Hydrogen, and helium. These are currently the most common elements in the Universe.
Very little is known about the make up of the surface of the outer planets. The outer planets are generally referred to as gas giants. While most of them are made up of mostly gasses, it is is believed that their cores are made up of liquified heavy metals.
Becuase they are eather too hot, cold, have poisonus gasses, or don't have an atmosphere we can breathe.
Jupiter and most of the planets.
The inner planets
Jupiter, Saturn, Uranus, and Neptune are often referred to as gas giants. They are composed mostly of hydrogen and helium, with no solid surface. These planets are also much larger in size compared to the terrestrial planets like Earth and Mars.
By mass, the majority of the matter orbiting the sun is hydrogen and helium. When the solar system was just starting to form heat from the sun and the strong solar wind drove most of the hydrogen, helium, and other gasses out of the inner solar system, leaving behind mostly rock and metal, which were much less abundant. The sunlight and solar wind in the outer solar system were much less intense, so these gasses remained in place long enough to become part of the giant planets.
The most obvious difference between terrestrial and jovian planets is their composition. Terrestrial planets are rocky and dense, while jovian planets are mostly composed of gases and lack a solid surface. Additionally, jovian planets are typically larger in size and have extensive ring systems.
Most of the gasses were swept out of the inner solar system by the solar wind, leaving rock as the most abundant material to form planets and moons.
Jupiter NeptuneThe planet that most extrasolar planets resembles Jupiter.Jupiter(apex)Most of the confirmed Exoplanets are larger gaseous planets with large masses. These are easier to detect and confirm due to their size. They most resemble Jupiter, although many are thought to be much larger than our largest planet.
Nitrogen and oxygen.
Yes, the four outer planets (Jupiter, Saturn, Uranus, and Neptune) have the most gravity in our solar system due to their larger size and mass compared to the inner planets. For example, Jupiter, the largest of the planets, has the strongest gravitational force.
Most planets have at least one moon (or natural satellite), with the exception of Mercury and Venus, which have no moons. The larger outer planets have many moons, Jupiter alone has over 60 named moons.