Q110. Consider the following statements about private entities in India’s space programme:
1. IN-SPACe is an autonomous agency facilitating private participation.
2. Agnikul Cosmos launched the world’s first flight using a 3D-printed rocket engine.
3. Skyroot Aerospace developed liquid fuel for GSLV.
Which statements are correct?
[UPSC CSE Prelims 2026]
(A) 1 only
(B) 2 and 3 only
(C) 1 and 2 only
(D) 1, 2 and 3
Answer: (C) 1 and 2 only
Explanation: IN-SPACe enables private participation in India’s space sector, while Agnikul demonstrated a flight using its additively manufactured engine. Skyroot develops independent launch vehicles; it did not develop GSLV’s liquid propellant. Therefore, the first two statements alone are correct.
Q109. Which of the following pairs of theories about the origin of Earth and their proponents is/are correctly matched?
1. Gaseous Hypothesis — Kant
2. Binary Star Hypothesis — Russell
3. Planetesimal Hypothesis — Chamberlin
[UPSC CDS (I) 2026 – General Knowledge]
(A) 1 only
(B) 2 and 3 only
(C) 1 and 3 only
(D) 1, 2 and 3
Answer: (D) 1, 2 and 3
Explanation: Immanuel Kant proposed an early gaseous nebular explanation, Russell is associated with the binary-star hypothesis, and Chamberlin with the planetesimal hypothesis. These are historical explanations developed before modern observations strengthened the solar nebular model.
Q108. Why is the Earth slightly flattened at the poles and bulged at the equator?
[UPSC NDA (II) 2026 – General Ability Test]
(A) Large oceans in the Southern Hemisphere
(B) The Earth’s rotational force
(C) The Earth’s revolution
(D) Greater gravitational force at the equator
Answer: (B) The Earth’s rotational force
Explanation: The rotation of Earth produces an outward centrifugal effect strongest at the equator and absent at the poles. Over geological timescales this contributes to an oblate spheroidal shape, with a larger equatorial radius than polar radius.
Q107. What is the acceleration due to gravity on a planet having twice Earth’s mass and twice Earth’s radius, if Earth’s value is g?
[RRB Group D, 3 February 2026, Shift 2]
(A) 2g
(B) g/4
(C) g
(D) g/2
Answer: (D) g/2
Explanation: Surface gravity is proportional to mass divided by the square of radius: g = GM/R². Doubling mass multiplies gravity by two, but doubling radius divides it by four. The combined factor becomes one-half.
Q106. Consider these statements:
I. The Prime Meridian and International Date Line are the same.
II. The region west of the International Date Line is generally one calendar day ahead of the east.
III. Earth rotates through 15° longitude per hour.
Which are correct?
[UPSC NDA (II) 2026 – General Ability Test]
(A) I and II only
(B) I and III only
(C) II and III only
(D) III only
Answer: (C) II and III only
Explanation: The Prime Meridian is approximately 0° longitude, while the International Date Line follows approximately 180°. Earth completes roughly 360° in 24 hours, or 15° per hour. Crossing the Date Line changes the calendar date.
Q105. Which planet has the highest density among Mercury, Venus, Jupiter and Earth?
[UPSC NDA (I) 2026 – General Ability Test]
(A) Mercury
(B) Venus
(C) Jupiter
(D) Earth
Answer: (D) Earth
Explanation: Earth has a mean density of approximately 5.51 grams per cubic centimetre, slightly exceeding Mercury and Venus. Jupiter is much less dense because it consists mainly of hydrogen and helium, despite being far more massive.
Q104. Consider the space missions
I. Axiom-4
II. SpaDeX
III. Gaganyaan.
How many of these missions encourage and support microgravity research?
[UPSC CSE Prelims 2025]
(A) Only one
(B) Only two
(C) All three
(D) None
Answer: (B) Only two
Explanation: Axiom-4 enables research aboard the International Space Station and Gaganyaan supports experiments during Indian human spaceflight. SpaDeX primarily demonstrates spacecraft rendezvous and docking rather than serving as a dedicated microgravity research mission. The examination key selects two.
Q103. Regarding GPS-Aided GEO Augmented Navigation (GAGAN), consider:
I. It improves navigation accuracy and integrity.
II. It supports more uniform and high-quality air traffic management.
III. Its benefits are limited exclusively to aviation.
Which statements are correct?
[UPSC CSE Prelims 2025]
(A) I, II and III
(B) II and III only
(C) I only
(D) I and II only
Answer: (D) I and II only
Explanation: GAGAN is India’s satellite-based augmentation system, developed by ISRO and the Airports Authority of India. It improves GPS reliability for aviation while having potential applications beyond aircraft, such as maritime navigation. Therefore the exclusivity claim is incorrect.
Q102. Which hypothesis explains the formation of the solar system from a rotating cloud of gas and dust?
[RRB NTPC (UG), 18 August 2025, Shift 1]
(A) Big Bang Theory
(B) Nebular Hypothesis
(C) Continental Drift Theory
(D) Plate Tectonics Theory
Answer: (B) Nebular Hypothesis
Explanation: The nebular hypothesis proposes that a rotating interstellar cloud collapsed under gravity, forming the Sun centrally and a surrounding disc of material. Planets developed by accretion within that disc. The Big Bang addresses the universe’s early expansion, not individual planetary systems.
Q101. What distinguishes ISRO’s Small Satellite Launch Vehicle (SSLV) from PSLV and GSLV?
[SSC CGL Tier I, 24 September 2025, Shift 3]
(A) A hybrid liquid-solid engine
(B) On-demand, low-cost launches of small satellites
(C) Launching only from sea-based platforms
(D) Launching foreign satellites exclusively
Answer: (B) On-demand, low-cost launches of small satellites
Explanation: SSLV is designed to carry relatively small payloads into low Earth orbit with quicker turnaround and streamlined launch operations. PSLV and GSLV are larger vehicles suited to wider payload classes. Responsiveness and lower mission costs are key SSLV objectives.
Q100. What distinguishes India’s Aditya-L1 solar mission?
[SSC CGL Tier I, 24 September 2025, Shift 1]
(A) It uses only radar to study the Sun
(B) It directly orbits the surface of the Sun
(C) It observes the solar corona from around Sun–Earth Lagrange Point 1
(D) It is in lunar orbit
Answer: (C) It observes the solar corona from around Sun–Earth Lagrange Point 1
Explanation: Aditya-L1 operates in a halo orbit around the Sun–Earth L1 region, providing a largely uninterrupted view of the Sun. Its instruments study the solar atmosphere, solar wind and energetic particles, helping scientists investigate space weather.
Q99. What is the full form of PSLV?
[SSC CGL Tier I, 22 September 2025, Shift 3]
(A) Polar Satellite Launch Vehicle
(B) Public Space Launch Vehicle
(C) Planetary Satellite Launch Vehicle
(D) Private Satellite Launch Vehicle
Answer: (A) Polar Satellite Launch Vehicle
Explanation: Polar Satellite Launch Vehicle is ISRO’s versatile launch rocket, famous for placing Earth-observation spacecraft into polar and Sun-synchronous orbits. It has also launched interplanetary missions and commercial payloads into other orbits through different vehicle configurations.
Q98. Which was India’s first interplanetary space mission?
[SSC CGL Tier I, 22 September 2025, Shift 1]
(A) Chandrayaan-1
(B) Gaganyaan
(C) Aditya-L1
(D) Mangalyaan (Mars Orbiter Mission)
Answer: (D) Mangalyaan (Mars Orbiter Mission)
Explanation: India’s Mars Orbiter Mission, popularly known as Mangalyaan, entered orbit around Mars in September 2014 after a 2013 launch. Chandrayaan explored the Moon, Aditya-L1 observes the Sun, and Gaganyaan is India’s human-spaceflight programme.
