EEV: Earth Entry Vehicle.

EFS: Entry Flight System.

EJSM: Europa Jupiter System Mission (proposed NASA-ESA mission).

electromagnetic induction: Production of voltage across a conductor due to a changing magnetic flux.

ELT: Extremely Large Telescope.

emission spectrum: A spectrum composed solely or predominantly of emission lines, indicating the presence of a hot gas and a nearby source of energy.

endogenic: Relating to a process of internal origin.

EPO: Education and public outreach.

EPOXI: The name of the extended mission of NASA’s Deep Impact spacecraft—a combination of Extrasolar Planet Observation and Characterization and Deep Impact Extended Investigation, the two phases of the extended mission.

ESA: European Space Agency.

ESMD: Exploration Systems Mission Directorate (NASA).

exogenic: Relating to a process of external origin.

exoplanets: Planets formed around stars other than the Sun.

felsic rock: A class of rock that crystallizes from silicate minerals at relatively low temperatures and has a high percentage of silica.

fluvial: Relating to flowing water or, by extension, another flowing liquid.

flux: A measure of the energy or number of particles passing through a given area of surface in unit time.

FUSE: Far Ultraviolet Spectroscopic Explorer (NASA).

GCM: General circulation model.

GN&C: Guidance, navigation, and control.

Gossamer ring: The outermost ring of Jupiter.

GRAIL: Gravity Recovery and Interior Laboratory (NASA mission).

GSFC: Goddard Space Flight Center (NASA).

Gusev crater: A 144-km-wide crater located some 15 degrees south of the equator of Mars that was the landing site for Spirit, one of the Mars Exploration Rovers.

Hadley-like convection: A type of circulation pattern seen in planetary atmospheres: warm, low-density material rises near the equator, flows toward the poles, and cools; cooler, high-density material sinks in the subtropics and flows equatorward along the surface.

HDO: A form of water in which one hydrogen atom is replaced by a deuterium atom.

Hesperian period: The middle of three broad time periods into which the geologic history of Mars has been divided, extending roughly from about 3.5 billion to about 1.8 billion years ago.

H/He ratio: Hydrogen-to-helium ratio.

HST: Hubble Space Telescope.

hydrosphere: All bodies of water on a planet, as distinguished from the lithosphere and the atmosphere.

hydrothermal: Relating to the action of hot liquid or gas within or on the surface of a planet.

ICE: Independent cost estimate; a specific methodology for determining the cost of a spacecraft mission.

IDP: Interplanetary dust particle.

ILN: International Lunar Network.

ionosphere: The region of a planet’s atmosphere that is kept partially ionized by solar ultraviolet and x-ray irradiation.

IR: Infrared.

IRTF: Infrared Telescope Facility (NASA ground-based telescope).

ISIS: Integrated Software for Imagers and Spectrometers.

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