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A range of theoretical habitable zones with stars of different mass. Earth is the only Goldilocks planet in our solar system (shown at center, not to scale).

"Goldilocks planet" is a colloquial term for a planet that falls within a star's habitable zone, often specifically used for planets close to the size of Earth.^[1][2] The name comes from the story of Goldilocks and the Three Bears, in which a little girl chooses from sets of three items, ignoring the ones that are too extreme (large or small, hot or cold, etc.), and settling on the one in the middle, which is "just right". Likewise, a planet following this Goldilocks Principle is one that is neither too close nor too far from a star to rule out life (as humans understand it) on the planet.

Goldilocks planets are of key interest to researchers looking either for existing (and possibly intelligent) life or for future homes for the human race. The Drake equation, which attempts to estimate the likelihood of non-terrestrial intelligent life, incorporates a factor (n_e) for the average number of life-supporting planets in a star system with planets. The discovery of extrasolar Goldilocks planets helps to refine estimates for this figure. Very low estimates would contribute to the Rare Earth hypothesis, which posits that a series of extremely unlikely events and conditions led to the rise of life on Earth. High estimates would reinforce the Copernican mediocrity principle, in that large numbers of Goldilocks planets would imply that Earth is not especially exceptional.

Finding Earth-sized Goldilocks planets is a key part of the Kepler Mission, which uses a space telescope (launched on 7 March 2009 UTC) to survey and compile the characteristics of habitable-zone planets.^[3]

Although the extrasolar planet 70 Virginis b was initially nicknamed "Goldilocks" because it was thought to be within the star's habitable zone, it is now believed to be far too warm to be "just right" for life, and is thus not a Goldilocks planet.^[4] Gliese 581 d is currently believed to be a rocky planet lying within the habitable zone of its star.

References

Exoplanets Classes Carbon planet • Chthonian planet • Circumbinary planet • Cold Jupiter • Cold Neptune • Desert planet • Eccentric Jupiter • Goldilocks planet • Hot Jupiter • Hot Neptune • Jovian planet • Ocean planet • Pulsar planet • Super-Earth • Terrestrial planet Systems Binary star • Hypothetical extrasolar planet • Interstellar planet • Planetary system • Extrasolar moon Missions COROT • Kepler Mission • PEGASE • Space Interferometry Mission • New Worlds Mission • Terrestrial Planet Finder • Darwin (ESA) See also: Stars with extrasolar planets • Extrasolar planet extremes • Unconfirmed exoplanets

Definition from Wiktionary, a free dictionary

English

Etymology

From children's story, "not too hot, not too cold".

Noun

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Goldilocks planet

Wikipedia

Goldilocks planet

1. Colloquial term used to describe a planet with conditions suitable for life.