Before the invention of the telescope, many believed the Moon was a perfectly smooth sphere. Italian astronomer Galileo Galilei challenged this notion in 1609 using his improved telescope. He observed the jagged line separating the light and dark sides of the Moon, which suggested the presence of high structures casting long shadows. This led Galileo to conclude the Moon possessed mountains and valleys, similar to Earth. The Moon does indeed have mountainous terrain, but these features are fundamentally different in their origin and composition compared to mountains found on our planet.
The Lunar Highlands: Answering the Question
The Moon’s mountainous regions are formally known as the Lunar Highlands, or Terrae. These are the lighter-colored, heavily cratered areas visible from Earth, elevated significantly above the darker, smoother plains known as maria (Latin for “seas”). The average elevation is 2 to 3 kilometers higher. These ancient geological units formed over 4 billion years ago and cover about 83% of the Moon’s total surface area. The rock is primarily anorthosite, an igneous rock rich in calcium and aluminum, responsible for their distinctively bright appearance.
How Lunar Mountains Formed
The primary mechanism for mountain formation on the Moon is catastrophic impact events from asteroids and comets, not slow geological uplift. These collisions created two main types of mountainous structures. The first type is the immense, circular rims and rings that surround large impact basins, such as the Imbrium Basin, formed by the displacement of crustal material during the impact’s excavation phase. The second type is the central peak, found in the middle of large craters typically greater than 20 kilometers in diameter. When a large impactor strikes, the compressed rock rebounds upward in a process known as elastic rebound, creating a convex dome that culminates in one or more central peaks formed in seconds.
Key Differences Between Lunar and Terrestrial Mountains
The fundamental difference between lunar and terrestrial mountains lies in their formative processes. Mountains on Earth are primarily created by plate tectonics, where continental plates collide, causing the crust to fold and uplift over millions of years. The Moon lacks plate tectonics, meaning its mountains did not form through this slow, compressional folding. Another major distinction is the near-total absence of erosion on the Moon. Earth’s mountains are constantly worn down by wind, water, and ice, but because the Moon lacks an atmosphere and liquid water, its mountains retain their sharp, ancient features over billions of years.