Q97. What does ISRO stand for?
[SSC CGL Tier I, 21 September 2025, Shift 2]
(A) Indian Scientific Research Organization
(B) Indian Space Research Organisation
(C) Indian Satellite Rocket Organization
(D) International Space Research Organization
Answer: (B) Indian Space Research Organisation
Explanation: The Indian Space Research Organisation is India’s national space agency. It designs and operates launch vehicles, satellites, Earth-observation services and planetary missions. ISRO was established in 1969 and operates under the Department of Space.
Q96. Under India’s Space Vision 2047, in which years are Bharatiya Antariksh Station and an Indian crewed lunar landing respectively envisioned?
[SSC CGL Tier I, 20 September 2025, Shift 1]
(A) 2030 and 2035
(B) 2035 and 2040
(C) 2040 and 2047
(D) 2028 and 2030
Answer: (B) 2035 and 2040
Explanation: India’s long-term space roadmap sets a goal for an Indian space station by 2035 and an Indian astronaut landing on the Moon by 2040. These are policy targets rather than completed achievements, and their feasibility depends on technological progress.
Q95. On which date did India successfully carry out its SpaDeX spacecraft docking operation?
[SSC CGL Tier I, 13 September 2025, Shift 3]
(A) 30 December 2024
(B) 1 January 2025
(C) 16 January 2025
(D) 26 January 2025
Answer: (C) 16 January 2025
Explanation: ISRO docked the two SpaDeX satellites on 16 January 2025 after their December 2024 launch. Docking technology allows two independently orbiting craft to connect, an important capability for future orbital servicing, human spaceflight and space stations.
Q94. What is the main function of the NVS-02 satellite launched by GSLV-F15?
[SSC CGL Tier I, 13 September 2025, Shift 2]
(A) Cyclone monitoring
(B) Television broadcasting
(C) Navigation and precise timing
(D) Communications with interplanetary probes
Answer: (C) Navigation and precise timing
Explanation: NVS-02 belongs to India’s NavIC navigation satellite family. Such spacecraft support positioning, navigation and timing services, which are useful to transport, timing networks and strategic applications. Navigation satellites differ from weather and broadcasting satellites in their payload objectives.
Q93. Which orbital regime was chosen for the NASA–ISRO Synthetic Aperture Radar mission, NISAR?
[SSC CGL Tier I, 13 September 2025, Shift 2]
(A) Geostationary Transfer Orbit
(B) Geostationary Orbit
(C) Polar Sun-synchronous Orbit
(D) Highly elliptical Earth orbit
Answer: (C) Polar Sun-synchronous Orbit
Explanation: NISAR observes Earth using L-band and S-band synthetic-aperture radar. Its near-polar, Sun-synchronous orbit provides repeated observations under consistent illumination conditions and helps track changes in forests, ice, terrain deformation and natural hazards.
Q92. What is the proposed Bharatiya Antariksh Station?
[SSC CGL Tier I, 26 September 2025, Shift 3]
(A) India’s first lunar surface base
(B) An Indian orbital space station
(C) A deep-space optical telescope
(D) An asteroid-mining station
Answer: (B) An Indian orbital space station
Explanation: Bharatiya Antariksh Station is the planned Indian crew-capable orbital outpost. Such stations enable extended human presence, scientific experiments and testing of life-support systems in microgravity. A space station orbits Earth rather than resting on the lunar surface.
Q91. What technology enabled hazard detection and avoidance by the Chandrayaan-3 Vikram lander?
[SSC CGL Tier I, 26 September 2025, Shift 2]
(A) Lander Hazard Detection and Avoidance Camera with processing algorithms
(B) Synthetic Aperture Radar
(C) Laser Doppler Imaging alone
(D) Laser Doppler Velocimeter alone
Answer: (A) Lander Hazard Detection and Avoidance Camera with processing algorithms
Explanation: Vikram employed a dedicated hazard-detection camera and onboard processing to assess surface conditions during descent. This helped identify safer landing terrain. Velocity-measurement instruments supported navigation, but hazard mapping specifically involved the camera and processing system.
Q90. What is a principal scientific objective of ISRO’s proposed Venus Orbiter Mission, Shukrayaan-1?
[SSC CGL Tier I, 26 September 2025, Shift 1]
(A) Investigating Venus’s atmosphere and surface
(B) Observing near-Earth asteroids only
(C) Exploring Saturn’s rings
(D) Studying the Martian atmosphere
Answer: (A) Investigating Venus’s atmosphere and surface
Explanation: Venus exploration aims to investigate its dense atmosphere, cloud chemistry and interactions with the solar wind, alongside surface and subsurface properties. Understanding Venus’s intense greenhouse conditions helps compare planetary climate evolution with Earth and Mars.
Q89. Which Mars Orbiter Mission payload captured full-disc colour images of Mars?
[SSC CGL Tier I, 26 September 2025, Shift 1]
(A) Liquid Apogee Motor
(B) Moon Mineralogy Mapper
(C) Terrain Mapping Camera
(D) Mars Colour Camera
Answer: (D) Mars Colour Camera
Explanation: The Mars Colour Camera was an imaging payload on Mangalyaan, taking views of Mars and its surrounding space. The Liquid Apogee Motor was propulsion hardware, while the Moon Mineralogy Mapper and Terrain Mapping Camera were associated with lunar exploration.
Q88. What technological capability was demonstrated in ISRO’s RLV-LEX-03 experiment of 23 June 2024?
[SSC CGL Tier I, 14 September 2025, Shift 1]
(A) In-flight fuel transfer
(B) Autonomous landing despite difficult cross-range and wind conditions
(C) Orbital crew escape
(D) Dual-mode scramjet deployment
Answer: (B) Autonomous landing despite difficult cross-range and wind conditions
Explanation: ISRO’s third Reusable Launch Vehicle Landing Experiment demonstrated autonomous runway landing after release from a helicopter, including more demanding dispersions and wind conditions. Reusable vehicle technology seeks to lower launch costs through controlled recovery and reuse.
Q87. In which year is the first module of Bharatiya Antariksh Station planned to be launched?
[SSC CGL Tier I, 12 September 2025, Shift 3]
(A) 2028
(B) 2030
(C) 2035
(D) 2040
Answer: (A) 2028
Explanation: India’s approved roadmap envisages a first station-related module in 2028 and an operational Bharatiya Antariksh Station by 2035. The first module is only a step in the larger development programme, not completion of the entire station.
Q86. What is the primary role of the Crew Escape System on the human-rated LVM3 for Gaganyaan?
[SSC CGL Tier I, 12 September 2025, Shift 1]
(A) Guiding the vehicle into orbit
(B) Carrying the crew module away from danger in a launch emergency
(C) Docking with a space station
(D) Providing re-entry heat shielding
Answer: (B) Carrying the crew module away from danger in a launch emergency
Explanation: An abort or crew-escape system provides rapid separation of the crew module if a serious launch failure threatens astronauts. It is a safety subsystem for ascent and must operate reliably across demanding flight conditions.
Q85. How frequently is NISAR planned to map the global land and ice surfaces?
[SSC CGL Tier I, 16 September 2025, Shift 2]
(A) Every 3 days
(B) Every 12 days
(C) Every 24 hours
(D) Every 5 days
Answer: (B) Every 12 days
Explanation: NISAR’s repeating orbit is designed to revisit and map the Earth’s surface on a 12-day cycle. Using radar permits measurements by day and night and through cloud cover, aiding detection of subtle changes over time.
Q84. Which of the following is NOT a benefit of the Gaganyaan mission?
