Our solar system consist of the sun, nine planets (and their moons), an asteroid belt, many comets and meteors. The sun is the center of our solar system, with the planets, their moons, comets, asteroids, and other gases and rocks all in orbit around the sun.
The nine planets (in order from the sun) are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. A belt of asteroids (minor planets made of rock and metal) lies between Mars and Jupiter. These objects all orbit the sun in roughly circular orbits that lie in the same plane (Pluto is an exception; it has an elliptical orbit tilted over 17 from the ecliptic.
The largest planet is Jupiter; it is followed by Saturn, Uranus, Neptune, Earth, Venus, Mars and Mercury.
The Inner Planets Verses the Outer Planets
The inner planets (those planets that orbit the close to the sun) are quite different from those that orbit further from the sun (outer planets). The inner planets are Mercury, Venus, Earth and Mars. They are relatively small, composed of mostly rock, and have few or no moons. The outer planets on the other hand are larger, are ringed, have many moons and are composed of mostly gas. These planets include Jupiter, Saturn, Uranus and Neptune. Pluto is also an outer planet but it’s small, composed more so of rock and has only one moon.
Temperature on the Planets
Generally the further from the sun one is to travel, the colder the planet. Venus is an exception because it has a thick atmosphere and greenhouse gases have warmed to significantly.
Density and Mass of the Planets
The outer, gaseous planets are much less dense then the inner, rocky planets. The Earth is the densest planet, while Saturn is the least dense it could float on water.
Jupiter is by far the most massive planet; Saturn trails it, followed by Uranus, Neptune, Earth, Venus, Mars and Pluto.
Gravitational Forces on the Planets
The planet with the strongest gravitational attraction at its surface layer is Jupiter. Although Saturn, Uranus and Neptune are also very massive planets, their gravitational forces are about the same as Earth. This is because the gravitational force planet exerts upon an object at the planet’s surface, is about the same as its mass and to the inverse of the planet’s radius squared.
A Day on Each of the Planets
A day is about the amount of time it takes for a planet to rotate 360 on its axis. A day on Earth is almost 24 hours. Jupiter has the shortest day of 9.8 Earth hours, while Venus has the longest day of 248 Earth days.
Average Orbital Speed of the Planets
As the planets orbit the sun, they travel at different speeds. Each planet speeds up when it’s closer to the sun, and slows down when it’s further from the sun.