of our solar system
are embedded deep in this extended stellar atmosphere, or heliosphere (Figure 1.1), the domain of solar
and space physics.
The energy Earth receives from the Sun determines Earth’s environment. This energy, primarily visible
light, but also including ultraviolet and X-ray radiation, establishes the temperature, structure, and composition of Earth’s uppermost atmosphere and ionosphere. The Sun also has a corpuscular output—the
magnetized solar wind and energetic particles—that expands throughout interplanetary space, interacting
with Earth and affecting humans in numerous ways (see Chapter 3). Because these latter sources of the
Sun’s power are highly variable in location, intensity, and time, Earth’s near-space environment is profoundly dynamic and hosts numerous phenomena that present hazards to spacecraft, humans in space,
and society’s ground-based technological infrastructure.
Solar and space physics research seeks to understand the history, evolution, and detailed workings of
the Sun and to characterize and understand Earth’s space environment, including its upper atmosphere,
and its response to the periodic, but highly variable, forcing by the Sun. The Earth system and its parent
star also provide an accessible cosmic laboratory for studies that can lead to understanding the environs
of other planets, stars, and cosmic systems. The research elements of solar and space physics span solar
electromagnetic and radiative processes, the generation of solar magnetic fields, the solar wind and interplanetary magnetic fields, and their evolution, development, and interaction with planets and moons that
1 An astronomical unit (AU) is the mean distance between Earth and the Sun; it is approximately 150 million kilometers (km). For
comparison, the distance from the Sun to the Pluto-Charon system is currently approximately 32 AU.
Solar and Space Physics: A Science for a Technological Society
15
1
Enabling Discovery in Solar
and Space Physics
EARTH’S DYNAMIC SPACE ENVIRONMENT
We live on a planet whose orbit traverses the tenuous outer atmosphere of a variable magnetic star, the
Sun. This stellar atmosphere is a rapidly flowing plasma—the solar wind—that envelops Earth as it rushes
outward, creating a cavity in the galaxy that extends to some 140 astronomical units (AU). 1 There, the
inward pressure from the interstellar medium balances the outward pressure of the solar plasma, forming
the heliopause, the boundary of our home in the universe. Earth and the other planets of our solar system
are embedded deep in this extended stellar atmosphere, or heliosphere (Figure 1.1), the domain of solar
and space physics.
The energy Earth receives from the Sun determines Earth’s environment. This energy, primarily visible
light, but also including ultraviolet and X-ray radiation, establishes the temperature, structure, and composition of Earth’s uppermost atmosphere and ionosphere. The Sun also has a corpuscular output—the
magnetized solar wind and energetic particles—that expands throughout interplanetary space, interacting
with Earth and affecting humans in numerous ways (see Chapter 3). Because these latter sources of the
Sun’s power are highly variable in location, intensity, and time, Earth’s near-space environment is profoundly dynamic and hosts numerous phenomena that present hazards to spacecraft, humans in space,
and society’s ground-based technological infrastructure.
Solar and space physics research seeks to understand the history, evolution, and detailed workings of
the Sun and to characterize and understand Earth’s space environment, including its upper atmosphere,
and its response to the periodic, but highly variable, forcing by the Sun. The Earth system and its parent
star also provide an accessible cosmic laboratory for studies that can lead to understanding the environs
of other planets, stars, and cosmic systems. The research elements of solar and space physics span solar
electromagnetic and radiative processes, the generation of solar magnetic fields, the solar wind and interplanetary magnetic fields, and their evolution, development, and interaction with planets and moons that
1 An astronomical unit (AU) is the mean distance between Earth and the Sun; it is approximately 150 million kilometers (km). For
comparison, the distance from the Sun to the Pluto-Charon system is currently approximately 32 AU.