Why Are Planets Round

Have you ever wondered why all the planets are mostly round? The spherical shape of all the planets is caused by gravity. When the planets in our solar system began to form, space was filled with billions and billions of pieces of dust and gas.

As these pieces bumped into each other, they began to form clumps that slowly grew larger and larger. Eventually these clumps of material grew large enough to develop their own gravitational fields. As the forming planets continued to grow, the force of the collisions with additional matter caused them to become hot and molten. Each planet's gravitational force is centered at its core. It pulls equally in every direction from the core, thus pulling all the molten material into a spherical shape. Scientists call this process "isostatic adjustment."

Think of a bicycle wheel. The center of the wheel is like the core of a planet, where the planet's center of gravity is. The gravity pulls equally in every direction, like the spokes of the wheel. The natural shape of the wheel formed as a result is a circle. In the case of a three-dimensional object, it becomes a sphere.

Planets are not actually perfectly round, because they also spin. When planets spin, the forces created by spinning work against gravity, causing planets to bulge out around their equators. Scientists call this extra width the "equatorial bulge." None of this has anything to do with getting older and developing our own human 'equatorial bulge' around the middle.

Pluto and the Naming of the Planets

With all the publicity surrounding the recent photos of Pluto, Seems fitting to look at it and the other (real) planets and how they received their names. Pluto is the largest and second-most-massive known dwarf planet in the Solar System and the ninth-largest and tenth-most-massive known object directly orbiting the Sun.

It had been discovered many times by astronomers, who did not realize what they found. It was discovered 'for real' in 1930 by Clyde Tombaugh, and was originally considered the ninth planet from the Sun. After 1992, its status as a planet fell into question following the discovery of several objects of similar size, in particular Eris, which is 27% more massive than Pluto. This led the International Astronomical Union to define the term planet formally for the first time. This definition excluded Pluto and reclassified it as a member of the new "dwarf planet" category. The other dwarf planets are Ceres, Eris, Haumea, and Makemake (sic).

The tradition of naming planets after mythological gods was passed continued after Roman names for the five extraterrestrial planets they were aware of.

• Earth is the only planet not named for a mythological god.
• Venus is named after the goddess of love. It is thought this planet got its name from the fact that it is “pretty” to look at as the third most bright object in our solar system in the sky as viewed from Earth (after the Sun and the Moon).
  
• Mercury is named after the god of thievery, tradesmen or commerce, and travel. It is thought that the planet probably was named such due to how quickly, relatively speaking, it travels across the sky.
• Pluto, although no longer a "real" planet is named after the god of the underworld. The name was proposed by Venetia Burney, a then eleven-year-old schoolgirl in Oxford, England, who was interested in classical mythology.
• Saturn is named after the Roman god of agriculture. It followed the Greek designation for Cronus. In modern Greek, the planet retains its ancient name Cronus—Κρόνος: Kronos.
  
• Neptune was named after the god of the sea. It got its name thanks to the fact that it has a blue color.
  
• Uranus is named after the very early god of the sky (and father to the Titans).
• Mars was named after the Roman god of war. It’s thought that it was labeled such based on the reddish hue of the planet, relating to blood.
• Jupiter is named after the god of thunder and the sky, and king of the gods. It is probable that it was named such as it is the largest non-star in our solar system.

Incidentally, many languages have their own name for Earth, such as ‘terra’ in Portuguese, ‘dünya’ in Turkish and ‘aarde’ in Dutch. However, the common thread in all languages is that they were all derived from the same meaning, which is ‘ ground’ or ‘soil’. The modern English word and name for our planet Earth likely extends back more than 1,000 years. The name was also found in early English translations from the bible.