Problem 15 - Astronomy: At Play in the Cosmos

Question

Which of the following statements about the Moon is true? a. The side of the Moon not visible from Earth is always dark. b. The two hemispheres of the Moon (near and far) are symmetric in structure and similar in appearance. c. Maria appear only on the near side of the Moon. d. Most of the Moon's craters have disappeared because of weathering effects. e. An impact crater always takes the exact shape of the object that created it by striking the Moon.

Step-by-Step Solution

Answer

Statement c is true: "Maria appear only on the near side of the Moon."

Step 1: Evaluate Statement a

Statement a claims that the side of the Moon not visible from Earth (the far side) is always dark. This is incorrect, because while we don't see the far side from Earth, it experiences day and night just like the near side due to the Moon's rotation and orbit around Earth.

Step 2: Assess Statement b

Statement b suggests that the near and far hemispheres of the Moon are symmetric in structure and appearance. This is not true. The far side has a thicker crust and more craters, while the near side has more maria, which are large, dark basalt plains.

Step 3: Examine Statement c

Statement c states that maria appear only on the near side of the Moon. This is mostly correct, as the majority of the maria are found on the near side due to thinner crust and past volcanic activity there. The far side has very few maria.

Step 4: Consider Statement d

Statement d claims that most of the Moon's craters have disappeared because of weathering effects. This is false since the Moon's surface experiences negligible weathering due to the lack of an atmosphere, so most craters remain visible.

Step 5: Review Statement e

Statement e proposes that an impact crater takes the exact shape of the impacting object. This is incorrect. Impact craters are generally circular regardless of the shape or angle of the impacting body, due to the explosive force of the impact.

Key Concepts

Far Side of the Moon

The far side of the Moon is often surrounded by mystery and intrigue. Due to the Moon's synchronous rotation, we only see one side of it from Earth, while the other side, known as the far side, remains hidden from our direct view.
Yet, it isn't always in darkness. The Moon rotates on its axis and orbits Earth, so the far side gets as much sunlight as the near side. Just like the near side, it experiences day and night cycles.

• The far side is often mistakenly called the "dark side," but this is a bit misleading because it receives sunlight half the time during a lunar cycle.
• Despite our inability to see it from Earth, spacecraft have successfully captured images and provided valuable data about the far side.

Understanding the far side helps us appreciate the Moon's dynamic nature and how its rotation impacts our perspective from Earth.

Moon Maria

"Maria" or "mare" in singular, are large, dark basaltic plains on the Moon's surface. They are striking because they contrast notably with the brighter lunar highlands.
Most of these maria are located on the near side of the Moon.

• This phenomenon occurs because the near side has a thinner crust, which made it easier for volcanic activity to take place billions of years ago.
• The result of this volcanic activity filled large craters with lava, which then cooled and formed these broad plains.

On the far side, very few maria exist as the crust there is thicker, limiting volcanic activity.

Impact Craters

Impact craters are fascinating geological features found all over the Moon's surface. They form when a meteoroid, asteroid, or comet strikes the Moon, resulting in an explosive release of energy that digs out a bowl-shaped cavity.
The shape of an impact crater is typically circular, irrespective of the shape or size of the impacting object.

• The explosive energy of the impact leads to the creation of a symmetrical crater.
• Due to the lack of atmosphere on the Moon, these craters are well-preserved because there are no weathering agents like wind or rain.

Studying impact craters gives insight into the Moon’s history and the solar system's past.

Lunar Crust

The lunar crust is the Moon's outer shell and varies in thickness between the near side and the far side.

• On the near side, the crust is thinner, which is one reason for the many maria located there.
• Conversely, the far side has a thicker crust, which explains the fewer maria and greater abundance of craters.

The differences in crust thickness between the two hemispheres were likely influenced by the gravitational interaction between the Earth and the Moon during its formation phase.
Understanding the lunar crust helps scientists in determining the Moon’s geological history and evolution.
Studying these differences aids in piecing together the puzzle of why the Moon's two sides are so distinct from one another.