Chapter 8: Mercury and the Moon

Mercury’s orbit is inside the Earth’s orbit, it never strays very far from the Sun.

Why does Mercury never stray too far from the Sun in the night sky, and does not set too long before or after the Sun does?

mass

Mercury and the Moon have less __________ than Earth, which is causes them to have less gravity and a lower escape speed.

atmosphere

The low escape speeds that Mercury and the Moon have make it hard for them to hold onto an _____________ due to their weak gravitational pull.

The daytime temperatures are too high for liquid water to exist on both bodies and there are extreme temperatures differences between day and night.

What is true about temperature differences experienced between day and night on Mercury and the Moon as a result of these two bodies lacking an atmosphere?

The dark, flat, and smooth features of the Moon primarily located on the near side of the Moon. Some craters are present.

What are lunar maria?

The lighter areas on the Moon that are elevated several kilometers above the maria. They have more craters, are on the far side of the Moon, less dense, and older than maria.

What are lunar highlands?

Moon’s

Mercury’s surface is similar to the ________, but craters are less dense across the surface.

intercrater plains

Mercury also has ____________, which are the oldest features on Mercury and cover many older craters.

synchronous orbit

The Moon has a ____________, which means it takes the same amount of time to rotate as it does to complete one orbit, which explains why we see the same side of the moon.

27.3

The Moon’s orbital and rotational periods are _____ days.

59

The rotation of Mercury is ______ days.

Pointing large pulses of radio waves at Mercury.

The rotation rate of Mercury is 59 days, as measured by _____________.

88

The rotation of Mercury is 59 days. This is exactly two-thirds of Mercury’s orbital period of ____ days.

resonance

For every 3 rotations, Mercury undergoes exactly 2 orbits (or Mercury years). We call this a 3:2 _________.

Relation between the spin of a planet and an orbit of a planet.

What is resonance?

perihelion

The orbit of Mercury is almost synchronous at the _________.

Mercury’s orbit is too eccentric (elongated)

Why can’t Mercury settle into a 1:1 spin-orbit resonance like the Moon?

Lack of surface activity and atmosphere. It does experience impacts.

Why does the Moon have many craters on its surface?

10

The diameter of the crater is about _____ times that of the incoming meteoroid.

ejecta blanket

The material thrown out by the explosion causes a layer to form around the crater called an _________.

A layer of lunar dust made up of particles from the ejecta from meteoroid impacts that covers the Moon. (Chalk-like, up to 100 meters deep)

What is a regolith?

A long, narrow valley/trench on the surface of the Moon. Looks like dried up river beds where molten lava once flowed.

What are rilles? (Ex: Hadley Rille)

3 billion years ago.

When is the Moon believed to have had volcanic activity?

Rilles

What features are our best evidence for the claim for volcanic activity?

No evidence

Does Mercury’s surface show any evidence of plate tectonics?

Cliffs which do not appear to be a result of volcanic activity or other geological activity. Resemble wrinkles.

What are scarps?

Formed when the planet’s interior cooled a long time ago and contracted/shrank.

How are scarps believed to have formed on Mercury’s surface?

Possibly the last great geological event in Mercury; its largest impact basin.

What is the Caloris Basin?

Formed by a large meteoroid impact.

How is the Caloris Basin believed to have formed on Mercury’s surface?

Iron and other heavy metals.

The Moon is deficient in what?

No

Does the Moon have a global magnetic field?

Extends over the entire surface of a celestial body, generated by the motion of electrically conductive fluids within that body.

What is a global magnetic field?

It is about a hundredth of the strength of Earth’s.

How does Mercury’s magnetic field compare to Earth’s?

Because you need a electrically conducting liquid core that rotates rapidly, which Mercury didn’t have.

Why was it a surprise to a planetary scientists to find a global magnetic field on Mercury?

It’s from a molten outer core just like Earth (partially liquid outer core).

What feature within Mercury’s interior might be responsible for its global magnetic field?

The Impact Theory

What is the name of the currently accepted theory for the formation of the Moon?

The idea that a Mars-sized object crashed into the Earth and splattered material both from the Earth and the original impactor in a disk surrounding the Earth.

What is the Impact Theory?

Metals from the impactor were attracted towards the Earth as they were heavier and more affected by Earth’s gravitational field. The object that formed and orbited the Earth was the leftover material that was light and rocky.

What is the explanation for the Moon forming into a rocky body that is overall less dense than the Earth?

4.6 billion years ago

How long ago is the Moon believed to have formed?