[Physics Class Notes] on Solar System Pdf for Exam

Let’s Go Snooping Around the Milky Way!

The solar system consists of the Sun, 8 planets, stars in the Milkyway galaxy, which are orbiting around the sun along with 210 planetary satellites and countless asteroids.  The solar system also contains comets and other icy bodies, which are made of highly tenuous gases and dust particles. The icy bodies in the solar system are also known as interplanetary mediums. Initially, the solar system had 9 planets, later astronomers announced Pluto as the icy body as a result, the number of planets in the solar system is eight. 

Ancient astronomers viewed the sun, moon and the brightest planet Venus with their naked eyes and calculated their movements. Further, they gave rise to the science of astronomy. Many other small components and smaller bodies were present even beyond the solar system, which are considered as part of the Universe. This article explains the composition of the solar system, planets, moons, asteroids and comets in the solar system with their orbits in detail. 

Composition of the Solar System

The sun is the centre of our solar system, influencing the motion of all other bodies in the solar system with its gravitational force. The total mass of the sun is about 99% of the mass of the entire solar system. The eight planets of the solar system are in an ascending order of increasing distance of the planets from the sun. The order of the planets is  Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Each of the planets is located at a particular distance from the sun. Here, four planets namely Jupiter, Saturn, Uranus, and Neptune have a ring system.  Mercury and Venus have one or more satellites.  Also, Mercury is the smallest planet in the solar system. 

In 1930, astronomers officially announced Pluto as the planet, which was orbiting beyond Neptune. Later, In 1992 astronomers discovered that Pluto is an icy object, which was located far away from the Sun. Some other researchers also discovered an object in the solar system called Eris, that looks like Pluto. So, they kept the similar groups and named it the Kuiper belt.  In August 2006, the scientific community of the International Astronomical Union (IAU) gathered and voted to remove Pluto from the planetary states. Also, they kept it under a new classification called a dwarf planet. 

All the objects in the solar system other than the sun, planets, dwarf planets and moon in the solar system are called small bodies. The small bodies in the solar system include meteoroids, asteroids and comets. The solar system has several millions of asteroids and maximum asteroids are orbiting between Mars and Jupiter and created a flat ring, which is known as the asteroid belt. 

The small solid matter present in the interplanetary space is termed meteoroids, which are different from the larger asteroidal bodies. The solar system has several billion comets and a distant one among them is called the Oort cloud.  Its distance is 1000 times more than the distance of Pluto’s orbit, which is approximately 50000 astronomical units. The Kuiper belt is located about 30 to 50 AU from the Sun. Here, one AU refers to the average distance between Earth and Sun, which is 150 million km.  

Orbits

In the solar system, all the planets, dwarf planets, icy bodies in the Kuiper belts and asteroids will revolve around the sun in the elliptical path in the same direction is known as Orbit. The motion of the components is prograde or direct. The shape of an object in orbit is termed eccentricity.  For the exact circular orbit, the eccentricity is zero.  For the elongated orbit, the eccentricity will increase towards the value 1. The orbit of Venus and Neptune around the sun is almost circular, so their eccentricities are 0.007 and 0.009 respectively.  Even though Mercury is the closest planet to the sun, its eccentricity is high, with a value of 0.206. The eccentricity of the dwarf planet Pluto is 0.25. 

Another important characteristic of the object that is orbiting around the sun is its inclination. Every object has certain inclinations like, Earth’s orbit is in the ecliptic plane. Mercury, which is the smallest planet in the solar system, has the greatest inclination which is about  7°. Pluto has a steep inclination of about 17.2°. Some comets from the Oort have a greater inclination of more than 90°, so it looks like they are rotating in opposite directions.

Solar System Planets and Their Moons

The solar system contains eight planets and is broadly divided into two distinct categories based on their densities. Here, Mercury, Venus, Earth and Mars are the four inner or terrestrial planets that have rocky compositions. Also, its densities are greater than  3 grams per cubic cm.  Jupiter, Saturn, Uranus, and Neptune are the four outer planets or Jovian or giant planets and their densities are less than 2 grams per cubic centimetre. Here, Jupiter and Saturn are primarily composed of hydrogen and helium and Uranus and Neptune are mainly composed of ice, rocks, helium and hydrogen. 

In the solar system, Venus, Earth and Mars are the only planets that have a significant amount of oxidised compounds such as carbon dioxide. In the list of Inner planets, Earth is the only planet that has a strong magnetic field, which helps them to protect itself from the interplanetary medium. The magnetic field of the earth also attracts some electrically charged particles in the interplanetary medium towards itself, which is known as the magnetosphere.  

The four outer planets in the solar system mainly consist of hydrogen and helium. They don’t even have a solid surface.  So, the density of the planets is low. Saturn has floated in the water.  All the outer planets have their magnetic field and ring system, also they have moons. Likewise, Pluto does not have rings but it has five moons. Even some asteroids have moons.  Most of the moons of the planets will rotate around their planet in the same direction. Saturn has the largest moon called Titan. The moon of Neptune, Triton moves around it in a retrograde orbit. 

Asteroids and Comets

The asteroid and comets in the solar system are the leftover pieces from the planet-building process.  The asteroids and comets are widely spread over the inner and outer solar system. The rocky bodies of the asteroid belts are known as the largest asteroids. The diameter of the ceres is about 940 km.  Some asteroids in the universe travel in the orbit of the planets that have the opportunity to collide with the planets. Usually, asteroids that are observed from the spacecraft are in irregular shapes.  The physical characteristics of comet nuclei are completely different from the asteroids.  Comets mainly contain frozen waters, frozen carbon dioxide, carbon monoxide, methanol, and other ices. The ices in comets don’t have any dust particles and it was rich in organic components. 

But sometimes, the comets will have more dirt and tiny grains with their ices. The comets are mainly classified based on their orbital period, which completely depends on the time taken by them to revolve around the sun. Some comets will take more than 200 years to revolve around the sun and are called long-period comets. Some comets will take less time to revolve around the sun and are called short-period comets. The nucleus of the long-period comets are in irregular shape and they are a few kilometres away from the sun. The orbital period of such comets is about millions of years. It spends most of its life moving a greater distance
from the sun. The comets will reach about one-fifth of the way to the nearest star. This range is also known as Oort cloud. 

Conclusion

This article explained, what is the solar system, the composition of the solar system, interesting facts about orbits, planets, moons, asteroids and comets in detail with many solar system facts. In the PDFs, which are also downloadable for free, students can go through concepts, Definitions, and questions carefully and understand the concepts used to solve these questions. This will help the students immensely in their examinations.