Glossary

albedo - the ratio of the amount of light reflected by an object to the amount of incident light. An object which reflects all of the light that reaches it has an albedo of 1.0, while an object which absorbs all of the light that reaches it has an albedo of 0.0.

ALH84001 - the famous martian meteorite which was found to contain possible evidence of martian microbes. ALH84001 was discovered in Antarctica in 1984.

altocumulus cloud - a middle cloud, usually white or gray. Often occurs in layers or patches with wavy, rounded masses or rolls.

amino acid - simple organic molecules which link together in chains to form proteins.

archean - The period in Earth's history between 2.5 billion years ago and 4.0 billion years ago.

astrobiology - a branch of astronomy that deals with the identification of habitable regions within the universe, the search for extraterrestrial life and the effects of outer space environments on living organisms. It is the study of the origin and distribution of life in the universe.

atmosphere - the layer of gases surrounding the surface of a planet, moon, or star.

ATP (Adenosine triphosphate) - the molecule which is the source of energy for most metabolic processes in living organisms.

autotroph - an organism which can nourish itself.

bacteria - a microscopic group of living organisms which usually have only one cell containing no nucleus. Bacteria are the most abundant of all organisms.

biome - a major regional group of distinctive plants and animals.

biosignature - a sign of the presence of life.

carbonaceous chondrite - a rare type type of meterorite that is rich in organic material.

cells - the basic unit of life. The smallest structural unit in an organism which can function independently.

chlorophyll - A green substance that enables the leaves of plants to use solar energy, carbon dioxide, water and organic nutrients from the soil to make the sugars and starches they use as food.

chloroplast - special organelles found in the cells of green plants in which photosynthesis takes place.

cirrus clouds - are wispy, fibrous-like clouds generally located above 6,000 meters (20,000 feet) and composed of ice crystals.

cyanobacteria (blue green algae) - a class of bacteria which make use of oxygen producing photosynthesis.

DNA (deoxyribonucleic acid) - molecules which carry the genetic information needed for living cells to function.

Drake Equation - an equation proposed by SETI pioneer Frank Drake to calculate the number of civilizations in the galaxy.

earthshine - the faint light reflected from the Earth onto the dark part of the moon.

endosymbiosis - symbiosis in which one organism lives within the body of the other.

enzyme - a protein which causes chemical reactions to happen while not being changed themselves.

extrasolar planet - a planet orbiting a star other than the sun.

extrasolar terrestrial planet - an earth-like planet orbiting a star other than the sun.

extraterrestrial - beyond the earth.

extremophile - an organism adapted to life in extreme conditions.

genome - the complete set of genetic information for a particular organism.

habitable - suitable for life

habitable zone - the region around a star where an Earth-like planet can maintain liquid water on its surface.

hyperthermophile - an organism which can live at very high temperatures.

meterorite - a meteor that reaches the earth's surface.

photosynthesis - the process that converts energy in sunlight to chemical forms of energy that can be used by biological organisms.

plankton - tiny marine animals (zooplankton) and plants (phytoplankton) which live at or near the surface of the ocean. Plankton are the first link in the marine food chain.

RNA (Ribonucleic acid) - a molecule which can carry genetic information in a similar way to DNA.

SETI - The Search for Extraterrestrial Intelligence.SETI projects aim to detect radio or other signals from advanced civilizations elsewhere in the galaxy.

spectra - the plural of spectrum

spectral signatures - measurement of the properties of an object at one or several wavelength intervals.

spectrum - a plot of the intensity of light at different frequencies or wavelengths

stratocumulus cloud - low altitude gray colored clouds composed of water droplets that have a patchy appearance.

stromatolite - layered structures built by colonies of microorganisms which are commonly found in fossil records.

sulfite - a salt of sulfurous acid.

thermophile - an organism adapted to life at high temperatures.

wavelength - The distance between adjacent crests of a wave.