[SSC CGL Tier I, 19 September 2025, Shift 2]
(A) Greater international collaboration
(B) Advances in space technology
(C) Stronger Indian human-spaceflight capability
(D) Reduction of Earth’s global temperature
Answer: (D) Reduction of Earth’s global temperature
Explanation: Gaganyaan develops crewed spacecraft, safety systems, flight control and related scientific capabilities. The programme can strengthen research partnerships and India’s launch ecosystem. It does not directly cool the planet or function as a climate-engineering intervention.
Q83. Which ISRO mission provided evidence of water or hydroxyl on the lunar surface?
[SSC CGL Tier I, 19 September 2025, Shift 2]
(A) Chandrayaan-1
(B) Chandrayaan-2
(C) Chandrayaan-3
(D) Chandrayaan-4
Answer: (A) Chandrayaan-1
Explanation: The Moon Mineralogy Mapper aboard Chandrayaan-1 helped identify spectral signatures associated with water and hydroxyl on the Moon. This discovery substantially changed scientific understanding of lunar surface chemistry and encouraged further exploration of polar volatile deposits.
Q82. What is a central role of the Vikram Sarabhai Space Centre?
[SSC CGL Tier I, 18 September 2025, Shift 3]
(A) Operating all space launchpads
(B) Designing and developing launch vehicles
(C) Training every Indian astronaut
(D) Operating all communication satellites
Answer: (B) Designing and developing launch vehicles
Explanation: The Vikram Sarabhai Space Centre in Thiruvananthapuram is a major ISRO centre for rocket and launch-vehicle design and development. Actual launches take place at spaceports such as the Satish Dhawan Space Centre in Sriharikota.
Q81. Which satellite-type/application pair is incorrectly matched?
[SSC CGL Tier I, 18 September 2025, Shift 1]
(A) Weather satellite — cyclone tracking
(B) Communication satellite — TV broadcasting
(C) Navigation satellite — forest-fire monitoring
(D) Remote-sensing satellite — land-use mapping
Answer: (C) Navigation satellite — forest-fire monitoring
Explanation: Navigation satellites primarily provide positioning and precise timing signals. Detection and mapping of forest fires rely mainly on imaging or thermal remote-sensing satellites. Weather and communication spacecraft perform the other functions listed in the question.
Q80. Arrange the events chronologically:
1. Introduction of World Wide Web
2. Development of intercontinental ballistic missiles
3. Launch of the first communication satellite.
[UPSC NDA (II) 2025 – General Ability Test]
(A) 2 – 1 – 3
(B) 1 – 2 – 3
(C) 3 – 2 – 1
(D) 2 – 3 – 1
Answer: (D) 2 – 3 – 1
Explanation: Intercontinental ballistic missiles emerged during the 1950s. Early communications-satellite milestones came around the late 1950s and early 1960s. Tim Berners-Lee developed the World Wide Web much later, around 1989–1991, placing the events in order 2, 3, 1.
Q79. Which expression gives acceleration due to gravity at the surface of a spherical planet of mass M and radius R?
[RRB Group D, 11 December 2025, Shift 1]
(A) g = R/(GM²)
(B) g = GR/M²
(C) g = GM²/R
(D) g = GM/R²
Answer: (D) g = GM/R²
Explanation: Newton’s gravitational force on a body of mass m is GMm/R². Dividing that force by m gives the free-fall acceleration at the planetary surface, GM/R², when a roughly spherical mass distribution is assumed.
Q78. Statement I: Giant stars live much longer than dwarf stars.
Statement II: Giant stars have a greater rate of nuclear reactions than dwarf stars.
Which statement is correct?
[UPSC CSE Prelims 2024]
(A) Both are correct and II explains I
(B) Both are correct, but II does not explain I
(C) I is correct and II is incorrect
(D) I is incorrect and II is correct
Answer: (D) I is incorrect and II is correct
Explanation: Massive stars consume their nuclear fuel at a much faster rate despite having more fuel overall. Their higher luminosity therefore usually means shorter lifetimes than low-mass dwarf stars. The second statement is correct, but the claimed longevity is wrong.
Q77. Concerning the Square Kilometre Array (SKA), consider:
1. It is an international facility for an exceptionally sensitive radio telescope.
2. India has approved participation in the project.
Which is correct?
[UPSC NDA (I) 2024 – General Ability Test]
(A) 1 only
(B) 2 only
(C) Both 1 and 2
(D) Neither 1 nor 2
Answer: (C) Both 1 and 2
Explanation: SKA is a major international radio-astronomy project with antenna arrays in Australia and South Africa. India approved participation, strengthening its contribution to radio astronomy. It is designed to examine fundamental cosmic questions, including galaxy evolution and cosmic magnetism.
Q76. Who worked with Thomas Chamberlin in 1905 on a planetesimal explanation of the formation of the Solar System?
[SSC CPO Paper I, 27 June 2024, Shift 2]
(A) Inge Lehmann
(B) Forest Moulton
(C) Charles Lyell
(D) James Hutton
Answer: (B) Forest Moulton
Explanation: Forest Ray Moulton and Thomas Chrowder Chamberlin developed the Chamberlin–Moulton planetesimal hypothesis. It proposed that a close stellar encounter drew material from the Sun, subsequently forming small bodies. Modern models instead favour formation from a solar nebula.
Q75. Consider XPoSat:
1. It is India’s first dedicated polarimetry mission to study bright cosmic X-ray sources.
2. It carries two scientific payloads in low Earth orbit.
Which statements are correct?
[CGPSC Prelims, 11 February 2024 – General Studies]
(A) 1 only
(B) 2 only
(C) Both 1 and 2
(D) Neither 1 nor 2
Answer: (C) Both 1 and 2
Explanation: ISRO launched XPoSat to investigate polarisation of high-energy X-rays from astronomical sources including black-hole systems and neutron stars. Its two payloads, POLIX and XSPECT, provide complementary measurements from a low Earth orbit. Both statements are accurate.
Q74. Which pairs are correctly matched?
1. Cepheids — giant clouds of dust and gas
2. Nebulae — periodically brightening and dimming stars
3. Pulsars — neutron stars formed by collapse of massive stars.
How many are correct?
[UPSC CSE Prelims 2023]
(A) Only one
(B) Only two
(C) All three
(D) None
Answer: (A) Only one
Explanation: Cepheids are pulsating variable stars, while nebulae are clouds of gas and dust. Pulsars are rapidly rotating, magnetised neutron stars that produce observable periodic signals. Consequently, only the third identification is correctly paired.
Q73. Which of these countries has its own satellite-navigation system?
[UPSC CSE Prelims 2023]
(A) Australia
(B) Canada
(C) Israel
(D) Japan
Answer: (D) Japan
Explanation: Japan operates the Quasi-Zenith Satellite System, a regional navigation and augmentation constellation enhancing positioning over Japan and nearby areas. It complements other global navigation systems and can offer improved visibility in difficult urban and mountainous settings.
Q72. Which of the following was India’s first privately developed rocket launched in a mission facilitated by ISRO?
[UPSC NDA (I) 2023 – General Ability Test]
(A) Skyroot
(B) Prarambh
(C) Bazoomq
(D) Vikram-S
Answer: (D) Vikram-S
Explanation: Vikram-S was developed by Skyroot Aerospace and flew on the Prarambh mission in November 2022. Skyroot is the company, Prarambh the mission name, and Vikram-S the actual suborbital rocket. It was an important private-sector milestone.
Q71. Which is the correct descending order of density among Earth, Venus, Jupiter and Saturn?
