Download Conversations with the Earth

Conversations with the Earth
Tom Burbine
[email protected]
Last Quiz on Thursday
• Life in the Solar System and Galaxy
Final
• May 9 (Monday) – 11:30 am - (Monday, Wednesday,
Thursday class)
• May 11 (Wednesday) – 8 am - (Tuesday, Thursday class)
• 25 short answer questions
• No calculators
• Besides your new sheet of paper, you can bring in the sheet
of paper you used for the Midterm
• Currently, there are 547 candidate extra-solar
planets that have been identified, orbiting 458
stars
• It is estimated that there are 50 billion planets in
our galaxy
The only star we know that has
Earth-Like Planets is the Sun
• Sun is sometimes called Sol
Galactic Habitable Zone
• It is the area in the galaxy whose boundaries are
set by its calm and safe environment, and access
to the chemical materials necessary for building
terrestrial planets similar to the Earth.
http://astronomy.swin.edu.au/GHZ/
green is habitable zone
Habitable Zones
• http://en.wikipedia.org/wiki/Image:Habzonethinkquest.gif
HabCat
• Catalog of Nearby Habitable Systems made by
Jill Tarter and Margaret Turnbull
• These Sun-like, habitable stars have just the right
distance, constancy, and temperature to qualify in
a forthcoming enlarged radio search.
What do else do you need?
• You need “metals” to make planets
–Metals are elements heavier in mass
than helium
For simple life
• You need a planet with an atmosphere and some
water
• Stars must remain nearly constant in
brightness over billions of years for complex
life to have time to develop.
– On Earth, single cells may have developed
after only 800 million years or so, but the
fossil record indicates that it took another
~3 billion years before multi-cellular life
flourished.
• The number of HabCat stars,
as a function of distance
• M-type stars (solid red
histogram)
• K stars (dark-hatched green
histogram)
• G stars (light-hatched violet
histogram)
• F stars (horizontal-lined yellow
histogram)
• all stars (open blue histogram). 1 pc = 1 parsec = 3.26 light years
http://www.astrobio.net/news/article436.html
Drake Equation
• The Drake Equation is an attempt to estimate the
number of extraterrestrial civilizations in our
galaxy with which we might come in contact.
• http://www.activemind.com/Mysterious/Topics/SETI/drake_equation.html
Number of habitable planets
• 100 billion?
Fraction of Planets that have life in the Galaxy
• ?
Fraction of the Life-Bearing Planets in the
Galaxy upon which a Civilization capable of
interstellar communication
has at some time arisen
• ?
Intelligent Life
• Intelligent life that we can detect is usually
defined as life that can build a radio telescope
Radio
• Transmitting information over radio waves is very
cheap
• uses equipment that is easy to build
• has the information-carrying capacity necessary
for the task
• The information also travels at the speed of light.
Fraction of all civilizations that have existed
in the galaxy that exist now
• ?
Fermi’s Paradox
•
Where are they?
Fermi’s Paradox
•
Why have we not observed alien civilizations
even though simple arguments would suggest
that some of these civilizations ought to have
spread throughout the galaxy by now?
Reason for question
• Straightforward calculations show that a
technological race capable of interstellar travel at
(a modest) one tenth the speed of light ought to be
able to colonize the entire Galaxy within a period
of one to 10 million years.
Explanation
• Interested in us but do not want us (yet) to be
aware of their presence (sentinel hypothesis or
zoo hypothesis)
Explanation
• Not interested in us because they are by nature
xenophobic or not curious
Explanation
• Not interested in us because they are so much
further ahead of us
Explanation
• Prone to annihilation before they achieve a significant
level of interstellar colonization, because:
(a) they self-destruct
(b) are destroyed by external effects, such as:
(i) the collision of an asteroid or comet with their
home world
(ii) a galaxy-wide sterilization phenomenon (e.g. a
gamma-ray burster
(iii) cultural or technological stagnation
Explanation
• Capable of only interplanetary or limited
interstellar travel because of fundamental
physical, biological, or economic restraints
Fermi’s paradox
• The Fermi paradox is the apparent contradiction
between high estimates of the probability of the
existence of extraterrestrial civilizations and the
lack of evidence for, or contact with, such
civilizations.
• http://en.wikipedia.org/wiki/Fermi_paradox
Any Questions?