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abiotic               (adj) nonliving
absorption lines      (n) the dark lines in a spectrum where light of particular wavelengths has been absorbed
adapt                 (v) to change in structure or function to better suit the environment
adaptation            (n) any change in the structure and functioning of an organism that makes it better suited to its envi-
adenovirus            (n) the virus that causes the common cold
aerobic               (adj) with oxygen
algae                 (n) a group of unrelated simple organisms that can photosynthesize and that live in aquatic habitats
                      and moist land habitats; they are members of the kingdom Protoctista
alpha particle        (n) the nucleus of a helium atom, with two protons and two neutrons, making it positively charged
amino acids           (n) a group of water-soluble organic compounds, which are made of carbon, hydrogen, oxygen, nitro-
                      gen, and sometimes sulfur; some combine to form proteins
amoeba                (n) a genus of protoctists of the phylum Rhizopoda
amplitude             (n) the distance from the surface to the highest point of a wave
anaerobic             (adj) without oxygen
analog                (n) an environment or organism that may be similar to what might be found on other planets
Archaea               (n) a subkingdom of prokaryotic organisms containing archaebacteria, including methanogens, ther-
                      moacidophilic bacteria, and halophilic bacteria
artificial selection   (n) the modification of species by selective breeding; organisms with desirable characteristics are
                      interbred with the aim of producing a new strain of organism for a specific purpose
asteroid              (n) any of the many small rocky or metallic objects orbiting a star; in the solar system, most are found
                      in the asteroid belt
asteroid belt         (n) the region of the solar system, between the orbits of Mars and Jupiter, in which most asteroids are
astrobiologist        (n) a scientist who use the tools of scientific inquiry to look for clues to answer questions, such as
                      “Does extraterrestrial life exist?,” “How did life on Earth originate?,” and “What is the future of life on
astrobiology          (n) the science of finding answers to the question “Does life exist elsewhere in our universe?”
astrometry            (n) the process of detecting extrasolar planets by observing a star’s wobble
astronomical unit     (n) the distance between Earth and the sun, known as 1 AU; used to measure distances in the solar
atmosphere            (n) an envelope of gases surrounding a planet or moon
atom                  (n) the smallest particle of an element that still exhibits the properties of that element; atoms consist of
                      three kinds of particles—protons, neutrons, and electrons
atomic mass           (n) the average mass of all an element’s possible isotopes
atomic number         (n) the number of protons in an atom; different elements have different atomic numbers
ATP                   (n) adenosine triphosphate; the primary molecule the body uses to fuel its processes
autotrophs            (n) self-feeders
bacteria              (n) any of a class of microscopic organisms having single-celled or noncellular bodies, often found in
Big Bang              (n) the explosion that produced the universe; the most widely accepted theory of the origin and evolu-
                      tion of the universe

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biogenic elements    (n) the six elements essential to life: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur
                     — CHONPS (bio means life, and genic means beginning)
biomarker            (n) a telltale sign of life
biomass              (n) the total mass of all the organisms of a given type or in a given area
biosignature         (n) a sign that can be interpreted as evidence of life
biotic               (adj) living
black hole           (n) an object with such a strong gravitational field that even light cannot escape from its surface; one
                     possible remnant of a supernova
blue-shift           (n) the increase in the frequency of light caused by an object moving toward an observer
calorie              (n) the quantity of heat required to raise the temperature of 1 gram of water by 1 degree Celsius (1 K);
                     a measure of how much energy is available in a particular food
carbohydrates        (n) organic compounds based on the general fomula Cx(H2O)y; they have energy-rich chemical bonds,
                     which organisms use as a source of energy as well as for short-term energy storage
carbon               (n) the element, with atomic number 6, that is good at forming bonds; the chemical basis of all known
                     life on Earth
cell                 (n) the structural and functional unit of organisms; cells may exist as independent units of life, such as
                     bacteria, or they may form colonies or tissues, as in plants and animals
cell membrane        (n) the partially permeable covering tissue that forms the outer limit of a cell; it regulates the flow of
                     material in and out of the cell
cell theory          (n) the theory states that (a) all living things are made of one or more cells, (b) cells are the basic unit
                     of structure and function in living things, and (c) all cells come from preexisting cells
