Astrobiology Glossary M – Space

Term Definition
Magellanic Clouds The Magellanic Clouds are two dwarf irregular galaxies. Known as the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), the galaxies are in the Local Group. The closer LMC is 168,000 light-years from Earth. Both galaxies can be observed with the naked eye in the southern night sky.
Magnetic Field A region of space in which magnetic forces may be detected or may affect the motion of an electrically charged particle. As with gravity, magnetism has a long-range effect and magnetic fields are associated with many astronomical objects.
Magnetic-Field Lines Imaginary lines used to visualize a magnetic field. Magnetic field lines are related to the strength of the magnetic object’s influence and point in the same direction as a compass needle would.
Magnetopshere A region of space above the Earth’s (or other planet’s) atmosphere where magnetic fields influence the motions of charged particles. The magnetosphere magnetically deflects or traps charged particles from space that would otherwise bombard the planet’s surface.
Mantle The interior region of a terrestrial (rocky) planet or other solid body that is below the crust and above the core.
Maria A dark, flat, large region on the surface of the Moon. The term is also applied to the less well-defined areas on Mars. Although maria literally means ‘seas,’ watery regions do not exist on the Moon or Mars. Marias on the Moon may be evidence of past volcanic lava flows.
Mars The fourth planet in the solar system and the last member of the hard, rocky planets (the inner or terrestrial planets) that orbit close to the Sun. The planet has a thin atmosphere, volcanoes, and numerous valleys. Mars has two moons: Deimos and Phobos.
Marshall Space Flight Center (MSFC) NASA center overseeing the research, development, and implementation of three primary areas essential to space flight: reusable space transportation systems, generation and communication of new scientific knowledge, and management of all space lab activities. Located in Huntsville, Alabama, the center aided in the design, development, and construction of the Hubble Space Telescope.
Martian Meteorites Meteorites which originate from Mars, also known as SNC meteorites. Their martian origin is demonstrated by bubbles of gas trapped within them which have identical composition to the atmosphere of Mars.
Mass A measure of the total amount of matter contained within an object.
Matter-Antimatter Annihilation A highly efficient energy-generation process in which equal amounts of matter and antimatter collide and destroy each other, thus producing a burst of energy.
Megaparsec (MPC) Equals one million parsecs (3.26 million light-years) and is the unit of distance commonly used to measure the distance between galaxies.
Mercury The closest planet to the Sun. The temperature range on Mercury’s surface is the most extreme in the solar system, ranging from about 400° C (750° F) during the day to about -200° C (-300° F) at night. Mercury, which looks like Earth’s moon, has virtually no atmosphere, no moons, and no water.
Meteor A bright streak of light in the sky caused when a meteoroid enters the Earth’s atmosphere. The streak of light is produced from heat generated by the meteoroid traveling into the Earth’s atmosphere.
Meteorite A meteor that reaches the earth’s surface. There are many types of meteorites, the most important for astrobiology being the carbonaceous chondrites which contain organic material, and the martian meteorites.
Meteorite The remains of a meteoroid that plunges to the Earth’s surface. A meteorite is a stony or metallic mass of matter that did not completely vaporize when it entered the Earth’s atmosphere.
Meteoroid A small, solid object moving through space. A meteoroid produces a meteor when it enters the Earth’s atmosphere.
Microlensing Gravitational lensing of a star indicated by the brightening of the star as the lensing object moves in front of it. Analysis of the light curve of a microlensing event can reveal the presence of an extrasolar planet.
Micrometeoroid A very small meteoroid with a diameter of less than a millimeter. Micrometeoroids form the bulk of the interplanetary solid matter scattered throughout the solar system.
Milky Way Galaxy The Milky Way, a spiral galaxy, is the home of Earth, the Sun, and the rest of our solar system. The Milky Way contains more than 100 billion stars, has a diameter of 100,000 light-years, and belongs to the Local Group of galaxies. The Sun is about 28,000 light-years from the Milky Way’s center in the Orion spiral arm.
Miller Urey Experiment An experiment carried out by Stanley Miller and Harold Urey in 1952 which demonstrated the synthesis of amino acids in conditions simulating a thunderstorm on the early Earth.
Miller-Urey Experiment An experiment that simulated the conditons on primitive Earth that led to the origin of life.
Mitochondria The organelles in eukaryotic cells in which aerobic respiration takes place, providing a supply of chemical energy (in the form of ATP) for the cell.
Molecular Cloud A cloud of cool gas in interstellar space. These clouds provide the raw material out of which new stars form and contain many types of interstellar molecules.
Molecular Cloud A relatively dense, cold region of interstellar matter where hydrogen gas is primarily in molecular form. Stars generally form in molecular clouds. Molecular clouds appear as dark blotches in the sky because they block all the light behind them.
Molecular Velocity The average speed of the molecules in a gas of a given temperature.
Molecule A tightly knit group of two or more atoms bound together by electromagnetic forces among the atoms’ electrons and nuclei. For example, water (H2O) is two hydrogen atoms bound with one oxygen atom. Identical molecules have identical chemical properties.
Moon A large body orbiting a planet. On Earth’s only moon, scientists have not detected life, water, or oxygen on this heavily cratered body. The Moon orbits our planet in about 28 days.
Multi-Layer Insulation (MLI) A ‘skin’ or blanket of insulation covering the Hubble Space Telescope, which protects the observatory from temperature extremes. This insulation protects the telescope from the cold of outer space and also reflects sunlight so that the telescope does not become too warm. The MLI on Hubble is made up of many layers of aluminized Kapton, with an outer layer of aluminized Teflon.

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