CDS (II) 2022 General Knowledge · Question 112 of 120

Correct — D, Saturn. Read the stem carefully: it asks for known satellites, and that is a count that changes as telescopes improve. Saturn took the lead from Jupiter in 2019, when a haul of new discoveries carried it to 82 against Jupiter's 79 — the first time since 2000 that Saturn had been ahead. It still held the lead when this paper was set in September 2022, and it holds it comfortably today. The reason is not luck. Saturn's swarm of small, distant, irregular moons is far richer than Jupiter's: down to a diameter of about 2.8 kilometres there are roughly three times as many Saturnian irregulars as Jovian ones, so every survey sensitive enough to find them widens the gap.

• (a)Mars — Mars has just two moons, Phobos and Deimos, both small and irregular in shape and probably captured. It is nowhere near the top of this list.
• (b)Neptune — Neptune has a modest family in the mid-teens, dominated by Triton — remarkable because it orbits backwards, which points to capture from the Kuiper belt — but nothing like the counts of the two large gas giants.
• (c)Jupiter — The trap, and a reasonable one, because Jupiter held this title for most of the twentieth century and older textbooks still say so. It was overtaken in 2019 and has not regained the lead except for a few months in 2023, when a batch of confirmations briefly took it to 95 before Saturn jumped to 145.

Planetary moons fall into two very different groups. Regular satellites orbit close in, near the planet's equatorial plane and in the same direction as the planet spins; they formed in the disc around the young planet, and they include the large famous ones — Jupiter's four Galilean moons and Saturn's Titan. Irregular satellites are small, far out, often steeply inclined and frequently retrograde; they were captured, and they are what surveys keep adding by the dozen. Almost every announcement that raises a planet's count is an announcement about irregulars.

This is one of the few general-knowledge facts that has genuinely changed twice in living memory, so anchor it to dates rather than to a single number. Jupiter held the record for most of the last century; Saturn passed it in 2019; Jupiter briefly retook it in February 2023 at 95; and Saturn settled the matter in May 2023 with 145, becoming the first planet known to have more than a hundred moons, then 274 after 128 new ones were announced at once in March 2025. As of 2026 the counts stand at about 293 for Saturn and 115 for Jupiter. Note the honest consequence: a UPSC prelims question from 2009, UPSC_2009_GS1_Q66, asked exactly this and its correct answer was Jupiter. Both keys were right on the day they were written. If you meet this question in a paper, answer it for the year the paper was set.

• Saturn overtook Jupiter in 2019, reaching 82 confirmed moons against Jupiter's 79.
• Jupiter's count reached 95 in February 2023, briefly taking the lead back.
• Saturn reached 145 in May 2023, becoming the first planet known to have more than a hundred moons.
• A single announcement in March 2025 added 128 Saturnian moons, taking the total to 274; the count stood at 293 in 2026, against 115 for Jupiter.
• Mars has two moons; Mercury and Venus have none.

• Answering from an older textbook that still gives Jupiter the record.
• Overlooking the word 'known' in the stem — this is a count of discoveries, not a fixed property of the planet.
• Assuming the largest planet must have the most moons; Saturn's advantage comes from its irregular swarm, not its size.

As a direct comparison between planets, or inside a statements item mixing moon counts with ring systems and the presence or absence of an atmosphere.

• practice — not a real PYQ

  Which two planets of the Solar System have no natural satellites?

  • (a)Mercury and Venus
  • (b)Venus and Mars
  • (c)Mercury and Mars
  • (d)Mars and Neptune

  Answer(a) Mercury and Venus — the two innermost planets; Mars has Phobos and Deimos.

• practice — not a real PYQ

  Triton, the largest moon of Neptune, is unusual chiefly because it

  • (a)Has a permanent liquid water ocean on its surface
  • (b)Orbits its planet in a retrograde direction
  • (c)Is larger than the planet Mercury
  • (d)Has no measurable gravity

  Answer(b) Orbits its planet in a retrograde direction — evidence that it was captured rather than formed in orbit around Neptune.