C
Glossary
Aitken Basin
Largest impact basin known, located in the Moon’s southern polar region
alpha decay
Radioactive decay of a nucleus by the emission of an alpha particle, the nucleus of a helium-4 atom
amino acid
Class of basic molecules that make up proteins
apoptosis
Cell death
Archean
Period in Earth’s history from 3.8 to 2.5 billion years ago, when life arose
Argyre
Major impact basin on Mars
asteroid
Rocky fragments left over from the formation of the solar system
astrosphere
Zone of interaction between a star and its interstellar environment
beta decay
Radioactive decay of a nucleus by the emission of an electron (or positron) and an electron antineutrino (or electron neutrino)
biosphere
Life zone of Earth, which includes all living organisms and all organic matter that has not yet decomposed
bolide
Meteor that often explodes as a fireball
carbonaceous chondrite
Stony meteorite that contains carbonaceous compounds
Chicxulub
Impact basin in Mexico, which was created at the end of the Cretaceous and the beginning of the Tertiary
chirality
Degree to which an object is different from its mirror image
chromosphere
Visually transparent layer above the Sun’s visible photosphere
clay
Generic term for an aggregate of hydrous silicate particles less than 4 µm in diameter
comet
Relatively small planetary body similar to an asteroid but composed largely of ice
cosmic rays
High-energy particles originating outside Earth
cross strand exchange
Process in which bases along one double helix strand separate and link across to a separate double helix and vice versa
Darwin
European Space Agency’s large infrared-wavelength space interferometer
Deep Impact
NASA mission to collide a spacecraft to create a deep crater in Comet Tempel 1
Deinococcus radiodurans
Gram-positive aerobic bacteria, the most radiation-resistant organism known
dichroism
Differential absorption of left- and right-hand circularly polarized light in a material
DNA
Deoxyribonucleic acid, the molecule that carries genetic information
DOE
U.S. Department of Energy
dose
Absorbed amount of radiation
dose rate
Rate at which tissue absorbs radiation
double-strand break
Break in both strands of the DNA molecule, usually caused by oxidative stress or certain forms of radiation
D-ribose
Right-handed form of a five-carbon sugar, found in all living cells
early stars
Stars that formed primarily from hydrogen and helium and are deficient in heavier elements
endogenous
Organic matter synthesized on Earth and necessary for the appearance of life (see exogenous)
exogenous
Organic matter delivered from space and necessary for the appearance of life (see endogenous)
Exploration Initiative
U.S. multiagency Vision for Space Exploration
field reversal
Periodic reversal of the magnetic field of a star or planet
flare star
Star that sporadically flares in brightness by an order of magnitude or more
gamma ray
Most energetic form of electromagnetic radiation
gamma-ray burst
Energetic cosmic event that produces a burst of gamma rays
habitable zone
Radial zone in which certain parameters thought to be necessary for life are met
Hadean
Era in Earth’s history 4.5 to 3.8 billion years ago, before life is thought to have arisen
heliosphere
Huge magnetic bubble created in interstellar space by the outrushing solar wind and associated magnetic field
Hellas
Major impact basin on Mars
Herschel
European Space Agency’s far-infrared and submillimeter telescope project, due to launch in 2007
homochirality
Molecules possessing structure with the same handedness
hypermutable
Genes that have a high rate of mutation
impact basin
Large crater produced by a meteorite impact
in silico
Relating to processes that occur in computer simulations
in vitro
Relating to processes that occur in a laboratory
in vivo
Relating to processes that occur in living matter
isotope
Atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights due to different numbers of neutrons
K-T boundary
Boundary between the Cretaceous and Tertiary periods, about 65 million years ago
Kuiper Belt
Area of the solar system extending from within the orbit of Neptune (at 30 AU) to some 50 AU from the Sun
Lake Acraman
Large meteor impact crater in South Australia
L-enantiomer
Molecule with left-handed chirality
L-isomer
Molecule with left-handed chirality
Long-Duration Exposure Facility
NASA experiment involving a satellite that was retrieved after several years to determine the effects of long-term exposure to space
L-ribose
Left-handed form of a five-carbon sugar
LUCA
Last Universal Common Ancestor (of life)
magma chamber
Underground pocket containing molten rock
meiosis
Reproduction through cell division
metals
To astronomers, any element except hydrogen or helium
mtDNA
Mitochondrial DNA
NAI
NASA Astrobiology Institute
NASA
U.S. National Aeronautics and Space Administration
NSCORT
NASA Specialized Centers of Research and Training
NEO
Near-Earth object, an asteroid or comet that comes relatively close to Earth
NIH
U.S. National Institutes of Health
NSF
U.S. National Science Foundation
obliquity
Angle between the plane of a planet’s orbit and that of the planet’s equator
Oklo
Series of natural fission reactors that were active in the Oklo Valley of Gabon, Africa, about 1.5 billion years ago
Oort Cloud
Spherical cloud of comets with semimajor axes between 1,000 and 50,000 AU
oxygen radical
Oxygen atom with an unpaired electron. Radicals are powerful oxidizing agents that can cause structural damage to proteins and nucleic acids.
