THE MEMBERS OF THE SOLAR SYSTEM

The members of the solar system consist of the Sun, Planets, and Satellites, those celestial objects that orbit planets. In addition, comets, asteroids, and meteors are also members of the solar system.

A.     Planets

A planets is a celestial body orbit around a star and massive enough to have its own gravity.

There are eight planets in our solar system, namely :

1.    Mercury,

2.   Venus,

3.   Earth,

4.   Mars,

5.   Jupiter,

6.   Saturn,

7.   Uranus, and

8.   Neptune.

The planets orbit around the Sun because of an attracting force called gravity. The gravity was fist studied by Isaac Newton, and used to explain the motion of the celestial bodies.

Mercury, Venus, Earth, Mars, Jupiter, and Saturn can be seen without using telescope and had been studied by astronomers for thousands of years. Uranus and Neptune were observed only after the discovery of the telescope.

Those eight planets are classified into inner planets and outer planets. The inner planets and the outer planets are bounded by the asteroids belt.

1.    The inner planets   : Mercury, Venus, Earth, and Mars.

2.   The outer planets  : Jupiter, Saturn, Uranus, and Neptune.

º    Mercury

Mercury is  the nearest planet to the Sun. orbit of this planets is more allipetical compared to the other planets. The longest distance between Mercury and the Sun is 69,818,000 km and the shortest distance is 46,002,000 km. its sky is dark because it has no atmosphere. The daytime temperature is 425°C and the night temperature is -173°C. The diameter is 4,878 km with an orbital speed of 47 km/s. Mercury only needs 88 Earth days to orbit around the Sun once.

º    Venus

Venus is the second nearest from the sun after Mercury. This planet has a diameter of 12,102 km and orbits around the Sun in 224.7 Earth days. Its atmosphere consists of 97% carbon dioxide (CO₂) and 3% Nitrogen. Thus, it is almost impossible to live o Venus. The orbital speed of Venus is 35.4 km/s. The average distance from the Sun is 108 million km. The average temperature on its surface is 490°C.

º    Earth

The Earth lies between Venus and Mars. The Earth is a planet which is suitable for life. This planet arbits around the Sun with a speed of 30.2 km/s, at the nearest point and 29.2 km/s at the farthest point. The average temperature on its surface is about -75°C to 55°C.

º    Mars

In 1970, the US spacecrafts Mariner and Viking successfully orbited and landed on Mars. From the data obtained, Mars is a red desert which on its polar regions are found icebergs that contain carbon dioxside and slightly water. This planet has an atmosphere which consists of carbon dioxide, slightly water vapor, nitrogen, argon, and oxygen. The average temperature on its surface is about -120°C to 25°C. Mars has two satellites, namely Phobos and Deimos.

º    Jupiter

Jupiter is the biggest planet in the solar system. From the research of NASA spacecrafts, Voyager I and Voyager II, data was obtained about Jupiter. The diameter is ±142,793 km. The surface of Jupiter consists of solid and liquid hydrogen and a small amount of metals. Its atmosphere consists of hydrogen and helium; its clouds consists of ammonia gas and ice crystals. One days on Jupiter is equal to 9 hours and 55 minutes on Earth. Jupiter has 63 satellites; some of its big satellites are Lo, Ganymede, Europa, and Callisto.

º    Saturn

Saturn is a second largest planet in the solar system. Saturn has a rocky core and gaseous surface. Its atmosphere consists of hydrogen, helium, methane, and ammonia crystals.

Saturn observed by Galileo Galilei, Christiaan Huygens, and Giovanni Domenico Cassini.

Saturn is wel known with its rings which consists of ice crystals, which are 402,000 km wide and 15 km thick. In 1981, Voyager II seceded in approaching the planet and took pictures. Saturn has 60 satellites; the biggest one is Titan.

º    Uranus

Uranus was found by William Herschel on March 13, 1781. The discovery of Uranus was the first discovery of a panet in the modern era. According to its size, Uranus is the third largest planet. Uranus consists of gases, and has the fourth biggest mass.

In 1986, the NASA spacecrafts, Voyager II, succeeded in approaching Uranus. This mission got data that the Uranus surface consists of rocks and ice surrounded by an atmosphere which consists of hydrogen, helium, and methane. Its average surface temperature is -218°C. Until now, it is known that Uranus has 13 rings and there are 27 moons orbit around it.

º    Neptune

This planet was frst observed by Galileo Galilei in 1612. However, at that time Galilei considered this planet to be a star. The scientists who are considered to be the discoverers of Neptune are Urbain Le Verrier, Johann Galle, and John Couch Adams. They made calculations of its orbit and published their findings separately in 1846.

