Lecture 14 - Terrestrial Planet (Venus, Earth, and Mars)

Terrestrial Planets

Small, rocky planets made of heavy elements with thin atmospheres and few moons.

Which planet still has active volcanoes today?

Venus

Why do Venus and Earth have fewer visible craters than Mercury or the Moon?

Active geology (volcanism, erosion, tectonics) erase old craters.

Which terrestrial planet cooled the fastest?

The Moon

Heavy Bombardment

Early Solar System era (~4 billion years ago) when leftover planetesimals heavily impacted planets.

What is the largest volcano in the Solar System?

Olympus Mons on Mars.

Which planets show evidence of recent volcanism?

Venus and Earth

Volcanism

The eruption of molten rock (magma/lava) that reshapes a planet’s surface.

Why does Venus still have volcanic activity while Mars does not?

Venus is larger, so it retains internal heat longer.

What evidence suggests Venus has an active interior?

Young, smooth surface

What is the estimated surface age of Venus?

About 300–600 million years.

Which planet’s surface is oldest?

Mercury

Mares (Maria)

Smooth, dark lunar plains formed by ancient lava flows.

Why are craters on Earth less visible than on other planets?

Erosion and tectonic recycling erase them.

What planetary process created Mares on the Moon and smooth plains on Mercury?

Lava flooding

Plate Tectonics

Movement of Earth’s crustal plates driven by convection in the mantle.

Which terrestrial planet shows active plate tectonics?

Earth

What geological features form at converging plates?

Mountain ranges (e.g., the Himalayas).

Subduction

When an oceanic plate is forced beneath a continental plate.

Why doesn’t Venus have plate tectonics like Earth?

No water to lubricate plates

Erosion

Breakdown and transport of surface material by wind, water, or ice.

Which process causes erosion on Earth but not on Mercury or the Moon?

Flowing water

What do dried riverbeds on Mars suggest?

Mars once had liquid water flowing on its surface.

What does the presence of craters inside dried Martian riverbeds indicate?

Water dried up long ago

Atmospheric Pressure of Venus

About 92 bar, nearly 90 times Earth’s surface pressure.

What causes Venus’s extreme surface temperature (~464°C)?

A runaway greenhouse effect from its thick CO₂ atmosphere.

How many impact craters are on Venus’s surface?

~900

What erased most craters on Venus’s surface?

Global resurfacing by volcanic activity.

Olympus Mons

The tallest known volcano, 21 km high on Mars.

Which terrestrial planet shows evidence of both ancient volcanism and dried river

Mars