Why Do The Moon's Two Sides Look Different?

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?

Moon's Two Sides

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.

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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