Introduction

The study of our solar system first began more than 4,000 years ago, with Chinese astronomers and Babylonians who were observing the stars and planets. Many of the constellations today are named after the gods of ancient times. Galileo, Copernicus, Ptolemy were some of the earlier astronomers who made some early predictions providing the groundwork for today’s scientists, who are making new discoveries daily.

At the center of out solar system is the sun. Our solar system comprises of the sun, nine planets that orbit the sun (and their moons), an asteroid belt, and several comets and meteors.

The Planets

The nine planets that orbit the sun are Mercury, Venus, Earth, Mars, Jupiter Saturn, Uranus, Neptune, and Pluto. These planets are further divided into inner planets, which orbit close to the sun and outer planets that orbit far from the Sun.

The inner planets are: Mercury, Venus, Earth, and Mars. They are relatively small, composed mostly of rock, and have few or no moons. The outer planets include: Jupiter, Saturn, Uranus, Neptune, and Pluto. They are mostly huge, mostly gaseous, ringed, and have many moons (the exception is Pluto which is small, rocky, and has one moon).

Sun

The Sun is one of more than 100 billion stars in our galaxy. It is classified as being in the 10% by mass. The Sun is a big ball of reacting gases and presently it is composed of 75% hydrogen and 25% helium. The Sun does not burn in the same way as a fire does, intense pressure and heat cause the hydrogen and helium atoms to come together in a scientific process called fusion. When this occurs a type of energy called nuclear energy is produced. The heat on the surface of the Sun is estimated to be a whopping 6000 C. The Sun shows some awesome features and should not only be thought of as providing light and heat. Sunspots, one of these features are dark spots on the Sun's surface and are formed by the cooler areas on the Sun's surface. Another of these features are solar flares. They can be seen as spectacular arcs of flames being emitted from the Sun's surface.
The Sun has been around for approximately 4.5 billion years and is expected to have enough fuel to be around for another 5 billion, so nothing for us alive to worry about.

Mercury

Mercury is the eighth largest planet and the closest to the Sun. It takes 89 earth days to complete one revolution (that is a day on Mercury lasts 89 earth days). Mercury's surface is scarred with many craters probably due to many meteoroids attacks during the early years of the solar system. It has a very thin atmosphere and this is constantly replenished by solar winds. Temperatures on the surface range from 427 to -170 C.

One of the largest features on Mercury's surface is the Caloris Basin it is about 1300 km in diameter. It is thought to be similar to the large basins (maria) on the Moon. Like the lunar basins, it was probably caused by a very large impact early in the history of the solar system. That impact was probably also responsible for the odd terrain on the exact opposite side of the planet.

Surprisingly observations of the North Pole show evidence of water ice in the protected shadows of some craters.

Venus

Venus is the sixth largest planet and the second closest to the Sun. It takes 243 Earth days to complete one full rotation, and only 225 Earth days to complete one revolution around the Sun. This makes Venus unique in that a year on the planet lasts longer than a day. Another unique fact about Venus is that it is the only planet in the solar system, which rotates clockwise. Venus's atmosphere is extremely thick, approximately 90 times thicker than that of earths and is compromised mainly of carbon dioxide. This, along with active volcanoes and sulphuric acid has created a runaway greenhouse effect, which cause temperatures on Venus to rise up to 482 C. It is believed that oceans at one time existed, but the extreme hot climate and greenhouse effect would have evaporated them.

The majority of Venus's surface is covered with gently rolling planes. Unlike Mercury, Venus shows very little scars from meteoroid attacks. This is likely the case because meteoroids would have burned up in the very dense atmosphere. Where there is evidence of craters these appear in bunches indicating that large meteoroids that do reach the surface usually break up in the atmosphere.

Earth

Earth is the third planet from the Sun and the fifth largest. As seen from satellite images it is a beautiful, bright blue planet filled with patches of white water vapour (clouds) that cover about 40% of the earth.
Unlike all other planets, earth actually supports life. Well, it is uncertain whether any of the planets in this solar system has living organisms or used to have.

Scientists believe that earth was formed 4.5 billion years ago when many other planets formed. The earth takes 365 days (1 year) to orbit the Sun and completes one rotation in 24 hours (a day). It is known that the tilt of the earth's axis is 23.5 degrees, which accounts for the seasons on earth. The tilt causes certain parts of the planet to be heated differently thus causing seasonal changes.