cell wall            (n) the rigid outer layer that surrounds the cell membrane of plant, bacterial, and algal (not animal)
                     cells; it protects and gives shape to the cell
center of mass       (n) the fixed point within a body or system at which the entire mass can be considered to be concen-
                     trated; the center of a system’s rotation
chemical bond        (n) a strong force of attraction holding atoms together in a molecule or crystal
chemotrophs          (n) chemical feeders
chloroplasts         (n) the structures in leaf cells that produce and store pigments; chlorophyll-containing organelles that
                     are found in large numbers in photosynthesizing organisms
chromosomes          (n) threadlike structures found in the nucleus of eukaryotic cells; they determine the characteristics of
                     an organism
classification        (n) the arrangements of organisms into a series of groups based on biochemical, anatomical, or other
comet                (n) a small body, composed of ice and dust, in orbit around a star; when a comet is far from the sun,
                     its nucleus is frozen solid; then, when it nears the sun, the nucleus heats up and releases gases and
                     dust, possibly forming a tail
concept map          (n) a visual way to show how a topic’s components or factors are connected or related
condense             (v) to change state or phase from a gas to a liquid
conservation of      (n) the scientific law saying that matter can be neither created nor destroyed; if the input mass does
mass                 not equal the output mass, then some particles must have changed into something else.
consumer             (n) an organism that feeds upon organisms lower than it is on the food chain; an organism that gets
                     its carbon-containing macromolecules by eating producers or other consumers
continent            (n) a huge “raft” of rock on a molten substrate, which can move as the result of global convection
control              (v) to check or test using evidence or by experimentation; (n) an experiment or experimental group
                     that is used as a standard of comparison

568                 Glossary — Astrobiology: An Integrated Science Approach
convection           (n) the process that transfers heat based on the mass movement of particles; liquids and gases rise
                     and fall depending on differences in density, with less dense materials rising above denser ones
covalent bond        (n) a bond between atoms formed by the sharing of electrons
crater               (n) a bowl-shaped depression in a planetary surface, usually caused by an impact or volcanic activity
crest                (n) the highest point of a wave
cyanobacteria        (n) the bacteria thought to be the earliest photosynthesizers
cytoplasm            (n) a thick liquid inside the plasma membrane of a cell, mostly made of water and containing organic
                     and inorganic molecules important to the cell’s chemical reactions
cytoskeleton         (n) part of the cell, found in the cytoplasm of eukaryotic cells, that serves to provide additional struc-
                     ture, particularly when a cell divides to make two new duplicate cells
dark reaction        (n) the second stage of photosynthesis, which uses some of the products of the first stage and does
                     not require sunlight
data                 (n) factual information
decay                (n) the chemical breakdown of organic matter into its constituents by the actions of decomposers
decomposers          (n) organisms that extract carbon and energy from dead organisms’ tissues
density              (n) the number of particles in a particular volume
dependent variable   (n) factor in an experiment that is measured to determine the effect(s) of having changed another
                     factor—the independent variable; a variable whose value is determined by other variables
dissolve             (v) to break apart a substance and form a solution with the water
diversity            (n) the wide number and greatly varying types (of life)
DNA                  (n) deoxyribonucleic acid; nucleic acids essential to life; DNA, the main component of a cell’s genetic
                     material, stores the instructions for assembling amino acids into proteins; through DNA, these instruc-
                     tions can be passed from generation to generation during reproduction
domain               (n) the highest taxonomic category, in some classification systems, consisting of one or more king-
Doppler Effect       (n) the apparent change in frequency caused by the motion of a source or observer
double bond          (n) the bond formed when atoms share two electrons
dust lanes           (n) the dark regions between the arms of a spiral galaxy that contain material too cool to glow
ecosystem            (n) the collection of living and nonliving components of an environment that interact with and influence
                     each other
ejecta               (n) material thrown out from an explosive event, such as a crater-forming impact or volcanic eruption
electromagnetic      (n) energy that travels as a wave, including visible light, X rays, radio waves, and ultraviolet light;
radiation            energy emitted by changes in an electric or a magnetic field
electron micro-      (n) a microscope that uses a beam of electrons instead of a beam of light, as in an optical microscope,
