Ch 8: The Terrestrial Planets

How do Mercury, Venus, & Mars each compare with Earth in mass & radius?

Mercury: mass is 1/18 of Earth’s & radius is 1/3 of Earth’s

Venus: similar mass & radius to Earth

Mars: mass is 1/10 of Earth’s & radius is 1/2

How to the interior structures of Mercury, Venus, & Mars compare with Earth’s?

Mercury: large molten core, almost no mantle activity due to small size

Venus: iron core & rock mantle similar to Earth, crust isn’t broken into plates

Mars: cooler interior than Earth, dormant mantle

What is the surface of Mercury like?

Covered in craters, rays, scarps (steep cliffs), troughs (wrinkles in crust formed from shrinking), & hollows (irregular shaped pits created by volcanic activity)

Does Mercury have an atmosphere?
Why or why not?

Not really. There are trace amounts of gas around Mercury; the atmosphere is trillions of times thinner that Earth’s atmosphere

Its gravity is too weak to hold an atmosphere & high temps cause molecules to move so fast they escape to space

What is peculiar about Mercury’s rotation?
What causes this oddity?

It spins 3 times for every 2 trips it makes around the Sun (3 Mercury days = 2 Mercury years)

Due to a combination of the Sun’s tidal forces slowing Mercury’s orbit & spin and Mercury’s highly elliptical orbit affecting its rotational speed

What is the dominant gas in Venus’s atmosphere?
How do astronomers know this?

Carbon Dioxide

Determined by spectroscopy & space probe measurements

What are the clouds of Venus made of?

Sulfuric acid

Why is Venus so hot?

It has a runaway greenhouse effect
The dense atmosphere traps a lot of infrared light

Can we see the surface of Venus?
How do astronomers know what the surface of Venus is like?

No, the thick clouds cover our view

Scientists use radar from spacecraft or stations located on Earth to map Venus

What sort of features are seen on Venus’s surface?
Is the surface young or old?

Lava fields, only 2 major highland regions, many volcanoes, narrow fault lines

Surface is young (scarcity of impact craters) do to volcanic activity

Some of the youngest surfaces on Earth are from plate ridges—is the same true on Venus?

No, Venus does not have plate tectonics like Earth, so new crust doesn’t form at plate ridges

Describe some of the surface features seen on Mars.

Valles Marineris (deep canyon as big as U.S.), huge uplands, many volcanoes (Olympus Mons is largest volcano in Solar System), frozen polar caps

What are the Martian polar cap composed of?

Frozen water covered by frozen carbon dioxide (dry ice)

What is the Martian atmosphere like?

Mostly carbon dioxide, very low density atmosphere makes Mars unable to trap much heat, dry ice & water-ice crystals, strong winds

What is the evidence that Mars once had running water on its surface?

Dry riverbeds, teardrop shaped island formations, winding channels, “Martian blueberries” - small hematite sphere usually formed from minerals in water, rocks that contain minerals indicating they formed in a lake

What is the likely origin of Mars’s 2 moons?
What evidence supports this?

Possibly captured asteroids or an asteroid that was pulled apart by tidal forces

Most likely chunks of Mars that were knocked into orbit from a great impact. Scientists believe this possibility since the moons contain elements found in Mars’s crust & they have a nearly circular orbit

What explanations have been offered for why the atmospheres of the terrestrial planets are so different?

A planet’s mass & distance from the Sun play a major role

Mass affects gravitational strength which determines if a planet can retain gases, & distance from Sun influences greenhouse effect

How do astronomers explain why Earth’s atmosphere ended up with so little CO₂, compared with that of Mars & Venus?

Due to life & water on Earth
Our water & microorganisms removed much Carbon Dioxide from the atmosphere

Venus’s thick atmosphere trapped CO₂, & Mars’s CO₂ was trapped in rock form