Exam 2 - Terrestrial Planets and their Moons

Why is the inner part of the protoplanetary disk warm?

It is closer to the Sun

What could form in the inner disk?

Only small, dense planetesimals of metal and rock

What is the process of the formation of terrestrial planets?

The planetesimals grew larger through accretion, and as the mass increased, their self-gravity became strong enough to shape them into spheres

What are the four terrestrial planets?

Mercury, Venus, Earth, Mars

What did the planetesimals go through when becoming terrestrial planets?

They underwent continuous collisions during the heavy bombardment period of the young Solar System.

How did the planets become hot?

The stick collisions converted a significant amount of kinetic energy from the collisions into thermal energy.

What did the planets go through during the differentiation process?

Most dense materials, like metals, sank to the center, and less dense materials, like rock, rose to the surface.

What else happened during the differentiation process?

It converted gravitational energy into thermal energy, further heating the planets.

When was differentiation completed?

About 100 millions years

What was the primary source of internal energy for the terrestrial planets for most of the Solar System's history?

radioactive decay

How is radioactive decay significant?

Over time, radioactive materials decay into stable daughter products and continue to release heat.

What drives the geologic activity of a terrestrial planet?

The internal energy is primarily sourced from radioactive decay.

What does the radioactive decay do to the planet's interior?

The energy heats the interior, potentially weakening some layers of rock or making them partially molten, allowing for volcanic activity and plate tectonics

Why do large terrestrial planets have long geologic lifetimes?

They have long lifetimes due to their greater mass, meaning there is more radioactive atoms to decay and provide energy over time.

Why do smaller planets have shorter geologic lifetimes?

They have less mass because of fewer radioactive atoms and a limited supply of internal energy.

What happens as more radioactive atoms decay?

The interior of the planet becomes most solid, and geologic activity ceases, rendering the planet dead.

What happens to the surface of larger terrestrial planets?

As they continue to experience geologic activity, their surfaces are less likely to retain heavily cratered surfaces, as impacts are erased or covered by volcanic activity or tectonic processes.

What happens to the surface of smaller terrestrial planets?

These planets have little to no geologic activity over most of their history, and tend to retain heavily cratered surfaces, with craters from asteroid and comet impacts being visible.

How does a terrestrial planet generate a magnetic field?

It generates from circulating currents of molten metal in its core caused by the rotation of the planet.

How can larger terrestrial planets maintain their magnetic fields over extended periods?

They have more internal energy and longer geologic lifetimes and the molten cores remains active/

Why do smaller terrestrial planets not sustain a magnetic field for as long?

These planets, with shorter geologic lifetimes, even if they have a reasonably rapid rotation, there is still a quicker depletion of internal energy.

What happens as radioactive decay diminishes the planet's internal energy and what does it lead to?

The core cools, and much of it solidifies; it leads to the weakening and eventual loss of the planet's magnetic field

What is a planet's atmosphere?

A layer of gas held in place by gravity

What are terrestrial planets born with?

They are born with a primary atmosphere, which is mostly hydrogen and helium, but their gravitational attraction is too weak to maintain it.

What is the secondary atmosphere of terrestrial planets composed of?

Gases such as water vapor, nitrogen, carbon dioxide, methane, and others

What do the gases come from?

Volcanic outgassing

What is volcanic outgassing?

It occurs because terrestrial planets were once mostly molten; as volcanic eruptions release not just lava but also gases, which contribute to the formation of the secondary atmosphere

What are key greenhouse gases?

Water vapor, carbon dioxide, and methane

How do greenhouse gases impact the planets and what is it called?

It traps heat, warming the planet more than it would be based solely on its distance from the Sun; the greenhouse effect

What is the atmospheric history of a terrestrial planet influenced by?

The size and distance from the sun

True or False: Small terrestrial planets can retain their secondary atmosphere

False

Why can't small terrestrial planets retain their secondary atmosphere?

Their short geologic lifetimes prevent them from maintaining volcanic outgassing, which is necessary to replenish their atmosphere.

Why do small terrestrial planets need a magnetic field?

It protects the planets from being vulnerable to the Sun's solar wind, which gradually strips away their atmosphere over time.

What layer do small terrestrial planet's have in their atmosphere at best?

An exosphere which begins at the surface of the small terrestrial planet and smoothly transitions into the very cold temperatures of the surrounding outer space.

