Physics 55: Two Classes About Astrobiology
Professor Henry Greenside
hsg@phy.duke.edu
April 9, 2012
Great Scientific Question:
Does Life Exist Outside of Earth?
1.
2.
3.
4.
Why life is likely elsewhere in the universe
How to search for life
Where are the aliens?
Travel to the stars? Not likely, not even by probes
What is Life? Start with discussion:
How is fire like or not like a living creature?
Duke-Maryland game, 2002
Brownian Motion?
Belousov-Zhabotinsky Reaction?
Is a star living or not?
Characteristics of Life
Requires nutrients (atoms, molecules)
Requires energy (chemicals, sunlight)
Requires water (???)
Produces waste products
Can reproduce
Can respond to environmental changes
Can evolve.
Biologists and computer scientists have especially made
progress with artificial life: evolving reproducing mutating
computer codes “living” in memory of computer, viruses and
ecologies spontaneously appear.
Key Slide: Why life is likely elsewhere:
Same ingredients (atoms) everywhere
Life started rapidly on Earth
Laboratory experiments suggest
spontaneous formation of biological
molecule, comets support this.
Earth life can survive extreme environments
Earth does not seem special
1011 stars in a galaxy, 1011 galaxies
Universe is ancient, lots of time for life
to have started elsewhere
Relative Abundance of the Elements:
Why H-C-N-O Based Life is Likely
Relative Abundance of the Elements
On Earth's Surface
What Can You Make With H, C, O, N, P?
Polysaccharides (sugars)
Amino acids and proteins
Nucleic acids, DNA, RNA
“Inner Life of a Cell” Movie
Why is Life Likely: Life Appeared on
Earth as Soon as Life Was Possible!
Earth “born” 4.5 billion years ago
Heavy bombardment sterilized Earth 4 billion years
ago, life appeared shortly after, 3.85 billion years ago!
Life Appeared on Earth as Soon as Life
Was Possible
Evidence of age:
- Radiodating of fossils
- Increased ratio of carbon-12
isotope to carbon-13 isotope
in rocks indicates presence of
life.
Australian stramatolites
Some are 3.5 billion years old!
Two Possibilities
About Rapid Appearance of Life
Life can arise easily and spontaneously.
Panspermia: life arrived on Earth from some other
location, perhaps Mars or comets or from outside solar
system, but that just shifts question of origin to
another location (and Mars was also bombarded).
Possible Example of Panspermia:
Rocks from Mars on Earth
Martian meteorite that crashed in Tissint, Morocco, July 2011
Why Is Life Likely:
Suggestive Chemistry Experiments
Miller-Urey Experiment, 1953
Amino acids, nucleic acids found
Why Life Might Be Likely:
Extreme Forms of Life on Earth
Bacterial mats
Yellowstone
Pitch Lake, Trinidad
black smoker
Extremophiles: acidophile, anaerobe, lithoautotroph,
oligotroph, cryptoendolith, xerophile, piezophile,
radioresistant, etc
But “Advanced” Life Forms Might be Rare:
Complexity Transitions Are Difficult
Single cell creatures persisted in ocean for first
billion years, then multi-cell creatures appeared.
Dinosaurs existed for about 130,000,000 years
but, to our knowledge, never developed
technological civilization.
Humans around 3-4 millions years, but technology
arose only in last 100,000 years!
Looking For Life in the Solar System
Key assumption: liquid water is essential!
Stellar Habitable Zone: Where Liquid
Water Might Occur
Habitable Zone = Goldilocks Zone
Only One Other Planetary Candidate : Mars
Mars
Traces of water found
No signs of life
Water on Mars
Gravitational Tides Might Allow Life
Outside the Goldilock's Zone
This complicates search for life around other stars,
remote moons hard to study!
Life in Europa's Icy Ocean?
4th largest moon,
about same size
as Earth's Moon
Gravitational tides warm ice, create
salty ocean possibly ~60 miles deep,
versus ~7 miles for Earth.
Life Around Other Stars
Galactic Habitable (“Goldilocks”) Zone
Many Exoplanets Now Known:
~760 Planets In 600 Planetary Systems!
Not Know Yet if
Earth-Like Planets Are Rare
Searching For Exolife
Terrestrial Planet Finder (TPF)
Block light from star, observe planets directly!
Look Spectroscopically for Biosignatures
Water vapor
Excess oxygen
Excess methane (found on Mars!)
Complex molecules like chlorophyll
Infrared Spectroscopic Signature of Life
Based onSolar Sysem
SETI:
The Search for Extraterrestrial Intelligence
Drake Equation: How To Estimate Number
Of Intelligent Civilizations in Galaxy
How To Search For Intelligent Life
Arecibo Radio Telescope in Puerto Rico
How to Communicate?
Interstellar Travel:
Implications for SETI
How to Communicate: Lincos?
?
How to Communicate?
Where is Everybody?
Galaxy has radius of 50,000 light-years so time to colonize less than
ten million years with v ~ 0.1c, ok grant 100,000,000 years, still
much less than 1/10 age of universe!
Travel to the Stars by Fusion
Implications
We are the only technological civilization in the
Milky Way.
Civilizations are common but it's hard to colonize
space (interstellar travel is hard!
There is a galactic civilization but it is hiding
from us.
Why is the search for life worthwhile?
Class Discussion: are snowflakes alive?
Prof Kenneth Libbrecht. Caltech
www.its.caltech.edu/~atomic/snowcrystals/