One of many millions of small, rocky, and/or metallic objects that orbit the Sun, consisting of fragments of once-larger planetesimals, or chunks of protoplanetary material; most lie in the region between Mars and Jupiter.
The layer of the mantle that lies between 100-150 km and 350 km deep; the asthenosphere is relatively soft and can flow when acted on by force.
A cataclysmic explosion that scientists suggest represents the formation of the Universe; before this event, all matter and all energy were packed into one volumeless point.
A ball of ice and dust, probably remaining from the formation of the Solar System, that orbits the Sun.
In the context of planet formation, the process by which a planet separates into a metallic core and a rocky mantle very early in its history.
The global interconnecting web of physical and biological phenomena involving the solid Earth, the hydrosphere, and the atmosphere.
expanding Universe theory
The theory that the whole Universe must be expanding because galaxies in every direction seem to be moving away from us.
The outer planets (Jupiter, Saturn, Uranus, Neptune) that are very large and consist mostly of volatile elements.
Water that resides under the surface of the Earth, mostly in pores or cracks of rock or sediment.
The relatively rigid, non-flowable, outer 100- to 150-km-thick layer of the Earth; constituting the crust and the top part of the mantle.
The deepest section of the mantle, stretching from 670 km down to the core-mantle boundary.
A solid composed almost entirely of atoms of metallic elements; it is generally opaque, shiny, smooth, and malleable, and can conduct electricity.
An object that has entered a planetรs atmosphere and is glowing and evaporating as it streaks to the planetรs surface.
A homogenous, naturally occurring, solid inorganic substance with a definable chemical composition and an internal structure characterized by an orderly arrangement of atoms, ions, or molecules in a lattice. Most minerals are inorganic.
The seismic-velocity discontinuity that defines the boundary between the Earthรs crust and mantle.
The concept that planets grow out of rings of gas, dust, and ice surrounding a -born star.
A carbon-containing compound that occurs in living organisms, or that resembles such compounds; it consists of carbon atoms bonded to hydrogen atoms along with varying amounts of oxygen, nitrogen, and other chemicals.
A relatively large, spherical object that orbits a star and has cleared its orbit of most debris.
Tiny, solid pieces of rock and metal that collect in a planetary nebula and eventually accumulate to form a planet.
A body that grows by the accumulation of planetesimals but has not yet become big enough to be called a planet.
The flattened cloud of dust, gas, and ice that orbits a nascent star prior to the formation of planets.
A dense body of gas that is collapsing inward because of gravitational forces and that may eventually become a star.
The phenomenon in which a source of light moving away from you very rapidly shifts to a lower frequency; that is, toward the red end of the spectrum.
A coherent, naturally occurring solid, consisting of an aggregate of minerals or a mass of glass.
An accumulation of loose mineral grains, such as boulders, pebbles, sand, silt, or mud, that are not cemented together.
The Sun and all the objects that orbit it (including planets, moons, comets, and asteroids).
A large sphere, composed dominantly of hydrogen and helium, in which fusion reactions are producing energy.
A short-lived, very bright object in space that results from the cataclysmic explosion marking the death of a very large star; the explosion ejects large quantities of matter into space to form nebulae.
The middle portion of the mantle, from 400 to 670 km deep, in which there are several jumps in seismic velocity.
Space that contains very little matter in a given volume (e.g., a region in which air has been removed).
A means of transmitting energy from one location to another; waves can be vibrations that propagate through a material, or undulations of electromagnetic fields that can propagate either through a material or in a vacuum.