Astrobiology Glossary I – Space

Term Definition
Image Intensifier A device capable of intensifying light from a faint source so that it may be more easily detected.
Impact When one body strikes another with great force. Some examples include a meteor colliding with the Moon or a comet, such as Shoemaker-Levy 9, slamming into Jupiter.
Impact Event A collision between two solar system bodies that releases exceptionally large amounts of energy. Some examples are the 1908 Siberian Tunguska impact by a comet or an asteroid and the asteroid that struck Earth 65 million years ago, which may have led to the extinction of the dinosaurs and other species of the Cretaceous-Tertiary era.
Impact Frustration The hypothesis that during the heavy bombardment phase, impacts of massive objects may have wiped out emerging life several times before it was able to permanently establish itself on Earth.
Inflation The theory that the universe expanded very rapidly shortly after the Big Bang.
Infrared Radiation that has longer wavelengths and lower frequencies and energies than visible light.
Infrared Telescope An instrument that collects the infrared radiation emitted by celestial objects. There are several Earth- and space-based infrared observatories. The Infrared Telescope Facility, an Earth-bound infrared telescope, is the U.S. national infrared observing facility at the summit of Mauna Kea, Hawaii. A planned space-based infrared observatory is the Space Infrared Telescope Facility (SIRTF).
Intensity The amount, degree, or quantity of energy passing through a point per unit time. For example, the intensity of light that Earth receives from the Sun is far greater than that from any other star because the Sun is the closest star to us.
Interferometer An instrument which makes use of the phenomenon of interference of light. Space interferometers may play an important role in the search for extrasolar planets.
Interferometer An instrument that combines the signal from two or more telescopes to produce a sharper image than the telescopes could achieve separately.
International Ultraviolet Explorer (IUE) The longest operating (1978-1996) and most productive ultraviolet space observatory launched into a high geosynchronous orbit.
Interplanetary Matter Dust, gas, and other debris found within the solar system.
Interplanetary Space The region of space surrounding our Sun. Asteroids, comets, Earth, and the solar wind are examples of things occupying interplanetary space.
Interstellar Dust Small particles of solid matter, similar to smoke, in the space between stars.
Interstellar Medium Interstellar space including streams of positively-charged protons moving from the stars.
Interstellar Medium (ISM) The sparse gas and dust located between the stars of a galaxy.
Interstellar Molecule Well over a hundred molecular species have been detected in gas and dust. Some of the more complex molecules found include acetic acid, acetone and ethanol.
Interstellar Space The dark regions of space located between the stars.
Inverse Square Law A law that describes any quantity, such as gravitational force, that decreases with the square of the distance between two objects. For example, if the distance between two objects is doubled, then the gravitational force exerted between them is one-fourth as strong. Likewise, if the distance to a star is doubled, then its apparent brightness is only one-fourth as great.
Invisible Radiation Radiation that the eye cannot detect, such as gamma rays, radio waves, ultraviolet light, and X-rays.
Io The innermost of Jupiter’s four large moons. Due to Jupiter’s gravitational might, Io is geologically active; its surface is peppered with volcanoes that send sulfurous eruptions into its thin atmosphere. Io appears to have the most active volcanoes in the solar system.
Io Plasma Torus A bagel-shaped region of trapped sulfur ions around Jupiter that originates from the surface of Io, one of Jupiter’s moons. Gravitational tidal forces between Jupiter, other Galilean moons, and Io cause tidal friction in Io’s interior, producing geysers that spew sulfur at tremendous speeds. Some of the sulfur ions leave Io’s surface and become trapped around Jupiter.
Ion An atom with one or more electrons removed (or added), giving the atom a positive (or negative) charge.
Ionization The process by which ions are produced, typically by collisions with other atoms or electrons, or by absorption of electromagnetic radiation.
Ionosphere A region of the Earth’s upper atmosphere where solar radiation ionizes the air molecules. This region affects the transmission of radio waves and extends from 50 to 400 kilometers (30 to 250 miles) above the Earth’s surface.
Irregular Galaxy A galaxy that appears disorganized and disordered, without a distinct spiral or elliptical shape. Irregular galaxies are usually rich in interstellar matter, such as dust and gas. The Large and Small Magellanic Clouds are examples of nearby irregular galaxies.
Isotope An atom of a given element having a particular number of neutrons in the nucleus. Isotopes of a given element differ in the numbers of neutrons within the nucleus. Adding or subtracting a neutron from the nucleus changes an atom’s mass but does not affect its basic chemical properties.

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