| aberration of starlight | The angular shift in the apparent direction of a star caused by the orbital motion of the Earth.
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| aerosol | Liquid droplets and solids suspended in the atmosphere of a planet or satellite.
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| aesthenosphere | A layer of plastic, deformable rock located in the upper mantle of a planet directly below the lithosphere.
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| aurora australis | Light emitted by atoms and ions in the upper atmosphere near the south magnetic pole. The emission occurs when atoms and ions are struck by energetic particles from the Sun.
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| aurora borealis | Light emitted by atoms and ions in the upper atmosphere near the north magnetic pole. The emission occurs when atoms and ions are struck by energetic particles from the Sun.
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| basalt | An igneous rock often produced in volcanic eruptions.
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| bow shock | The region where the solar wind is slowed as it impinges on the Earth’s magnetosphere.
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| core | The innermost region of the interior of the Earth or another planet.
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| Coriolis effect | The acceleration that a body experiences when it moves across the surface of a rotating body. The acceleration results in a westward deflection of projectiles and currents of air or water when they move toward the Earth’s equator and an eastward deflection when they move away from the equator.
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| crust | The outermost layer of the interior of a planet or satellite.
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| differentiation | The gravitational separation of the interior of a planet into layers according to density. When differentiation occurs inside a molten body, the heavier materials sink to the center and the light materials rise to the surface.
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| dynamo | A process in which electric currents within a rotating, convective body produce a magnetic field.
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| exosphere | The outer part of the thermosphere. Atoms and ions can escape from the exosphere directly into space.
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| greenhouse effect | The blocking of infrared radiation by a planet’s atmospheric gases. Because its atmosphere blocks the outward passage of infrared radiation emitted by the ground and lower atmosphere, the planet can not cool itself effectively and becomes hotter than it would be without an atmosphere.
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| igneous rock | A rock formed by solidification of molten material.
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| ionosphere | The lower part of the thermosphere of a planet in which many atoms have been ionized by ultraviolet solar photons.
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| lava | Molten rock at the surface of a planet or satellite.
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| lithosphere | The rigid outer layer of a planet or satellite, composed of the crust and upper mantle.
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| magma | Molten rock within a planet or satellite.
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| magnetopause | The outer boundary of the magnetosphere of a planet.
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| magnetosphere | The outermost part of the atmosphere of a planet, within which a very thin plasma is dominated by the planet’s magnetic field.
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| magnetotail | The part of the magnetosphere of a planet stretched behind the planet by the force of the solar wind.
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| mantle | The part of a planet lying between its crust and its core.
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| mesopause | The upper boundary of the mesosphere layer of the atmosphere of a planet.
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| mesosphere | The layer of a planet’s atmosphere above the stratosphere. The mesosphere is heated by absorbing solar radiation.
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| metamorphic rock | A rock that has been altered by heat andpressure.
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| mineral | A solid chemical compound.
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| oblateness | A departure from spherical shape of a body in which the body’s polar diameter is smaller than its equatorial diameter.
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| outgassing | The release of gas from the interior of a planet or satellite.
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| plate | A section of the Earth’s lithosphere pushed about by convective currents within the mantle.
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| plate tectonics | The hypothesis that the features of the Earth’s crust, such as mountains and trenches, are caused by the slow movement of crustal plates.
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| primeval atmosphere | The original atmosphere of a planet.
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| seafloor spreading | The splitting of the oceanic crust where magma forces the existing crust apart, creating new ocean floor.
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| secondary atmosphere | The atmosphere that forms after a planet has lost any original atmosphere it had.
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| sedimentary rock | A rock formed by the accumulation of small mineral grains carried by wind, water, or ice to the spot where they were deposited.
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| seismic wave | Waves that travel through the interior of a planet or satellite and are produced by earthquakes or their equivalent.
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| seismometers | Sensitive devices used to measure the strengths and arrival times of seismic waves.
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| silicate | A mineral whose crystalline structure is dominated by silicon and oxygen atoms.
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| solar wind | The hot plasma that flows outward from the Sun.
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| stratosphere | The region of the atmosphere of a planet immediately above the troposphere.
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| subduction | The process through which lithospheric plates of a planet or satellite are forced downward into the mantle.
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| thermosphere | The layer of the atmosphere of a planet lying above the mesosphere. The lower thermosphere is the ionosphere. The upper thermosphere is the exosphere.
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| transform fault | The boundary between two of the Earth’s crustal plates that are sliding past each other.
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| tropopause | The upper boundary of the troposphere of the atmosphere of a planet.
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| troposphere | The lowest layer of the atmosphere of a planet, within which convection produces weather.
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| Van Allen belts | Two doughnut-shaped regions in the Earth’s magnetosphere within which many energetic ions and electrons are trapped.
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| zone of convergence | According to plate tectonics, a plate boundary at which the crustal plates of a planet are moving toward one another. Crust is destroyed in zones of convergence.
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| zone of divergence | According to plate tectonics, a plate boundary at which the crustal plates of a planet are moving away from one another. Crust is created in zones of divergence.
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