What are the atmosphere layers of a large terrestrial planet?

The lowest layer is the troposphere, the next layer is the thermosphere, then the ionosphere, next the exosphere which is beyond the thermosphere, along with having an ozonosphere which leads to additional layers like the stratosphere and mesosphere.

What is the troposphere layer?

It warms the altitude as it gets closer to the ionosphere.

What does the ionosphere layer do?

It absorbs X-rays from the Sun shielding the surface of the planet from the X-rays.

What does the exosphere layer do?

It transitions into the cold vacuum of outer space?

What does the ozonosphere do?

It shields the surface from UV radiation.

What happens to water vapor on a large planet that is too far from the Sun?

water vapor may freeze into solid ice, removing the greenhouse gas and cooling the planet further

What happens to water vapor on a large planet that is too close to the Sun?

the water vapor remains gaseous, contributing to a warmer atmosphere

What happens to water vapor on a large planet that is at an intermediate distance from the Sun?

the planet may maintain an ideal temperature for water to exist in all three states—solid, liquid, and gas—helping to stabilize its temperature

How is a large planet's atmosphere influenced by its rotation?

slow rotation weakens its magnetic field, exposing the atmosphere to solar wind, which can ionize and strip it away

What is the closest planet and smallest planet to the Sun?

Mercury

What is the orbital period of Mercury?

About 3 months

True or False: Mercury does not have any moons

True

Is Mercury geologically alive?

Due to its small size, Mercury likely had few radioactive atoms to provide internal energy, meaning it was geologically active for only a brief period—perhaps just a few hundred million years.

Does Mercury have an atmosphere?

No, its weak gravity is insufficient to retain an atmosphere, and without ongoing volcanic outgassing to replenish it, Mercury has had virtually no atmosphere throughout its existence; the best it has is an exosphere.

What does Mercury's surface look like?

With no geological activity to erase or cover craters from asteroid and comet impacts, its surface is heavily cratered, resembling the Earth's Moon in appearance.

What is unusual about Mercury?

It has an unusually large metallic core compared to its size

What is the theory about Mercury's core?

It was originally a larger terrestrial planet, about the size of Mars. During the heavy bombardment period, a large planetesimal collided with this Mars-sized planet, stripping off its outer layers and reducing its size. This collision left the planet with a disproportionately large metallic core.

How did Mercury's smaller size and weaker gravity impact it?

It allowed the stripped material to escape into space, preventing the formation of a moon. The collision also caused Mercury to lose a significant portion of its mass and radioactive atoms, which are essential for internal energy and geological activity. As a result, Mercury's internal cooling was rapid, causing the planet to contract.

What did the contraction do to Mercury?

It gave Mercury an even smaller size, forming fractures known as scarps on its surface.

What are scarps?

Thought to be the result of the planet's sudden thermal contraction as it shifted from a geologically active to a geologically dead planet

What is the common misconception about Mercury?

It is the hottest planet in the solar system because it is closest to the Sun

What is unique about Mercury?

It is one of the hottest and coldest planets at the same time. Additionally, regions near the poles of Mercury remain in permanent shadow, causing these areas to stay near absolute zero, despite being the closest planet to the Sun

What is the second planet closest to the Sun?

Venus

What is the orbital period of Venus?

Roughly 7 months

Why is Venus referred to as Earth's twin sister planet?

It is almost identical in size and mass to Earth, giving it nearly the same density and gravity

True or False: Venus has no moons

True

Venus's atmosphere is incredibly ______, and it is completely shrouded by clouds.

thick

Why is Venus the brightest object in the Earth's sky, after the Sun and the Moon?

The dense atmosphere reflects so much sunlight

The thick atmosphere of Venus reflects so much sunlight that Venus appears to be the....

brightest object in the Earth's sky, aside from the Sun and the Moon

Venus appears to be so bright in the west shortly after sunset that it is often called

the evening star

Venus appears to be so bright in the east shortly before sunrise that it is often called

the morning star

How have we successfully learned about Venus' surface features?

We sent artificial satellites to orbit the planet, allowing us to map the topography of Venus

How is Venus still geologically active?

Since Venus is nearly the same size as Earth, it has a similar amount of radioactive atoms, which means it has roughly the same supply of internal energy as Earth. Consequently, Venus has a geologic lifetime comparable to that of Earth.

