Life Beyond Earth - Astrobiology

What type of orbit does Mars have and what could this result in?

Elliptical, seasons

What makes a planet habitable?

1. Liquid water
2. Energy source
3. Element source
4. Suitable physical conditions

What is water like on Mars surface today?

Night frost that sublimates

Why does Mars not have liquid water on the surface?

Surface is at the triple point

Why does Mars have high radiation levels?

Thin atmosphere

What is present in the Martian soil that may decrease its potential for life?

Oxidants (e.g. perchlorates)

How much higher would damage to DNA be on Mars compared to Earth?

1000x

What evidence suggests a long period of liquid water on the surface of Mars?

1. Sediments and clays
2. Calcium sulfate deposits
3. River deltas

Why is Mars' small size a problem?

1. No tectonic plates
2. No magnetic field
3. Atmospheric loss

Why does Mars not have plate tectonics or a magnetic field?

Core solidified

What does Mars' small size mean for atmospheric loss?

1. Lower escape velocity
2. Sputtering by solar wind

Where could there potentially be liquid water on Mars today?

Caves (places where the pressure is above the triple point)

What was Mars like during the Noachian period?

1. Lots of water
2. Neutral pH

What was Mars like during the Hesperian period?

1. Water decreases
2. pH lower due to water loss

Which element might be limiting for life on Mars?

Nitrogen

How much higher is ionising radiation on Mars compared to Earth?

100x

How could the issue of high radiation on Mars be negated?

Go below the surface

What is a meteorite thought to be from Mars?

ALH 84001

What evidence is there that meteorite ALH 84001 came from Mars?

1. Trapped atmospheric gas bubbles
2. Comparison of isotopic ratios

What potential evidence of microbes was found in Mars meteorite ALH 84001?

1. Magnetite grains
2. Organic compounds (e.g. PAHs)

What problems could there be with the potential evidence of microbes was found in Mars meteorite ALH 84001?

1. Mineral deposits
2. Smaller than Earth microbes
3. Contaminated by Earth

What evidence of potential life on Mars has been found by rovers?

1. Sulfur fractionations
2. Carbon fractionations

What does the large radiation field of Jupiter mean for the surrounding environment?

1. Large magnetic field
2. Lots of charged particles

What does the large mass of Jupiter mean for the surrounding environment?

1. Attracts bodies on collision course
2. Regular delivery of exogenous material

How is interior heat generated on Europa?

Gravitational effects from other moons deform Europa

What does it mean for Europa to be tidally locked?

One hemisphere always faces Jupiter

How many probes have visited Europa?

6

How long does Europa take to orbit Jupiter?

3.5 days

What does it mean for Europa to have a flat surface with few impact craters?

Surface regularly renewed (tectonics?)

What are the dark patches on Europa thought to be?

Younger ice rising to the surface

What is the average temperature on Europa?

103K

What is the average temperature on Callisto?

120K

What is the average temperature on Ganymede?

109K

What are the raft and chaos regions on Europa?

Where ice has broken away from the liquid ocean and refrozen

What limits the density of the ice on Europa?

Dissolved metal ions

How high are the tallest raft regions on Europa?

100m

What causes Europa's tidal heating?

Non circular orbit

How much is Europa's surface though to distort due to tidal heating?

50m (explanation for cracked ice surface)

What is the degree of tidal heating influenced by?

1. Orbital characteristics
2. Body features (e.g. size, rigidity & strains)

How thick is the ice layer on Europa thought to be?

100km

What feature similar to Earth can Europa generate?

Induced magnetic field

What more information is needed about Europa's subsurface oceans before any guesses about life can be made?

Temperature and saltiness

Is Ganymede thought to have subsurface oceans?

Potential for several oceans sandwiched between ice layers

What is the largest moon in the solar system?

Ganymede

What is the surface of Callisto like?

Ancient, heavily cratered and geologically stable

What radiation does Callisto experience?

Low

Is Callisto likely to have a subsurface ocean?

No

Does Callisto experience tidal heating?

No (too far from other moons)

What geological activity does Io experience?

