The solar system is made up by the Sun, which lies at its center and dictates pretty much everything that goes on in its gravitational field, 4 inner planets, 4 outer planets, 5 dwarf planets, and billions of other objects, including asteroids. The solar system was formed approximately 5 billion years ago from a molecular cloud that also served as the birthplace for several other stars and solar systems.
When the central star formed, only the metals and silicates could exist in the region near the sun because of their high boiling points. Thus, the inner planets, which are denser than the more massive gas giants, were formed close to the Sun, whereas gas giants such as Jupiter and Saturn were formed farther away.
►Facts About Our Solar System
✱The last planet, Neptune, is more than 4.5 billion km away from the Sun. If these gigantic distances were to be scaled down to a 100 m football pitch, the Earth would be the size of a flea!
✱Besides being the first planet, Mercury also became the smallest one after the demotion of Pluto. Mercury is actually smaller than Ganymede and Titan, moons of Jupiter and Saturn respectively, and is only slightly larger than Callisto, another of Jupiter's moons. Jupiter is by far the largest planet, and actually plays some part in interplanetary gravitational activity.
✱The five dwarf planets orbiting the Sun are Pluto, Ceres, Eris, Haumea, and Makemake. Pluto was only added to this list in 2006, based on the fact that its mass is actually smaller than Eris, a dwarf planet.
✱Over 99% of the solar system's mass is made up by the Sun. Jupiter and Saturn make up more than 90% of the rest. The four inner planets put together contain less than 0.5% of the total mass in the solar system!
✱The Sun's core, however, is much, much hotter than anything else in the solar system - 27 million°F (15 million°C)!
✱The Earth is the largest of the four inner planets.
✱Venus is one of only two planets to rotate in a clockwise direction (when viewed from the Sun's North pole), the other being Uranus. This is due to the high axial tilt of both planets. Venus is tilted at an angle of almost 180°! For comparison, the Earth is only tilted about 23°.
✱Venus is also one of only two planets to have no known satellites, the other being Mercury.
✱Venus is the hottest planet in the solar system, despite being farther from the Sun than Mercury. It has a thick atmosphere containing 96% carbon dioxide, the consequent greenhouse effect carrying the temperatures to 460°C (860°F).
✱Mercury has no atmosphere, and suffers from the largest variation in daytime and nighttime temperatures seen in the solar system: as low as −173°C (−280°F) at night to 427°C (800°F) during daytime at the equator.
✱The Earth is, of course, the only planet yet known to support life. The emergence of life on Earth has occurred due to it being in the circumstellar habitable zone of the Sun. In about 3 billion years, the Sun is expected to expand into the next stage of stellar evolution, and Earth will become inhabitable.
✱Mars, called the 'red planet', appears so due to the iron oxide deposits on its surface.
✱The second highest mountain in the solar system, Olympus Mons, is found on Mars.
The asteroid belt lies between the orbits of Mars and Jupiter. Sometimes called 'minor planets', asteroids are rocky objects that are the remnants of the Solar System when it formed. Detected asteroids range in size from just a meter or so in diameter to hundreds of kilometers. However, only around 250 are more than 100 km across, most of them tending to be about 1 km wide. Half of the total mass in the region is made up by just 4 asteroids: the dwarf planet Ceres, Vesta, Pallas, and Hygiea.
✱Jupiter, Saturn, Uranus, and Neptune are called gas giants. They are made up mainly of hydrogen and helium.
✱Uranus and Neptune are called 'ice giants', since they contain ice, ammonia, and methane under the gaseous surface.
✱Uranus has an axial tilt of about 98° (97.77). This means that its poles actually face the Sun, while its equator lies in the 'polar region'! This can be contrasted with Venus, which is effectively 'on its head' due to its 177° axial tilt. So Venus' equator still faces the Sun, and the poles lie on the longitudinal extremities, albeit the other way round.
✱Uranus is also the coolest of all the planets, radiating significantly lower amounts of heat than even its twin ice planet, Neptune.
✱Jupiter has more moons than any other planet. It has 67 confirmed moons, while Saturn has 62. Many smaller objects are also considered to be moons of these two planets; including them, Saturn has more than 150 satellites.
✱Neptune is the densest gas giant.
✱The blue color of Uranus and Neptune is due to the high concentration of methane ice, which absorbs red light.
✱Neptune hosts one of the most active and violent atmospheres in the solar system. Winds as fast as 2100 kph (1300 mph), the fastest in the solar system, have been observed in Neptune's atmosphere.