Our solar system is made up of the sun, the planets (so far we have discovered 9 of them), the moons or satellites of the planets, the rings, the asteroids, the comets and the smaller objects such as the dust grains or the meteors.
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The Sun is the dominant member of the solar system. It alone contains about 99.80% of the total mass of the solar system. Hence it holds the planetary system together by the gravitational force it exerts and is center of the solar system. >> more info
So far 9 planets have been discovered by the scientists. They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
The first 6 are known since antiquity and the others were discovered in 1781, 1846, 1930 respectively with the help of theory and telescopes.
Most of the material in the planetary system is concentrated in Jupiter, the largest planet. Jupiter contains about 0.10% of the total mass of the solar system.
These 9 planets are classified into 3 classes as follows:
Class 1: Terrestrial or inner - 1st 4 planets (Mercury, Venus, Earth & Mars) & our Moon
<< Click here to see Class 1 planets
Class 2: Jovian or Outer or Giant - next 4 planets (Jupiter, Saturn, Uranus & Neptune)
Class 3: Neither - Pluto
<< Click here to see Class 2 & 3 planets
The orbits of the planets are ellipses with the Sun at one focus, though all except Mercury and Pluto are very nearly circular. The orbits of the planets are all more or less in the same plane (called the ecliptic and defined by the plane of the Earth's orbit). The ecliptic inclined only 7 degrees from the plane of the Sun's equator. Pluto's orbit deviates the most from the plane of the ecliptic with an inclination of 17 degrees. The above diagrams show the relative sizes of the orbits of the nine planets from a perspective somewhat above the ecliptic (hence their non-circular appearance). They all orbit in the same direction (counter-clockwise looking down from above the Sun's north pole); all but Venus, Uranus and Pluto also rotate in that same sense.
The Moons or Satellites of the Planets
A satellite is a body that revolves around a larger body. It may be natural or man-made. The larger body is called the satellite's primary. Natural satellites that orbit planets are called moons.
[Planet: Number of moons/satellites]
Earth: 1 Mars: 2 Jupiter: 16 Saturn: At least 18
Uranus: 17 Neptune: 8 Pluto: 1
The satellites of the planets mentioned above will be discussed in more details in the respective sections of the planets.
Only Mercury and Venus have no natural moons/ satellites. As for the other planets, there may be other satellites waiting to be discovered. The discovered satellites could be as small as 15 km to as large as 4800 km across.
Each of the jovian planets (Jupiter, Saturn, Uranus & Neptune) has a system of rings. The rings of Saturn are the most prominent and were first seen by Galileo. The rings of Uranus were first discovered in 1977, those of Jupiter in 1979 and those of Neptune in 1985.
The asteroids are small rocky objects with most of them in the
Asteroid belt, which lies at a distance of 2.2 - 3.3 AU ( 1 AU = distance
between Earth and Sun = 1.5 x 1011
m ) from the sun.
There are more than 5000 numbered asteroids. Probably there are about million asteroids larger than km across. But their total mass is less than 0.1% of the Earth's mass.
The first discovered and largest is Ceres (1801, 946 km in diameter). Icarus, another well-known asteroid was only discovered only in 1949. It has a diameter of 2 km.
Comets are small objects (a few kms across) that revolve about the Sun in highly elongated orbits. They consist of frozen gases and ice. They release gases and dust from an envelope around the core of the Sun. Comets are invisible except when they are near the Sun.
Smaller
Objects, Meteors, Meteorites, Meteoroids
There are many objects in the solar system that are smaller than even the comets. They range in size from dust grains to boulders, orbiting around the Sun.
When one of these falls into the Earth, it is headed by friction with the atmosphere and at least partially vaporized. We will then see a trail of luminous vapors for a few seconds in the night sky. These are the meteors or "falling stars" or "shooting stars".
If part of it reaches the surface of the Earth, it will be known as a meteorite. Before they encounter the Earth, they are known as meteoroids.
Fast Facts Of The Planets In Our Solar System:
| Largest Known Planet | Jupiter |
| Nearest Known Planet to the Sun | Mercury |
| Nearest Known Planet To Earth | Venus |
| Furthest Known Planet from the Sun/ Earth | Pluto |
| Hottest Known Planet | Mercury (440 Kelvin) |
Comparison Chart Between Planets:
| Planets | Mean Distance (AU) | Equatorial Radius (Earth) | Mass (Earth = 1) |
Mean Density (g/cm3) | Temperature (Kelvin) |
| Mercury | 0.39 | 0.38 | 0.55 | 5.43 | 440 |
| Venus | 0.72 | 0.95 | 0.81 | 5.25 | 250 |
| Earth | 1.00 | 1.00 | 1.00 | 5.52 | 280 |
| Mars | 1.52 | 0.53 | 0.11 | 3.93 | 230 |
| Jupiter | 5.202 | 11.19 | 317.89 | 1.33 | 125 |
| Saturn | 9.54 | 9.46 | 95.18 | 0.71 | 95 |
| Uranus | 19.19 | 3.98 | 14.54 | 1.24 | 60 |
| Neptune | 30.06 | 3.81 | 17.13 | 1.67 | 60 |
| Pluto | 39.53 | 0.18 | 0.02 | 1.89-2.14 | unknown |
Model of Our Solar System
The model of our solar system is known as the heliocentric model (developed first by Aristarchus, then later revived by Copernicus), i.e. the sun is the center of the universe.