Volcanism

What gives Io its yellow colour?

Complex sulfur cycle

What is the definition of a habitat?

An environment that can support the activity of at least one known organism

What are the limits of habitability (in terms of what can live there)?

Different places can be habitable with respect to different groups of organisms

Why are we biased in terms of the definition of habitability?

Everything based on Earth (only place we know with life)

Why is geochemical turnover important for habitability?

Reforms redox couples

How is the presence of liquid water maintained on Earth?

Carbon silicate cycle acts as a thermostat

How does the moon stabilise Earth?

Stabilises the obliquity (tilt)

What could have been the benefits of Earth being stabilised by the moon?

Prevented large climate changes

How abundant is Energy for life on Mars?

Limited

What type of star has the largest habitable surrounding region?

F stars

What type of star has the smallest habitable surrounding region?

M star

When does the traditional habitable region not apply?

1. Looking for life below surface
2. Different atmospheric gases
3. Everything we know based on Earth - could be different

What are the consequences of being close to the centre of the galaxy?

Supernova explosions more likely (life could still evolve but dangerous place to live)

What are the consequences of being far from the centre of the galaxy?

Few heavy materials (planets still form)

What are the 3 required characteristics of a biosignature?

1. Produced by life
2. Negligible production by abiotic processes
3. Clearly detectable

Which two gases in high concentrations could be seen as a biosignature?

Oxygen and nitrous oxide

Why is the methane cycle not seen as a biosignature?

1. Cycle still not understood
2. Methane produced by biotic and abiotic processes

What could be seen as a biosignature of an advanced civilisation?

Technosignatures

What could be classed as a technosignature?

1. Nitrous oxide
2. Radiowaves

What limits the gases we can look for as a sign of life?

Have to be included in emitted blackbody radiation

What could a high ozone concentration in an absorption spectrum indicate?

High oxygen concentration

What is an abiotic way of forming oxygen?

Photolysis of water

What do forests give off that could be used as a biosignature?

Red edge (chlorophyll reflects high levels of the infra red)

What could make the red edge hard to detect?

High cloud cover

What is a false negative biosignature?

No surface signature but a gaseous biosignature

What is a false positive biosignature?

When a potential biosignature is detected but is not produced by life

What is the surface of Enceladus made up of?

Water ice

Which planet does Enceladus orbit?

Saturn

Which of Saturn's rings in Enceladus found in?

E-ring

How can the surface of Enceladus be described?

Young and geologically active

Which spacecraft did a fly by of Enceladus?

Cassini-Huygens

What does the deformation of craters on Enceladus suggest?

Warming from beneath

What erupts from the South pole of Enceladus?

Water and trapped gases

What was found in Enceladus' water plume?

methane, CO2, complex organics (ethane, propane)

What is the theory for the existence of Enceladus' water plumes?

1. Surface cracks
2. Material escapes
2. Ice next to crack sublimes

What is the largest moon of Saturn?

Titan

Which is the only moon in the solar system with a substantial atmosphere?

Titan

What is Titan's atmosphere made of?

98% Nitrogen, 1.4% methane

What does the interaction of UV light with Titan's atmosphere result in?

Breaks up methane to form hydrocarbon smog

What have Earth experiments proved could potentially form in Titan's atmosphere?

Amino acids

What is the surface temperature of Titan?

94K

What fills the role of water on Titan?

Methane

What forms the greenhouse gas effect on Titan?

Methane (prevents atmosphere freezing out)

What spacecraft landed on Titan?

Huygens lander

What is the evidence of a subsurface ocean on Titan?

Variations in rate of Titan's spin around it's axis of rotation

What does Titan's lower gravity mean for the atmosphere?

Stretched out layers (similar to Earth)

What is Neptune's largest moon?

Triton

What orbit does Triton have and what does this indicate?

Retrograde, captured 3-4bya

What is the surface temperature of Triton?

36K

What atmosphere does Triton have?

Thin nitrogen

What is causing Triton to spiral inwards and what will this eventually result in?

Tidal forces, moon demolished and new ring system formed