Terrestrial Worlds in the Inner Solar System

Terrestrial worlds include Mercury, Venus, Earth, Mars, and Luna (Earth’s Moon).
These worlds have both similar and dissimilar properties.
Comparative planetology involves studying planets and moons by comparing them to one another.

Four processes that have shaped Earth:
- Tectonism (moving crustal plates).
- Volcanism.
- Impacts (cratering).
- Erosion (wind or water).

Tectonism is the deformation of Earth’s crust.
The crust is broken into plates.
Continental drift and plate tectonics describe the movement of these plates.
Crustal plates are moved by convection, which is the rising and falling of hot/cold material.
Earth has seven major plates and six smaller ones.
Plates can separate or collide.
Most volcanoes and earthquakes occur along plate boundaries due to these motions.

Magnetic fields act like a giant bar magnet.
They originate from motions of the iron core, which are not fully understood.
Iron-bearing minerals indicate changes in orientation over time.
Without a strong enough magnetic field, the solar wind will strip a terrestrial planet of its atmosphere.
Mars lost its magnetic field and most of its atmosphere as a result.

Asteroids are rocky/metal objects originating from the Asteroid Belt.
A small cometary or asteroid fragment in space is called a meteoroid.
- Ranges in size from a speck of dust to 100 meters across.
A meteoroid that enters and burns up in an atmosphere is called a meteor.
Any meteoroid that survives to hit the ground is called a meteorite.

Stony meteorites are mostly made of silicate minerals and are hard to distinguish from Earth rocks.
- They make up 75-90% of all meteorites.
Iron meteorites are mostly made of iron and nickel and are the easiest to spot and find.
- They make up 10-25% of all meteorites.
Stony-iron meteorites are a combination of the previous two types.

Closest planet to the Sun.
Named after the Roman Messenger God.
Smallest of the terrestrial planets.
Lacks an atmosphere.
Experiences extreme temperature variations: 800°F (427°C) facing the Sun and -279°F (-173°C) facing away.
Geologically active with an active magnetic field.
Surface shrank after cooling, forming kilometer-high cliffs called scarps.
Surface is covered in impact craters.
Also has smooth surfaces from past volcanism and a few inactive volcanoes.

Second planet from the Sun.
Named after the Roman God of Beauty.
Nicknamed “Earth’s twin” due to similar size.
Has a surface temperature of 870°F (465°C), hot enough to melt lead.
Has the largest number of volcanoes in the Solar System, some active.
Lacks tectonism, so volcanoes are formed like those in Hawaii (hot spots).
Wind modifies the surface due to an extremely heavy atmosphere (92 bars compared to Earth’s 1 bar).
Has a weak magnetic field induced by the solar wind interacting with the planet’s ionosphere, not produced internally.
Experiences substantial atmosphere loss due to the weak magnetic field.

Third planet from the Sun.
Located inside the goldilocks zone of the solar system.
Only planet known to have life.
We model Earth’s interior by studying earthquakes.
Seismic waves travel differently through different materials.
Primary waves travel through solids and liquids.
Secondary waves go through solids only.
Earth's Interior:
- Crust (only Earth has its crust broken up into plates).
- Mantle.
- Core (dense materials).
  - Produced by differentiation in the early Earth: dense materials sink; low-density materials rise.
Has a substantial magnetic field.
Protects the Earth from the Solar Wind.
Produces the Auroras via charged particles from the solar wind interacting with gas in Earth’s upper atmosphere.

Located in Arizona and formed by a large meteorite impact.
- The meteorite weighed 300,000 tons and was 150 feet across.
- The impact released energy equivalent to 250,000,000 tons of TNT, 150 times the nuclear bomb dropped on Hiroshima.

About 65 million years ago, a 10 km-wide meteoroid struck the Yucatan Peninsula.
Caused massive climate changes, leading to the extinction of the dinosaurs and other life forms.
Iridium found in a layer of soil worldwide is the “smoking gun.”

Earth’s Moon.
Used to be geologically active and had a magnetic field.
Source of the tides on Earth (along with the Sun).
Visited by the Apollo missions.
Formed in a large collision between Earth and a Mars-sized protoplanet.
The material collected to form the Moon.
Composition is similar to Earth’s crust.
Geologically inactive, having lost its magnetic field and volcanism due to heat loss.
Does not have any volcanoes, but lava flows smoothed out parts of its surface.
The side facing Earth is covered in lunar maria from ancient lava flows.
Covered in impact craters, mostly from the Late Heavy Bombardment.

Fourth planet from the Sun.
Named after the Roman God of War.
Located inside the goldilocks zone of the solar system.
Only terrestrial planet other than Earth to have moons (Deimos & Phobos).
Geologically dead with no active magnetic field.
Experienced extensive tectonism.
Features the massive chasm Valles Marineris (4000 km long, 200 km wide, 7 km deep).
Wind modifies the surface.
Used to experience water erosion.
Volcanoes are the largest mountains in the Solar System, formed similarly to Hawaii.
Olympus Mons is the largest volcano in the solar system.