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The study of the origin, evolution, distribution, and future of life in the universe. Example: NASA's search for microbial life on Mars is a project in astrobiology.

Organisms that thrive in physically or geochemically extreme conditions that are detrimental to most life on Earth. Example: Thermophiles living in hydrothermal vents.

Indicators of past or present life, either direct or indirect, that provide scientific evidence of life. Example: The presence of methane in Mars' atmosphere could be a biosignature.

The suitability of an environment to support life, typically referring to celestial bodies that may support Earth-like life. Example: The habitability zone around a star where water can exist as a liquid.

Hypothesis that life exists throughout the Universe and is distributed by space dust, meteoroids, asteroids, comets, planetoids or potentially by spacecraft in the form of unintended contamination by microorganisms. Example: The discovery of extremophiles in meteorites supports panspermia.

Life that currently exists, as opposed to extinct life, which once existed on Earth or elsewhere. Example: Studying extremophiles as models for extant life on other planets.

An equation used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy. Example:

The apparent contradiction between the high probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations. Example: Despite the vastness of the Milky Way, we have no conclusive contact with alien life.

One of Jupiter's moons, believed to harbor a subsurface ocean beneath its icy crust, making it a target of interest for astrobiological research. Example: The future Europa Clipper mission aims to assess Europa's habitability.

Planets that orbit a star outside the solar system. Example: The Kepler space telescope has discovered thousands of exoplanets.

A situation where an astronomical body always faces the same side towards the object it is orbiting due to gravitational forces. Example: The Moon is tidally locked to Earth.

The natural process of life arising from non-living matter, such as simple organic compounds. Example: The Miller-Urey experiment simulated early Earth conditions to test abiogenesis.

The hypothetical process of deliberately modifying the atmosphere, temperature, surface topography, or ecology of a planet or moon to make it habitable for Earth-like life. Example: Concepts for terraforming Mars include importing ammonia.

An organism (often a bacterium or fungus) that lives inside rock, coral, animal shells, or in the pores between mineral grains. Example: Bacteria found living in deep subsurface rocks.

Microorganisms that produce methane as a metabolic byproduct in anoxic conditions. Example: Methanogens are considered in the search for life on Mars due to methane plumes detected in the atmosphere.

The speculative branch of astrobiology that studies the potential forms and behaviors of extraterrestrial animals. Example: Theoretical models of silicon-based life forms.

A state in which an organism's metabolic activities come to a reversible standstill, allowing it to survive in inhospitable conditions. Example: Tardigrades entering cryptobiosis to survive extreme dehydration.

The region around a star where conditions might be right to allow liquid water to exist, which is thought to be necessary for life as we know it. Example: Earth is located in the Sun's circumstellar habitable zone.

The biological conversion of one or more carbon molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic molecules as a source of energy, rather than sunlight (as in photosynthesis). Example: Giant tube worms near hydrothermal vents relying on chemosynthesis.

The study of the interactions between living organisms and their space environments. Example: Research on how plants might grow in Martian soil.

An environment that lacks oxygen. Example: Some extremophiles can metabolize in anoxic conditions, which could be similar to subsurface environments on Mars.

The branch of science that deals with the possibility and likely nature of life on other planets or in space. Example: The study of potential cellular structures of life forms on Europa.

The study of the abundance and reactions of chemical elements and molecules in the universe, and their interaction with radiation. Example: Identifying complex organic molecules in interstellar clouds.

The process by which elements are created within stars by combining the protons and neutrons together from the nuclei of lighter elements. Example: The formation of carbon from lighter elements in a star's core.