(1) Material that is formed or introduced from somewhere other
than the place it is presently found. (2) Fragmented rock thrown
out of the crater during its formation that either falls back to
partly fill the crater or blankets its outer flanks after the impact
The Northern Lights caused by the interaction between the
solar wind, the Earth's magnetic field and the upper atmosphere;
a similar effect happens in the southern hemisphere where it is known as
the aurora australis.
The temperature of an object if it is reradiating all the thermal
energy that has been added to it; if an object is not a blackbody radiator,
it will not reradiate all the excess heat and the leftover will go toward
increasing its temperature.
A large, basin-shaped volcanic depression that is more or less
circular in form. Most volcanic calderas are produced by collapse of the
roof of a magma chamber due to removal of magma by voluminous eruptions or
subterranean withdrawal of the magma, although some calderas may be formed
by explosive removal of the upper part of a volcano.
A compound containing carbon and oxygen; an example is calcium carbonate (limestone).
1) The upper level of the solar atmosphere,
characterized by low densities and high temperatures (> 1.0E+06 K);
it is not visible from the Earth except during a total eclipse of the
sun or by use of special telescopes called coronagraphs.
2) An ovoid-shaped feature.
A special telescope which blocks light from the
disk of the Sun in order to study the faint solar atmosphere.
Electromagnetic rays of extremely high frequency and energy;
cosmic rays usually interact with the atoms of the atmosphere before
reaching the surface of the Earth. Some cosmic rays come from outside the
solar system while others are emitted from the Sun and pass through
holes in the corona.
1) A depression formed by the impact of a meteorite. 2) A depression
around the orifice of a volcano.
The relatively stable portions of continents composed of shield
areas and platform sediments; typically, cratons are bounded by tectonically
active regions characterized by uplift, faulting and volcanic activity.
A major stratigraphic boundry on Earth marking the end of the
Mesozoic Era, best known as the age of the dinosaurs. The boundary
is defined by a global extinction event that caused the abrupt demise
of the majority of all life on Earth.
Einstein's famous theory of relativity formula known as
the energy-mass relation. The energy e is equal to
the mass m multiplied by the speed of light squared
c2. A small mass produces an enormous
amount of energy.
A relative quiet volcanic eruption which puts out basaltic lava
that moves at about the speed one walks. The lava is fluid in nature.
The eruptions at the Kilauea volcano on the island of Hawaii are effusive
A closed curve that is formed from two foci or points in which the
sum of the distances from any point on the curve to the two foci is a
constant. Johannes Kepler first
discovered that the orbits of the planets are ellipses, not circles;
he based his discovery on the careful observations of
A dramatic volcanic eruption which throws debris high into the
air for hundreds of miles. The lava is low in silicate and can be very
dangerous for people near by. An example is Mount St. Helens in 1980.
A crack or break in the crust of a planet along which slippage or
movement can take place.
A strand of cool gas suspended over the
photosphere by magnetic fields, which
appears dark as seen against the disk of the Sun;
a filament on the limb of the Sun seen in
emission against the dark sky is called a
An elongated, relatively depressed crustal unit or block that is
bounded by faults on its sides.
A direct, circular, low-inclination orbit in which the satellite's
orbital velocity is matched to the rotational velocity of the planet;
a spacecraft appears to hang motionless above one position of the
A pattern of small cells seen on the surface of
the Sun caused by the convective motions of the hot solar gas.
In this phase, mineral forms that are stable only at the extremely high pressures
typical of Earth's deep interior but not its surface. Such pressures are
generated instantaneously during meteorite impact.
Stishovite is the high-pressure polymorph of
quartz, a common crustal mineral.
Rocks melted during impact, including small particles dispersed in
various impact deposits and ejecta, and larger pools and sheets of melt
that coalesce in low areas within the crater. Impact melts are extremely
uniform in their composition but highly variable in texture. They are
composed predominantly of the target rocks, but can contain a small but
measurable amount of the impactor.
The inclination of a planet's orbit is
the angle between the plane of its orbit and the
The inclination of a moon's orbit is
the angle between the plane of its orbit and the plane of its
The planets Mercury and Venus are inferior planets because their
orbits are closer to the Sun than is Earth's orbit.
A region of charged particles in a planet's upper atmosphere;
the part of the earth's atmosphere beginning at an altitude of about
400 kilometers (25 miles) and extending outward 400 kilometers
(250 miles) or more.
One of the solutions to the three-body problem discovered by the
eighteenth century French mathematician Lagrange; the two stable
Lagrangian points, L-4 and L-5, lie in the orbit of the primary body,
leading and trailing it by a 60-degree arc.
Molten rock within the crust of a planet that is capable of intrusion
into adjacent crustal rocks or extrusion onto the surface.
Igneous rocks are derived from magma through
solidification and related processes or through eruption of the magma
at the surface.
