Geography Notes for UPSC, Solar System UPSC
Table of Contents
The Solar System UPSC
Origin of Solar System – in origin of Earth.
Who discovered the solar system?
The main idea of the solar system was proposed by the Polish astronomer Nicolaus Copernicus (1473-1543) who said that “the Sun is the center of the Universe” and made the planets move around it in perfect circles.
The sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar System/Family.
All the planets in our solar system were formed in the same period sometime about 4.6 billion years ago.
Out of the eight planets, mercury, venus, earth and mars are called the inner planets as they lie between the sun and the belt of asteroids the other four planets are called the outer planets.
Alternatively, the first four are called Terrestrial planets, meaning earth-like as they are made up of rock and metals, and have relatively high densities. The rest four are called Jovian or Gas Giant planets. Jovian means jupiter-like. Most of them are much larger than the terrestrial planets and have a thick atmosphere, mostly of helium and hydrogen.
Why are the inner planets rocky while others are mostly in gaseous form?
The difference between terrestrial and jovian planets can be attributed to the following conditions:
(i) The terrestrial planets were formed in the close vicinity of the parent star where it was too warm for gases to condense to solid particles. Jovian planets were formed at quite a distant location.
(ii) The solar wind was most intense nearer the sun; so, it blew off lots of gas and dust from the terrestrial planets. The solar winds were not all that intense to cause similar removal of gases from the Jovian planets.
(iii) The terrestrial planets are smaller and their lower gravity could not hold the escaping gases.
Member of Solar System
1. The Sun
2. Planets
3. Dwarf planet
4. Satellite
5. Asteroids and Asteroid belt
6. Meteoroid – Meteors / Shooting Star –Meteorite
7. Comets
8. Kuiper belt and Oort Cloud
9. Goldilocks Zone
1. The Sun UPSC
The sun is in the centre of the solar system. It is huge and made up of extremely hot gases.
It provides the pulling force that binds the solar system.
The sun is the ultimate source of heat and light for the solar system.
But that tremendous heat is not felt so much by us because despite being our nearest star, it is far away from us. The sun is about 150 million km away from the earth.
The next nearest star to earth is “Alpha Centuari”.
2. Planets UPSC
Formation of Planets
The following are considered to be the stages in the development of planets:
(i) The stars are localised lumps of gas within a nebula. The gravitational force within the lumps leads to the formation of a core to the gas cloud and a huge rotating disc of gas and dust develops around the gas core.
(ii) In the next stage, the gas cloud starts getting condensed and the matter around the core develops into small rounded objects. These small-rounded objects by the process of cohesion develop into what is called planetesimals.
Larger bodies start forming by collision, and gravitational attraction causes the material to stick together. Planetesimals are a large number of smaller bodies.
(iii) In the final stage, these large numbers of small planetesimals accrete to form a fewer large bodies in the form of planets.
There are eight planets in our solar system. In order of their distance from the sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. An easy way to memorise the name of the planets in order of their distance from the sun is:
My Very Efficient Mother Just Served Us Nuts
3. Dwarf Planet UPSC
In 2006, the International Astronomical Union (IAU), which governs the classification of celestial objects, introduced the “dwarf planet” category. A dwarf planet is a celestial body that orbits the Sun and meets three key criteria:
- Large enough to be pulled into a nearly round shape by its own gravity
- Orbits the Sun directly
- Has not cleared the neighborhood around its orbit
- Is smaller than the planet Mercury
Current Recognized Dwarf Planets
As of 2024, five objects are officially recognized as dwarf planets:
- Eris
- Most massive
- Discovered in 2003
- Moon: Dysnomia
- Pluto
- Largest by size
- Discovered in 1930
- Moons: Charon, Nix, Hydra, and two unnamed moons
- Haumea
- Discovered in 2003
- Moons: Hi’iaka and Namaka
- Makemake
- Discovered in 2005
- No known moons
- Ceres
- Smallest by size
- Closest dwarf planet to Earth
- First spotted in 1801
- No known moons
- Located in the asteroid belt between Mars and Jupiter
- Hygiea – Newly discovered but not recognised yet.
Historical Context
Ceres was initially classified as a planet when discovered in 1801. Throughout the 19th century, as more objects were found in its orbital region, it was reclassified as an asteroid. In 2006, the International Astronomical Union (IAU) created the “dwarf planet” category, officially recognizing Ceres as a dwarf planet.
Pluto, previously considered the Solar System’s ninth planet, was reclassified into this new category alongside Ceres, Eris, Haumea, and Makemake. Some astronomers believe that there may be as many as 50 dwarf planets in the Solar System awaiting discovery.
Trans-Neptunian Objects (TNOs)
A trans-Neptunian object is any minor planet or dwarf planet orbiting the Sun at a greater average distance than Neptune (beyond 30.1 AU). Many dwarf planets, including Pluto, Eris, Haumea, and Makemake, are classified as TNOs.
4. Natural Satellite UPSC
A satellite is a moon, planet or machine that orbits a planet or star. For example, Earth is a satellite because it orbits the sun. Likewise, the moon is a satellite because it orbits Earth. Usually, the word “satellite” refers to a machine that is launched into space and moves around Earth or another body in space.
Asteroids (minor planet) – Meteoroid – Meteors (Shooting Star) –Meteorite
5. Asteroids and Asteroid belt UPSC
Asteroids are numerous tiny bodies that also move around the Sun apart from the stars, planets, and satellites.
Asteroids are the remnants of a planet that revolves around the Sun in its orbit.
They are made up of metals and rocks and also consist of organic compounds.
They are similar to comets but don’t have a coma-like comet. Asteroids tend to have shorter and elliptical orbits.
They are found between the orbits of Mars and Jupiter. (Known as Asteroid belt)
These bodies bear resemblance to the dwarf planets.
