AAG: Astronomy and Astrophysics Research Grants (National Science Foundation program).
abiotic: Of or relating to nonliving things; independent of life or living organisms.
accretion: The process by which an astronomical object increases in mass by the gravitational attraction of matter.
aeolian: Of or relating to the wind.
aerocapture: A technique employing a single pass through a planetary body’s atmosphere to shed sufficient velocity to place a spacecraft into orbit, thus avoiding the need for retrorockets.
albedo: The fraction of light that is reflected from the surface of a planetary body.
Alice: The NASA-provided ultraviolet imaging spectrometer on the European Space Agency’s Rosetta comet rendezvous mission.
ALMA: Atacama Large Millimeter Array.
amino acid: Any organic compound containing an amino (NH2) and a carboxyl (COOH), which polymerize to form peptides and proteins.
ANSMET: Antarctic Search for Meteorites (National Science Foundation program).
anthropogenic: Caused or produced by humans.
AO: Adaptive optics.
APL: Applied Physics Laboratory (Johns Hopkins University).
aquifer: Any geologic formation containing or conducting groundwater.
ARTEMIS: Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun (NASA spacecraft).
ASPERA (Analyzer of Space Plasmas and Energetic Atoms): The Energetic Neutral Atoms Analyzer instruments that have flown on several European Space Agency spacecraft.
ASRG: Advanced Stirling Radioisotope Generator.
astrobiology: The study of the origins, evolution, and distribution of life in the universe.
AU: Astronomical unit; the mean distance from Earth to the Sun.
biosignature: A sign that can be interpreted as evidence of life.
biosphere: The life zone of Earth or, by extension, of another planetary body.
biota: Living organisms of a particular place or period.
bolometer: An instrument used to measure radiant energy.
bulk composition: The makeup of a celestial body as a whole.
CAPTEM: Curation and Analysis Planning Team for Extraterrestrial Materials.
carbide: A compound of carbon with a more electropositive element or group.
CAREER award: National Science Foundation Faculty Early Career Development Program.
CATE: Cost and technical evaluation; specifically, a particular methodology for assessing the cost, schedule, and technical risk associated with a spacecraft mission.
CCSR: Cryogenic Comet Sample Return.
chirality: The right- or left-handedness of an asymmetric molecule.
CHNOPS: Carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur—the six elements essential to life as we know it.
chondrite: A stony meteorite, unaltered from its parent body.
chondrule: Round grains that make up a fraction of chondrites, formed from molten or partially molten droplets of minerals.
CIDA: Cometary and Interstellar Dust Analyzer (on NASA’s Stardust spacecraft).
circumstellar disk: A broad ring of material orbiting around a star.
clathrate: A chemical substance consisting of a lattice of one type of molecule (e.g., water) trapping and containing a second type of molecule (e.g., methane).
clathration: The chemical process leading to the formation of a clathrate.
CNES: Centre National d’Etudes Spatiales (the French space agency).
CNSR: Comet Nucleus Sample Return.
CoBRA: Complexity Based Risk Assessment.
comparative planetology: Use of the knowledge gained from the study of one planetary body to understand processes and phenomena of another.
COMPLEX: Committee on Planetary and Lunar Exploration (National Research Council).
corotating: To rotate jointly, as with another object.
covalent bond: A chemical bond formed when atoms share electrons.
cryogenics: The branch of physics dealing with the behavior of matter at very low temperatures.
cryosphere: Portions of a planetary body where water is in solid form.
cryovolcanism: The eruption of water and other volatile materials onto the surface of a planet or moon due to internal heating.
CSSR: Comet Surface Sample Return.
D/H ratio: Deuterium-to-hydrogen ratio.
DARPA: Defense Advanced Research Projects Agency.
diagenesis: The sum of the physical, chemical, and biological changes that take place in sediments as they become consolidated into rocks, including compaction and cementation, but excluding weathering and metamorphic changes.
differentiation: The process by which the interior of a planetary body separates into layers of different compositions.
DOE: Department of Energy.
dropsonde: A meteorological instrument package designed to be dropped from altitude in a planetary atmosphere and to make measurements as it falls to the planet’s surface.
DSN: Deep Space Network (NASA).
dynamo: An electromagnetic process in which the movement of conductive material gives rise to a magnetic field.
eccentricity: A measurement of the degree to which an elliptical orbit deviates from a circular orbit. An ellipse of zero eccentricity is a circle.
ecliptic: The plane of Earth’s orbit around the Sun.
