The ordinary astronomical term for a planet, such as Earth, Mars, or Jupiter.
Earth is a planet that orbits the Sun.
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.
This young team is attracting attention as the dark horse of the tournament.
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