What is the evidence of Venus' geologic activity?

The igneous and seismic activity, as well as the presence of mountains

What are the tallest mountains on Venus?

Skadi Mons

Where are the Skadi Mons located?

The Maxwell Montes massif

What is a massif?

a collection of mountains

True or False: The Theory of Plate Tectonics applies to Venus

False

Why is Venus' atmosphere significantly ionized by the Sun's solar wind?

Venus has a partially molten metallic core, but its slow rotation results in a very weak magnetic field

What are the layers in Venus's atmosphere?

Troposphere, thermosphere, ionosphere, and the exosphere

Does Venus have an ozonosphere and why does it need this layer?

Venus lacks an ozonosphere because it does not have oxygen in its atmosphere, and as a result, it does not have a stratosphere or mesosphere. Without an ozonosphere to shield the planet, the surface of Venus is exposed to far ultraviolet radiation from the Sun.

Why is Venus considered the hottest planet in the Solar System?

Since Venus is closer to the Sun, its hotter temperatures caused more water vapor and carbon dioxide to be released from volcanic activity. As both are greenhouse gases, they trap more heat, raising Venus' temperature further. This increase in temperature caused even more volcanic outgassing, leading to a runaway greenhouse effect

Why is there very little water vapor in Venus' atmosphere?

Without a magnetic field to protect it, the Sun's solar wind stripped hydrogen atoms from the water molecules, allowing them to escape into space

What are the clouds in Venus' composed of?

sulfuric acid

What happens to the acid rain before it reaches Venus' surface?

Most of it evaporates before reaching the ground, though gaseous sulfuric acid may still exist

What would happen to a person standing on the surface of Venus?

they would simultaneously be crushed by the extreme air pressure, poisoned by sulfuric acid, burned alive by the greenhouse effect, and irradiated by ultraviolet radiation from the Sun

What is the fourth planet from the Sun?

Mars

What is the orbital period of Mars?

Roughly two Earth-years

Why is Mar's referred to as Earth's "twin brother planet"?

It has an axial tilt similar to Earth's, has similar polar ice caps, and rotates once every 24 hours

Why does Mars have a less severe planetary differentiation?

Mars is smaller than Earth, meaning it has less mass and weaker gravity

Why is Mar's nicknamed the "Red Planet"?

Mars has a greater abundance of metals like iron on its surface. The iron on Mars has reacted with oxygen to form iron oxide (rust), giving the planet its characteristic red color

Why is Mar's the only terrestrial plane to have been both geologically active and inactive for significant durations?

While Mars is smaller than Earth and Venus, it is larger than Mercury and the Moon, meaning it has more radioactive atoms and a greater internal energy supply than the latter but less than the former. As a result, Mars remained geologically active for a couple of billion years before becoming geologically dead

True or False: Mars had a partially molten metallic core, and with a rotation rate similar to Earth's, which generated a substantial magnetic field.

True

What was ancient Mar's secondary atmosphere composed of?

It was composed primarily of water vapor, nitrogen, carbon dioxide, methane, and other gases.

True or False: Mar's magnetic field shielded the ancient Martian atmosphere from significant ionization by the Sun's solar wind.

True

True or False: The temperature of ancient Mars may have been sufficient for water to exist in all three physical states—solid, liquid, and gas—allowing water vapor to condense into liquid water and precipitate as rain

True

Why did the Martian climate remain relatively warm?

The remaining abundance of carbon dioxide

What layer of the atmosphere does Mar's lack and how did it impact its surface?

The ozonosphere and without it, Mar's has never been shielded from the Sun's far-ultraviolet radiation

What are the layers of Mar's atmosphere?

Troposphere, thermosphere, ionosphere, and the exosphere

Why was Mar's unable to retain its thinning atmosphere?

Because of its smaller size and weaker gravity compared to Earth and Venus

The atmosphere of Mars is too thin to cause a significant greenhouse effect. Therefore, Mars is significantly ____ than the earth

colder

Unlike the Earth's polar ice caps which are composed of solid water (ice), the polar ice caps of Mars are composed of....

carbon dioxide (dry ice)

Where are the largest geologic features in the entire Solar System found on?

Mars

The largest and tallest mountain on Mars and in the entire Solar System

Olympus Mons

What is the Olympus Mons?

an extinct shield volcano

Where is the Olympus Mons located?

Near the Tharsis Montes massif