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The Search for Life's Origins
Progress and Future Directions in Planetary Biology and Chemical Evolution
Glossary
Å: Angstrom; unit of length.
achondrite: Differentiated meteorite.
anticodon: Triplet of bases in transfer RNA complementary to the codon.
archaebacteria: Organisms constituting one of the three biological kingdoms.
Archean: Period of Earth's history from 3.8 to 2.4 billion years ago.
arc sec: Arc second; unit of angular measurement in astronomy.
ATF: Astrometric telescope facility.
AU: Astronomical unit; mean distance between the Earth and the Sun.
biogenic elements: Elements making up the bulk of living organisms.
CAI: Calcium-aluminum inclusion, found in meteorites.
carbonaceous chondrite: Meteorite with granules containing carbon-rich matter.
CCD: Charge coupled device.
CIT: Circumstellar Imaging Telescope.
cm: Centimeter.
codon: Triplet code of bases in DNA specifying an amino acid in protein synthesis.
COMPLEX: Committee on Planetary and Lunar Exploration.
CRAF: Comet Rendezvous Asteroid Flyby mission.
Cretaceous: Period of Earth's history from 145 to 65 million years ago.
D/H: Deuterium-to-hydrogen ratio.
DNA: Deoxyribonucleic acid.
DOE: Department of Energy.
ECHO: Evolution of Complex and Higher Organisms; report.
EIRP: Effective isotropic radiated power.
ESA: European Space Agency.
eubacteria: All other bacteria besides the archaebacteria.
eukaryote: Cells with true nucleus and other internal organelles.
FGS: Fine guidance sensor.
FIRST: Far-Infrared Space Telescope.
Fischer-Tropsch reaction: Process in which carbon monoxide and hydrogen mixtures are converted into hydrocarbons and related compounds.
FOS: Faint object spectrograph.
genome: The complete set of genes in an organism.
GHz: Gigahertz; unit of frequency.
HD/H2: Ratio of deuterated hydrogen to hydrogen.
heterocyclic organic polymers: Compounds consisting of monomeric units of organic ring molecules in which not all atoms in the rings are alike.
heterotroph: Organism requiring organic compounds as food source.
HIMS: Hubble imaging Michelson spectrometer.
IR: Infrared region of electromagnetic spectrum.
IRAS: Infrared Astronomical Satellite.
ISO: Infrared Space Observatory.
ISOCAM: Infrared Space Observatory camera.
J: Joule; unit of heat energy.
K: Kelvin; unit of temperature.
KAO: Kuiper Airborne Observatory.
L183: Interstellar cloud.
LDR: Large deployable reflector.
m: Meter.
MAP: Multichannel astrometric photometer.
MHz: Megahertz; unit of frequency.
MIPS: Multiband imaging photometer for SIRTF.
mRNA: Messenger RNA; directs the synthesis of proteins.
NAD: Nicotinamide adenine dinucleotide; coenzyme involved in redox reactions.
NASA: National Aeronautics and Space Administration.
NICMOS: Near-infrared camera and multiobject spectrometer.
NIH: National Institutes of Health.
NMR: Nuclear magnetic resonance.
NRAO: National Radio Astronomy Observatory.
NRC: National Research Council.
NSF: National Science Foundation.
nucleoside: Precursor of nucleic acids; consists of an organic base and a sugar.
nucleosynthesis: Production of elements heavier than hydrogen.
oligonucleotide: Short chain of nucleic acid monomers.
oligopeptide: Short chain of amino acids.
PAH: Polyaromatic hydrocarbon.
Paleozoic: Period of Earth's history from 670 to 245 million years ago.
Permian: Period of Earth's history from 285 to 245 million years ago.
Phanerozoic: Period of Earth's history from 670 million years ago to present.
phenotype: Observable physiological behavior of an organism.
phosphomonoesterase: Hydrolytic enzyme; releases inorganic phosphate.
phototroph: Organism deriving its energy from light.
phylogeny: Ordering of biological species based on their evolutionary relationships.
planetesimal: Solar-system body; of the order of a kilometer in size.
planetoid: Solar-system body; tens to hundreds of kilometers in size.
prebiotic: Before the appearance of life on Earth.
Precambrian: Period of Earth's history from its formation to 600 million years ago.
prokaryote: Organism lacking a true nucleus.
Proterozoic: Period of Earth's history from 2.5 billion to 600 million years ago.
pyrolysis: Destruction of organic compounds by combustion.
regolith: Surface debris on solar-system objects produced by impacting bodies.
RFI: Radio frequency interferences.
ribonucleotide: Monomeric unit of RNA.
ribooligonucleotide: Short chain of ribonucleotides.
ribosome: Cellular particle; site of protein synthesis.
RNA: Ribonucleic acid.
RNA polymerase: Enzyme that polymerizes ribonucleotides.
RNase P: tRNA-processing enzyme containing a catalytic RNA subunit.
rRNA: Ribosomal RNA; involved in protein synthesis.
S: Svedberg unit; sedimentation constant used in ultracentrifugation.
SAO: Smithsonian Astrophysical Observatory.
SETI: Search for extraterrestrial intelligence.
SIRTF: Space Infrared Telescope Facility.
SNC: Shergottite, hakhlite, and chassignite meteorites; possibly from Mars.
SSB: Space Science Board/Space Studies Board.
T4 RNA ligase: Enzyme causing ribonucleic acid fragments to join together.
template: Molecule that is copied to form its complement in nucleic acid synthesis.
thiol ester: Sulfur-containing ester.
TMC-1: Interstellar cloud.
translation: Process by which DNA code specifies sequencing of amino acids.
tRNA: Transfer RNA; combines with specific amino acid in protein synthesis.
UV: Ultraviolet region of electromagnetic spectrum.
Van der Waals force: Weak attractive force between nonpolar molecules.
Viking: U.S. mission to Mars in 1975.
W: Watt; unit of power.
WFC: Wide-field camera. 
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