ISRO Missions and Discoveries

Unraveling the Lunar Landscape: Near, Far, and Dark Sides


From UPSC perspective, the following things are important :

Prelims level: Near, Far, and Dark Sides, KREEP

Mains level: Lunar study by Chandrayaan 3

far dark side lunar moon

Central Idea

  • The Chandrayaan-3 mission’s recent lunar landing has sparked curiosity about the moon’s various sides – near, far, and even the intriguing ‘dark’ side.
  • Delving into these distinctions sheds light on the moon’s enigmatic nature and how space exploration helps us unravel its mysteries.

Facts for Prelims

Impact/Landing point names on Moon:

1. Chandrayaan 1: Jawahar Point

2. Chandrayaan 2: Tiranga Point

3. Chandrayaan 3: Shivshakti Point

 Moon’s Visible and Hidden Faces

  • Near and Far Sides: The moon’s ‘near side,’ visible from Earth, covers around 60% of its surface. In contrast, the ‘far side’ remained hidden from us until modern spacecraft brought it into view.
  • Clarifying the ‘Dark’ Side: Often misconstrued as constantly dark, the ‘dark side’ simply refers to the unseen side. It gets illuminated during the ‘new moon’ phase, challenging the misconception of its perpetual darkness.

Why is their composition different?

  • The composition of the Moon’s near and far sides is different, and scientists believe they have identified the reasons behind this discrepancy.
  • A study published in the journal Nature Geoscience reveals that the presence of KREEP, a rock enriched in potassium (K), rare-earth elements (REE), and phosphorus (P), plays a crucial role.

Key Points from the Study:

  • Moons Near and Far Sides: The Moon’s near side, always facing Earth, has visible dark and light patches known as “maria.” Telescopic observations showed that these were not seas as early astronomers thought, but rather craters or volcanic features. The far side of the Moon has fewer maria than the near side.
  • Moon’s Formation: The uneven distribution of volcanism and the KREEP signature between the near and far sides of the Moon puzzled scientists.
  • Radioactive Unstable Elements: Potassium (K), thorium (Th), and uranium (U) are unstable, radioactive elements that have various isotopes with different numbers of neutrons. The radioactive decay of these elements generates heat that can melt rocks and contribute to volcanic activity.
  • Heat and Melting: The study found that the inclusion of KREEP in rocks not only enhances heating but also lowers their melting temperature. This combination increases volcanic activity beyond what is predicted by radiogenic decay models.
  • Geological Record: The Moon’s surface preserves geological events from the early history of the Solar System due to the absence of erosion processes. Concentrations of radioactive elements like uranium (U) and thorium (Th) on the near side provide insights into the Moon’s formation and early Earth conditions.

Phases and Illumination

  • New Moon Phase: The ‘new moon’ phase unveils the moon’s ‘far side,’ exposing it to sunlight for about two weeks.
  • Historic Revelation: In 1968, astronauts aboard Apollo 8 became the first humans to observe the ‘far side,’ demystifying its hidden features.

Chandrayaan-3’s Approach

  • Closest South Pole Landing: Chandrayaan-3’s landing at coordinates 69.36 S and 32.34 E marks the closest approach to the lunar South Pole.
  • Exploring Permanently Shadowed Regions: The strategic landing aimed to study regions that never receive sunlight, potentially containing frozen water ice and other lunar resources.
  • Sunlight Necessity: Vikram’s nearness to the South Pole ensures sunlight for solar battery recharging, crucial for its operation.
  • Choice of Landing Site: The decision to land on the ‘near side’ was driven by mission objectives, including real-time communication with Earth. Landing on the ‘far side’ would have required relay satellites and introduced delays.

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