A dozen years ago, astronomers debated, “What is a planet?” They may soon have to wrangle another question of solar system classification: “What is a moon?”

On Tuesday, scientists led by Scott S. Sheppard of the Carnegie Institution for Science announced the discovery of a dozen moons around Jupiter, bringing the total number orbiting the solar system’s largest planet to 79. Next to the famous moons that Galileo spotted through his telescope in 1610 — bigger-than-Mercury Ganymede, deeply cratered Callisto, volcanic Io, icy Europa — the new ones are slight. They measure between a half mile and two miles wide and orbit millions of miles from the planet — good explanations for why no one had seen them until now.

As telescopes get better, astronomers will assuredly find more and more moons, smaller and smaller, around Jupiter and other giant planets orbiting the sun. When the count rises into the hundreds, maybe thousands, scientists might start to wonder whether it’s worth keeping track.

Does every pebble going around a planet qualify as a moon?

“We might have to start calling the ones that are less than a kilometer in size maybe ‘dwarf moons,’” Dr. Sheppard said. Pluto was demoted from planet to dwarf planet in 2007.