Difference between inner and outer planets
The solar system is a system of eight planets , moons, asteroids and other celestial bodies orbiting the sun. Outside our solar system, thousands of exoplanets have been discovered orbiting their host stars. Some host stars can have dozens of planets. Most of the characteristics of planets differ from planet to planet. Still, there are some salient differences between inner and outer planets. The main difference between inner and outer planets is that inner planets have a high temperature compared to outer planets. This article mainly focuses on the differences between the inner and outer planets of our solar system.
What are the inner planets?
As the term inner suggests, inner planets are the planets closest to the sun. Inner planets are also known as terrestrial planets and are mainly made up of rocks and metals. They are small compared to the outer planets. They have a solid surface and a molten metal core.
Scientists believe that these planets emerged from a nebula. A nebula is a massive cloud of dust and gas. The cloud collapsed as the gravitational pull pulled the material together. Most of the material accumulated in its center to form the sun. The rest of the matter continued to contract as it rotated and was flattened into a disk called a protoplanetary disk. The light gases were swept away from the interior of the solar system by the strong solar radiation . The heavy rock particles inside the disk formed planetesimals and eventually inner planets.
In our solar system, the four innermost planets Mercury, Venus, Earth and Mars are called the inner planets. They lie within the asteroid belt. They have volcanoes and valleys and are very hot compared to outer planets. The first two planets Mercury and Venus have no moons, while a moon orbits the third planet Earth. Mars, the outermost inner planet, has two natural satellites or moons.
Earth is the dominant planet of four inner planets, and all inner planets are almost the same in size and composition. Hence the four inner planets are sometimes referred to as Earth-like planets.
What are the outer planets?
The light gases and ice in the outer part of the protoplanetary disk attracted and stuck together, forming large celestial bodies. Eventually they collided with each other and merged into massive gas giants known as the outer planets. All of these planets are beyond the asteroid belt.
There are four outer planets in our solar system, namely Jupiter, Saturn, Uranus and Neptune. They are large compared to inner planets. Jupiter is the largest outer planet while Uranus is the smallest. All outer planets have many moons and thin ring systems of dust and rocks. Their thick atmosphere consists mainly of hydrogen and helium. They are very cold as they are far from the sun. Sometimes the last two planets Uranus and Neptune are referred to as ice giants.
However, the former ninth planet, Pluto, is no longer considered a planet. It's a dwarf planet. ( Why is Pluto no longer a planet )
Difference between inner and outer planets
Inner planets: Inner planets are also known as terrestrial planets or earth-like planets .
Outer planets: Outer planets are known as gas giants .
Members of the category
Inner planets: Mercury, Venus, Earth and Mars are the four inner planets of the solar system.
Outer planets: Jupiter, Saturn, Uranus and Neptune the four outer planets of the solar system.
Inner planets: Inner planets are denser compared to outer planets.
Outer planets: Outer planets are less dense compared to inner planets.
Nature of the atmosphere
Inner planets: The atmosphere of the inner planet is thin. (Mercury has no atmosphere).
Outer planets: The atmosphere of the outer planets is very thick.
Inner planets: Most of the inner planets are smaller than the outer planets. Earth is the largest inner planet while Mercury is the smallest.
Outer Planets: Most of the outer planets are very large. Jupiter is the largest, Neptune the smallest.
Inner planets: Inner planets have a high temperature.
Outer planets: Outer planets are cold compared to inner planets.
Inner planets: Inner planets rotate slowly.
Outer planets: Outer planets rotate faster than the inner planets.
Speed of rotation
Inner planets: Inner planters orbit the sun quickly.
Outer planets: Outer planets orbit the sun slowly compared to inner planets.
Inner planets: Inner planets lie within the asteroid belt.
Outer planets: Outer planets are beyond the asteroid belt.
Number of moons
Inner planets: only Earth and Mars have moons. One moon orbits the earth and two moons orbits Mars.
Outer Planets: All inner planets have many moons.
Inner planets: Inner planets do not have rings.
Outer planets: Outer planets have rings.
"Inner Planets" by NASAMercury Image: JHUAPLVenus Image: JPLMars Image: HST - Mercury Globe-MESSENGER mosaic centered at 0degN-0degE.jpgVenus globe.jpgThe earth seen from Apollo 17.jpgMars 23 August 2003 hubble.jpg, (Public Domain) via Commons Wikimedia
Outer Planets from NASA - JPL (Public Domain) image via Commons Wikimedia