scope                to form a large image of a very small object
electrons            (n) tiny particles with a negative electrical charge that orbit the nucleus of an atom in a series of con-
                     centric shells
element              (n) a substance that cannot be split into simpler substances by any chemical process; there are 92
                     naturally occuring elements
elliptical galaxy    (n) a type of galaxy shaped like a football, lacking a spiral galaxy’s distinct parts, and containing little
                     or no current star formation
emission             (n) the release of a photon from an atom when an electron in the atom jumps from a higher to a lower
                     energy level
emit                 (v) to give off
endoplasmic          (n) An organelle made up of a membrane similar to the cell’s outer plasma membrane; its main func-
reticulum            tion is to create new proteins, via the ribosomes, and transport them to other parts of the cell

                     Glossary — Astrobiology: An Integrated Science Approach                                                   569
energy                 (n) usable power; one of the requirements of life
enzyme                 (n) a protein that acts like a catalyst in biochemical reactions; life uses enzymes to help build macro-
                       molecules and break their bonds to release energy
estimate               (v) to determine roughly based on available information
eukaryotic cell        (n) one of the two basic types of cells on Earth; its genetic material is contained in a nucleus and has
                       the more complex structure
evaporate              (v) to change state or phase from a liquid to a gas
evidence               (n) an indication or sign of something; data that build toward a (possible) conclusion
evolution              (n) the process through which one species can give rise to another. According to Darwin, evolution
                       happens because (a) in a population, traits vary due to mutations, so individuals emerge with different
                       capabilities, (b) some of the variation can be passed from parents to offspring, and (c) advantageous
                       traits inherited by offspring increase their chances of reproducing successfully
experimental           (n) a procedure to create an experiment or series of experiments that have the potential to move scien-
design                 tists toward a better understanding of their question
extrasolar planet      (n) a planet orbiting a star other than the sun (extra means “beyond” and solar means “sun-related”—
                       planets beyond the sun)
extraterrestrial       (adj) and (n) originating outside Earth’s atmosphere; a being or organism originating somewhere other
                       than Earth
extremophiles          (n) organisms living under extreme conditions, which most life forms find harsh (philia is Greek for
fats                   (n) lipids that organisms use to store energy
fitness                 (n) a measure of how well an organism copes with the selection pressures in its environment
flagellum               (n) a whip-like cell structure built of protein; the flagellum (some cells have more than one) is
                       anchored in the plasma membrane and rotates, allowing the organism to swim about
force                  (n) cause of motion or change; action on an object that causes its momentum to change
fossil                 (n) a remnant, impression, or trace of an organism that has been preserved over geologic time
freeze                 (v) to change state or phase from a liquid to a solid
frequency              (n) the number of waves per second
fusion                 (n) the process in which two atomic nuclei join together to form a larger, single nucleus; energy is
galactic core          (n) the central region or nucleus of a galaxy
galactic disk          (n) the major structural component of a spiral (or sometimes irregular) galaxy, containing stars, gas,
                       and dust orbiting the galaxy’s core
galaxy                 (n) a collection of stars, gas, and dust bound together by gravity; they come in different shapes, sizes,
                       and colors
glucose                (n) a sugar formed during photosynthesis and used by all plant and animal cells as an energy source;
                       one of the simplest carbohydrates
golgi body             (n) a stack of cellular membranes; the main function of this organelle is the modification of proteins
                       produced in the endoplasmic reticulum; it also serves in transporting the modified proteins to other
                       parts of the cell
gravitational force    (n) the force of attraction that exists between all bodies
gravity                (n) the force of attraction that exists between all bodies; the weakest of the four fundamental forces but
                       which acts over large distances
greenhouse effect      (n) the exchange of energy between the planet’s surface and atmosphere
greenhouse gases       (n) gases that are made of molecules that can store considerable amounts of energy

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groups               (n) columns of the periodic table; within a group, the atoms of the elements have the same outer shell
habitable            (adj) capable of supporting life
habitable zone       (n) a region around a star or in a galaxy where some form of life could exist
