Classical planet Classical planet In classical antiquity, the seven classical planets were the seven non-fixed astronomical objects in the sky visible to the naked eye: Mars, Jupiter, Venus, Saturn, Mercury, the Sun, and the Moon. The word "planet" comes from two related Greek words, πλάνης "planēs" (whence πλάνητες ἀστέρες "planētes asteres" "wandering stars, planets") and πλανήτης "planētēs", both with the original meaning of "wanderer", expressing the fact that these objects move across the celestial sphere relative to the fixed stars. The term "planet" in modern terminology is only applied to natural satellites directly orbiting the Sun, so that of the seven classical
Terrestrial planet on "Kepler" space mission data, that there could be as many as 40 billion Earth- and super-Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way. 11 billion of these estimated planets may be orbiting Sun-like stars. The nearest such planet may be 12 light-years away, according to the scientists. However, this does not give estimates for the number of extrasolar terrestrial planets, because there are planets as small as Earth that have been shown to be gas planets (see KOI-314c). Several possible classifications for terrestrial planets have been proposed: Terrestrial planet A