[UPSC NDA (I) 2023 – General Ability Test]
(A) Earth > Jupiter > Venus > Saturn
(B) Jupiter > Earth > Saturn > Venus
(C) Earth > Venus > Jupiter > Saturn
(D) Earth > Venus > Saturn > Jupiter
Answer: (C) Earth > Venus > Jupiter > Saturn
Explanation: Earth and Venus are rocky and relatively dense, whereas Jupiter and Saturn are gas giants. Earth has the highest mean density of the four, followed by Venus. Jupiter is denser than Saturn, whose mean density is below water.
Q70. Which statements about planets are correct?
1. Mercury has no atmosphere.
2. Venus has two moons.
3. Jupiter has no solid land surface.
4. Saturn’s rings consist of ice and dust.
[UPSC CDS (II) 2023 – General Knowledge]
(A) 1 and 2 only
(B) 3 and 4 only
(C) 1, 2 and 3
(D) 1, 3 and 4
Answer: (B) 3 and 4 only
Explanation: Venus has no natural moon, so statement 2 is false. Mercury possesses an extremely thin exosphere rather than a substantial atmosphere. Jupiter is a gas giant without a conventional solid surface, and Saturn’s rings contain ice particles and dust.
Q69. Approximately what percentage of carbon dioxide is present in the atmospheres of Venus and Mars?
[UPSC CDS (II) 2023 – General Knowledge]
(A) 45–47%
(B) 52–55%
(C) 74–77%
(D) 95–97%
Answer: (D) 95–97%
Explanation: Both Venus and Mars have atmospheres dominated by carbon dioxide, with shares close to 95–97 percent. Their atmospheric pressures differ enormously: Venus has a dense atmosphere causing extreme greenhouse warming, while Mars has a much thinner atmosphere.
Q68. Which Indian musician had a minor planet between Mars and Jupiter named in his honour by the International Astronomical Union?
[SSC CGL Tier I, 24 July 2023, Shift 1]
(A) Pandit Hariprasad Chaurasia
(B) Pandit Ravi Shankar
(C) Ustad Zakir Hussain
(D) Pandit Jasraj
Answer: (D) Pandit Jasraj
Explanation: Minor planet 300128 Panditjasraj was named in honour of the renowned Hindustani classical vocalist Pandit Jasraj. Minor planets, many of them in the asteroid belt, receive formally approved names through international astronomical naming procedures.
Q67. Which is the largest planet in the Solar System?
[SSC MTS 2022, held 13 June 2023, Shift 1]
(A) Neptune
(B) Earth
(C) Uranus
(D) Jupiter
Answer: (D) Jupiter
Explanation: Jupiter is the largest planet by both mass and diameter. It is predominantly hydrogen and helium, possesses the Great Red Spot, and has a powerful magnetosphere. Its large size distinguishes it from other gas and ice giant planets.
Q66. Which is the smallest of the eight planets in the Solar System?
[SSC MTS 2022, held 20 June 2023, Shift 3]
(A) Earth
(B) Mars
(C) Mercury
(D) Venus
Answer: (C) Mercury
Explanation: Mercury is the smallest recognised planet and the closest to the Sun. Pluto is classified as a dwarf planet, not one of the eight major planets. Mercury has a rocky surface, a large metallic core, and virtually no substantial atmosphere.
Q65. Which planet is NOT among the four inner planets?
[SSC CHSL Tier I 2022, held 13 March 2023, Shift 4]
(A) Mars
(B) Venus
(C) Mercury
(D) Jupiter
Answer: (D) Jupiter
Explanation: The four inner, terrestrial planets are Mercury, Venus, Earth and Mars. Jupiter lies beyond the asteroid belt and is a gas giant. Inner planets are smaller and predominantly rocky compared with the outer giant planets.
Q64. Which hypothesis is most widely accepted for the origin of the Solar System?
[SSC CPO Paper I, 3 October 2023, Shift 1]
(A) Nebular hypothesis
(B) Gas hypothesis
(C) Solar hypothesis
(D) Cloud hypothesis
Answer: (A) Nebular hypothesis
Explanation: The modern solar nebular model explains the Sun and planets forming from the gravitational collapse of a rotating cloud of gas and dust. A flattened circumstellar disc supplied material that accreted into planetesimals and eventually planets.
Q63. Which recent ISRO scientific mission was launched to undertake a comprehensive study of the Sun?
[MPPSC State Services Prelims, 17 December 2023]
(A) Aditya-L1
(B) Bhaskara-L2
(C) Solar Mission-L1
(D) Solar Orbiter
Answer: (A) Aditya-L1
Explanation: Aditya-L1 is India’s first dedicated solar observatory mission, launched in September 2023. Its instruments study the Sun’s atmosphere, particle environment and magnetic activity from a halo orbit around the Sun–Earth L1 region.
Q62. Which launch vehicle carried the Chandrayaan-3 mission?
[WBCS Main Examination 2023 – Paper IV]
(A) GSLV
(B) LVSM
(C) GSLV Mk III (LVM3)
(D) PSLV
Answer: (C) GSLV Mk III (LVM3)
Explanation: Chandrayaan-3 launched on 14 July 2023 aboard LVM3-M4, the vehicle formerly designated GSLV Mk III. ISRO’s official mission record confirms this. Some commercial answer keys list generic GSLV, but the technically precise choice is option C.
Q61. What was the last PSLV mission launched by ISRO during calendar year 2022?
[CGPSC Prelims 2023 – General Studies]
(A) PSLV-C54
(B) PSLV-C53
(C) PSLV-C52
(D) PSLV-C51
Answer: (A) PSLV-C54
Explanation: PSLV-C54 lifted off on 26 November 2022 carrying EOS-06, an ocean-observation spacecraft, and several co-passenger satellites. It was the final PSLV launch that calendar year, following the earlier C52 and C53 missions.
Q60. If a major solar storm reaches Earth, which effects are possible?
1. GPS failure
2. Equatorial tsunamis
3. Damage to power grids
4. Strong auroras
5. Planet-wide forest fires
6. Disturbed satellite orbits
7. Interrupted polar shortwave aircraft radio.
[UPSC CSE Prelims 2022]
(A) 1, 2, 4 and 5 only
(B) 2, 3, 5, 6 and 7 only
(C) 1, 3, 4, 6 and 7 only
(D) All seven
Answer: (C) 1, 3, 4, 6 and 7 only
Explanation: Geomagnetic storms can induce grid currents, disrupt GPS and radio signals, alter atmospheric drag on satellites and produce auroras. They do not directly trigger tsunamis or widespread forest fires. Statements 1, 3, 4, 6 and 7 are therefore valid.
Q59. Which statement about GPS is NOT correct?
[UPSC NDA (I) 2022 – General Ability Test]
(A) It relies on a network of orbiting satellites
(B) It uses positioning calculations based on satellite signals
(C) Receivers can report latitude, longitude and altitude
(D) It supplies information exclusively for military operations
Answer: (D) It supplies information exclusively for military operations
Explanation: GPS began as a US military system but is used extensively by civilian receivers worldwide. A GPS receiver derives position from the timing of signals transmitted by several satellites; ordinary applications include mapping, transport and emergency response.
Q58. The thick yellowish clouds in Venus’s atmosphere are mainly associated with which substance?
[UPSC CDS (II) 2022 – General Knowledge]
(A) Chlorine
(B) Sulphuric acid
(C) Nitric acid
(D) Bromine
Answer: (B) Sulphuric acid
Explanation: Venus’s global clouds consist largely of sulphuric-acid droplets. They reflect much incoming sunlight, while the thick carbon-dioxide atmosphere traps heat and produces an intense greenhouse effect. The surface remains extremely hot beneath these clouds.
Q57. Which planet had the greatest number of known natural satellites among these options at the time of the paper?
