Planetary Science - Key terms





ATMOSPHERE:

In general, an atmosphere is a blanket of gases surrounding a planet. Unless otherwise identified, however, the term refers to the atmosphere of Earth, which consists of nitrogen (78%), oxygen (21%), argon (0.93%), and other substances that include water vapor, carbon dioxide, ozone, and noble gases such as neon, which together comprise 0.07%.

BIOSPHERE:

A combination of all living things on Earth—plants, mammals, birds, reptiles, amphibians, marine life, insects, viruses, single-cell organisms, and so on—as well as all formerly living things that have not yet decomposed. Typically, after decomposing, a formerly living organism becomes part of the geosphere.

CENTRIFUGAL:

A term describing the tendency of objects in uniform circular motion to move outward, away from the center of the circle. Though the term centrifugal force often is used, it is inertia, rather than force, that causes the object to move outward.

CENTRIPETAL FORCE:

The force that causes an object in uniform circular motion to move inward, toward the center of the circle.

COMPOUND:

A substance made up of atoms of more than one element chemically bonded to one another.

COSMOLOGY:

The study of the origin, structure, and evolution of the universe.

COSMOS:

The universe.

ELECTROMAGNETIC ENERGY:

A form of energy with electric and magnetic components that travels in waves and which, depending on the frequency and energy level, can take the form of long-wave and short-wave radio; microwaves; infrared, visible, and ultraviolet light; xrays, and gamma rays.

ELEMENT:

A substance made up of only one kind of atom. Unlike compounds, elements cannot be chemically broken into other substances.

GEOCENTRIC:

Earth-centered.

GEOCHEMISTRY:

A branch of the earth sciences, combining aspects of geology and chemistry, that is concerned with the chemical properties and processes of Earth.

GEOLOGY:

The study of the solid earth, in particular, its rocks, minerals, fossils, and land formations.

GEOPHYSICS:

A branch of the earth sciences that combines aspects of geology and physics. Geophysics addresses the planet's physical processes as well as its magnetic and electric properties and the means by which energy is transmitted through its interior.

GEOSPHERE:

The upper part of Earth's continental crust, or that portion of the solid earth on which human beings live and which provides them with most of their food and natural resources.

HELIOCENTRIC:

Sun-centered.

HYDROSPHERE:

The entirety of Earth's water, excluding water vapor in the atmosphere but including all oceans, lakes, streams, groundwater, snow, and ice.

HYPOTHESIS:

An unproven statement regarding an observed phenomenon.

INERTIA:

The tendency of an object in motion to remain in motion and of an object at rest to remain at rest.

JOVIAN PLANETS:

The planets between Mars (the last terrestrial planet) and Pluto, all of which are large, low indensity, and composed primarily of gases.

LAW:

A scientific principle that is shown always to be the case and for which no exceptions are deemed possible.

LITHOSPHERE:

The upper layer of Earth's interior, including the crust and the brittle portion at the top of the mantle.

MANTLE:

The layer, approximately 1,429 mi. (2,300 km) thick, between Earth's crust and its core.

MASS:

A measure of inertia, indicating the resistance of an object to a change in itsmotion. (By contrast, weight—which people tend to think of as similar to mass—is a measure of gravitational force, or mass multiplied by the acceleration due to gravity.)

PLANETARY SCIENCE:

The branch of the earth sciences, sometimes known as planetology or planetary studies, that focuses on the study of other planetary bodies. This discipline, or set of disciplines, is concerned with the geologic, geophysical, and geochemical properties of other planets but also draws on aspects of astronomy, such as cosmology.

PROTON:

A positively charged particle in the nucleus of an atom.

SCIENTIFIC METHOD:

A set of principles and procedures for systematic study that includes observation; the formation of hypotheses, theories, and laws; and continual testing and reexamination.

SCIENTIFIC REVOLUTION:

A period of accelerated scientific discovery that completely reshaped the world. Usuallydated from about 1550 to 1700, the Scientific Revolution saw the origination of the scientific method and the introduction of such ideas as the heliocentric (Sun-centered) universe and gravity.

TERRESTRIAL PLANETS:

The four inner planets of the solar system: Mercury, Venus, Earth, and Mars. These planets are all small, rocky, and dense; have relatively modest amounts of gaseous elements; and are composed primarily of metals and silicates. Compare with Jovian planets.

THEORY:

A general statement derived from a hypothesis that has withstood sufficient testing.

UNIFORM CIRCULAR MOTION:

The motion of an object around the center of a circle in such a manner that speed is constant or unchanging.