EDL: Entry, descent, and landing.
EEV: Earth Entry Vehicle.
EFS: Entry Flight System.
EJSM: Europa Jupiter System Mission (proposed NASA-ESA mission).
electromagnetic induction: Production of voltage across a conductor due to a changing magnetic flux.
ELT: Extremely Large Telescope.
emission spectrum: A spectrum composed solely or predominantly of emission lines, indicating the presence of a hot gas and a nearby source of energy.
endogenic: Relating to a process of internal origin.
EPO: Education and public outreach.
EPOXI: The name of the extended mission of NASA’s Deep Impact spacecraft—a combination of Extrasolar Planet Observation and Characterization and Deep Impact Extended Investigation, the two phases of the extended mission.
ESA: European Space Agency.
ESMD: Exploration Systems Mission Directorate (NASA).
exogenic: Relating to a process of external origin.
exoplanets: Planets formed around stars other than the Sun.
felsic rock: A class of rock that crystallizes from silicate minerals at relatively low temperatures and has a high percentage of silica.
fluvial: Relating to flowing water or, by extension, another flowing liquid.
flux: A measure of the energy or number of particles passing through a given area of surface in unit time.
FUSE: Far Ultraviolet Spectroscopic Explorer (NASA).
GCM: General circulation model.
GN&C: Guidance, navigation, and control.
Gossamer ring: The outermost ring of Jupiter.
GRAIL: Gravity Recovery and Interior Laboratory (NASA mission).
GSFC: Goddard Space Flight Center (NASA).
Gusev crater: A 144-km-wide crater located some 15 degrees south of the equator of Mars that was the landing site for Spirit, one of the Mars Exploration Rovers.
Hadley-like convection: A type of circulation pattern seen in planetary atmospheres: warm, low-density material rises near the equator, flows toward the poles, and cools; cooler, high-density material sinks in the subtropics and flows equatorward along the surface.
HDO: A form of water in which one hydrogen atom is replaced by a deuterium atom.
Hesperian period: The middle of three broad time periods into which the geologic history of Mars has been divided, extending roughly from about 3.5 billion to about 1.8 billion years ago.
H/He ratio: Hydrogen-to-helium ratio.
HST: Hubble Space Telescope.
hydrosphere: All bodies of water on a planet, as distinguished from the lithosphere and the atmosphere.
hydrothermal: Relating to the action of hot liquid or gas within or on the surface of a planet.
ICE: Independent cost estimate; a specific methodology for determining the cost of a spacecraft mission.
IDP: Interplanetary dust particle.
ILN: International Lunar Network.
ionosphere: The region of a planet’s atmosphere that is kept partially ionized by solar ultraviolet and x-ray irradiation.
IRTF: Infrared Telescope Facility (NASA ground-based telescope).
ISIS: Integrated Software for Imagers and Spectrometers.
isotope: 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.
ISS: International Space Station.
ITAR: International Traffic in Arms Regulations.
jarosite: A yellowish or brownish mineral, a hydrous sulfate of potassium and iron, occurring in small crystals or large masses.
JAXA: Japan Aerospace Exploration Agency.
JEO: Jupiter Europa Orbiter (proposed NASA mission).
JGO: Jupiter Ganymede Orbiter (proposed ESA mission).
JPL: Jet Propulsion Laboratory.
KBO: Kuiper belt object.
Keck: Keck Observatory.
Kuiper belt: A region of the outer solar system containing icy planetesimals distributed in a roughly circular disk extending some 40 to 100 AU from the Sun.
lacustrine: Pertaining to a lake or other standing body of liquid.
LADEE: Lunar Atmosphere and Dust Environment Explorer.
late heavy bombardment: A postulated period of enhanced impact activity in the inner solar system approximately 4.1 billion to 3.8 billion years ago. During this period, also known as the lunar cataclysm, a large number of impact basins and craters formed on the Moon.
LCROSS: Lunar Crater Observation and Sensing Satellite.
LGN: Lunar Geophysical Network.
lidar: Light identification detection and ranging. A form of optical radar and target characterization.
lithosphere: The rigid outermost shell of a rocky planetary body.
LLNL: Lawrence Livermore National Laboratory (operated by the U.S. Department of Energy).
LRO: Lunar Reconnaissance Orbiter.
