Physics 55: Part II Astrobiology
Professor Henry Greenside
hsg@phy.duke.edu
April 11, 2012
From Previous Class:
Why life is likely elsewhere
Same ingredients (atoms) everywhere
Life started rapidly on Earth
Earth life can survive extreme environments
1011 stars in a galaxy, 1011 galaxies, most
stars have planets.
Universe is 14 billion years ancient, lots of
time for life to have started elsewhere.
Today's Class:
Search for life in the solar system
Search for life around other stars
SETI: Search for Extraterrestrial Intelligence
Interstellar travel: where are the aliens?
Essential Ingredients of Life
Nutrients (chemicals ==> planets,
moons, comets)
Energy (light energy, heat, chemicals)
Time (for evolution to take place)
Water (for terrestrial life)
Stellar Habitable Zone: Where Liquid
Water Might Occur
Only One Planetary Candidate : Mars
Mars
Traces of water, methane
No signs of life.
Martian Meteorite ALH84001: False Alarm?
Electron microscopic image of ALH84001
sample: chain-like molecules!
Many non-biological phenomena produce
intricate life-like patterns.
Life in Europa's Icy Ocean?
4th largest moon, about same
size as Earth's Moon
Arthur C Clarke's
“2010: Space Odyssey II”
Gravitational tides warm ice, create salty
ocean possibly ~60 miles deep, versus
~7 miles deep on Earth. Would have to
drill through ~15 miles of ice!
Constraints On Extrasolar Life
Star mass can't be too massive (star dies too
quickly for evolution to occur).
Star must allow stable planetary orbits, life
around multiple star system unlikely.
Planet must be in star's Goldilocks zone so liquid
water is likely.
This still leaves many stars to study,
perhaps 50% of all stars.
Life Around Other Stars
Galactic Goldilocks Zone
Too close to center, stars too
close, supernovas frequent and
will destroy life.
Too far from center, not enough
atoms beyond He, lack nutrients
Look For Planets Around Remote Stars:
Kepler Spacecraft (http://kepler.nasa.gov)
Galactic Range of Kepler Spacecraft
Many Exoplanets Now Known:
~760 Planets In 600 Planetary Systems!
Tools For Finding Exolife:
Telescope and Spectroscope
Look Spectroscopically for Biosignatures
Water vapor
Excess oxygen
Excess methane (found on Mars!)
Complex molecules like chlorophyll
21% O2 in
Earth's air
Searching For Exolife Around ~2025
Terrestrial Planet Finder (TPF)
Block light from star, observe planets directly.
Use interferometry for precise measurements
Use high-precision atomic clocks to coordinate telescopes
Technological Life Might Be Easier to Find
Hot spots: power generators
X-ray flashes from nuclear bombs
Neutrino emissions.
Radio waves (60 year old technology!)
Intentional signaling: high-power laser
Warning: Advanced Technology
More Efficient, Less Visible, Less Intelligible
Highly compressed signals look
like random noise.
The Search for Extraterrestrial Intelligence:
SETI
Drake equation more a summary of what we don't know
than a physical description of nature.
Challenges of SETI: Where, What, How?
Where to look in sky? Too many objects :(
Too many frequencies to scan: radio waves, visible
light, microwave, X-rays, neutrinos, gravitational
waves?
How to identify intelligent signal, distinguish from
noise? Pulsars sound artificial...
http://www.jb.man.ac.uk/pulsar/Education/Sounds/sounds.html
http://www.youtube.com/watch?v=uHEVo-LkDrQ
How To Search For Intelligent Life
Arecibo 300 m Radio Telescope in Puerto Rico
Discussion: Instead of Listening,
Should We Communicate?
Message in a Bottle
In the Ocean of Space
Voyager 2 spacecraft
Travel to the Stars by Fusion
Time to Colonize Milky Way by Fusion
100 Million Years: Where is Everybody?
We are the only technological civilization in the
Milky Way (so Earth is special!!!)
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.
Goal of Looking For Life in the Universe?
“We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time.”
T. S. Eliot, Four Quartets, 1944
How to Communicate: Lincos?
?
Stressing by Gravitational Tides Might
Allow Life Outside the Goldilock's Zone
This complicates search for life around other stars,
remote moons hard to study!
ITER: International Thermonuclear
Experimental Reactor
Being built in Cadarache, France
TFTR: Tokamak Fusion Test Reactor
Allen SETI Array: Partially Built
Interior of TFTR: A Donut Shaped Star!