Lecture 9 - Extrasolar Planets

Question 1

Where and how were planetoids/asteroids formed?

Answer 1

In the gap between Mars and Jupiter. An unstable location because of Jupiter’s gravity.

Jupiter was heavy enough to be differentiated internally so after its collisional disruption, several diff asteroid types were formed.

Question 2

Why is it not possible for asteroids to be habitable?

Answer 2

• Too small
• No atmosphere
• No liquid medium
• No internal source of heat
• Extreme temperature changes
• Exposed to cosmic rays and UV radiation

Question 3

What is the important contribution of asteroids?

Answer 3

Brung water to terrestrial planets through impacts

Question 4

What is the structure of Jovian planets?

Answer 4

• No solid surfaces
• Density progressively increases from gaseous to liquid forms
• Mostly hydrogen and helium with traces of heavy elements
• Solid only found in very (Hydrogen in metallic form)
• Centres are hot (Radiates thermal IR radiation)

Question 5

How do the clouds and wind on Jupiter move?

Answer 5

In bands due to strong horizontal winds (But there are also vertical winds)
- Some areas are stable low pressure systems that stay fixed (The Red Spot)

Vertical winds cause matter to constantly move through high and low temp, causing electric charge accumulation (lightning) and aurora in the poles from the magnetic field

Question 6

What are the properties of Jupiter’s clouds?

Answer 6

• Visible, very low temperature at top later
• Made of ammonia, ammonium sulfide, NH4HS (Water vapour found below)
• Overall mainly crystallized ammonia with phosphorus sulfur and hydrocarbon compounds

Question 7

Why is there no chance of life on Jupiter?

Answer 7

Pros:

• Liquid water present
• Temp and pressure okay in reasonable depth

Cons:

• STRONG VERTICAL WINDS
• Would cause complex molecules to go into deep hot layers where they will get destroyed
• Meteorites carrying life would be thrown down into the heat or up into the cold

Question 8

How did the moons of Jovian planets form?

Answer 8

They formed as “mini solar-systems” from small gaseous disks orbiting the large solar proto-planetary nebula

Exception: Triton who is on retrograde orbit (Probs captured Kuiper belt object)

Question 9

Describe the composition of Jovian moons.

Answer 9

Jupiter:

• Only water-ice
• More ice and less density further away from Jupiter (Europe, Ganymede, Callisto)
• High density rock (Io)

Saturn and beyond:

• More water-ice than Jupiter moons
• Methane and other ice also found

Question 10

Describe the shape of the smaller captured moons of Jovian planets.

Answer 10

Odd shapes because gravity too weak to force rock into sphere
Mainly captured planetoids

Question 11

What are Jovian planet’s rings made of?

Answer 11

Many orbiting bodies (ranging from boulders to dust)

Saturn’s most prominent with 300,000 km diameter and 0.2-3 km thickness

Question 12

Where would water ice condense?

Where would methane and ammonia ice condense?

Answer 12

Water ice - Distance of Jupiter from Sun

Methane and ammonia ice - Distance of Saturn and beyond

Question 13

When do the four Galilean moons rotate and how long is their orbital period?

Answer 13

Rotate about axis once per orbital period.

By the time Ganymede orbits once…
Ganymede orbit - 1 orbit (7 days)
Europa orbit - 2 orbits
Io - 4 orbits

Question 14

Explain synchronous rotation.

Answer 14

The same side of the moon is always facing towards its planet as it rotates

Question 15

Explain tidal forces

Answer 15

The moon deforms Earth’s oceans by 2m and land by 1cm because of its gravity.
Causes Earth to lose energy and slow rotation as Earth tries to pull back the tidal bulge that’s leading.
Also pushes Moon away.

This is applicable for any 2-body system

Question 16

Describe how Io has volcanism

Answer 16

Rock inside is heated to 2000°C, leading to volcanic eruptions and sulfur snow (frozen sulfur dioxide).