LSST: Large Synoptic Survey Telescope.
magnetohydrodynamics: The branch of physics that studies the motion of electrically conductive fluids in electric and magnetic fields.
magnetometry: The technique of measuring the strength and direction of a magnetic field.
magnetosphere: The region of space in which a planet’s magnetic field dominates that of the solar wind.
mantle: The part of a planet between its crust and core, composed of relatively dense materials.
MAV: Mars Ascent Vehicle.
MAVEN: Mars Atmosphere and Volatile Evolution (NASA mission).
MAX-C: Mars Astrobiology Explorer-Cacher (proposed NASA mission).
MCS: Mars Climate Sounder.
mean motion resonance: The dynamical situation in which the ratio of the orbital periods of two orbiting objects can be expressed as the ratio of two integers.
MEPAG: Mars Exploration Program Analysis Group.
MER: Mars Exploration Rover.
Meridiani Planum: A plain located some 2 degrees south of the martian equator, in the westernmost portion of Terra Meridiani. It was the landing site for Opportunity, one of the Mars Exploration Rovers.
meridional circulation: An atmospheric circulation pattern that is primarily oriented in the north-south plane.
MESSENGER: Mercury Surface, Space Environment, Geochemistry, and Ranging (NASA mission).
methanogenic organism: An organism that produces methane as a by-product of its metabolism.
MEX: Mars Express (European Space Agency spacecraft).
MGS: Mars Global Surveyor.
microlensing: A technique used in the search for extrasolar planets that takes advantage of the gravitational lensing phenomenon.
MidEx: NASA’s program of medium-size Explorer spacecraft.
MIRO: Microwave Instrument for the Rosetta Orbiter (one of NASA’s contributions to the European Space Agency’s Rosetta comet rendezvous mission).
MMH: Monomethylhydrazine, a common rocket fuel.
MMRTG: Multi-Mission Radioisotope Thermoelectric Generator.
Montgolfière balloon: A hot-air balloon.
MOO: Mission of Opportunity.
MRO: Mars Reconnaissance Orbiter.
MRSH: Mars Returned-Sample Handling (facility).
MSL: Mars Science Laboratory.
MSR: Mars Sample Return.
MSR-L: Mars Sample Return Lander.
MSR-O: Mars Sample Return Orbiter.
N+: A nitrogen atom that has lost one of its electrons.
N2: Molecular nitrogen.
: NAI: NASA Astrobiology Institute.
NAIF: Navigation and Ancillary Information Facility.
NASA: National Aeronautics and Space Administration.
NEAR: Near Earth Asteroid Rendezvous (NASA mission).
nebula: A cloud of gas and dust in space.
NEO: Near-Earth object.
NEP: Nuclear-electric propulsion.
NEXT: NASA Evolutionary Xenon Thruster.
NFSS: New Frontiers in the Solar System (National Research Council report, the first decadal survey of the planetary sciences).
NH: New Horizons.
Nili Fossae region: A trough in the surface of Mars that has been eroded and partly filled in by sediments and clay-rich ejecta from a nearby crater.
NIMS: Near-Infrared Mapping Spectrometer.
NLSI: NASA Lunar Science Institute.
NOAA: National Oceanic and Atmospheric Administration.
Noachian period: The oldest of three time periods into which the geologic history of Mars has been divided, spanning from about 4.1 billion to about 3.5 billion years ago.
NOAO: National Optical Astronomy Observatory.
NOSSE: New Opportunities in Solar System Exploration (National Research Council report).
NRA: NASA Research Announcement.
NRAO: National Radio Astronomy Observatory.
NRC: National Research Council.
NSF: National Science Foundation.
nucleosynthesis: The nuclear process by which chemical elements are produced in stellar interiors and during supernovae.
nucleotide: A class of organic molecules that play a variety of important roles in biological processes. They form, for example, the major structural subunits of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) and also serve as a source of energy for biochemical processes.
O2: Molecular oxygen.
obliquity: The angle between an object’s rotation axis and the normal to the plane of its orbit.
occultation: The passage of an astronomical body across the line of sight to another astronomical body of smaller angular diameter; that is, a planet passing across the line of sight to a background star.
OLAF: On-Line Archiving Facility.
olivine: A magnesium iron silicate mineral (FeMg)2SiO4.
Oort cloud: A spherical distribution of comets having semimajor axes between 1,000 and 50,000 AU, typically with low orbital eccentricity.
OPAG: Outer Planet Assessment Group.
Opportunity: The second of the two rovers of NASA’s ongoing Mars Exploration Rover mission, which landed on Mars on January 25, 2004.
