Extra-Terrestrial Life and the Drake Equation

Astronomy 311Professor Lee

CarknerLecture 26

Observing Project

Due Friday Project should be neat, organized,

labeled and have all questions fully answered

Telescope objects: Venus, Uranus, Neptune, Saturn, Moon

We will try for the Sun on Friday Meet in planetarium

We will try to observe tonight at 9pm Check web page

Is There Anybody Out There? People have long speculated about life on

other worlds

Modern observations indicate that the solar system is uninhabited

How can we estimate the possibility of extra-terrestrial life?

The Drake Equation In 1961, astronomer Frank Drake developed a

formula to predict the number of intelligent species in our galaxy that we could communicate with right now

Solving the Drake equation helps us to think

about the important factors for intelligent life

The Drake Equation

N=R* X fp X ne X fl X fi X fc X fL

N = The number of civilizations in the galaxy R* = Number of stars in the galaxy

fp = Fraction of stars with planets

ne = Average number of suitable planets per star

fl = Fraction of suitable planets on which life evolves

fi = Fraction on which intelligence develops

fc = Fraction that can communicate

fL = Lifetime of civilization / Lifetime of star

The Milky Way

R* -- Stars We start with the number of stars in the

galaxy

We are ruling out life around neutron stars or white dwarfs or in non-planetary settings (nebulae, smoke rings, etc.)

The H-R Diagram

The Orion Star Forming Region

Protoplanetary Disk in Orion

Extra-Solar Planets

fp -- Planets Very high mass stars go supernova

before planets can form

Need medium mass stars (stars like the Sun)

fp -- Finding Planets

Studies of star forming regions reveal that circumstellar disks are common around young stars

Only about 75 have been found,

but we can only find the most obvious ones

The Carbonate-Silicate Cycle

Water+

CO2

(rain)

Ocean

Carbonate + silicate(Sea floor rock)

CO2

Volcano

Atmosphere

Carbonate+ water(stream)

CO2 + silicate(subvectivemelting)

Venus

Mars

ne -- Suitable Planets What makes a planet suitable?

Must be in habitable zone

Heat may also come from another source like tidal heating (Europa)

ne -- Unsuitable Planets The Moon --

Mars --

Jupiter --

Venus --

Earth at 2 AU -- CO2 builds up to try and warm planet, clouds form, block sunlight

The Miller-Urey Experiment

Comet

fl -- Life The building blocks of life on Earth

are organic compounds

The Miller-Urey experiment demonstrates that organic material could have formed from the material available on the early Earth

The KT Impact

fi -- Intelligence Life alone is not sufficient, intelligence is

needed to communicate Many things could interfere with evolution in

this time

Life on Earth has gone through many disasters (e.g. mass extinctions), but has survived

Europa

fc -- Communication Even intelligent life may not be able to

communicate

What could keep intelligent life from building radio telescopes?

O’Neill Colony

O’Neill Colony -- Interior

fL -- Lifetime

fL = Lifetime of civilization / Lifetime of star

How long does a civilization last

for?

fL -- Destroying Civilization

What could destroy a civilization?

Space colonization greatly reduces

risk or extinction

The Fermi Paradox Physicist Enrico Fermi asked, “If

there are many civilizations in the galaxy why haven’t they contacted us?” Cosmic Zoo --

Berserker Theory --

The Gibson Continuum --

The Von Neumann Problem Build a self replicating space probe (a Von

Neumann machine)

Even if it takes 100,000 years to get to the next star and 1000 years to make a copy, in 100 million years the galaxy is full of machines

Summary: Life in the Galaxy Medium size, medium luminosity star with a

planetary system A planet of moderate mass in the habitable zone Organic compounds reacting to form simple life Life evolving over billions of years with no

unrecoverable catastrophe Intelligent life building and using radio telescopes A long lived civilization