Of all the inner planets (Mercury, Venus, Earth, and Mars), Earth is the only one that contains water in its liquid form. This is essential to the development of life on Earth, as scientists believe. Since water was so important for life on earth, scientists today use liquid water as one of the key factors when searching for life on other planets inside and out of our solar system.

Earth has an atmosphere made up of nitrogen, carbon dioxide, hydrogen, oxygen and water vapour. One of the more important layers in the atmosphere is the ozone layer. This layer helps to protect earth from dangerous radiation and reflects most of the radiation from entering earth. The ozone layer is approximately 10 miles up from the ground.

The surface of the earth is covered by land and water. Approximately 72% of the earth's surface is covered by water, the greatest concentration of this being found in the oceans. The remaining 28% forms the landmasses. The land is shaped with many mountains, hills and valleys. The highest sets of peaks are the Himalayan Mountains, with the tallest Mount Everest reaching some 29,035 feet into the air. Although Everest is the tallest peak starting from the land surface, the highest mountain can actually be found on the island of Hawaii. Mauna Kea stretches 13,796 feet above water and 19,680 feet underwater, for a total of 33,476 feet!

Mars

Mars is the fourth planet from the Sun and is commonly referred to as the Red Planet. The rocks, soil and sky have a red or pink hue.The atmosphere of Mars is quite different from that of Earth. It is composed primarily of carbon dioxide with small amounts of other gases. The six most common components of the atmosphere are: Carbon Dioxide (CO2): 95.32% , Nitrogen (N2): 2.7%
Argon (Ar): 1.6% , Oxygen (O2): 0.13% , Water (H2O): 0.03% , Neon (Ne): 0.00025 % . Martian air contains only about 1/1,000 as much water as our air.

The surface of Mars is dry, rocky, and mostly covered with iron rich dust. There are low-lying plains in the northern hemisphere, but the southern hemisphere is dotted with impact craters. The ground is frozen; this permafrost extends for several kilometers.

Each day on Mars takes 1.03 Earth days (24.6 hours). A year on Mars takes 687 Earth days; it takes this long for Mars to orbit the sun once. Mars has 2 tiny moons, Phobos and Deimos.

Jupiter

Jupiter is the fifth and largest planet in our solar system. This gas giant has a thick atmosphere, 39 known moons, and a dark, barely-visible ring. Its most prominent features are bands across its latitudes and a great red spot (which is a storm).

Jupiter is composed mostly of gas. This enormous planet radiates twice as much heat as it absorbs from the Sun. It also has an extremely strong magnetic field. It is slightly flattened at its poles and it bulges out a bit at the equator.

It takes Jupiter 9.8 Earth hours to revolve around its axis (this is a Jovian day). It takes 11.86 Earth years for Jupiter to orbit the sun once (this is a Jovian year).

Jupiter is made up of gases and liquids, so as it rotates, its parts do not rotate at exactly the same velocity. It rotates very rapidly, and this spinning action gives Jupiter a large equatorial bulge; it looks like a slightly-flattened sphere (it is oblate) Jupiter is 5.2 times farther from than the Sun than the Earth. On average, it is 480,000,000 miles (778,330,000 km) from the sun. Jupiter has four large moons and dozens of smaller ones (there are 39 moons known so far).

Saturn

Saturn is the sixth planet from the sun in our solar system. It is the second-largest planet in our solar system (Jupiter is the largest). It has beautiful rings that are made mostly of ice chunks (and some rock) that range in size from the size of a fingernail to the size of a car. Saturn is made mostly of hydrogen and helium gas.

Saturn is about 74,898 miles (120,536 km) in diameter (at the equator at the cloud tops). This is about 9.4 times the diameter of the Earth. 764 Earths could fit inside a hollowed-out Saturn.

Saturn is the most oblate (flattened) planet in our Solar System. It has a equatorial diameter of 74,898 miles (120,536 km) (at the cloud tops) and a polar diameter of 67,560 miles (108,728 km). This is a difference of about 10%. Saturn's flattened shape is probably caused by its fast rotation and its gaseous composition.

Saturn is visible without using a telescope, but a low-power telescope is needed to see its rings. Saturn's beautiful rings are only visible from Earth using a telescope. Saturn's bright rings are made of ice chunks.Saturn's mass is about 5.69 x 1026 kg. Although this is 95 times the mass of the Earth, the gravity on Saturn is only 1.08 times the gravity on Earth.