OPR: Outer Planets Research.
orbital migration: A major change in a planet’s orbit around its host star, either sudden or gradual, caused by interaction with one or more other large bodies (such as neighboring planets), with the remnants of a protoplanetary nebula, or by some other process.
outgassing: Venting of volatile materials from the crust of a planetary body.
paleoclimate: The climate of some former period of geologic time.
pallasite: A meteorite composed primarily of olivine and metallic iron.
PDS: Planetary Data System.
PDS SBN: Planetary Data System (of NASA) Small Bodies Node.
perchlorate: A salt containing the ClO4– ion.
PG&G: Planetary Geology and Geophysics (NASA grants program).
Phase A, B, C, D, E: Various stages of spacecraft development, including (A) the preliminary outline of design, (B) definition and detailed design, (C) development/manufacture, (D) integration/testing, and (E) extended operations, respectively.
photodissociation: The breakup of molecules through exposure to light.
phyllosilicate: A family of clay mineral characterized by having the tetrahedral silicate groups linked in sheets, each group containing four oxygen atoms, three of which are shared with other groups so that the ratio of silicon atoms to oxygen atoms is two to five.
PI: Principal investigator.
PICA: Phenolic impregnated carbon ablator.
PIDDP: Planetary Instrument Definition and Development Program.
planetary protection: Measures designed to protect Earth and other planetary bodies from cross contamination by biological materials.
planetesimal: A rocky and/or icy body a few kilometers to several tens of kilometers in size, which was formed in the protoplanetary nebula.
plasma: A highly ionized gas, consisting of almost equal numbers of free electrons and positive ions.
PLD: polar layered deposits (Mars).
porosity: The percentage of the total volume of a body that is made up of open spaces.
prebiotic: Not yet alive; a chemical system that may be a precursor to life.
presolar grains: Microscopic dust grains that existed in the interstellar cloud from which the Sun formed.
protoplanet: A planet in the process of accretion from material in a protoplanetary disk.
protoplanetary disk: A circumstellar disk of matter, including gas and dust, from which planets may eventually form or be in the process of forming.
238Pu (plutonium-238): An isotope of plutonium whose physical properties make it ideally suited for use as a heat source in radioisotope power systems.
pyroclastic: Rocks composed solely or primarily of fragments of volcanic materials.
pyrrhotite: An unusual iron sulfide mineral with a variable iron content.
Q factor: A parameter that describes the extent to which an oscillatory system is under-damped; the higher the Q, the more slowly oscillations die out after being excited.
R&A: Research and analysis.
radiative balance: Accounting for all sources of incoming and outgoing radiation in a system.
radiogenic heating: The thermal energy released by the decay of naturally occurring radioactive materials.
radiolysis: The dissociation of molecules by ionizing radiation.
radionuclide: A radioactive nuclide.
regolith: The layer of dust and fragmented rocky debris that forms the uppermost surface on many planets, satellites, and asteroids. It is formed by a variety of processes including meteoritic impact.
REP: Radioisotope-electric propulsion.
retrograde: Orbital motion or rotation in a clockwise direction as viewed from the north pole of the ecliptic or of the rotating object; that is, in the opposite direction of the rotation of Earth and most of the other planetary bodies in the solar system.
REU: Research Experience for Undergraduates.
RMA: Rapid mission architecture (study).
ROSES: Research Opportunities in Space and Earth Sciences.
Rosetta: A European Space Agency spacecraft, launched in 2004, that will rendezvous with Comet 67P/Gerasimenko in 2014, flying past two asteroids on the way.
RPS: Radioisotope power system.
RY: Real year.
SALMON: Stand Alone Mission of Opportunity (NASA program).
SDT: Science Definition Team.
SED: Spectral energy distribution.
SEP: Solar-electric propulsion.
serpentinization reaction: A metamorphic process in which ultrabasic rocks react with water to create a variety of hydrous, magnesium-iron phyllosilicate minerals known collectively as serpentine. The process is endothermic and results in the liberation of hydrogen, methane, and hydrogen sulfide.
SHEC: Sample handling, encapsulation, and containerization.
silicate volcanism: Volcanic activity in which the lava flow consists of silicate materials.
SMD: Science Mission Directorate (NASA).
SmEx: NASA’s program of small-class Explorer spacecraft.
SNC meteorites: A group of meteorites that are thought to have come from the surface of Mars, named after the places where the first three were found: Shergotty, India; Nakhla, Egypt; and Chassigny, France.
