Glossary 925
orbital architecture of the planets or of the environment of
the solar system. The most prominent members of the
extended scattered disk population are 2000 CR 105 and 90377
Sedna.
External comet A returning comet with a semimajor axis
greater than∼34.2 AU. External comets have Tisserand
parameters with respect to Jupiter less than 2. Also known as a
long-period comet.
Extrasolar planet A planetary companion to a star other
than the Sun.
Feldspar A common group of aluminum silicate minerals.
Filaments Near-horizontal magnetic field lines on the Sun
suspended above magnetic inversion lines that are filled with
cool and dense chromospheric mass, seen on the solar disk.
Flares A magnetic instability in the solar corona that
impulsively releases large energies that go into heating of
coronal and chromospheric plasma, as well as into acceleration
of high-energy particles. A flare is usually accompanied by
impulsive emission in gamma rays, hard x-rays, soft x-rays, EUV,
and radio emission.
Fluctus (pl., flucti) Term meaning (on Io) a volcanic flow
field.
Fluorescence Photons emitted immediately after electron
decay. The electron had been elevated to a higher energy state
by external stimulation of their parent atoms, ions, and
molecules. In planetary atmospheres, the external stimulation is
usually sunlight or electrons.
Flux density Power per unit area and per unit frequency
interval received from an object. The units of flux density are
Janskies: 1 Jy= 10 −^26 Wm−^2 Hz−^1.
Flux transfer event A localized spatial region in which
magnetic reconnection links the solar wind magnetic field to a
planetary magnetic field producing a configuration that
transports flux from the day side to the night side of the planet.
Flux The flux of particles (denotedφwith units of cm−^2 s−^1 )
given by the product of the speed of the neutrons,v(cm/s), and
the number density (particles per cm^3 ).
Fractionation Separation of elements or isotopes based on
their masses or chemistry.
Frequency–time spectrogram A graph of the emission
intensity as a function of frequency and time. Usually the
intensity is shown on a gray scale ranging from black to white or
one of several color schemes, with frequency plotted along the
verticaly-axis and time along the horizontalx-axis.
Galactic cosmic rays Energetic particles, including photons,
electrons, protons, and heavy ions, that originate outside the
heliosphere.
Galilean satellites The four major satellites of Jupiter: Io,
Europa, Ganymede and Callistio, discovered by Galileo in 1610.
Gamma ray A high energy quantum of electromagnetic
radiation (photon) emitted by nuclear transitions. Gamma rays
originate from nuclear processes, such as radioactive decay and
the de-excitation of residual nuclei produced by nuclear
reactions.
Gas chromatography A chemical technique for separating
gas mixtures, in which the gas is passed through a long column
containing a fixed absorbent phase that separates the gas into its
component parts.
Gas drag Drag force experienced by a solid object when it
moves through a surrounding gas.
Gaussian year The orbital period of a massless particle in a
circular orbit with a semimajor axis of 1 AU, equal to
365.256898326...days. Formally, the Gaussian year is defined
as 2p/k, wherekis the Gaussian gravitational constant,
0.01720209895.
Geochemistry The study of the chemical components of the
lithosphere of the Earth and other planets, chemical processes
and reactions that produce and modify rocks and soils, and the
cycles of matter and energy that transport chemical components
in space and time.
Geodesy The measurement and representation of Earth’s
topography, its gravitational field and geodynamic phenomena
(e.g., polar motion, tides, and crustal motion) in 3-dimensional,
time-varying space.
Geomagnetic activity Disturbances in the magnetized
plasma of a magnetosphere associated with fluctuations of the
surface field, auroral activity, reconfiguration and changing flows
within the magnetosphere, strong ionospheric currents, and
particle precipitation into the ionosphere.
Geomagnetic storm The response of the Earth to the
arrival of an interplanetary medium disturbance, usually
associated with a CME.
Geomagnetism The Earth’s magnetic field, which is
approximately a magnetic dipole, with the magnetic poles offset
from the corresponding geographic poles by approximately
11.3◦, and extending several tens of thousands of kilometers into
space.
Geometric albedo Ratio of the brightness at a phase angle
of zero degrees (full illumination) compared with a diffuse,
perfectly reflecting disk of the same size and under the same
illumination conditions.
Geomorphology Science of landscape analysis. Geomorphic
investigations deal with the processes and timescales of
landscape formation and degradation.
Geospace The Earth’s magnetosphere and upper
atmosphere, including the ionosphere.
Graben A long, usually linear fault trough (valley) produced
by subsidence between two inward dipping boundary faults. It is
the result of extensional stresses in a body’s upper crust.
Granite Light-colored intrusive rock containing more than
50% silica. On Earth, continents are largely granite and other
high silica rocks.
Gravitational focusing The tendency of an object’s
trajectory to curve toward a massive body due to gravitational
attraction.