Why is wanderer an appropriate word for describing a planet

Our word "planet" comes from the Greek word planetes , meaning "wanderer. To the people of many ancient civilizations, the planets were thought to be deities. Our names for the planets are the Roman names for these deities. For example, Mars was the god of war and Venus the goddess of love. Plato wondered why the starlike planets moved relative to the stars. However, as many other celestial bodies of a similar size were discovered, scientists had to decide whether to include these newly discovered celestial bodies as new planets.

In , when scientists came up with their three point definition of a planet, it was recognized that Pluto fulfilled the first two points, but did not fulfill the third. The third stated that a planet had to dominate and clear the neighborhood of its orbit. Scientists identified two areas in which Pluto did not do this. It was, therefore, decided that Pluto was not a planet and was then demoted to the status of a dwarf planet.

If we use roundness as an important distinction for objects, what should we call moons? Should moons be considered planets if they are round and asteroids if they are not round? Or are they somehow different from planets and asteroids altogether? For much of human history, it was the only Moon known, so there was no need to have a word that referred to one celestial body orbiting another. This changed when Galileo discovered four large objects orbiting Jupiter.

This makes people think the technical definition of moon is a satellite of another object, and so we call lots of objects that orbit Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, Eris, Makemake, Ida and a large number of other asteroids moons. When you start to look at the variety of moons, some, like Ganymede and Titan, are larger than Mercury.

Some are similar in size to the object they orbit. Some are small and irregularly shaped, and some have odd orbits. If we try to fix the definition for what is a moon and how that differs from a planet and asteroid, we are likely going to have to reconsider the classification of some of these objects, too. You can argue that Titan has more properties in common with the planets than Pluto does, for example.

The most recent naming challenge astronomers face arose when they discovering planets far from our Solar System orbiting around distant stars. These objects have been called extrasolar planets, exosolar planets or exoplanets. Astronomers are currently searching for exomoons orbiting exoplanets. Ideas for how planets form also suggest that there are planetary objects that have been flung out of orbit from their parent star.