SO2: Sulfur dioxide.
SOFIA: Stratospheric Observatory for Infrared Astronomy.
SOHO: Solar and Heliospheric Observatory (ESA-NASA mission).
solar nebula: The cloud of gas and dust from which the Sun, the planets, and other bodies in the solar system formed.
solar zenith angle: The angle between the local zenith and the line of sight to the Sun.
sounding rocket: A relatively small research rocket capable of carrying a scientific payload to the upper atmosphere or near space on a suborbital trajectory.
South Pole-Aitken Basin: The largest, deepest, and oldest impact basin on the Moon.
SPA: South Pole-Aitken Basin.
space weathering: Alteration of an atmosphereless planetary body’s surface materials by exposure to the space environment.
spectral resolution: A measurement of the ability to resolve the features of an electromagnetic spectrum.
spectroscopy: The process of dissecting electromagnetic radiation from an object into its component wavelengths so as to determine its chemical composition.
SPICAM: Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars. The imaging ultraviolet and infrared spectrometer on European Space Agency’s Mars Express spacecraft.
SPICAV: Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus. The imaging ultraviolet and infrared spectrometer on the European Space Agency’s Venus Express spacecraft.
Spirit: The first of the two rovers of NASA’s ongoing Mars Exploration Rover mission, which landed on Mars on January 4, 2004.
sputtering: A process of chemical alteration caused by atomic particles striking a surface at high speed.
SSE: Solar System Exploration.
Stardust: A spacecraft launched in 1999 with the objective of returning a sample of the comet Wild-2 to Earth.
STEM: Science, technology, engineering, and mathematics.
STEREO: Solar Terrestrial Relations Observatory (NASA mission).
stratigraphy: A branch of geology dealing with the classification, nomenclature, correlation, and interpretation of stratified rocks.
sublimation: The act of changing a substance directly from a solid to a gas without its passing through a liquid stage.
subnebula: A circumplanetary gas disk that is thought to form early on in the planetary formation process.
superrotating: The rotation of a planet’s atmosphere at a rate faster than the surface rotation.
surface morphology: The structure and form of a particular surface.
SwRI: Southwest Research Institute.
tectonism: The processes of faulting, folding, or other deformation of the lithosphere of a planetary body, often resulting from large-scale movements below the lithosphere.
tessera: Unique geologic feature found on some of the plateau highlands on Venus and characterized by their extremely rugged topography. They are also known as complex ridged terrain and are believed to be formed when crustal stresses cause the surface to fold, buckle, and break.
tidal dissipation: The loss of energy from a planetary body’s orbit, typically depositing energy within the body as heat.
TMC: A specific methodology for determining the technical, managerial, and cost risk associated with a spacecraft mission.
TNO: Trans-Neptune object. Another name for a Kuiper belt object.
TPS: Thermal Protection System.
TRACE: Transition Region and Coronal Explorer (NASA mission).
trace gas: A gas that makes up less than 1 percent by volume of a planet’s atmosphere.
transit: The passage of an astronomical object across the face of one of larger angular diameter.
TRL: Technology readiness level.
Trojan asteroids: Asteroids located near the two stable Lagrangian points of Jupiter’s orbit (60° preceding and following the planet).
TSIP: Telescope System Instrumentation Program.
TSSM: Titan Saturn System Mission (proposed NASA-ESA mission).
TTRV: Trojan Tour and Rendezvous (proposed NASA mission).
ultramafic: Igneous rock composed principally of mafic (magnesium and iron) minerals, such as olivine and pyroxene.
USGS: United States Geological Survey.
VCM: Venus Climate Mission.
VEXAG: Venus Exploration Analysis Group.
VFDRM: Venus Flagship Design Reference Mission.
VIMS: Visual and Infrared Mapping Spectrometer.
VIRTIS: Visible and Infrared Thermal Imaging Spectrometer.
VISE: Venus In Situ Explorer (proposed NASA mission).
VLA: Very Large Array (radio telescope).
VLBA: Very Long Baseline Array (of radio telescopes).
VLT: Very Large Telescope.
VME: Venus Mobile Explorer.
VNIR: Visible/near-infrared spectrometer.
VOI: Venus Orbit Insertion.
volatile: A substance that vaporizes at a relatively low temperature.
VSTDT: Venus Science and Technology Definition Team.
Zeta ring: The innermost ring of Uranus.