Astrobiology Glossary E – Space

Term Definition
Earth The third planet from the Sun and one of four terrestrial planets in the inner solar system. Earth, the only planet where water exists in large quantities, has an atmosphere capable of supporting myriad life forms. The planet is 150 million kilometers (93 million miles) away from the Sun. Earth has one satellite – the Moon.
Ediacaran Fauna A fossil fauna of soft bodied organisms with an age of about 560 million years, first found in the Flinders Ranges of South Australia. They are the earliest known animals.
Electromagnetic Force A fundamental force that governs all interactions among electrical charges and magnetism. Essentially, all charged particles attract oppositely charged particles and repel identically charged particles. Similarly, opposite poles of magnets attract and like magnetic poles repel.
Electromagnetic Radiation A form of energy that propagates through space as vibrations of electric and magnetic fields; also called radiation or light. All electromagnetic radiation is a form of light.
Electromagnetic Spectrum The entire range of wavelengths of electromagnetic radiation, including radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays.
Electromagnetism The science dealing with the physical relationship between electricity and magnetism. The principle of an electromagnet, a magnet generated by electrical current flow, is based on this phenomenon.
Electron A negatively charge elementary particle that typically resides outside the nucleus of an atom but is bound to it by electromagnetic forces. An electron’s mass is tiny: 1,836 electrons equals the mass of one proton.
Electron Volt (eV) A unit of energy that is equal to the energy that an electron gains as it moves through a potential difference of one volt. This very small amount of energy is equal to 1.602 * 10-19 joules. Because an electron volt is so small, engineers and scientists sometimes use the terms MeV (mega-million) and GeV (giga-billion) electron volts.
Element A substance composed of a particular kind of atom. All atoms with the same number of protons (atomic numbers) in the nucleus are examples of the same element and have identical chemical properties. For example, gold (with 79 protons) and iron (with 26 protons) are both elements, but table salt is not because it is made from two different elements: sodium and chlorine. The atoms of a particular element have the same number of protons in the nucleus and exhibit a unique set of chemical properties. There are about 90 naturally occurring elements on Earth.
Elementary Particles Particles smaller than atoms that are the basic building blocks of the universe. The most prominent examples are photons, electrons, and quarks.
Ellipse A special kind of elongated circle. The orbits of the solar system planets form ellipses.
Elliptical Galaxy A galaxy that appears spherical or football-shaped. Elliptical galaxies are comprised mostly of old stars and contain very little dust and ‘cool’ gas that can form stars.
Emission Line A bright line in a spectrum caused by emission of light. Each chemical element emits and absorbs radiated energy at specific wavelengths. The collection of emission lines in a spectrum corresponds to the chemical elements contained in a celestial object.
Enantiomer The name given to the two mirror image forms of a chiral molecule.
Endosymbiosis Symbiosis in which one organism lives within the body of the other. More specifically refers to the theory that eukaryotic cells arose from the symbiosis of a number of organisms, with the organelles such as mitochondria and chloroplasts being descended from bacteria.
Enzyme A protein that acts as a catalyst. Most chemical processes in living cells are enzyme catalysed.
Erosion Natural processes that wear or grind away the surface of an object. On Earth, the major agents of erosion are water and wind.
Escape Velocity The minimum velocity required for an object to escape the gravity of a massive object.
Eubacteria An alternative name for the domain bacteria (or true bacteria) as distinct from the archaebacteria or archaea.
Eucarya (or Eukarya) One of three domains of life along with the Archaea and the Bacteria. The Eucarya domain covers all organisms with cells which have a nucleus and organelles (Eukaryotic cells). The Eucarya domain includes the animals, plants, fungi and protists.
Eukaryote An organism belonging to the domain Eucarya. Eukaryotes have cells with the genetic material contained in a nucleus and with separate organelles. Eukaryotic cells are typically about 10 times bigger in each dimension than prokaryotic cells.
European Space Agency (ESA) A fifteen-member consortium of European countries for the design, development, and deployment of satellites. The Space Telescope – European Coordinating Facility (ST-ECF) supports the European astronomical community in exploiting the research opportunities provided by the Earth-orbiting Hubble Space Telescope. The ESA members are Austria, Belgium, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, and the United Kingdom, with Canada as a cooperating state.
Event Horizon The spherical outer boundary of a black hole. Once matter crosses this threshold, the speed required for it to escape the black hole’s gravitational grip is greater than the speed of light.
Evolution The theory that groups of organisms change with passage of time, mainly as a result of natural selection.
Excited State A greater-than-minimum energy state of any atom that is achieved when at least one of its electrons resides at a greater-than-normal distance from its parent nucleus.
Extrasolar Planet A planet orbiting a star other than the sun.
Extraterrestrial An adjective that means ‘beyond the Earth.’ The phrase ‘extraterrestrial life’ refers to possible life on other planets.
Extremophile An organism adapted to life in extreme conditions. For example thermophiles and hyperthermophiles are adpated to high temperatures.

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