habitat              (n) the place where an organism lives
helium flash          (n) the blinding release of energy that occurs when helium burning begins in the core of a low-mass
heterotrophs         (n) other-feeders
high-mass star       (n) stars with a mass greater than three solar masses
hydrogen bond        (n) the weak type of bond formed between a hydrogen atom and an unshared pair of electrons in
                     another atom
hydrogen ion         (n) a charged particle
hydrothermal vent    (n) opening in the seafloor that ejects very hot, mineral-rich water
hypothesis           (n) a guess, based on previous knowledge of the subject, that can be tested, such as by designing and
                     carrying out an experiment
impact               (n) a forceful collision of one body against another
independent          (n) one factor in an experiment to change in order to measure its effects
infrared light       (n) electromagnetic radiation with a slightly longer wavelength than that of visible light
intensity            (n) brightness
inverse square law   (n) the mathematical formula describing how light varies with distance in a predictable, measurable
ionic bond           (n) the bond formed between oppositely charged ions
ions                 (n) atoms that have positive or negative charges, as a result of giving or acquiring electrons
irregular galaxy     (n) a type of galaxy with a peculiar shape
isotope              (n) one of two or more atoms of the same element that have the same number of protons in the
                     nucleus but a different number of neutrons
light                (n) electromagnetic radiation that can be seen by the human eye
light reaction       (n) the first stage of photosynthesis, which requires sunlight
light-year           (n) the distance light travels through space in one year — 9.5 quadrillion meters; used to measure
                     distances between stars and galaxies
lipids               (n) long waxy, fatty, or oily molecules, made of carbon, hydrogen, and oxygen, that serve as long-term
                     energy storage molecules and structural components in the cell
low-mass star        (n) stars between 0.8 and 3 solar masses, having sufficient mass to burn hydrogen in their cores
macromolecules       (n) large molecules (macro means “big”)
magnetosphere        (n) the magnetic field surrounding Earth
main sequence        (n) a diagonal strip on the Hertzprung-Russell diagram of stars; a star is said to be main sequence at
                     the stage of its life when it shines by converting hydrogen to helium
mass                 (n) a measure of the amount of matter in a body
melt                 (v) to change state or phase from solid to liquid
metabolism           (n) the sum of all the chemical reactions in the cell that allow it to live, grow, and reproduce; the pro-
                     cess of bringing in raw materials, using energy to build new molecules and cell parts, distributing what
                     they build, and getting rid of any waste produced in the process
meteor               (n) any particle entering Earth’s atmosphere from space; most meteors burn up
meteorite            (n) a natural object from space that hits the surface of Earth or another planetary body

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micrometeorites      (n) microscopic particles that drift down to Earth from meteors that mostly burn up in the atmosphere
microorganism        (n) any organism that can only be observed with the use of a microscope
microscope           (n) a device that allows something small to be viewed under magnification
Milky Way Galaxy     (n) the spiral galaxy containing Earth, the sun, and all the stars that can be seen at night
mitochondria         (n) the site in the cell where the energy stored in glucose is converted to ATP, providing energy for
molecule             (n) groups of atoms held together by bonds
moon                 (n) satellite; a small, natural body in orbit about a planet
mutation             (n) a permanent change in a cell’s genetic material that may be passed on to cells derived from this cell
nanobacteria         (n) a term that refers to some very controversial objects, including those found in the Mars meteorites,
                     that measure in the nanometers (one billionth of a meter); these objects, thought to be living by some
                     of the scientists who study them, are significantly smaller than the smallest cells known to exist
natural selection    (n) the process that brings about the evolution of new species
nebula               (n) a cloud of gas and dust produced by a supernova
neutron star         (n) a dense star made up of neutrons; one possible remnant of a supernova
neutrons             (n) one of the two types of particles that cluster together to form the nucleus at the center of an atom;
                     neutrons have no electrical charge
noble gases          (n) the elements with full outer shells; these are extremely stable and thus tend not to react
noise                (n) unorganized electromagnetic waves
nuclear fusion       (n) the process in which two atomic nuclei join together to form a larger, single nucleus — creating
                     new elements and releasing energy
nucleic acid         (n) a complex organic molecule in living cells that consists of a chain of nucleotides; there are two
                     types: RNA and DNA
