Environment for Life - Astrobiology

What is the speed of light?

299,792,458 m/s

What symbol is given to the speed of light in equations?

c

What is the red shift?

When the wavelengths from distant galaxies shift towards the red end of the spectrum. An increase in wavelength due to galaxies moving away from us.

What are the two different types of excitation?

Collisional and Radiative

How does an excited atom return to the ground state?

Emits a photon

How are stars born?

Collapse of a dense, low pressure molecular cloud

When is a star born?

When gravity overcomes thermal pressure

At what temperature does nuclear fusion begin?

10 million K

How large are low mass stars?

When do low mass stars reach the main sequence?

50-150 million years

How is Hydrogen fused to Helium in a low mass star?

Proton-proton chain

How does energy reach the surface of a star?

Radiative diffusion and convection

What is convection important for in stars?

Solar flares and Coronal mass ejections

After how long does a low mass star enter the red giant phase?

10 billion years

Why does a low mass star enter the red giant phase?

Runs out of Hydrogen in the core

What causes the core of a star to collapse?

Gravity (outward pressure has reduced)

At what temperature does Helium begin to burn?

100 million K

How many helium nuclei fuse together when making carbon?

3

What supports the core of a star during Helium burning?

Degeneracy pressure

AT what temperature would Carbon fusion begin?

600 million K

What cause the ejection of the outer layers of a low mass star during death?

Thermal pulses (Stellar wind)

At what temperature during the death of a low mass star can solid particles form in the outflowing wind?

1000-2000 K

What is the remaining inert Carbon core of a low mass star called?

White dwarf

What does a low mass star become after the red giant phase?

Planetary Nebulae

What causes a planetary nebulae to glow?

Radiation ionising the gases

How large are high mass stars?

>8 solar masses

What is the theory for the formation of a high mass star?

Competitive accretion:
1. Forms as a low mass
2. Accretes gas until depleted

How does Hydrogen fusion occur in a high mass star?

CNO cycle

When does a high mass star reach the main sequence?

150,000 years

Why are high mass stars hotter then low mass stars?

Stronger gravity

How is Helium formed in a high mass star (explain CNO cycle)?

4 protons = 1 Helium atom + Energy

What is used as a catalyst during the CNO cycle?

Carbon

What do high mass stars become during death?

Super Giants

What can occur during the death of a high mass star that can't occur during a low mass star death?

Carbon fusion

What is the simplest type of advanced nuclear burning?

Helium - capture reactions

What elements can be formed from Helium capture reactions?

Carbon - Oxygen

What element piles up in the core of a dying high mass star?

Iron

How large are intermediate mass stars?

2-8 solar masses

What do intermediate mass stars end up as?

White dwarfs

How are intermediate mass stars similar to high mass stars?

Use the CNO cycle

Why can Iron not be used for fusion or fission?

Lowest mass per nucleon

How are elements lighter than Iron formed?

Nuclear fusion

How are elements heavier than Iron formed?

Nuclear fission

What does the Iron core of a high mass star collapse to form?

Neutron star

What prevents the further collapse of a neutron star?

Neutron degeneracy pressure

What does the collapse of a high mass star produce?

Supernova explosion

What can a neutron star become if it has a high mass?

Black hole

What is needed for a black hole to form?

Gravity needs to overcome neutron degeneracy pressure

What elements are formed in a supernova?

Elements heavier than iron

Where is most Carbon produced?

Low mass stars

What process forms elements heavier than Iron?

Nucleosynthesis

What is evidence for the origin of elements?

Helium capture reactions add 2 protons at a time and nuclei with an even number of protons outnumber those with an odd number.

What makes a solar nebula spin faster?

Angular momentum

How is the existence of a planetary disc inferred?

Infrared excess

What is the suggested lifetime of a planetary disc?

~5 million years

What planets are formed first?

Gas giants

Why are terrestrial planets formed later than gas giants?

No gas left and too small to attract large amounts of gas

What do solids condense to form?

Grains

What is formed when grains grow and collide?

Planetesimals

What must the energy of an escaping body be to escape?

Kinetic energy > gravitational potential energy

AT what temperature can Hydrogen compounds condense?

What is the boundary in a solar system called where ices can begin to form?

Snow/frost line

Why do ice and giants form past the snow/frost line?

More planet building material

What happens if the mass of a planetary embryo > critical mass?

Runaway gas accretion (gas giants)

What is the isolation mass of a forming planet?

When the area around it is cleared of planetesimals

What type of planet is formed within the snow/frost line?

Terrestrial planets

Where is the asteroid belt?

Between Mars and Jupiter

Where are short period comets found?

Kuiper belt

Where are long period comets found?

Oort Cloud

Why is Ar40 often used for dating?

Usually a gas, only solid in meteroites formed from K40 decay

What is the half life of K40?

1.25 billion years

What is the Ar40 : K40 ratio?

11.5 : 1

Why does a planet shine?

Reflected light

What is the definition of a planet? (3 points)

1. Orbits a star
2. Massive enough that gravity causes it to be spherical
3. Largely cleared neighbourhood of other bodies

What are some dwarf planets? (5 total)

Pluto, Ceres, Eris, Haumea, Makemake

What direction do the planets orbit in?

Same direction

Which two planets do not rotate in the same direction as the others?

Venus and Uranus

How can planetary orbits be described?

1. Close to the ecliptic
2. Nearly coplanar
3. Almost circular

What direction do moons rotate in?

Same as planet

Where do moons lie in relation to their planets?

Close to equatorial plane

Which two planets do not have moons?

Mercury and Venus

What are the four Galilean moons?

Io, Europa, Ganymede, Callisto

Which planets have rings?

All 4 Jovian planets

What forms planetary rings?

Small particles (mainly water ices)

Where is the dwarf planet Ceres found?

Asteroid belt

What can asteroids be described as?

Rocky with an irregular shape

What can comets be described as?

Balls of dust and ice

What shape are comet orbits?

Highly elliptical

What are the two tails of a comet?

Dust tail and ion tail

What is a meteor shower?

When the Earth passes through the orbit of a comet. Comets leave a 3rd tail of pebble sized particles behind.

What is a meteorite?

A rocky object that reached the ground

How far from the sun is the Kuiper belt?

30 - 50AU

What dwarf planets are found in the Kuiper belt?

Pluto, Eris, Huamea, Makemake

How far from the sun is the Oort cloud?

50,000 AU

Does a blackbody reflect, absorb or transmit light?

All light is absorbed

What happens when a body absorbs light?

Electrons gain energy

How can transits be used to locate exoplanets?

1. Planet moves between us and parent star, blocking some of the light
2. The amount of light blocked tells us the planet radius
3. If the period is calculated, the semi-major axis can be determined

How does microlensing work?

1. A star in the foreground can gravitationally focus light from a background star
2. If the foreground star has a planet orbiting, an anomaly may be produced

What planets can be detected using microlensing?

Low mass planets (~Earth mass)

What is a limitation of direct imaging?

Works with very dim stars and bright planets (brown dwarfs and young/massive planets)