GRAIL Mission

NASA’s GRAIL mission has recently highlighted notable distinctions between the moon’s nearside and farside. These variations have been linked to tidal forces and differing levels of volcanic activity across the lunar surface.

Overview of the GRAIL Mission

The Gravity Recovery and Interior Laboratory (GRAIL) is a NASA initiative launched in 2011 to explore the moon’s gravitational field. The mission deployed two spacecraft, named Ebb and Flow, which orbited the moon in tandem. By monitoring slight changes in the distance between the two, the mission produced the most precise gravity map of the lunar surface ever created.

GRAIL’s main objective was to detect variations in the moon’s gravitational pull, shedding light on its internal structure and geological evolution. Tiny shifts in the spacecrafts’ separation, influenced by gravitational anomalies, revealed key details about the thickness of the crust, hidden structures beneath the surface, and variations in internal composition.

One of the mission’s notable discoveries was that the moon’s crust is more porous and thinner than earlier estimates. It also identified long, narrow structures called “dikes,” which suggest the moon expanded by a few kilometers during its early history.

Recent Discoveries

The mission uncovered major contrasts between the two hemispheres of the moon, attributed to:

• Tidal Deformation and Gravitational Differences:
  The nearside of the moon exhibits slightly greater flexing than the farside due to its elliptical orbit around Earth—a phenomenon called tidal deformation. This is caused by Earth’s gravitational pull being stronger on the side of the moon that faces our planet.
• Volcanic Activity and Thermal Distribution:
  Historically, the moon’s nearside experienced more intense volcanic activity, forming vast basaltic plains known as “mare.” This activity concentrated heat-producing radioactive elements, such as thorium and titanium, within the nearside mantle. As a result, there is a long-standing temperature imbalance between the two sides, influencing the moon’s geological development over billions of years.
• Differences in Crustal Thickness and Composition:
  The lunar nearside has a considerably thinner crust compared to the farside, which made it easier for magma to reach the surface in the past. This led to widespread lava flows and contributed to the stark visual and structural differences between the two hemispheres.