Planetballs are circle-Drawn (though no circle tool) characters in the Polandball universe, similar to countryballs. They represent Planets, Moons, Dwarf Planets, Stars, Star Remants, black holes, and even Parallel Universes. Space Probes and Asteroids also appear but they aren't drawn in ball shape. They have been a little-known staple of Polandball since its founding on Krautchan, they can be crossed over with polandball comics (e.g: Sunball making a cameo in a comic about Germany & Sweden).
The most Poland-like planet is Plutoball, which cannot into planet like Poland cannot into space
(well Polandball went into space once in a video in no idea animations gylala and a few more well its like Polandball went into space and Plutoball was a planet) Earth is similar to USAball ( USAball thinks he owns Earth and the moon because he one the space race and the first person on the moon) Classic jokes include how the Sun will 'betray' the solar system by becoming a red giant, and how Uranus is made fun of, and how Mars hates Earth for throwing probes/having life.
Major communities of Planetball include /r/Planetball which was founded in 2013, and here. Popularity of Planetball ranges from time to time.