Abiotic: Of or relating to nonliving things; independent of life or living organisms.
Albedo: The fraction of light that is reflected by a surface; commonly used in astronomy to describe the reflective properties of planets, satellites, and asteroids.
Amino acid: Any organic compound containing an amino (NH2) and a carboxyl (COOH) group. There are 20 α-amino acids from which proteins are synthesized during ribosomal translation of mRNA.
Anaerobe: An organism that can survive and reproduce in the absence of dissolved oxygen, instead using oxidants such as iron and sulfur compounds in energy metabolism.
Aqueous: Of or containing water, typically as a solvent or medium.
Archaea (Archaebacteria): Organisms making up one of the three branches on the phylogenetic tree of life. Their cells do not contain a defined nucleus, and they are genetically and biochemically distinct form the Bacteria. See Bacteria.
Back contamination: The biological contamination of Earth by possible life forms that may be returned from other solar system bodies.
Bacteria: Organisms making up one of the three branches on the phylogenetic tree of life. Their cells do not contain a defined nucleus, and they are genetically and biochemically distinct form the Archaea. See Archaea.
Basalt: A volcanic rock composed largely of plagioclase, feldspar, and dark minerals such as pyroxene and Olivine. A common surface rock on Mars. Thought to be the material from which martian soils were formed.
Bioburden assay: A test that measures the total number of viable microorganisms on an instrument. This number is used to determine the most appropriate parameters for its final sterilization.
Biofilm: An aggregate of microbes with a distinct architecture.
Biotic: Of or relating to living things; caused or produced by living organisms.
Brine: A solution of mineral salt in water.
Calcium perchlorate: The mineral with the lowest eutectic temperature relevant to Mars. See Eutectic.
Chaotropic compound: A molecule in water solution that can disrupt the hydrogen bonding network between water molecules. This affects the stability of other molecules in the solution, mainly macromolecules (nucleic acids, proteins), by weakening the hydrophobic effect.
Chemolithoautotroph: An organism deriving all of its carbon and energy requirements from inorganic compounds. The “litho” component of the name implies that the organism derives energy from minerals via, for example, the oxidation of hydrogen.
Clathrate: A compound in which one component is enclosed in a cage-like structure of another compound.
COSPAR: Committee on Space Research.
Cryopeg: A layer of unfrozen ground that forms a permanent part of the permafrost. See Permafrost.
Cryoprotectant: A substance used to protect biological surfaces from freezing damage.
Cryosphere: Near-surface, frozen layer including ground ice and permafrost. See Permafrost.
Cyanobacteria (Blue-green algae): A phylum of bacteria that obtain their energy through photosynthesis.
Dehalorespiration: Anaerobic respiration in some bacterial species that eliminates one or more halide atoms from halogenated compounds to yield energy for growth.
Deliquescent: Becoming or having the tendency to become liquid.
Desiccation: The state of extreme dryness, or the process of extreme drying.
EPS: Extrapolymeric substances. See Extrapolymeric substances.
Eutectic, value/temperature: The lowest possible melting temperature of a mixture of substances. This melting temperature is lower than that of any of the constituent substances and of any other mixture composed of the same constituents in different proportions.
Extrapolymeric substances (EPS): Compounds secreted by microorganisms into their environment consisting primarily of carbohydrates with some proteins, lipids, and DNA. EPS establish the functional and structural integrity of biofilms. See Biofilm.
Extremophile: A microorganism capable of growing under extreme physical and chemical conditions such as high temperatures, pressures, and acidity.
Forward contamination: The biological contamination of an extraterrestrial body by terrestrial organisms inadvertently carried aboard a spacecraft.
Halogens: A group on the periodic table consisting of five chemically related elements (fluorine, chlorine, bromine, iodine, astatine), which are missing one valence electron.
Halophilic: Requiring a high salt concentration for optimal growth.
Horizontal gene transfer: Exchange of genetic material that occurs without direct cell-cell contact, as in reproduction. This allows for inheritance of genetic information between distantly related lineages outside the vertical inheritance pathway implicit in cell division.
Hydrogenoclastic methanogenesis (Wood-Ljungdahl Pathway): A set of biochemical reactions used by some bacteria and archaea for energy production. The pathway uses hydrogen and carbon dioxide (CO2) to produce methane and Acetyl-CoA, an important molecule for energy production. This is a biological source of methane production.