Lack of water and extreme volcanism means no life

Question 17

Explain Io’s tidal heating.

Answer 17

Since the orbit is elliptical, the strength and direction of tidal forces change as distance between Io and Jupiter changes.
Cause interior of Io to get stretched and squeezed every orbit, generating a lot of heat.

Question 18

What did tidal forces cause Jupiter’s moons to do?

Answer 18

Be in synchronous rotation (1:2:4 in 7 day period)
Periodic alignment pushes them into eccentric orbits (like child on a swing)

The periodic alignment is called orbital resonance

Question 19

Describe evidence of heating on Iapetus (Saturn’s moon).

Answer 19

Large ridge around moon - Signals massive internal restructuring in response to internal heating

Unknown source of heating tho

Question 20

Describe Europa’s surface.

Answer 20

• Covered in ice and very bright
• Surface is young because few impact craters and smooth
• Very hard but liquid ocean might be present under ice because of tidal heating of interior

Question 21

Explain a cause for Europa’s magnetic field

Answer 21

Has magnetic field when core shouldn’t be molten anymore so maybe polar salts and Jupiter’s magnetic field induces currents to flow in it
- This requires salty liquid ocean

Question 22

Does Europa meet the requirements for life?

Answer 22

• Has source of elements and molecules to build organisms
• Liquid medium
• Source of energy unsure
  Maybe chem rxns supplying energy cause diffs in chem potential
  Or maybe turbines or volcanic vents to exploit temp differences or diffs in water level (Would be hard to find bcuz very deep tho)

Question 23

What is chemical disequilibrium?

Answer 23

Rxn proceeding both ways to reach equilibrium must be broken to produce energy

Question 24

Describe the properties of Ganymede

Answer 24

• Largest moon in solar system
• Surface of hard brittle ice
• Magnetic field (molten core)
• Magnetic field varies w/ Jupiter’s rotation period (Indicating liquid ocean)
• Weaker tidal heating, thicker ice crust

Question 25

Describe Callisto’s properties

Answer 25

• Water ice and rock, covered w/ old craters
• No differentiation (Not warm enough for melted interior)
• Magnetic field (presence of salty ocean)

Question 26

Describe the properties of Titan

Answer 26

• Second largest moon of solar system
• Similar to Callisto, mix of ice and rock
• Thick atmosphere w/ organic materials like methane (very high amount) and ethane (But mainly N2; levels similar to Earth)
• 1.5x atmospheric pressure if Earth (Comfortable; planes + balloons can fly here)

Question 27

What is the chemistry of Titan driven by?

Answer 27

• Presence of ammonia and methane ices (directly condensed from proto-planetary nebula)
• Partial escape of hydrogen from atmosphere
• UV radiation from Sun

Question 28

What are the dark channels on Titan probably carved by?

Answer 28

Liquid methane or ethane brought there by soft-landing comets

Question 29

What are the dunes on Titan made of?

Answer 29

Hydrocarbon sediments organized by winds into dunes

Question 30

Is it possible for Titan to have a subsurface ocean?

Answer 30

Yes

Thru softer tidal interactions

Question 31

Is Titan good for life?

Answer 31

Very similar to Earth:

• Liquid methane instead of water
• Ice instead of rock
• Slush ice w/ ammonia instead of lava
• Hydrocarbons and smog particles instead of surface dirt
• Has organic molecules

But temps to low - Would make chem rxns and metabolism very slow

Question 32

Describe the properties of Enceladus

Answer 32

Young, icy surface (reflects 100% of sunlight)

Has ice vents or geysers - Means liquid water under surface

Question 33

Describe the properties of Triton (Neptune’s Moon)

Answer 33

• Covered by water ice or ammonia ice
• Clouds visible
• Rotates and orbits opposite of everything else (Sign of captured dwarf planet)

Question 34

Describe the properties of Trans-Neptunian objects

Answer 34

• Have strongly inclined orbits extending far into space
• Several have small moons
• Physical properties poorly known