[UPSC CDS (II) 2022 – General Knowledge]
(A) Mars
(B) Neptune
(C) Jupiter
(D) Saturn
Answer: (D) Saturn
Explanation: Saturn was the answer in the examination’s contemporary moon counts. Discovery totals change as astronomers confirm additional small satellites, so such questions must be understood using the tally known when the examination was held.
Q56. Why do planets generally not twinkle in the same way as distant stars?
[RRB Group D, 18 August 2022, Shift 3]
(A) They scatter less light
(B) They act as extended light sources
(C) They behave as ideal point sources
(D) They scatter more light
Answer: (B) They act as extended light sources
Explanation: Planets appear as tiny discs rather than ideal points. Atmospheric refraction fluctuations from different parts of each disc average out, reducing brightness scintillation. Distant stars appear almost point-like, so their light varies more noticeably through turbulent air.
Q55. Which planet has the highest average density among Mercury, Venus, Jupiter and Earth?
[UPSC NDA (I) 2022 – General Ability Test]
(A) Mercury
(B) Venus
(C) Jupiter
(D) Earth
Answer: (D) Earth
Explanation: Earth’s relatively large iron core contributes to its high mean density of about 5.51 grams per cubic centimetre. Venus and Mercury are also rocky and dense, while Jupiter has a much lower average density due to its gaseous composition.
Q54. Why are astronomical distances often measured in light-years?
[UPSC CSE Prelims 2021]
(A) Distances between stars never change
(B) Gravity between stars never changes
(C) Light always travels in a straight line
(D) The speed of light in vacuum is constant
Answer: (D) The speed of light in vacuum is constant
Explanation: A light-year is a unit of length: the distance light travels through vacuum in one Julian year, approximately 9.46 trillion kilometres. The fixed speed of light makes it a convenient standard for communicating very large stellar distances.
Q53. Which is NOT part of our Solar System?
[RRB NTPC CBT I, 23 July 2021, Shift 2]
(A) Europa
(B) Moon
(C) Pole Star
(D) Sun
Answer: (C) Pole Star
Explanation: Polaris, the Pole Star, is a distant stellar system rather than a body orbiting our Sun. Europa is a moon of Jupiter, the Moon orbits Earth, and the Sun is the Solar System’s central star.
Q52. Which is the nearest star to Earth?
[RRB NTPC CBT I, 5 April 2021, Shift 1]
(A) Altair
(B) Sun
(C) Vega
(D) Moon
Answer: (B) Sun
Explanation: The Sun is Earth’s nearest star and provides the energy sustaining life. The Moon is a natural satellite, not a star. Stars such as Altair and Vega are many light-years farther away than the Sun.
Q51. Which theory best explains the origin of the Universe?
[UPSC NDA (I) 2021 – General Ability Test]
(A) Nebular hypothesis
(B) Binary theory
(C) Big Bang theory
(D) Planetesimal hypothesis
Answer: (C) Big Bang theory
Explanation: The Big Bang model describes the early hot, dense universe and its subsequent expansion. The nebular and planetesimal hypotheses deal with planetary-system formation, not the initial history of the universe as a whole.
Q50. Which planet is closest to the Sun?
[SSC JE, 23 March 2021, Morning]
(A) Neptune
(B) Mercury
(C) Mars
(D) Venus
Answer: (B) Mercury
Explanation: Mercury occupies the innermost planetary orbit, completing a revolution around the Sun in about 88 Earth days. Despite being closest to the Sun, it is not the hottest planet; Venus has a denser greenhouse atmosphere.
Q49. Which frequency band is not normally used for INSAT/GSAT satellite communication?
[RPSC RAS Prelims, 27 October 2021]
(A) Ka band
(B) C band
(C) MF band
(D) Ku band
Answer: (C) MF band
Explanation: Communication satellites commonly use microwave bands such as C, Ku and Ka for reliable, high-capacity links. The medium-frequency (MF) band is much lower in frequency and is associated mainly with terrestrial services such as AM broadcasting.
Q48. Which project employs three spacecraft in an equilateral triangle with sides approximately one million kilometres long and laser beams exchanged between them?
[UPSC CSE Prelims 2020]
(A) Voyager 2
(B) New Horizons
(C) LISA Pathfinder
(D) Evolved LISA
Answer: (D) Evolved LISA
Explanation: The evolved Laser Interferometer Space Antenna concept uses precisely measured laser links between widely separated spacecraft to detect gravitational waves. Its immense baseline is suited to low-frequency waves from massive cosmic systems that ground-based observatories cannot easily access.
Q47. What are the four planets nearest the Sun collectively called?
[UPSC CDS (II) 2020 – General Knowledge]
(A) Terrestrial planets
(B) Giant planets
(C) Dwarf planets
(D) Gas planets
Answer: (A) Terrestrial planets
Explanation: Mercury, Venus, Earth and Mars are terrestrial planets, built mainly from rock and metal and possessing relatively solid surfaces. Jupiter, Saturn, Uranus and Neptune are larger outer planets with thick gaseous layers.
Q46. Which solar-system statements are correct?
I. Mercury is the hottest planet.
II. Ganymede is Saturn’s largest moon.
III. Neptune has extremely cold methane-rich atmospheric features.
IV. Phobos and Deimos orbit Mars.
[CGPSC Civil Services Prelims 2020 – Paper I]
(A) I and II only
(B) II and III only
(C) III and IV only
(D) All four
Answer: (C) III and IV only
Explanation: Venus, not Mercury, has the highest average surface temperature because of its runaway greenhouse atmosphere. Ganymede is Jupiter’s moon, not Saturn’s. Neptune contains atmospheric methane, while Phobos and Deimos are the two small Martian moons.
Q45. Which was the first Arab nation to launch a mission to Mars in July 2020?
[UPPSC Civil Services Prelims 2020 – General Studies I]
(A) Saudi Arabia
(B) Kuwait
(C) United Arab Emirates
(D) Qatar
Answer: (C) United Arab Emirates
Explanation: The United Arab Emirates launched the Hope orbiter, also called Al-Amal, toward Mars in July 2020. The probe was intended to study the Martian atmosphere and weather patterns and marked the first interplanetary mission by an Arab nation.
Q44. For the Northern Hemisphere, which date-event pairs are conventionally correct?
1. Winter solstice — 22 December
2. Autumn equinox — 23 September
3. Summer solstice — 21 June
4. Spring equinox — 21 March.
[WBCS Prelims 2020]
(A) 1 and 2 only
(B) 2 and 3 only
(C) 3 and 4 only
(D) All are conventionally matched
Answer: (D) All are conventionally matched
Explanation: Solstices occur when the Sun reaches its extreme apparent north–south positions; equinoxes occur when the Sun crosses the celestial equator. Exact dates can shift by a day depending on year and time zone, but the listed dates are standard textbook approximations.
Q43. What was the significance of detecting the merger of massive black holes billions of light-years away?
[UPSC CSE Prelims 2019]
(A) Detection of Higgs bosons
(B) Detection of gravitational waves
(C) Confirmation of intergalactic wormhole travel
(D) Proof of the exact nature of singularities
Answer: (B) Detection of gravitational waves
Explanation: Merging black holes radiate gravitational waves, ripples in spacetime predicted by general relativity. Their detection opened a new way to observe cosmic events that may emit little or no ordinary light and test strong-gravity physics.
Q42. For which measurements can satellite images or remote-sensing data be used? 1. Vegetation chlorophyll 2. Greenhouse-gas emissions from rice fields 3. Land-surface temperature.