Interplanetary Comparison Data

Planet name	Average distance from the Sun (Earth = 149.6 million km)*	Diameter (thousands of km)	Mass 9Earth = 5.98 x 1024 kg)*	Density (water = 1 g/cm3)*	Rotation period	Revolution period
Mercury	0.39	4.9	0.055	5.40	590.0 days	88.0 days
Venus	0.72	12.1	0.820	5.25	-243.0 days	225.0 days
Earth	1.00	12.7	1.000	5.25	23.9 hors	365.0 days
Mars	1.52	6.8	0.110	3.93	24.6 hours	687.0 days
Jupiter	5.20	143.0	3180.00	1.33	9.8 hours	11.7 days
Saturn	9.54	120.0	950.00	0.71	10.2 hours	29.5 days
Uranus	19.20	51.0	150.00	1.27	-10.8 hours	84.0 days
Neptune	30.10	50.0	170.00	1.70	15.8 hours	164.8 days

    The planets in the solar system can also be classified based on their composition and size. According to this classification, there are terrestrial planets and jovian planets. Terrestrial planets are rocky planets; there are Mercury, Venus, Earth, and Mars. Jovian planets are large planets consists of gas; they are Jupiter, Saturn, Uranus, and Neptune.

   

Shape of a planet’s orbit

The nearest point of a planet’s orbit to the Sun is called perihelion, while the farthest point is called aphelion.

Long planets around the Sun

The planet orbit around the Sun. the motion of planets orbit the sun is called revolution. The time needed for one revolution is called the revolution period. The revolution period of each plant is different depending on its distance to the Sun. The farther the distance of a planet to the Sun, the longer its revolution period.

Planet also rotate on their axis, called rotation. The time needed for one rotation is called the rotation period.

Comparison data between

revolution period and rotation period

Planet Name	Revolution Period	Rotation Period
Mercury	88 days	590 days
Venus	225 days	-243 days
Earth	365 days	23.9 hours
Mars	687 days	24.6 hours
Jupiter	11.7 years	9.8 hours
Saturn	29.5 years	10.2 hours
Uranus	84 years	-10.8 hours
Neptune	164.8 years	15.8 hours

The planets orbit

Counterclockwise is considered as the “east direction”, that is from the west to the east

Astronomers consider the east direction or the counterclockwise direction as the direct or prograde, while the clockwise direction is retrograde. Almost all of the planets rotate with direct motion, except Venus and Uranus.

B.      Satellites

Besides planets, there is another celestial body which orbits around a planet and often called a satellites. A satellites orbits its planet in the same direction as rotation of the planets.

The satellites perform three moyions simultaneously, namely :

1.    A satellites rotates on its axis (rotation)

2.   A satellites orbits around its planet (revolution)

3.   Together with the planet, the satellite orbit around the Sun (revolution)

C.      Interplanetary Objects

In our solar system there are interplanetary objects, namely asteroids, comets, and meteorites which orbit the Sun.

a) Asteroids

Asteroid is the small celestial bodies which orbit between Mars and Jupiter. There are numerous asteroids, reaches 100,000 objects which have total mas of only  of Earth’s mass.

The diameter of the biggest asteroids is 1,000 km. the size of asteroids are so small, the scientists called them planetoids (planet-like) or minor planet.Example of asteroids are : Ceres, Pallas, Juno, Vesta

The discovery of asteroids

Asteroid name	Discoverer	Discovery Date	Diameter (km)
Ceres	Piazzi	Jan 1, 1801	1,003
Pallas	Olbers	March 28, 1082	608
Juno	Handing	Sept 1, 1804	250
Vesta	Olbers	March 29, 1845	538
Astraea	Hancke	Dec 8, 1845	117
Hebe	Hancke	July 1, 1845	195
Iris	Hind	Aug 13, 1847	209
Flora	Hind	Oct 18, 1847	151
Metis	Graham	Apr 29, 1848	151
Hygiea	De Gasparis	Apr 12, 1849	450
Phartenope	De Gasparis	May 11, 1850	153
Victoria	Hind	Sept 13, 1850	112
Egeria	De Gasparis	Nov 2, 1850	208
Irene	Hind	May 19, 1851	182
Eunomia	De Gasparis	July 29, 1851	330
Bellona	Luther	March 1, 1854	120
Leukothea	Luther	Apr 19, 1855	103
Fides	Luther	Oct 5, 1855	108

b) Meteorites and meteors

Meteors are fragments of broken comet and they travel in the broken comet’s orbit.

Meteorites are meteors which fell to the Earth’s surface

c)  Comets

Comet is long streaks of light with oval orbital. The name of comet comes from the word “cometes” which means long hair. A comet also called a “tailed star”, as while on the move, the rear looks like luminous tail.

A comet consists of the core, coma, hydrogen cloud, and tail. The core is the solid part that resembles a very small star. A haze around the core is called coma. The core and coma form the comet head.

A comet tail always change and away from the Sun

When the comet core approaches the Sun, the heat from the Sun melts and evaporates the materials on the core’s surface. Then, the evaporated gases move to the coma. Trese gases will be driven by the solar wind and the pressure of the sun’s radiation, thus it forms the comet tail that away from the Sun.

It can be visible, because :

1.    The gas and dust which are brought along by the comet reflect the sunlight,

2.   A part of the dust absorbs the ultraviolet light and emits it in the visible light.

The comet tail is a luminous gas which is formed when the comet is near the Sun.