The Solar System

1. Which one of the following statements with reference to the Nebular Hy

Which one of the following statements with reference to the Nebular Hypothesis for the origin of Solar System is correct ?

The initiation of the nebular hypothesis can be considered as a diffuse, roughly spherical, slowly rotating expanding nebula
As a result of rotation and expansion, a disk is formed with matter concentrated in the centre
Expansion continues with the formation of the proto-Sun and the rings of material are left behind
The material in the rings get condensed and form the planets that revolve in orbits around the Sun
This question was previously asked in
UPSC CAPF – 2024
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Statement D correctly describes a part of the process according to the Nebular Hypothesis.
The Nebular Hypothesis postulates that the Solar System formed from a contracting cloud of gas and dust (a nebula). As the nebula contracted under gravity, it rotated faster and flattened into a disk. The central part formed the proto-Sun, and the material in the disk accreted and condensed into planetesimals, which further combined to form the planets orbiting the Sun.
Statements A, B, and C incorrectly describe the initial state or the process as involving expansion rather than contraction. The formation of a disk and the subsequent condensation and accretion of material into planets within that disk are key stages of the hypothesis.

2. Which one of the following represents the inner planets ?

Which one of the following represents the inner planets ?

Planets between the sun and the earth
Planets between the sun and the belt of asteroids
Planets near the earth
Planets around the sun
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UPSC CAPF – 2019
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The solar system is broadly divided into inner and outer planets, separated by the asteroid belt. The inner planets are the four planets closest to the Sun: Mercury, Venus, Earth, and Mars. These are also known as terrestrial planets due to their rocky composition. The outer planets are Jupiter, Saturn, Uranus, and Neptune, which are gas giants. Therefore, the inner planets are located between the Sun and the belt of asteroids.
– Inner planets are Mercury, Venus, Earth, and Mars.
– The asteroid belt lies between Mars and Jupiter.
– Inner planets are located closer to the Sun than the asteroid belt.
The inner planets are smaller, denser, and have solid surfaces compared to the outer gas giants. The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Mars and Jupiter, that is occupied by a great many irregularly shaped bodies called asteroids or minor planets.

3. Which of the following statements relating to the solar system is/are

Which of the following statements relating to the solar system is/are correct?
1. Venus and Uranus rotate opposite to the direction of rotation of Earth
2. Venus is the nearest planet to Earth
Select the correct answer using the code given below:

1 only
2 only
Both 1 and 2
Neither 1 nor 2
This question was previously asked in
UPSC CAPF – 2016
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The correct option is C) Both 1 and 2.
Statement 1 refers to the rotation direction of Venus and Uranus compared to Earth. Statement 2 refers to the relative distance of Venus from Earth.
1. **Venus and Uranus rotate opposite to the direction of rotation of Earth:** Correct. Earth rotates counter-clockwise when viewed from above the North Pole (prograde rotation). Venus rotates clockwise (retrograde rotation). Uranus also has a unique rotation; it rotates on its side, but its rotation direction is also considered retrograde relative to its orbit.
2. **Venus is the nearest planet to Earth:** Correct, in the context of being Earth’s closest planetary neighbour at its point of closest approach. While Mercury is closer to the Sun and, on average, closer to Earth than Venus is, Venus makes the closest approach to Earth among all planets. In common parlance and many educational contexts, Venus is referred to as Earth’s nearest planet.
Both statements are considered correct in a general knowledge context like a UPSC exam.

4. Which one from among the following planets is largest in size ?

Which one from among the following planets is largest in size ?

Earth
Venus
Mars
Mercury
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UPSC NDA-2 – 2021
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Earth is the largest planet in size among the given options.
Comparing the approximate mean diameters of the planets listed:
– Mercury: ~4,880 km
– Venus: ~12,100 km
– Earth: ~12,740 km
– Mars: ~6,780 km
Among Mercury, Venus, Earth, and Mars, Earth has the largest diameter and is therefore the largest in size. The order from largest to smallest among these is Earth > Venus > Mars > Mercury. In the entire solar system, the planets in order of decreasing size are Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, and Mercury.

5. Which one of the following is the correct arrangement of the given pla

Which one of the following is the correct arrangement of the given planets in descending order of their density (in gm/cm³)?

”Earth
”Jupiter
”Earth
”Earth
This question was previously asked in
UPSC NDA-1 – 2023
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The correct option is C.
Planets can be broadly classified into terrestrial (rocky) planets and Jovian (gas giant) planets. Terrestrial planets (like Earth and Venus) are generally much denser than gas giants (like Jupiter and Saturn) because they are primarily composed of rock and metal, while gas giants are mostly hydrogen and helium.
Approximate average densities in g/cm³:
– Earth: ~5.52
– Venus: ~5.24
– Jupiter: ~1.33
– Saturn: ~0.69 (Saturn is less dense than water!)
Arranging these in descending order: Earth > Venus > Jupiter > Saturn.

6. Which one of the following planets has the highest density?

Which one of the following planets has the highest density?