[UPSC CSE Prelims 2019]
(A) 1 only
(B) 2 and 3 only
(C) 3 only
(D) 1, 2 and 3
Answer: (D) 1, 2 and 3
Explanation: Remote sensing uses recorded radiation in different spectral bands to infer vegetation condition, surface temperature and certain atmospheric trace-gas patterns. Combining satellite measurements with models and ground observations also supports estimates of agricultural greenhouse-gas emissions.
Q41. Which planet has the least mass among Neptune, Jupiter, Mars and Mercury?
[UPSC CDS (I) 2019 – General Knowledge]
(A) Neptune
(B) Jupiter
(C) Mars
(D) Mercury
Answer: (D) Mercury
Explanation: Mercury has the smallest mass of any of the eight major planets. Jupiter and Neptune are giant planets, and Mars is considerably more massive than Mercury. Mercury remains dense because of its unusually large metallic core.
Q40. What is the name of the Chandrayaan-2 lander?
[UPSC NDA (II) 2019 – General Ability Test]
(A) Vigyan
(B) Anusandhan
(C) Pragyan
(D) Vikram
Answer: (D) Vikram
Explanation: Chandrayaan-2 comprised an orbiter, the Vikram lander and the Pragyan rover. Vikram was named in honour of physicist Vikram Sarabhai. The lander’s soft-landing attempt in 2019 did not achieve its intended touchdown.
Q39. Which of the following planets is farthest from the Sun?
[SSC CHSL, 2 July 2019, Shift 3]
(A) Jupiter
(B) Venus
(C) Mars
(D) Neptune
Answer: (D) Neptune
Explanation: Neptune is the eighth and outermost recognised major planet. Its average distance from the Sun is about 30 astronomical units, so it receives much less sunlight than the inner planets. Pluto is classified as a dwarf planet.
Q38. Which scientist is associated with the heliocentric model of the Solar System?
[SSC GD, 12 February 2019, Shift 2]
(A) Murphy
(B) Newton
(C) Copernicus
(D) Vasco da Gama
Answer: (C) Copernicus
Explanation: Nicolaus Copernicus developed a systematic Sun-centred model in which Earth and other planets orbit the Sun. Earlier heliocentric ideas existed, but Copernicus’s mathematical presentation became central to the scientific revolution and later planetary-motion theories.
Q37. Which are predictions of Einstein’s General Theory of Relativity?
1. Light is affected by gravity.
2. The Universe is constantly expanding.
3. Matter curves surrounding spacetime.
[UPSC CSE Prelims 2018]
(A) 1 and 2 only
(B) 3 only
(C) 1 and 3 only
(D) 1, 2 and 3
Answer: (D) 1, 2 and 3
Explanation: General relativity relates matter and energy to the curvature of spacetime, explaining gravitational lensing and allowing cosmological expansion solutions. It underpins modern models of black holes, gravitational waves and the large-scale evolution of the universe.
Q36. Consider these Indian navigation satellite statements:
1. IRNSS has three geostationary and four geosynchronous satellites.
2. Its coverage is limited to India plus 5,500 square kilometres outside its borders.
3. It was to provide full global coverage by 2019.
Which is correct?
[UPSC CSE Prelims 2018]
(A) 1 only
(B) 1 and 2 only
(C) 2 and 3 only
(D) None
Answer: (A) 1 only
Explanation: The original NavIC/IRNSS configuration included three geostationary and four inclined geosynchronous spacecraft. Its regional service covers India and an extensive surrounding area, not merely 5,500 square kilometres, and it was not a full global navigation constellation.
Q35. Which statement about Indian launch vehicles is correct?
1. PSLV chiefly serves Earth-resource missions and GSLV mainly communication satellites.
2. PSLV satellites always appear fixed over Earth.
3. GSLV Mk III consists of four stages.
[UPSC CSE Prelims 2018]
(A) 1 only
(B) 2 and 3 only
(C) 1 and 2 only
(D) 3 only
Answer: (A) 1 only
Explanation: PSLV has often launched Earth-observation spacecraft, whereas GSLV was developed for heavier geosynchronous communication payloads. Geostationary appearance depends on the satellite’s orbit rather than launcher. LVM3/GSLV Mk III is not the four-stage vehicle described.
Q34. Which ISRO centre-location pairs are correct?
A. VSSC — Thiruvananthapuram
B. U R Rao Satellite Centre — Bengaluru
C. NRSC — Dehradun
D. IIRS — Hyderabad.
[RPSC RAS Prelims 2018]
(A) A and B only
(B) A, B and C only
(C) B, C and D only
(D) All four
Answer: (A) A and B only
Explanation: Vikram Sarabhai Space Centre is in Thiruvananthapuram and U R Rao Satellite Centre is in Bengaluru. The other locations are reversed: National Remote Sensing Centre is in Hyderabad, while Indian Institute of Remote Sensing is in Dehradun.
Q33. How many satellites did PSLV-C37 place into orbit in a single mission on 15 February 2017?
[RPSC RAS Prelims 2018]
(A) 80
(B) 104
(C) 72
(D) 98
Answer: (B) 104
Explanation: PSLV-C37 carried Cartosat-2 series satellite and 103 co-passengers, successfully deploying 104 satellites in one flight. This was a record at the time and demonstrated ISRO’s capacity for coordinated deployment of numerous small satellites.
Q32. Which space agency launched the unusually small SS-520-5 orbital rocket?
[RPSC RAS Prelims 2018]
(A) NASA
(B) ISRO
(C) CNSA
(D) JAXA
Answer: (D) JAXA
Explanation: The Japan Aerospace Exploration Agency successfully launched an orbital-class SS-520-5 rocket in 2018. Its small size attracted attention because it demonstrated the feasibility of placing a miniature satellite into orbit using a compact launch vehicle.
Q31. Among Mars, Mercury, Venus and Jupiter, which planet is considered a relatively promising candidate for possible life?
[UPPSC Civil Services Prelims 2018 – General Studies I]
(A) Mars
(B) Mercury
(C) Venus
(D) Jupiter
Answer: (A) Mars
Explanation: Mars has evidence of ancient liquid water, sedimentary environments and chemical ingredients relevant to habitability. These observations make it an important target in astrobiology. They do not establish that life currently exists or previously existed there.
Q30. The terms event horizon, singularity, string theory and Standard Model are associated primarily with what?
[UPSC CSE Prelims 2017]
(A) Understanding and observing the Universe
(B) Studying only eclipses
(C) Launching satellites around Earth
(D) Origin of life on Earth
Answer: (A) Understanding and observing the Universe
Explanation: Event horizons and singularities arise in gravitational theories of compact objects. String theory and the Standard Model investigate fundamental particles and interactions. Together these terms concern basic physical descriptions of the cosmos, not spacecraft launches alone.
Q29. What is the purpose of the evolved Laser Interferometer Space Antenna (eLISA)?
[UPSC CSE Prelims 2017]
(A) Neutrino detection
(B) Gravitational-wave detection
(C) Testing missile-defence effectiveness
(D) Studying only solar-flare effects
Answer: (B) Gravitational-wave detection
Explanation: eLISA was conceived as a space-based gravitational-wave observatory using laser interferometry between distant spacecraft. It targets tiny distortions in distance generated by massive accelerating systems such as black-hole binaries, beyond many frequencies accessible from Earth.
Q28. How many planets are recognised in the Solar System?
[SSC MTS, 21 September 2017, Shift 1]
(A) 8
(B) 10
(C) 9
(D) 7
Answer: (A) 8
Explanation: The International Astronomical Union recognises eight major planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto was reclassified as a dwarf planet in 2006 because it had not cleared its orbital neighbourhood.
Q27. Which planet was explored by NASA’s Cassini mission, which ended in September 2017?