Hydrolysis: A reaction involving the breaking of a bond in a molecule using water. The reaction mainly occurs between an ion and water molecules and often changes the pH of a solution.
Hydrothermal: Relating to the action of heated water inside the crust of a planetary body.
Hyperthermophile: An organism with an optimum growth temperature of 80°C or higher.
Hypolith: A photosynthetic organism that lives underneath rocks for radiation and wind protection in climatically extreme deserts.
IDP: Interplanetary dust particle.
Lithoautotroph: A microbe which derives energy from reduced compounds of mineral origin. See Chemolithoautotroph.
MARSIS: Mars Advanced Radar for Subsurface and Ionosphere Sounding.
MEPAG: Mars Exploration Program Analysis Group.
Metabolism: The processes or chemical changes in a cell by which food is built up (anabolism) into living protoplasm and by which protoplasm is broken down (catabolism) into simpler compounds with the exchange of energy.
Metabolite: A substance that is formed in or necessary for metabolism. See Metabolism.
Methanogen: An organism capable of producing methane from the decomposition of organic material.
Microbe: A generic term for any prokaryotic or eukaryotic single-cell organism.
MSL: Mars Science Laboratory.
Oligotroph: A microorganism specifically adapted to grow under conditions of low nutrient supply.
Olivine: a magnesium iron silicate mineral (FeMg)2SiO4.
Oxidation/Reduction: The change in the oxidation state of atoms or ions due to the “loss” or “gain” of electrons.
Permafrost: A thick subsurface layer of soil that remains frozen throughout the year.
PHX: Phoenix Mars Lander.
Polar dark dune streaks: Dark markings along dune ridges, revealed during what is believed to be polar defrosting.
PP: Planetary Protection.
Psychrotolerant organism: An organism that has a maximum growth temperature of 35°C, an optimal growth temperature of 15°C or lower, and a minimum growth temperature of 0°C or lower.
Psycrophile: An organism that has a maximum growth temperature of 20°C, an optimal growth temperature of 15°C or lower, and a minimum growth temperature of 0°C or lower.
Recurring Slope Lineae (RSL): Narrow, dark markings on steep slopes in the equatorial regions of Mars that appear and incrementally lengthen during warm seasons and fade in cold seasons.
Redox couples: A coupled series of chemical reactions driven by the simultaneous loss of electrons from one species (oxidation) and the gain of electrons from a second species (reduction). See Oxidation/Reduction.
RSL: Recurring Slope Lineae. See Recurring Slope Lineae.
Saturated porosity: The open space of a rock (between grains or within cavities) being completely full of frozen water or carbon dioxide (CO2) with respect to Mars.
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.
SHARAD: Shallow Subsurface Radar.
Slope streaks: Narrow, avalanche-like features common on dust-covered slopes around the equatorial regions of Mars.
Spore: A single-celled asexual reproductive unit created by a variety of microorganisms to aid in their dispersal and survival over extended periods of time in adverse environmental conditions.
SR: Special Region.
SR-SAG2: Special Regions Science Analysis Group 2.
Sterilization: A procedure that destroys all living microorganisms, including vegetative forms and spores. In practice, a completely sterile state is rarely achieved.
Sublimate: The change of a solid substance directly to vapor upon heating.
Tetrad: A group of four. In context, a group of four microbial cells.
TGO: Trace Gas Orbiter.
Thermophile: An organism that can survive and grow in high-temperature environments.
Translocation: Removal of things from one place to another; substitution of one thing for another.
Vapor pressure: The pressure exerted by a vapor in thermodynamic equilibrium with its solid or liquid phases at a given temperature in a closed system. The equilibrium vapor pressure is an indication of a liquid’s evaporation rate.
Water activity (aw): Effective or useable water content of a system. Water activity is defined as the ratio of the partial pressure of water vapor associated with a system to that of pure water at the same temperature. As such, water activity is related to relative humidity expressed as a fraction. Therefore, pure water has an aw of 1. Whereas, an aw of 0 indicates the absence of “free” water molecules.
Wood-Ljungdahl Pathway (hydrogenoclastic methanogenesis): A set of biochemical reactions used by some bacteria and archaea for energy production. The pathway uses hydrogen and carbon dioxide (CO2) to produce methane and Acetyl-CoA, an important molecule for energy production. This is a biological source of methane production.