Last updated on March 17, 2014 at 9:49 EDT

Astrobiology Glossary A – Space

Term Definition
Absolute Zero The coldest possible temperature, at which all molecular motion stops. On the Kelvin temperature scale, this temperature is the zero point (0 K), which is equivalent to -273Â° C and -460Â° F.
Active Galaxy A galaxy possessing an active galactic nucleus at its center.
Advanced Camera For Surveys (ACS) An optical camera aboard the Hubble Space Telescope that covers twice the area, has twice the sharpness, and is up to ten times more efficient than the telescope’s Wide Field and Planetary Camera 2. The camera’s wavelength range spans from ultraviolet to near-infrared light. The camera’s sharp eye and broader viewing area enable astronomers to study the life cycles of galaxies in the remotest regions of the cosmos. Astronauts installed the camera aboard the telescope in March 2002.
ALH84001 Martian meteorite discovered in the Allan Hills ice field in Antarctica in 1984. It has been suggested that this meteorite contains evidence of martian microbial life.
Alkalinity pH values above 7
Amino Acid Simple organic molecules containing an amino group (NH2) and a carboxyl group (COOH). Amino acids link together in chains to form proteins.
Amplitude The size of a wave from the top of a wave crest to its midpoint.
Archaea One of three domains of life, along with the Bacteria and the Eucarya. The archaea are prokaryotic organisms which were shown to be a distinct group from the bacteria by molecular phylogeny using 16S ribosomal RNA. The archaeal domain includes many extremophilic organisms.
Archaebacteria An alternative name for the domain archaea.
Archean The period in the history of the Earth from 4000 million years ago to 2500 million years ago, part of the Precambrian. The Archean is preceeded by the Hadean and followed by the Proterozoic. The earliest fossil evidence for life on Earth appears during the Archean period.
Asexual Involving reproduction that occurs without the union of male and female gametes, as in binary fission or budding.
Association of Universities for Research in Astronomy, Inc. (AURA) A consortium of educational and other non-profit institutions that operates world-class astronomical observatories. Members include five international affiliates and 29 U.S. institutions, including the Space Telescope Science Institute in Baltimore, Maryland, the science operations center for NASA’s Hubble Space Telescope.
Asteroid A small, rocky object revolving around the Sun, sometimes called a minor planet or planetoid. The vast majority of asteroids is found in the asteroid belt, a region between the orbits of Mars and Jupiter. The largest known asteroid, Ceres, has a diameter of 926 kilometers (579 miles).
Asteroid Belt A region of space between Mars and Jupiter where the great majority of asteroids is found.
Astronomy The scientific study of matter in outer space.
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 processe in living organisms.
Aurora A phenomenon produced when the solar wind (made up of energized electrons and protons) disturbs the atoms and molecules in a planet’s upper atmosphere. Some of the energy produced by these disturbances is converted into colorful visible light, which shimmers and dances. Auroras have been seen on several planets in our solar system. On Earth, auroras are also known as the ‘Northern Lights’ (aurora borealis) or ‘Southern Lights’ (aurora australis), depending on in which polar region they appear.
Autotroph A self-nourishing organism.