9 Planets | Universe Today

Written by Abby Cessna

Planets and the dwarf planets. Image credit: IAU

Although several years ago the number of planets in our Solar System was reduced to eight – an issue that has caused much heated debate and upset many people – for over seventy years, there were 9 planets in our Solar System. Many people still want to see Pluto restored to the status of a planet  and not just because of sentimentality.

If Pluto was still a planet, Mercury would only be the second smallest planet. Although Mercury is even smaller than a couple of our Solar System's moons, Ganymede and Titan, it is much more massive because it is so dense.

Venus is nearly the same size as Earth, but size is the only similarity. Hidden by thick yellow clouds of toxic gas, the planet is a barren, burning landscape with many volcanoes. With only a few exceptions, all of the physical features on the planet were named after females.

Earth is the densest planet in our Solar System and the largest of the four inner planets. Our world has also been nicknamed the Blue Planet. It has one relatively large satellite known simply as the Moon.

Mars is only about half the size of Earth with a much lower density. With a thin atmosphere, the planet’s surface is easy to see. The planet gets its red color from the large amount of iron oxide present on the surface.

In order to understand Jupiter’s size, you need a comparison. The fifth planet from the Sun has a mass almost one-thousandth the Sun’s mass. However, Jupiter’s mass is also two and a half times greater than the mass of the other seven planets combined. In addition to being the largest planet, Jupiter also has the largest moon, Ganymede.

The second largest planet in our Solar System, the most distinctive feature of Saturn is its large planetary ring system. These rings are composed of ice, rock, and other small particles.

Uranus was the first planet discovered since ancient civilizations, such as the Greeks, discovered the first five planets. Found in the late 1700’s, Uranus is an ice giant, which is a subcategory of gas giants. There is a higher proportion of “ices,” such as methane and ammonia, in the planet than there is in the other gas giants.

Neptune is also an ice giant, and both Neptune and Uranus get their blue color from the methane in the atmosphere. Neptune has the fastest winds of any planet, reaching more than 2100 kilometers per hour.

Pluto was the ninth and smallest planet in our Solar System. It was discovered by the astronomer Clyde Tombaugh in 1930. Astronomers originally thought that Pluto was the elusive Planet X, which astronomers had been searching for, but it was soon proven that Pluto could not be Planet X. Astronomers soon came to the realization that there was no Planet X.

Universe Today has articles on nine planets and why Pluto is no longer a planet.

If you are looking for more information on 9 planets, check out all about the planets and an overview of the Solar System.

Astronomy Cast has episodes on all the planets including Mercury.

Filed under: Astronomy