Solar System

The Solar System includes the Sun, Earth and the Moon, the major planets including Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and meteoroids.

For many thousands of years, astronomers maintained a geocentric world view and did not recognize the existence of a Solar System. They believed that Earth was stationary at the center of the Universe and categorically different from the divine or ethereal objects that moved through the sky. In 17th-century, Galileo Galilei, Johannes Kepler, and Isaac Newton developed a modern understanding of physics that led to the gradual acceptance of the idea that Earth moves around the Sun and that the planets are governed by the same physical laws that govern Earth. Galileo was the first to use the telescope that dealt out that individual planets are part of the Solar System. He discovered that the Moon was cratered, that the Sun was marked with sunspots, and that Jupiter had four satellites in orbit around it. Christiaan Huygens followed up on Galileo’s discoveries by observing Saturn’s Moon Titan and the shape of the rings of Saturn. Giovanni Domenico Cassini later discovered four more moons of Saturn and also the gap between Saturn’s rings now known as the Cassini Division. The repeated sightings of a comet were recorded for the same object, returning regularly once every 75-76 years. This was the first evidence that comets orbit the Sun and not discharges from the Sun. Around this time (1704), the term “Solar System” first appeared in English.

The first four planets, Mercury, Venus, Earth and Mars are much nearer to the Sun than the other four planets. They are called inner planets. The inner planets have very few moons.

Mercury:

Mercury is the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 88 days is the shortest of all the planets in the Solar System. Mercury is a rocky body like Earth, with an equatorial radius of 2,439.7 kilometers which is 0.3829 times the radius of Earth and has low atmosphere of oxygen. May: metallic and 30% silicate material. Mercury has the second highest density in the Solar System at 5.427 g/cm³, only slightly less than Earth’s density of 5.515 g/cm³. Atmosphere is absent in Mercury and surface temperature ranges from 100 K to 700 K.

Venus:

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. It has the longest rotation period (243 days) of any planet in the Solar System and rotates in the opposite direction to most other planets. Venus is sometimes called Earth’s “sister planet” because of their similar size, mass, proximity to the Sun, and bulk composition. It has a dense atmosphere and is the furthest most planet, consisting of more than 96% carbon dioxide. The atmospheric pressure on the planet’s surface is 92 times that of Earth. Venus is the hottest planet in the Solar System, with a mean surface temperature of 735 K (462 °C), even though Mercury is closer to the Sun. The diameter of Venus is 12,103.6 km, only 638.4 km less than Earth—and its mass is 81.5% of Earth’s.

Earth:

Earth is the third planet from the Sun and the only planet on which life is known to exist. Earth formed over 4 billion years ago and has a natural satellite with other satellites in space, especially the Sun and the Earth. Earth’s equatorial diameter is 12,756 km and its mass is 386.26 × 10²⁴ kg. It has a total surface area of 510.1 million km² of which 71% (362.124 km²) is covered by water. Of its land (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%) and calcium (1.5%) are the elements that make the Earth. Earth’s atmosphere is composed of 78% nitrogen and 21% oxygen. Earth’s atmosphere of Earth has a composition of 78% nitrogen and 21% oxygen, with trace amounts of water vapour, carbon dioxide, and other gaseous molecules. The mass density and surface gravity of Earth is 5.514 g/cm³ and 9.807 m/s² respectively.

Mars:

Mars is the fourth planet from the Sun, orbiting it in 687 Earth (Earth) days. It is the second smallest planet in the Solar System after Mercury. It appears slightly reddish because of the iron oxide (rust) prevalent on its surface. It is often referred to as the “Red Planet”. Mars is approximately half the diameter of Earth. Mars is less dense than Earth, having about 15% of Earth’s volume and 11% of Earth’s mass, resulting to about 38% of Earth’s surface gravity. Mars surface temperatures vary from lows of about −143 °C at the winter polar caps to highs of up to 35 °C in equatorial summer. The wide range in temperatures is due to the thin atmosphere which cannot store much solar heat.

There is a large gap in between the orbits of Mars and Jupiter which is occupied by a large number of small objects that revolve around the Sun. These are called asteroids.

The planets outside the orbit of Mars, namely Jupiter, Saturn, Uranus and Neptune are much farther off than the inner planets. They are called the outer planets. They have a ring system around them. The outer planets have large number of moons.

Jupiter:

Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet composed primarily of gaseous and liquid matter. It is more than about 1300 earths can be placed inside this giant planet. However, the mass of Jupiter is about 318 times that of our Earth. Jupiter’s upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules. Its orbital period is approximately 4332.82 Earth days, or 11.86 years. Jupiter has a large number of satellites. It also has faint rings around it.

Saturn:

Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius about in the Solar System. Saturn is composed mostly of hydrogen and helium. Its average density is less than that of water. However, Saturn is over 95 times more massive than Earth. Saturn’s interior is probably composed of a core of iron–nickel and rock (silicon and oxygen compounds). This core is surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and helium, and an outer gaseous layer. Saturn rotates very quickly with a rotational period of 10.7 hours. It takes 10,759 Earth days (about 29 1/2 years) to finish one revolution around the Sun. Saturn is probably best known for its prominent planetary rings which make it visually unique. Saturn also has a large number of satellites.

Uranus:

Uranus is the seventh planet from the Sun. Uranus’s atmosphere is similar in composition to Jupiter’s. It is primarily composed of hydrogen and helium, but it contains more “ices” such as water, ammonia, and methane, along with traces of other hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (−224 °C). The interior of Uranus is mainly composed of ices and rock. Uranus orbits the Sun once every 84 years. Its rotational period is 17 hours 14 minutes. It has the third largest planetary radius and fourth largest planetary mass in the Solar System. As a result of this, Uranus is 1.27 g/cm³ makes Uranus the second least dense planet, after Saturn.

Neptune:

Neptune is the eighth and farthest known planet from the Sun in the Solar System. It is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. Neptune is 17 times the mass of Earth, slightly more massive than its near-twin Uranus. 164.8 years. Like Jupiter and Saturn, Neptune’s atmosphere is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen. It contains a higher proportion of “ices” such as water, ammonia, and methane. Neptune’s interior is primarily composed of ices and rock. In the Solar System, with the minimum temperature of approximately 55 K (−218 °C). Temperatures at the planet’s centre are probably 5,400 K (5,100 °C).