These bodies are called asteroids.
They are also called eternal planets.
They also orbit the sun from west to east.
The largest object of this belt is Ceres and the second largest object is Vesta but the largest asteroid is Vesta because in 2006 Ceres was promoted as Dwarf Planet.
Raigu, Didymus and Bennu are some other major asteroids.
According to new facts, the Kuiper belt located outside the eight planets in the solar system is also the source of asteroids.
6. Meteoroid – Meteors / Shooting Star –Meteorite UPSC
When asteroids leave their orbit and start moving towards a planet, these are called Meteoroid.
When Meteoroid enters the Earth’s atmosphere, due to friction, they ignite (in the Mesosphere) due to which they are also called Meteors / Shooting Stars.
Some of the meteor bodies are burnt and destroyed before reaching the earth. When a meteor falls on the earth in the form of a rock, it is called Meteorite.
This leads to the formation of a meteorite crater. The Lonar lake in Buldhana district of Maharashtra is an example of a meteorite crater.
The effect of meteorite on Earth-
1. The amount of dust in the atmosphere increases due to which the density of the atmosphere increases.
2. It rains red.
3. Earth’s mass increases.
4. Meteorite crater is produced.
5. The Earth’s rotation speed decreases when it falls opposite to the Earth’s rotation direction.
6. There is an increase in sea level.
7. Tilt changes on the Earth’s orbital axis.
7. Comets UPSC
Comets are made of dust, ice, and rock materials, while asteroids are composed of rocky materials and metals.
Comets also orbit the Sun and are relatively small bodies of the solar system.
They revolve around the Sun on irregular paths.
When they are far away from the Sun, comets are simple, solid bodies; but when they get closer to the Sun, they warm up, causing the ice in the comets’ outer surface to vaporize.
This results in a glowing halo that extends outwards as though sailing through space.
The ice and compounds like ammonia and methane develop a fuzzy cloud-like shell known as the coma. This forms a notable difference between comets and asteroids.
A comet has three main parts – the nucleus, coma and tail.
Nucleus – Made up of ice, gas, rock and dust, the nucleus of a comet is located in the center of the head and is always frozen. The gaseous part of the nuclei is composed of carbon monoxide, carbon dioxide, methane and ammonia. The area usually encompasses 0.6 to 6 miles or more. Most of the comet’s mass is located in the nucleus. The nucleus is known as one of the darkest objects in space.
Coma – The comet’s coma is made up primarily of gas and encompasses the nucleus. The size is about 600,000 miles across. Carbon dioxide, ammonia, dust, water vapor and neutral gases make up the coma. Together with the nucleus, the coma forms the head of the comet. The coma is the most visible part of a comet.
Tail – Three tails either follow or guide the nucleus and coma.
The ion, or plasma, tail is made up of charged ions that consistently face away from the sun due to solar winds. Because of this, the ion tail leads the comet away from the sun or it follows it towards the sun. The tail can be more than 60 million miles long.
The dust tail is long and wide. It is made up of microscopic dust particles that are buffeted by photons that the sun emits. Due to the comet’s motion, the tail curves. As the comet moves away from the sun, the tail fades.
The envelope/gas tail is composed of hydrogen gas and is usually located between the dust tail and ion tail. It is roughly 6 million miles across and 60 million miles long. The tail appears larger when it is near the sun.
The tail of a comet is directed away from the sun because the radiation emitted by the sun exerts a radialpressure on the comet throwing its tail away fromthe sun.
Note – Halley’s Comet or Comet Halley, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–76 years. (Visible to the naked eye from Earth)
| Difference Between Asteroid and Comet Asteroids and comets are debris left over from the formation of the moon and planets. Both the celestial bodies were formed 4.6 billion years ago. Main difference between asteroid and comet are: The main difference between asteroid and comet is their composition. Asteroids are small rocky planet (planetoids), while comets are made up of glacial gases, ice, dust and rocky material. Asteroid do not produce a coma or tail atmosphere. Comet produce thin, temporary atmospheric tail when close to the Sun.Asteroids have an elliptical orbit Comets have an eccentric orbit.Asteroid are 1 to larger than 100 kilometers in size. Comet are 1 to 10 kilometer in size (nucleus only).Asteroids were formed much closer to the sun where it was impossible for the ice to remain solid. Comets were formed farther away from the sun where the ice remained solid.Comets are located in the outermost regions of the solar system, while, asteroids are located in a belt between Jupiter and Mars. |
8. Kuiper belt and Oort Cloud UPSC
Kuiper Belt is shaped like a disk and resides within the shell-like structure of the Oort Cloud. The Oort Cloud is a vast shell of billions of comets.
The Kuiper belt is a great ring of debris similar to the asteroid belt but consisting mainly of objects composed primarily of ice.
Located on the outskirts of the solar system, the Kuiper Belt is a “junkyard” of countless icy bodies left over from the solar system’s formation.
The Kuiper Belt extends from inside Pluto’s orbit to the edge of the solar system. It extends between 30 and 50 AU from the Sun.
Pluto (39 AU) is the largest known object in the Kuiper belt. Charon is Pluto’s largest moon. When discovered in 1930, it was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of a planet.
9. Goldilocks Zone UPSC
The area around a star where there is a possibility of life.
It is an area of space in which a planet is just the right distance from its home star so that its surface is neither too hot nor too cold.
The conditions in the Goldilocks zone are just right so that liquid water remains on the surface of the planet without freezing or evaporating out into space.
Terrestrial planets are more likely to lie in the Goldilocks zone.
It is also called a habitable zone or life Zone.
10. Prelims PYQs on Solar System UPSC & Other Exams
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7. FAQs on Solar System UPSC & Other Exams
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