The degree of brightness of a celestial body designated on a
numerical scale, on which the brightest star has magnitude -1.4
and the faintest visible star has magnitude 6, with the scale
rule such that a decrease of one unit represents an increase in
apparent brightness by a factor of 2.512; also called apparent magnitude.
Latin word for "sea." Galileo thought the dark featureless
areas on the Moon were bodies of water, even though the Moon is
essentially devoid of liquid water. The term is still applied to the basalt-filled
impact basins common on the face of the Moon visible from Earth.
A fundamental particle supposedly produced in massive numbers by the
nuclear reactions in stars; they are very hard to detect because the vast
majority of them pass completely through the Earth without interacting.
A nuclear process whereby several small nuclei are combined to
make a larger one whose mass is slightly smaller than the sum of the small
ones. The difference in mass is converted to energy by
equivalence E=mc2. This is the source of the Sun's
energy and, ultimately, of (almost) all energy on Earth.
A type of basalt lava flow characterized by a smooth glassy skin, and
constructed of innumerable "flow units" called "toes"; pahoehoe flows
advance at rates of 1 to 10 meters (3 to 33 feet) hour and are associated with
low-effusion-rate eruptions with little to no fountaining.
A circular feature on the surface of dark icy moons such as
the relief associated with craters;
Pamlimpsests are thought to be impact craters where the topographic relief
of the crater has been eliminated by slow adjustment of the icy surface.
The visible surface of the Sun; the upper surface of a convecting
layer of gases in the outer portion of the sun whose temperature causes
it to radiate light at visible wavelengths;
and faculae are observed in the photosphere.
A volcanic eruption or explosion of steam, mud or other material
that is not incandescent; this form of eruption is caused by the heating
and consequent expansion of ground water due to an adjacent igneous
Microscopic features in grains of quartz or feldspar consisting
of very narrow planes of glassy material arranged in parallel sets that
have distinct orientations with respect to the grain's crystal structure.
Broad plains that occupy lowlands on planetary surfaces.
More accurately describes the motions of bodies in strong
gravitational fields or at near the speed of light than
newtonian mechanics. All
experiments done to date agree with relativity's predictions to a
high degree of accuracy. (Curiously,
Einstein received the Nobel prize in 1921 not for Relativity
but rather for his 1905 work on the photoelectric effect.)
The amount of small detail visible in an image; low resolution
shows only large features, high resolution shows many small details.
A fracture or crack in a planet's surface caused by extension.
On some volcanoes, subsurface intrusions are concentrated in certain
directions; this causes tension at the surface and also means that
there will be more eruptions in these "rift zones."
A line of cliffs produced by faulting or erosion;
a relatively straight, clifflike face or slope of considerable linear
extent, breaking the general continuity of the land by separating surfaces
lying at different levels.
A tenuous flow of gas and energetic charged particles, mostly
protons and electrons -- plasma -- which stream
from the Sun; typical solar wind velocities are almost 350 kilometers (217 miles)
An area seen as a dark spot on the
photosphere of the Sun. Sunspots are
concentrations of magnetic flux, typically occurring in
bipolar clusters or groups. They appear dark because they are cooler than
the surrounding photosphere.
The planets Mars, Jupiter, Saturn, Uranus, Neptune and Pluto
are superior planets because their
orbits are farther from the Sun than Earth's orbit.
The orbital radius at which the satellite's orbital period is equal to the
rotational period of the planet. A synchronous satellite with an
orbital inclination of zero (same plane as the planet's equator)
stays fixed in the sky from the perspective of an observer on the
planet's surface. These orbits are commonly used for communications
A satellite's rotational period is equal to its orbital period;
this causes the same side of a satellite to always face the planet.
Synchronous rotation occurs when a planet's gravity produces a tidal
bulge in its satellite. The gravitational attraction and bulge acts like a torque,
which slows down the satellite until it reaches a synchronous rotation.
Natural, silica-rich, homogeneous glasses produced by complete
melting, and dispersed as droplets during terrestrial impact events.
Tektites range in color from black or dark brown to gray or green and most
are spherical in shape. They have been found in four regional deposits
or strewn fields on the Earth's surface: North America,
Czechoslovakia, Ivory Coast and Australasia.
The gravitational pull on planetary objects from nearby planets and
moons. When the tidal forces of a planet and several moons are focused
on certain moons, particularly if the orbits of the various objects bring
them into alignment on a repeated basis, the tidal forces can generate a
tremendous amount of energy within the moon. The intense volcanic
acivity of Io is the result of the interaction
of such tidal forces.
When used to describe a planetary surface, "young" means
that the visible features are of relatively recent origin, i.e. that
older features have been destroyed by erosion or lava flows. Young
surfaces exhibit few impact craters and are typically varied and complex;
in contrast, an "old" surface is one that has changed
relatively little over geologic time. The surfaces of
Earth and Io are young;
the surfaces of Mercury and
Callisto are old.