The ordinary astronomical term for a planet, such as Earth, Mars, or Jupiter.
地球は太陽の周りを回る惑星です。
Earth is a planet that orbits the Sun.
木星は太陽系で最も大きな惑星だ。
Jupiter is the largest planet in the solar system.
dark horse; surprise contender
Figurative use for an unexpected strong contender, especially in sports, contests, or elections. Expressions such as 台風の目 may be more common in everyday commentary.
この若いチームは今大会の惑星として注目されている。
This young team is attracting attention as the dark horse of the tournament.
無名の候補者が選挙戦の惑星になった。
An unknown candidate became the surprise contender in the election race.
Earth is a planet that orbits around the sun.
An unknown newcomer is being talked about as the dark horse of this competition.
The astronomers discovered a new planet outside the solar system.
惑星 specifically means 'planet', a body that orbits a star, whereas 星 broadly covers stars and other celestial objects and doesn't distinguish planets.
惑星 means a full-sized planet like Earth or Mars, while 小惑星 refers to a much smaller rocky body orbiting the sun, mainly in the asteroid belt.
major planet · giant planet; Jovian planet
planetesimal