Exoplanets and Space Exploration

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Exoplanet Noun

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[ek-so-plan-it]

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Exoplanet

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A planet that is located outside of our solar system, orbiting a star other than the Sun.

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Example: An exoplanet is a planet that orbits a star outside our solar system, like the planets shown orbiting the star Kepler-90.

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Extrasolar Planet Noun

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[ek-struh-soh-ler plan-it]

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Extrasolar Planet

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An alternative scientific term for an exoplanet, meaning a planet that exists beyond our own solar system.

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Example: This image shows the size of a common type of extrasolar planet by comparing it to Earth and Jupiter, illustrating that exoplanets come in various sizes.

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Terrestrial Planet Noun

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[tuh-res-tree-uhl plan-it]

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Terrestrial Planet

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A type of planet that is primarily composed of silicate rocks or metals and possesses a solid surface.

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Example: This image shows the four terrestrial (or inner) planets of our solar system: Mercury, Venus, Earth, and Mars, which are all rocky planets.

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Gas Giant Noun

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[gas jai-uhnt]

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Gas Giant

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A very large planet composed mainly of hydrogen, helium, and other gases, lacking a well-defined solid surface.

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Example: This image shows the four gas giants in our solar system—Jupiter, Saturn, Uranus, and Neptune—which are large planets composed mostly of gases.

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Rogue Planet Noun

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[rohg plan-it]

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Rogue Planet

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A planetary-mass object that does not orbit a star and instead drifts through interstellar space on its own.

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Example: A rogue planet is a planet that does not orbit a star and drifts through space on its own.

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Habitable Zone Noun

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[hab-i-tuh-buhl zohn]

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Habitable Zone

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The specific orbital range around a star where surface temperatures could potentially allow for liquid water to exist.

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Example: The habitable zone is the orbital region around a star where a planet's surface temperature is 'just right' to allow liquid water to exist.

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Transit Method Noun

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[tran-sit meth-uhd]

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Transit Method

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A technique for detecting exoplanets by measuring the slight, periodic dimming of a star's light as a planet passes.

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Example: When a planet passes in front of its star, it blocks a small amount of the star's light, causing a temporary dip in brightness.

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Doppler Spectroscopy Noun

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[dop-ler spek-tros-kuh-pee]

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Doppler Spectroscopy

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A method for finding exoplanets by analyzing the shift in a star's spectrum caused by its gravitational wobble.

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Example: An unseen planet's gravity makes its star wobble, causing the starlight we see to shift towards blue (moving closer) or red (moving away).

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Radial Velocity Noun

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[rey-dee-uhl vuh-los-i-tee]

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Radial Velocity

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The speed of a star moving towards or away from an observer, which varies due to an orbiting planet's gravity.

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Example: An unseen planet's gravity makes its star wobble, changing the color of the starlight we see (Doppler shift), which helps us detect the planet.

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Doppler Shift Noun

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[dop-ler shift]

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Doppler Shift

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The change in the frequency or wavelength of light from a source due to its motion relative to the observer.

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Example: When a light source moves towards an observer, its light waves appear compressed (blueshift); when it moves away, the waves appear stretched (redshift).