[UPSC CDS (II) 2017 – General Knowledge]
(A) Sun
(B) Neptune
(C) Saturn
(D) Jupiter
Answer: (C) Saturn
Explanation: Cassini spent over a decade studying Saturn, its rings, magnetosphere and moons after arrival in 2004. Its mission ended with a deliberate atmospheric plunge in 2017 to protect potentially habitable moons from accidental biological contamination.
Q26. Which country launched the Venus environmental-research microsatellite in August 2017?
[UPSC CDS (II) 2017 – General Knowledge]
(A) India
(B) Russia
(C) China
(D) Israel
Answer: (D) Israel
Explanation: Venus, short for Vegetation and Environment monitoring on a New Micro-Satellite, was a joint Israeli–French Earth-observation satellite. Israel launched the spacecraft in 2017 for environmental and vegetation imaging, despite its planetary-sounding name.
Q25. Which statements about Astrosat are correct?
1. Besides the USA and Russia, India is the only country to have launched such an observatory.
2. Astrosat weighs 2,000 kg and orbits at a height of 1,650 km.
[UPSC CSE Prelims 2016]
(A) 1 only
(B) 2 only
(C) Both 1 and 2
(D) Neither 1 nor 2
Answer: (D) Neither 1 nor 2
Explanation: Astrosat, launched in 2015, was India’s first dedicated multiwavelength space observatory. The claims about exclusivity and a 2,000-kilogram spacecraft at 1,650 kilometres are inaccurate. Other countries had also launched space observatories before India.
Q24. Consider Mangalyaan:
1. It is also called Mars Orbiter Mission.
2. India was the second country to orbit Mars after the USA.
3. India succeeded in orbiting Mars on its first attempt.
Which statements are correct?
[UPSC CSE Prelims 2016]
(A) 1 only
(B) 2 and 3 only
(C) 1 and 3 only
(D) 1, 2 and 3
Answer: (C) 1 and 3 only
Explanation: Mangalyaan is the Mars Orbiter Mission and reached Mars orbit on India’s first interplanetary attempt. Other space agencies had already orbited Mars before ISRO, so India was not the second country overall. Statements 1 and 3 are correct.
Q23. Which statement about ISRO’s reusable launch-vehicle technology demonstrator is NOT correct?
[UPSC CDS (II) 2016 – General Knowledge]
(A) The demonstration flight occurred in 2016
(B) It launched from Sriharikota
(C) It reached approximately 65 km altitude
(D) It was initially boosted by a liquid-fuel rocket
Answer: (D) It was initially boosted by a liquid-fuel rocket
Explanation: ISRO tested its winged Reusable Launch Vehicle–Technology Demonstrator in May 2016 using a solid booster from Sriharikota. It reached suborbital altitude before a controlled descent. The claimed initial liquid-fuel booster is the incorrect detail.
Q22. In astronomical news, what does the term Goldilocks Zone refer to?
[UPSC CSE Prelims 2015]
(A) A habitable layer above Earth
(B) Shale-gas regions inside Earth
(C) The search for potentially Earth-like planets around other stars
(D) Meteorites containing precious metals
Answer: (C) The search for potentially Earth-like planets around other stars
Explanation: The circumstellar habitable zone is the orbital region where surface liquid water could persist on a suitable planet. It depends on stellar luminosity and atmospheric conditions. Being in this zone does not by itself establish that a planet has life.
Q21. For which activities are Indian Remote Sensing satellites used?
1. Crop productivity assessment
2. Locating groundwater
3. Mineral exploration
4. Telecommunications
5. Traffic studies.
[UPSC CSE Prelims 2015]
(A) 1, 2 and 3 only
(B) 4 and 5 only
(C) 1 and 2 only
(D) All five
Answer: (A) 1, 2 and 3 only
Explanation: Indian Remote Sensing satellites image the Earth for agriculture, resource inventories and geological investigations. Telecommunications generally depend on communication satellites, and ordinary traffic-management functions do not define the core applications asked in this question.
Q20. Which spacecraft was reported in March 2015 to have detected biologically useful nitrogen compounds on Mars?
[UPPSC Civil Services Prelims, 10 May 2015]
(A) Mangalyaan
(B) Mars Express
(C) Phoenix Mars Lander
(D) Curiosity Rover
Answer: (D) Curiosity Rover
Explanation: NASA’s Curiosity rover analysed Martian rocks and detected nitrogen-bearing compounds such as nitrates. Nitrogen is an important ingredient for life as known on Earth. Its detection strengthens evidence for potentially habitable chemistry, without proving the existence of Martian organisms.
Q19. Which spacecraft-purpose pairs are correct?
1. Cassini-Huygens — studying Venus
2. MESSENGER — investigating Mercury
3. Voyager 1 and 2 — exploring the outer Solar System.
[UPSC CSE Prelims 2014]
(A) 1 only
(B) 2 and 3 only
(C) 1 and 3 only
(D) All three
Answer: (B) 2 and 3 only
Explanation: Cassini-Huygens explored Saturn and Titan rather than Venus. NASA’s MESSENGER studied Mercury, while Voyager 1 and 2 investigated giant planets and their moons. Consequently, the second and third spacecraft-purpose pairs are the accurate ones.
Q18. Approximately how many times is the Sun’s diameter larger than Earth’s diameter?
[MPPSC State Service Prelims 2014]
(A) 124
(B) 100
(C) 109
(D) 115
Answer: (C) 109
Explanation: The Sun’s diameter is about 1.39 million kilometres, compared with Earth’s approximately 12,742 kilometres. Their ratio is close to 109. This comparison concerns linear diameter; the Sun’s volume is vastly greater, around 1.3 million Earth volumes.
Q17. ISRO and NASA discussed a bilateral working group in March 2013 for which areas?
1. Future Moon and Mars missions
2. Meteorology and space exploration
3. Heliophysics.
[UPPSC Civil Services Prelims 2013]
(A) Moon and Mars missions only
(B) Meteorology and space exploration only
(C) Heliophysics only
(D) All of the above
Answer: (D) All of the above
Explanation: ISRO–NASA cooperation encompasses planetary exploration, Earth observation and heliophysics. Joint technical discussions can address lunar and Martian missions, measurements of Earth’s atmosphere and investigations of the Sun and its influence on the space environment.
Q16. Which Indian satellite marked the country’s entry into the space age in 1975?
[RPSC RAS Prelims 2013]
(A) Bhaskara-I
(B) Aryabhata
(C) APPLE
(D) Agni
Answer: (B) Aryabhata
Explanation: Aryabhata was India’s first satellite, built domestically and launched in April 1975 using a Soviet rocket. It was named after the mathematician and astronomer Aryabhata. Bhaskara satellites and APPLE came later, while Agni denotes missile systems.
Q15. For which purpose was India’s GSAT-7 satellite primarily developed?
[RPSC RAS Prelims 2013]
(A) Weather forecasting
(B) Military communications
(C) Mars exploration
(D) Dedicated lunar coverage
Answer: (B) Military communications
Explanation: GSAT-7 is a multi-band communications satellite developed mainly for India’s defence services, especially the Indian Navy. Satellite communications can connect platforms separated by large ocean distances, strengthening secure operational coordination.
Q14. Which observations support the continuing expansion of the Universe?
1. Microwave background radiation
2. Cosmological redshift
3. Motion of asteroids
4. Supernova explosions.
[UPSC CSE Prelims 2012]
(A) 1 and 2 only
(B) 2 only
(C) 1, 3 and 4 only
(D) None of these
Answer: (A) 1 and 2 only
Explanation: The cosmic microwave background records relic radiation from the early universe, and the cosmological redshift of distant galaxies indicates the expansion of space. Ordinary asteroid movement is a local dynamical process and does not establish cosmic expansion.