nucleotides          (n) the sub-units of nucleic acids; organic molecules that consist of nitrogen-containing purine or
                     pyrimidine base linked to a sugar and a phosphate group
nucleus              (n) the organelle containing a cell’s genetic material
orbit                (n) the path of a planet around a star or a moon around a planet
orbital              (n) a region in which an electron may be found in an atom or molecule
organelles           (n) small cellular structures with specialized functions
organic              (adj) of, relating to, or derived from life
organic chemistry    (n) an entire branch of chemistry devoted to molecules and chemical reactions involving carbon
origins              (n) in an astrobiology context, the point at which life began
panspermia           (n) the hypothesis that life originated on another planet and was brought to Earth; also known as
                     “widespread seeding”
period               (n) the number of days required for a planet to make a complete orbit around its star
periodic             (adj) the same wave pattern repeats again and again
periodic table       (n) a table of elements arranged in order of increasing proton number to show the similarities of ele-
                     ments with related electonic configurations; a convenient tool that predicts an element’s chemical and
                     physical properties
periods              (n) the rows of the periodic table; these tell how many electron shells an element has
pH                   (n) a measure, using a logarithmic scale, of the acidity or alkalinity of a solution
phases               (n) solid, liquid, or gas; also known as a “state”
photosynthesis       (n) a series of chemical reactions by which some organisms convert the energy in sunlight into chemi-
                     cal energy

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phototrophs          (n) light feeders
pigments             (n) the colored materials that give plant leaves their color and allow plants to photosynthesize
planetary nebula     (n) a glowing ring of gas around a red giant, formed when the outer layers of the star break away
plasma membrane      (n) structure that encloses a cell and helps to isolate the inside of the cell from the outside environ-
                     ment; it allows certain molecules in, like nutrients, and other molecules out, like waste products
plate tectonics      (n) the movements of a planet’s crust
polar                (adj) a description of a molecule, such as a water molecule, that has positive and negative regions
population           (n) a large number of similar individuals living in the same place
prebiotic soup       (n) the abundant raw materials, in one view of early Earth, that could produce molecules and possibly
                     form chemical systems that could lead to the first life (pre = before; biotic = life)
precipitation        (n) a deposit on the planetary surface of hail, mist, sleet, or snow
pressure             (n) the force exerted over a surface divided by the area of the surface
procedure            (n) step-by-step directions
producers            (n) organisms that obtain their carbon directly from carbon dioxide
prokaryotic cell     (n) one of the two basic types of cells on Earth; it lacks an organized nucleus and is relatively simple in
                     its structure
prominence           (n) a cloud-like feature in the sun’s corona but cooler and denser than the corona
proteins             (n) any of a large group of organic molecules found in all organisms; they consist of one or more long
                     chains of amino acids linked in a characteristic sequence
protists             (n) single-celled organisms, such as amoeba and paramecium found in pond water
protons              (n) one of the two types of particles that cluster together to form the nucleus at the center of an atom;
                     protons have a positive electrical charge
pseudoscience        (n) “false science”; a way to explain or make claims about phenomena that cannot be proven scientifi-
                     cally through experimentation that can be reviewed and repeated by other scientists
qualitative          (adj) general and descriptive
quantitative         (adj) specific, often numerical, and tied to measurable differences
ratio                (n) the relationship in quantity, amount, or size of two things
red giant            (n) a cool, large, and highly luminous star that has used up the hydrogen fuel in its core
red-shift            (n) the decrease in the frequency of light caused by an object moving away from an observer
redox reaction       (n) an oxidation-reduction reaction that allows electrons to be transferred from one atom or molecule
                     to another
reflect               (v) to turn at an angle
replication          (n) the action or process of duplicating or producing a copy
reproduce            (v) to create a new individual more or less similar in form to the parent organisms
respiration          (n) the metabolic process in animals and plants in which organic substances are broken down, using
                     oxygen, to simpler products with the release of energy
ribosome             (n) structure inside a cell that is spread throughout the cytoplasm and helps build proteins
RNA                  (n) ribonucleic acid; nucleic acids essential to life; RNA “reads” the instructions stored in DNA and
                     does the actual work of bringing amino acids together to create proteins