Saturn is the only planet in our Solar System that is less dense than water. Each day on Saturn takes 10.2 Earth hours. A year on Saturn takes 29.46 Earth years; it takes 29.46 Earth years for Saturn to orbit the sun once.The mean temperature on Saturn (at the cloud tops) is 88 K (-185° C; -290° F). Saturn has 18 named moons.

Uranus

Uranus is the seventh planet from the sun in our solar system. This huge, icy planet is covered with clouds and is encircled by a belt of 11 rings and 22 known moons. Uranus' blue color is caused by the methane (CH4) in its atmosphere; this molecule absorbs red light. Uranus' rotational axis is strongly tilted on its side (97.9°).

Instead of rotating with its axis roughly perpendicular to the plane of its orbit (like all the other planets in our Solar System), Uranus rotates on its side (along its orbital path). This tipped rotational axis gives rise to extreme seasons on Uranus.Uranus is about 31,690 miles (51,118 km) in diameter. This is about 4 times the diameter of the Earth.

This gas giant is the third-largest planet in our Solar System (after Jupiter and Saturn). Each day on Uranus takes 17.9 Earth hours. A year on Uranus takes 84.07 Earth years; it takes 84.07 Earth years for Uranus to orbit the sun once. The mean temperature on the surface of Uranus' cloud layer is -350°F (59 K). Uranus radiates very little heat in comparison with the other gas giants, Jupiter, Saturn and Neptune).

Uranus is a frozen, gaseous planet with a molten core. Uranus' atmosphere consists of 83% hydrogen, 15% helium and 2% methane.

Neptune

Neptune is the eighth planet from the sun in our solar system. This giant, frigid planet has a hazy atmosphere and strong winds. This gas giant is orbited by eight moons and narrow, faint rings arranged in clumps. Neptune's blue color is caused by the methane (CH4) in its atmosphere; this molecule absorbs red light.

Neptune is about 30,775 miles (49,528 km) in diameter. This is 3.88 times the diameter of the Earth. If Neptune were hollow, it could hold almost 60 Earths.Neptune's mass is about 1.02 x 1026 kg. This is over 17 times the mass of the Earth, but the gravity on Neptune is only 1.19 times of the gravity on Earth.

Each day on Neptune takes 19.1 Earth hours. A year on Neptune takes 164.8 Earth years; it takes almost 165 Earth years for Neptune to orbit the sun once.Neptune's rotational axis is tilted 30 degrees to the plane of its orbit around the Sun (this is few degrees more than the Earth). This gives Neptune seasons. Each season lasts 40 years; the poles are in constant darkness or sunlight for 40 years at a time.

Pluto

Pluto is the ninth and usually the farthest planet from the sun in our solar system. It is also the smallest planet in our solar system and the last to be discovered. It is smaller than a lot of the other planets' moons, including our moon. Pluto is about 1,413 miles (2274 km) in diameter. This is about 1/5 the diameter of the Earth.
Pluto is the smallest planet in our Solar System.

Pluto's mass is about 1.29 x 1022 kg. This is about 1/500th of the mass of the Earth. The gravity on Pluto is 8% of the gravity on Earth. Each day on Pluto takes 6.39 Earth days. Each year on Pluto takes 247.7 Earth years (that is, it takes 247.7 Earth years for Pluto to orbit the Sun once).

Pluto is 39 times farther from than the sun than the Earth is. Pluto ranges from 2.8 to 4.6 billion miles (4.447 billion to 7.38 billion km) from the Sun.Pluto is VERY, VERY cold. Its temperature may range from between -396°F to -378°F (-238°C to -228°C, or 35 K to 45 K). The average temperature is -393°F (-236°C = 37 K).

Pluto's composition is unknown. It is probably made up of about 70% rock and 30% water. This is determined from density calculations; Pluto's density is about 2,000 kg/m3. There may be methane ice together with frozen nitrogen and carbon dioxide on the cold, rocky surface.

Not much is known about Pluto's atmosphere. It is probably mostly nitrogen with a little carbon monoxide and methane - definitely not breatheable by humans.Pluto has one moon, Charon, that is almost as big as Pluto itself.Pluto was the last planet to be discovered. Planet "X" was the temporary name given to the then-unknown planet beyond Neptune