NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission data reveals new insights into why the Moon’s two hemispheres differ in appearance.
What are the two sides of the moon?

- Nearside: It is that part which is always visible from the Earth.
- Covered by vast plains, known as mare, formed by volcanic activity.
- Crust on this side is thinner which allows magma to rise more easily.
- This side is warmer and more radioactive due to radioactive elements like thorium and titanium.
- Farside: This side is never visible from earth.
- It has more rugged terrain than plains.
- Crust on this side is thicker which prevents lava flows.
About GRAIL Mission
- GRAIL refers to Gravity Recovery and Interior Laboratory.
- It was a NASA lunar science mission.
- Launched in 2011.
- The mission used two spacecraft, Ebb and Flow, to map the Moon’s gravitational field.
- Significance: It helped to gain insights into its internal composition and geological evolution of the moon.
- Provides models for conducting deep studying of other celestial bodies such as Saturn’s Enceladus and Jupiter’s Ganymede.
- Increases understanding of formation and evolution of planets.
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Reasons Behind the Lunar Asymmetry
- Tidal Deformation and Gravitational Influence
- The Moon’s nearside is more geologically active and flexible due to Earth’s gravitational pull.
- Tidal deformation causes the nearside to experience greater internal movement, shaping its surface differently from the farside.
- Volcanic Activity and Heat Distribution
- The nearside was once much more volcanically active than the farside, resulting in the formation of large basaltic plains (mare).
- Heat-producing radioactive elements like thorium and titanium accumulated on the nearside, making it hotter than the farside (by around 100-200°C).
- This heat imbalance influenced the geological features of both hemispheres.
- Crust Thickness and Surface Composition
- GRAIL data revealed that the nearside has a thinner crust, allowing magma to flow more easily in the past.
- The farside has a thicker crust, preventing widespread lava flows, which explains its rugged, cratered surface.
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