clay

Generic term for an aggregate of hydrous silicate particles less than 4 µm in diameter

comet

Relatively small planetary body similar to an asteroid but composed largely of ice

cosmic rays

High-energy particles originating outside Earth

cross strand exchange

Process in which bases along one double helix strand separate and link across to a separate double helix and vice versa


Darwin

European Space Agency’s large infrared-wavelength space interferometer

Deep Impact

NASA mission to collide a spacecraft to create a deep crater in Comet Tempel 1

Deinococcus radiodurans

Gram-positive aerobic bacteria, the most radiation-resistant organism known

dichroism

Differential absorption of left- and right-hand circularly polarized light in a material

DNA

Deoxyribonucleic acid, the molecule that carries genetic information

DOE

U.S. Department of Energy

dose

Absorbed amount of radiation

dose rate

Rate at which tissue absorbs radiation

double-strand break

Break in both strands of the DNA molecule, usually caused by oxidative stress or certain forms of radiation

D-ribose

Right-handed form of a five-carbon sugar, found in all living cells


early stars

Stars that formed primarily from hydrogen and helium and are deficient in heavier elements

endogenous

Organic matter synthesized on Earth and necessary for the appearance of life (see exogenous)

exogenous

Organic matter delivered from space and necessary for the appearance of life (see endogenous)

Exploration Initiative

U.S. multiagency Vision for Space Exploration


field reversal

Periodic reversal of the magnetic field of a star or planet

flare star

Star that sporadically flares in brightness by an order of magnitude or more


gamma ray

Most energetic form of electromagnetic radiation

gamma-ray burst

Energetic cosmic event that produces a burst of gamma rays


habitable zone

Radial zone in which certain parameters thought to be necessary for life are met

Hadean

Era in Earth’s history 4.5 to 3.8 billion years ago, before life is thought to have arisen



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