sample               (n) a representative part of a larger whole or group; (v) to take a sample
sampling             (n) the taking of a sample for the purpose of learning about the whole or group
science              (n) a system or method of knowing and learning
scientific notation   (n) a shorthand means of writing very large or very small numbers

                     Glossary — Astrobiology: An Integrated Science Approach                                               573
shells                (n) the levels or orbits of an atom in which electrons exist; different shells correspond to different
                      energy levels
shooting star         (n) the popular term for a meteor; a brief streak of light in Earth’s atmosphere caused by the burning of
                      interplanetary debris
signal                (n) organized pattern of electromagnetic waves
silicon               (n) the element with atomic number 14; a possible, though unlikely, alternative to carbon as the basis
                      of life
solar flare            (n) a sudden release of energy in the sun’s corona
solar mass            (n) the mass of the sun, 1.989 x 10^30 kg; used as a measure of mass in stellar and galactic astron-
solar system          (n) the collective name for the sun and all the bodies that orbit it, including Earth, the other planets,
                      moons, asteroids, comets, and meteors
solar wind            (n) charged particles emitted from the sun
speciation            (n) the development of new species
species               (n) a category used in the classification of organisms that consists of groups of similar individuals that
                      can usually breed among themselves and produce fertile offspring
spectrograph          (n) an instrument that breaks light into spectral lines, using diffraction gratings to observe absorption
                      and emission lines
spectral lines        (n) the lines into which radition is divided when it passes through a diffraction grating
spectral signature    (n) the unique pattern of light produced by each element and molecule; provides information on the
                      composition of the gas emitting the light, and, in some cases, the speed and direction of the motion of
                      that gas
spectroscopy          (n) the process of viewing spectral lines to determine the characteristics of a gas and the nature of the
spiral arm            (n) a curved structure in the disk of a spiral (or sometimes an irregular) galaxy
spiral galaxy         (n) a type of galaxy with bright arms of stars, gas, and dust that extend in a spiral pattern from a cen-
                      tral hub
standard deviation    (n) a measure of the spread of a set of numbers around their mean
star                  (n) a hot, glowing ball of gas; at the core, hydrogen gas is fusing into helium gas through the process
                      of nucleur fusion
state                 (n) solid, liquid, or gas; also known as a “phase”
sublimate             (v) to change state or phase from a solid directly to a gas or from a gas directly to a solid
sun                   (n) the central body of the solar system; a G-type star
supernova             (n) a violent explosion by which certain stars end their lives; the explosion fuses the star’s elements
                      into all 92 naturally-occurring elements in the universe, including the very heavy ones such as gold,
                      lead, copper, nickel, tin, silver, and uranium
temperature           (n) a measure of the average speed of an individual particle in a particular substance
terraform             (v) to make another planet or moon more Earth-like for possible human habitation
tidally-locked        (adj) the same side of a planet always faces the star, or the same side of a moon always faces the
trait                 (n) characteristic of an organism
transcription         (n) a copy; the process of constructing a messenger RNA using DNA as a template
transit               (v) to cross, as a planet in front of its star
transverse waves      (n) a wave in which the vibration is perpendicular to the direction the wave is advancing
triple bond           (n) the bond formed when atoms share three electrons

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trough              (n) the lowest point of a wave
tsunamis            (n) giant tidal waves
ultraviolet light   (n) the region of the electromagnetic spectrum corresponding to wavelengths shorter than blue light
universal solvent   (n) water
universe            (n) the totality of all space, time, matter, and energy
vacuole             (n) a bubble-like area in a cell that stores liquid or gas
virus               (n) a very small particle that, inside a host cell, hijacks the cell’s machinery and makes it do what the
                    virus wants it to do; viruses are so simplified that they lack the ability to reproduce on their own; cells
                    infected by a virus start making new copies of the virus
water cycle         (n) the process by which water is continually changing phase, circulating from one environment to
wavelength          (n) the distance between the crest of one wave and the next
white dwarf         (n) a small, dense star formed from the collapse of stellar cores once nuclear fusion has ceased

                    Glossary — Astrobiology: An Integrated Science Approach                                               575

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