Mercury is the innermost and smallest planet in the solar system, and has been visited by two spacecraft missions: Mariner 10 and MESSENGER.
Venus is the second planet from the sun and the hottest and most inhospitable one. It has been explored by many spacecraft missions, such as Venera, Pioneer Venus, Magellan, Venus Express, and Akatsuki.
The Moon is the natural satellite of Earth and the only celestial body that humans have landed on. It has been explored by many spacecraft missions, such as Luna, Ranger, Surveyor, Apollo, Zond, Lunar Orbiter, Clementine, Lunar Prospector, SMART-1, Chandrayaan, Lunar Reconnaissance Orbiter, Chang'e, GRAIL, LADEE, and Artemis.
Mars is the fourth planet from the sun and the most similar to Earth in terms of climate and geology. It has been explored by many spacecraft missions, such as Mariner, Viking, Mars Global Surveyor, Mars Pathfinder, Mars Odyssey, Mars Express, Spirit, Opportunity, Mars Reconnaissance Orbiter, Phoenix, Curiosity, MAVEN, Mars Orbiter Mission, ExoMars, InSight, Hope, Tianwen-1, and Perseverance.
Jupiter is the fifth planet from the sun and the largest and most massive one in the solar system. It has been explored by many spacecraft missions, such as Pioneer, Voyager, Galileo, Cassini, New Horizons, and Juno.