Lecture 19: Extraterrestrial Life

Question 1

Are We Alone?

Answer 1

• assumed in 17th and 18th century that life was present on other worlds
• widely accepted by the public by the turn of the 20th century
• scientists became more skeptical once we began to explore the solar system
• now, life elsewhere seems inevitable, but intelligent life is the question
• extrasolar planets indicate that planetary systems are common
• liquid water can exist on other worlds
• interest has spawned a new science called astrobiology, which is the study of life in the universe

Question 2

Astrobiology

Answer 2

• Cosmos chemistry, especially origin of the elements
• chemical evolution
• origin and evolution of life
• space science
• expansion of extraterrestrial life into space

Question 3

Questions in extraterrestrial life

Answer 3

• Is there other intelligent life
• can we communicate with them
• did there use to be life in our solar system
• how did life originate on Earth
• could we recognize other forms of life

Question 4

What kinds of life can evolve on other planets

Answer 4

• most exoplanets have much larger mass than Earth
• high surface gravity would demand different evolutionary path

Question 5

It is “easy” to produce the building blocks of life

Answer 5

• miller and Urey experiment 1953
• produces amino acids
• not easy to turn them into life

Question 6

clues to growth of amino acids

Answer 6

• clustering of millions of amino acids into droplets which grow
• fossils compared with modern algae
• oily droplets ,made by exposing freezing mixture to strong UV light produce cell-like membranes
• life exists under very harsh conditions
• boiling water at right and rich sulphur clouds in ocean depths
• liquid water is common factor
• overall, biology may be common in the universe

Question 7

Dense Interstellar Clouds

Answer 7

• Dusty Cold and Dark
• nearly everything freezes out onto microscopic grains forming ice mantles
• UV and cosmic rays bombard the ice
• Murchison meteorite, organic matter

Question 8

From organic compounds to life: not an easy step

Answer 8

• No sign of large lifeforms or civilizations in the solar system
• we must search for microbial life

Question 9

Mars: The best candidate for extraterrestrial life

Answer 9

• apparently warm and wet for some periods in its distant past
• conditions similar to earth allowed life to evolve
• had the chemical ingredients for life
• had significant amounts of water ice
• pockets of underground water might exist if there is still volcanic heat

Question 10

Viking Lander (1976)

Answer 10

• searched for life on mars
• scooped up soil and dirt and ran tests
• no organic molecules found
• took readings at only two locations
• life could be elsewhere or underground
• sampled only surface soil

Question 11

Martian Meteorite ALH84001

Answer 11

• Had very different argon abundance than that of Earth’s

Question 12

Martian Meteorites

Answer 12

• rocks ejected by impact from mars have been found in Antarctica
• analysis of one revealed age of 4.5 billion years
• landed on Earth 13,000 years ago
• contained complex organic molecules and chains of crystals
• also found fossils of nanobacteria, recently discovered on Earth, have DNA
• since then structures could have been contaminated

Question 13

Jovian Moons

Answer 13

• Europa may have ocean of liquid water below its icy surface
• tidal heating keeps it warm
• possibly with volcanic vents on the ocean floor
• conditions may be similar to how Earth life arose
• Ganymede and Callisto may also have sub surface oceans but tidal heating is weaker

Question 14

Saturn Moons

Answer 14

• Titan has a thick atmosphere and oceans of methane and Ethane
• water is frozen
• perhaps life can exist in liquids other than water
• pockets of water might exist deep underground

Question 15

Life in other planetary systems

Answer 15

• must be old enough for life to have evolved
• star must survive long enough for life to evolve
• development of planetary crust, planet has to cool
• magnetic field
• composition of planet
• stability of life-sustaining conditions, no very large variations in surface temperature

Question 16

Which stars make good suns

Answer 16

• must be long lived, old enough that life could arise in a few million years
• must allow for stable planetary orbits, rules out binary and multiple star systems
• relatively large habitable zones
• width and location of habitable zone depend on type of star
• key is both habitable zone and time

Question 17

Planets and binary star systems

Answer 17

• must have stable uniform orb it to maintain the right conditions for life
• this is difficult so they may not be good places for life

Question 18

Have we found other habitable planets?

Answer 18

• maybe one or two
• current technology is insufficient
• The TESS mission is currently looking for habitable planets but progress is very slow

Question 19

Detecting habitable planets around other stars

Answer 19

• NASA plans to launch Terrestrial Planet Finder, which is an inferometer in space and will take spectra and make crude images
• Spectrum can tell us if it is habitable
• look for absorption lines of ozone and water

Question 20

Earth Like Planets: Rare or Common?

Answer 20

• Expectation is that they are common
• billions of stars in our galaxy have at least medium-size habitable zones
• theory of planet formation indicates terrestrial planets form easily in habitable zones

Question 21

Rare Earth Hypothesis

Answer 21

• Rare Earth hypothesis is that life on earth resulted from a series of lucky coincidences
• terrestrial planets form only around stars with high abundances of heavy elements
• the presence of Jupiter deflects comets and asteroids from impacting earth
• Jupiter did not migrate in towards the sun
• Earth has plate tectonics that allows the CO2 cycle to stabilize climate
• Moon keeps Earth’s tilt stable
• Won’t knows if these things are unique or ordinary until more data is retrieved on other planets

Question 22

Drake Equation

Answer 22

• estimates the number of civilizations detectable at radio wavelengths

Question 23

SETI (Search for Extra Terrestrial Life)

Answer 23

• Uses radio telescopes to listen for encoded radio signals
• can scan millions of frequencies at once
• now privately funded due to low chance of success and large amount of time required

Question 24

Where are Aliens

Answer 24

• WIthin a dew centuries we could colonize nearby stars, outposts throughout the galaxy in a few million years
• should be plenty of civilizations far ahead of us

Question 25

Fermi’s Paradox

Answer 25

• Why haven’t they visited us?
• nowhere and no-when, life is rare
• intelligent life is rare
• intelligent life is abundant , but quiet
  Solutions to Fermi’s Paradox
• no life
• we are alone
• Civilizations are common, but no one is talking to us and no one has colonized the galaxy
• there could be a galactic civilization that has deliberately concealed itself from us

Question 26

Why is interstellar travel difficult?

Answer 26

• Distance between stars is huge
• We will most likely be limited by the speed of light
• We would need to go 10,000 times faster than the Voyager spacecraft
• Requires new types of engines and new energy sources
• Special Relativity will complicate life for space travellers

Question 27

Starship propulsion

Answer 27

• Chemical rockets are impractical for interstellar travel
• going faster requires more fuel which makes the ship more massive and harder to accelerate
• Nuclear powered ships produce more energy
• matter anti-matter would be ideal but very hard to store
• Other options are solar sails and interstellar ramjets