panspermia
Hypothesis that life originated elsewhere in the universe and migrated through space to Earth and, potentially, elsewhere
photosynthesis
Biochemical process by which the energy of light is converted into chemical energy in plants, algae, and certain bacteria
phototroph
Organism that uses light as its main source of energy
phylogenetic
Of or related to the evolutionary development of a group of genetically related organisms
placer deposit
Alluvial deposit of sand and gravel representing stream beds
planetesimal
Small rocky and icy object that existed at an early stage in the development of the solar system
polymerase
Enzymes that catalyze the polymerization of nucleic acids
polyols
Polyhydric alcohols or sugar alcohols
polysaccharides
Polymers made up of chains of simple sugars. Examples include starch, cellulose, and glycogen
protein
Complex, high-molecular-weight organic compound that consists of amino acids joined by peptide bonds
Pseudomonas fluorescens
Common nonpathogenic, gram-negative bacteria that produces a soluble greenish fluorescent pigment, particularly under conditions of low iron availability
P-T boundary
Geologic boundary between the Permian and Triassic periods, about 250 million years ago
pyrimidine dimer
Two adjacent pyrimidine nucleotides, usually thymine, in which the pyrimidine residues are covalently joined by a cyclobutane ring. These dimers stop DNA replication.
pyrimidines
Organic compounds with a heterocyclic ring: two nitrogen atoms taking the place of carbon atoms at positions 1 and 3 relative to each other around the six-member ring
radiolarians
Single-celled organisms that form protective skeletons, usually made of silicon dioxide
ram pressure
Force per unit area required to stop the solar wind flow
redox state
Chemical reaction environment determined by the balance of negatively and positively charged atoms
replication
Reproduction from a template
ribose
Five-carbon sugar
RNA
Ribonucleic acid, a molecule involved in transcription of the instructions in DNA. Some theorize that RNA was the precursor to DNA.
single-strand break
When one strand of the DNA molecule is broken, usually by oxidative stress or certain forms of radiation
solar flare
Eruption of hot gas and radiation from the Sun’s photosphere
solar neighborhood
Sun and nearby stars
Stardust mission
NASA mission to return dust from Comet Wild 2
subduction
Geologic process by which one tectonic plate is forced under another
Sudbury
Ancient impact basin in northern Canada
supernova
Stellar explosion
tars
Complex hydrocarbons with high viscosity and melting point
tectonics
Theory that Earth’s lithosphere exists as separate and distinct plates that float on a fluid-like asthenosphere
Titan
Largest moon of Saturn
TPF
NASA’s Terrestrial Planet Finder
transition elements
Elements located in groups IB to VIIIB of the Periodic Table. They have many of the characteristics of metals.
ultraviolet
Electromagnetic radiation more energetic than visible light
UVB
Ultraviolet sunlight that penetrates the ozone layer and reaches Earth’s surface
UVC
Ultraviolet sunlight with shorter wavelength than UVB that is filtered out by Earth’s ozone layer
VPL
Virtual Planetary Laboratory, hosted by Caltech and the Jet Propulsion Laboratory
volatile
Substance with a low evaporation temperature
Vredefort
300-km impact crater in South Africa, formed about 2 billion years ago
x ray
Electromagnetic radiation more energetic than ultraviolet light