Mercury
Venus
Jupiter
Earth
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UPSC NDA-1 – 2021
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The correct answer is Earth.
Density is defined as mass per unit volume. The density of planets varies based on their composition. Terrestrial planets (Mercury, Venus, Earth, Mars) are primarily composed of rock and metal, making them relatively dense. Gas giants (Jupiter, Saturn, Uranus, Neptune) are primarily composed of lighter elements like hydrogen and helium, resulting in much lower densities. Among the options provided, Earth is a terrestrial planet and has the highest average density (approximately 5.51 g/cm³).
Comparing the densities of the given options:
– Earth: ~5.51 g/cm³
– Mercury: ~5.43 g/cm³
– Venus: ~5.24 g/cm³
– Jupiter: ~1.33 g/cm³
Earth has the highest density among these four planets, and indeed, it has the highest density among all planets in our solar system.

7. Which of the following are called ‘terrestrial planets’?

Which of the following are called ‘terrestrial planets’?

Earth, Mars, Jupiter, Mercury
Jupiter, Mercury, Saturn, Earth
Earth, Mercury, Mars, Venus
Mercury, Mars, Earth, Saturn
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UPSC Geoscientist – 2022
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Terrestrial planets are the inner, rocky planets of our solar system. They are characterized by having solid surfaces. In our solar system, the terrestrial planets are, in order from the Sun: Mercury, Venus, Earth, and Mars. The outer planets (Jupiter, Saturn, Uranus, Neptune) are gas giants or ice giants, primarily composed of gases and liquids, and are also known as Jovian planets.
– Terrestrial planets are rocky and located closer to the Sun.
– Jovian planets (gas/ice giants) are large, gaseous/liquid, and located farther from the Sun.
Besides their composition and location, terrestrial planets typically have higher densities, slower rotation, solid surfaces, and few or no moons or ring systems compared to Jovian planets. Earth is the largest of the terrestrial planets.

8. Consider the following statements about some planets in the solar syst

Consider the following statements about some planets in the solar system :

  • 1. Mercury has no atmosphere.
  • 2. Venus has two moons.
  • 3. There is no land on Jupiter.
  • 4. Rings of Saturn are composed of lumps of ice and dust.

Which of the statements given above are correct ?

1 and 2 only
3 and 4 only
1, 2 and 3
1, 3 and 4
This question was previously asked in
UPSC CDS-2 – 2023
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The correct answer is (D). Statements 1, 3, and 4 are correct.
Let’s evaluate each statement:
1. Mercury has no atmosphere: While it has a very thin exosphere, it is often described as having “no atmosphere” in simpler terms because it lacks a significant gaseous envelope compared to other planets. This statement is considered correct in this context.
2. Venus has two moons: This is incorrect. Venus has no moons.
3. There is no land on Jupiter: This is correct. Jupiter is a gas giant without a solid surface; it’s composed primarily of hydrogen and helium, transitioning to denser states towards the core.
4. Rings of Saturn are composed of lumps of ice and dust: This is correct. Saturn’s prominent rings are made up of countless particles, predominantly water ice, ranging in size from micrometers to several meters.
Terrestrial planets (Mercury, Venus, Earth, Mars) have solid rocky surfaces, while Jovian planets (Jupiter, Saturn, Uranus, Neptune) are gas or ice giants with no defined solid surface.

9. Which one among the following planets has the largest number of known

Which one among the following planets has the largest number of known satellites?

Mars
Neptune
Jupiter
Saturn
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UPSC CDS-2 – 2022
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As of May 2023, Saturn surpassed Jupiter in the number of known satellites. Astronomers confirmed 62 new moons orbiting Saturn, bringing its total to 146. Jupiter currently has 95 confirmed moons. Mars has 2, and Neptune has 14. Therefore, Saturn has the largest number of known satellites among the options provided.
The discovery of new moons is ongoing, especially around the gas giants, using advanced telescopic surveys. The largest planets, Jupiter and Saturn, due to their immense gravity, have captured or formed a vast number of moons, including many small, irregular ones.
The number of known moons for a planet can change as new discoveries are made and confirmed. The listing of moons often distinguishes between major moons (like the Galilean moons of Jupiter or Titan of Saturn) and numerous smaller, irregular satellites.

10. The four planets closest to the Sun are called

The four planets closest to the Sun are called

terrestrial planets
giant planets
dwarf planets
gas planets
This question was previously asked in
UPSC CDS-2 – 2020
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The Solar System’s planets are broadly classified based on their composition and location. The four planets closest to the Sun are Mercury, Venus, Earth, and Mars. These planets are primarily composed of rock and metal and have solid surfaces. They are called terrestrial planets, meaning ‘Earth-like’.
– The inner planets are Mercury, Venus, Earth, and Mars.
– They are characterized by solid, rocky surfaces.
– This class of planets is known as terrestrial planets.
The planets further from the Sun (Jupiter, Saturn, Uranus, Neptune) are much larger and consist mainly of gas and ice; they are known as giant planets, often subdivided into gas giants and ice giants. Dwarf planets are a distinct category of celestial bodies (like Pluto, Ceres, Eris).
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