Q13. Why does an artificial satellite in Earth orbit not simply fall vertically to the ground?
[UPSC CSE Prelims 2011]
(A) Earth’s gravity is absent
(B) The Moon cancels Earth’s gravity
(C) Gravity supplies steady speed
(D) Earth’s gravity provides the necessary centripetal acceleration
Answer: (D) Earth’s gravity provides the necessary centripetal acceleration
Explanation: An orbiting satellite is continuously falling under Earth’s gravity, but its forward velocity causes it to keep missing the surface. Gravitational acceleration continually bends the trajectory, supplying the centripetal acceleration needed for orbital motion.
Q12. Which statements distinguish asteroids and comets?
1. Asteroids are usually rocky; comets contain volatile ice.
2. Most comets occur between Mercury and Venus.
3. Comets can display a luminous tail, unlike most asteroids.
[UPSC CSE Prelims 2011]
(A) 1 and 2 only
(B) 1 and 3 only
(C) 3 only
(D) All three
Answer: (B) 1 and 3 only
Explanation: Many asteroids are rocky or metallic, whereas comets contain abundant ice and dust. Solar heating can release gas and dust from a comet, generating a coma and tail. Most comet reservoirs lie far beyond the inner planets.
Q11. A telecommunications satellite is geostationary if it has
1. A geosynchronous period
2. A circular orbit
3. An equatorial orbit
4. Altitude of 22,236 km.
Which conditions are correct?
[UPSC CSE Prelims 2011]
(A) 1, 2 and 3 only
(B) 1, 3 and 4 only
(C) 2 and 4 only
(D) All four
Answer: (A) 1, 2 and 3 only
Explanation: Geostationary satellites must orbit eastward in a circular equatorial orbit with a period equal to Earth’s sidereal rotation. Their actual altitude is approximately 35,786 kilometres, not the 22,236 kilometres given in the fourth statement.
Q10. Oceansat-2 helps India with which activities?
1. Estimating atmospheric water-vapour content
2. Studying and forecasting monsoon-related processes
3. Assessing coastal water quality.
[UPSC CSE Prelims 2010]
(A) 1 and 2 only
(B) 2 only
(C) 1 and 3 only
(D) 1, 2 and 3
Answer: (D) 1, 2 and 3
Explanation: Oceansat-2 carried instruments for monitoring ocean colour and surface winds, which support atmospheric and monsoon studies as well as assessments of coastal-water conditions. Satellite data are combined with observations and models for operational environmental applications.
Q9. What is Bhuvan in the context of Indian space technology?
[UPSC CSE Prelims 2010]
(A) A distance-education minisatellite
(B) A Moon impact probe
(C) ISRO’s geospatial portal with two-dimensional and three-dimensional views
(D) An Indian optical space telescope
Answer: (C) ISRO’s geospatial portal with two-dimensional and three-dimensional views
Explanation: Bhuvan is ISRO’s web-based geospatial platform for displaying and analysing Indian Earth-observation datasets. It provides imagery, mapping layers and 2D or 3D visualisation for uses such as planning, natural-resource management and disaster-related mapping.
Q8. Which country launched the SELENE-1 lunar orbiter, also called Kaguya?
[UPSC CSE Prelims 2008]
(A) China
(B) European Union
(C) Japan
(D) United States
Answer: (C) Japan
Explanation: Japan’s space agency JAXA launched the SELENE mission, better known as Kaguya, in 2007. It used multiple instruments to study lunar geology, topography, gravity and other properties, contributing to understanding the Moon’s origin and evolution.
Q7. Where is the Indian rocket-engine test facility used for a 2007 cryogenic-engine test located?
[UPSC CSE Prelims 2008]
(A) Balasore
(B) Thiruvananthapuram
(C) Mahendragiri
(D) Karwar
Answer: (C) Mahendragiri
Explanation: Mahendragiri in Tamil Nadu hosts major ISRO propulsion-test facilities, formerly associated with the Liquid Propulsion Systems Centre and now the ISRO Propulsion Complex. Cryogenic rocket engines use very cold liquid propellants and require specialised testing infrastructure.
Q6. Which of these is the NASA spacecraft that explored Saturn with the Huygens probe?
[UPSC CSE Prelims 2008]
(A) Apophis
(B) Cassini
(C) Spitzer
(D) TechSAR
Answer: (B) Cassini
Explanation: Cassini was a planetary exploration spacecraft studying Saturn and its moons. Apophis is an asteroid, Spitzer was an infrared observatory and TechSAR an Earth-observation satellite. Huygens separated from Cassini and landed on Saturn’s moon Titan.
Q5. Which comet nucleus was struck and examined by NASA’s Deep Impact mission?
[UPSC CSE Prelims 2007]
(A) Halley
(B) Hale-Bopp
(C) Hyakutake
(D) Tempel 1
Answer: (D) Tempel 1
Explanation: NASA’s Deep Impact spacecraft released a projectile that collided with comet Tempel 1 in July 2005. The resulting debris plume gave scientists clues about the comet’s internal material, helping research into primitive Solar System substances.
Q4. Which pairing is incorrect?
[UPSC CSE Prelims 2007]
(A) COBE — satellite programme
(B) FALCON — undersea cable system
(C) Discovery — space shuttle
(D) Atlantis — space station
Answer: (D) Atlantis — space station
Explanation: Atlantis was a NASA Space Shuttle orbiter, not a permanent space station. Discovery was another shuttle, while COBE examined cosmic microwave background radiation. FALCON refers to a submarine telecommunications cable system rather than an orbiting spacecraft.
Q3. Consider:
1. India launched METSAT, its first dedicated meteorological satellite, in September 2002.
2. PSLV-C4 placed a payload exceeding 1,000 kg into geosynchronous transfer orbit.
Which are correct?
[UPSC CSE Prelims 2003]
(A) 1 only
(B) 2 only
(C) Both 1 and 2
(D) Neither 1 nor 2
Answer: (C) Both 1 and 2
Explanation: PSLV-C4 launched METSAT, later renamed Kalpana-1, in September 2002. This spacecraft advanced India’s dedicated meteorological observation capability. Its launch also demonstrated PSLV’s ability to place a payload exceeding one tonne into geosynchronous transfer orbit.
Q2. Which statements about Indian satellites are correct?
1. All INSAT-series satellites had been launched abroad.
2. PSLV launched IRS-series satellites.
3. India had already used an indigenous cryogenic GSLV upper stage.
4. GSAT launched in 2001 carried digital broadcasting and internet-service demonstration payloads.
[UPSC CSE Prelims 2002]
(A) 1, 2, 3 and 4
(B) 2, 3 and 4 only
(C) 1, 2 and 4 only
(D) 1 and 3 only
Answer: (C) 1, 2 and 4 only
Explanation: At the time of this question, INSAT launches used foreign vehicles and PSLV served the Indian Remote Sensing series. Early GSLV cryogenic stages were not indigenous; GSAT-1 was a 2001 technology demonstrator. Hence statements 1, 2 and 4 apply.
Q1. Assertion: Artificial satellites are always launched from Earth eastward.
Reason: Earth rotates west to east and therefore supplies the satellite with escape velocity.
[UPSC CSE Prelims 2002]
(A) Both statements true; reason explains assertion
(B) Both true; reason does not explain assertion
(C) Assertion true; reason false
(D) Assertion false; reason true
Answer: (C) Assertion true; reason false
Explanation: The examination’s keyed response was C. Eastward launches gain speed from Earth’s rotation, reducing the propellant required for many prograde orbits. This boost does not automatically provide escape velocity. In modern terminology, the word “always” is overly absolute.