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ASTR-1010
Planetary Astronomy
Day - 39
Course Announcements
Homework Chapter 12: Due Wednesday April 28.
Homework Chapter 21: Due Wednesday April 28.
-this is extra credit.
Observatory Visit and Virtual Observations reports are due
Wednesday - 4/28/2010
Exam 4 and “Final”: Friday, April 30 – 1030 am
Next Spring (2011) ASTR-3040 Astrobiology
Extrasolar Planets
Most of the extrasolar planets discovered to date are quite massive and
have orbits that are very different from planets in our solar system
Astronomers have discovered planets orbiting
other stars
• Geoff Marcy is using the
10-meter Keck telescope
in Hawaii to measure the
Doppler effect in stars
that wobble because of
planets orbiting around
them
• So far, he and other
teams have found more
than 100 extrasolar
planets
How do you Find Exo-Planets?
• 3 Methods
– Radial velocity shifts of the parent star
– Direct Imaging
– Transits
Finding Extrasolar Planets
• The planets themselves are not visible; their
presence is detected by the “wobble” of the stars
around which they orbit
Radial Velocity
1st Direct IR Images
1st direct Optical Image
A Transit
USING PHOTOMETRY TO DETECT PLANETS
•
Transits
Planet crosses line of sight between
observer and star and blocks
a small amount of light from the star
Transit of Mercury in 2003
Transit of HD 209458 observed with HST
13
Eras in the Universe
In the standard model, there are several steps
from early times to the modern universe:
• Physical forces established.
• Era of photons, electrons, positrons.
• Antimatter annihilates matter, leaving many
photons and a little normal matter.
• Matter and photons cooled. Atomic nuclei
formed (Big Bang nucleosynthesis).
• Recombination: atoms, galaxies, stars.
Future of the Universe
• The universe will probably expand forever.
• In 1014 yr, stars die out, leaving white
dwarfs, brown dwarfs, neutron stars.
• In 1039 yr, normal matter decays, leaving
only black holes.
• In 10100 years, even largest black holes
will evaporate.
Searching for Extrasolar Planets
• This chapter primarily deals with searching
for extrasolar planets and the techniques
for finding them.
Most of this information is available in the
text and various sites on-line, such as:
http://en.wikipedia.org/wiki/Extrasolar_planet
Motion of Extrasolar Planets
Lecture Tutorial pg. 117
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with
one another. Take time to understand it now!!!!
• Come to a consensus answer you both agree
on and write complete thoughts into your LT.
• If you get stuck or are not sure of your answer,
ask another group.
Main Sequence Lifetimes
Mass (M)
Luminosity (L)
17.5
52,500
Lifetime in
billion years
0.01
2.0
14
1.1
1.0
1.0
10
0.67
0.15
53
0.21
0.011
290
Life, the Universe, & Everything
• Evolution is a normal consequence of physics.
• If a self-replicating molecule ever forms, then
complex structures will arise.
• Reproduction via heredity is not perfect; there
are always mutations.
• Natural selection: well-adapted molecules (or
organisms) will have more surviving offspring
than less well-adapted ones.
Are We Alone?
Estimate the number of advanced civilizations
using the Drake Equation. Multiply:
• number of stars in our galaxy
• fraction of stars with planets
• average number of planets per star
• fraction of planets with life
• fraction that develop advanced technology
• Result is the likelihood such planets exist
today.
The Drake Equation
• We know several numbers in the Drake
equation, particularly the astronomical
ones.
• For others, we have to guess.
• Optimistic values: nearest civilization only
40 light-years away.
• Pessimistic values: distance is 30 million ly.
The Drake Equation
• 1961 – 1st SETI conference, Green Bank, WV
• Number of civilizations in our galaxy (or the
Universe at large) from which we could
potentially get a signal.
• Does NOT give a definitive answer.
• Rather, it lays out the factors that are
important in determining this number.
The Drake Equation
•
•
•
•
Number of Civilizations = NHP X flife X fciv X fnow
NHP -Number of habitable planets in galaxy
flife -Number of habitable planets that have life
fciv -Fraction of life-bearing planets where a
civilization capable of IS communication at
some time has arisen.
• fnow -Fraction of habitable planets with
civilization now, not in the past.
Concept Quiz –
Life in the Universe
Even if there’s a very low chance that any one
planet has life on it, there may be many
advanced civilizations because …
A. There are billions of billions of stars in the
universe.
B. Simple life inevitably leads to complex life.
C. We know that Earth-like planets are
common in our galaxy.
4 Metabolic Classifications
•
•
•
•
•
Based on energy and carbon acquisition.
1. Photoautotrophs
2. Chemoautotrophs
3. Photoheterotrophs
4. Chemoheterotrophs
Is Intelligence Widespread?
• If life is widespread, what about intelligence?
• SETI is only successful if THEY
communicate.
• Homo sapiens have only started to
understand the environment and explore the
cosmos in the last <500 years.
– Suggests a long period of evolution is required to
produce technologically intelligent creatures.
– Chance events
• body plans in Cambrian explosion
• K-T extinctor
Convergent Evolution
• The tendency of organisms of different
evolutionary backgrounds that occupy
similar ecological niches to resemble each
other.
– Large marine predators – dolphins & sharks
– Eyesight (eyes evolved eight times).
Encephalization Quotient (EQ)
•
•
•
•
•
Raw brain power based on brain mass.
Simple measure
EQ = 1 line – general intelligence
Above line – capable of elaborate behavior
Below line – less mentally agile
Evolution of Intelligence
• Humans don't have the largest brains.
• Is the largest in relation to body mass.
Early SETI
• Marconi (1874-1937)
• Tesla (1856-1943)
• Both claimed to have heard aliens on the
radio.
– Probably “whistlers”
• Low frequencies which don't penetrate
atmosphere.
Modern SETI - Origins
• 1959 – Cocconi & Morrison – Cornell Univ.
• Galaxy is older than solar system, so could
be civilizations around linger than ours.
• Band –Frequencies receiver is sensitive to.
• Bandwidth – a particular freq. in the band.
• Governed by how much information is
transmitted.
SETI - Today
 Categories of Signals
1. Local communications
on other world.
2. Communications
between home world &
other site.
3. Intentional signal
beacons. (Project
Ozma)
 In theory, SETI can
detect all three types.
26m dish at NRAO-Green Bank
Our Own Signals
• Broadcast in ~1950, just past 50 ly distance.
– High power, high-frequency TV
– > 2000 stars in this volume.
– Star map
A Signal
Look for: repetition, prime numbers …
1974 – signal sent to M13 (bad choice in hind sight). – 21,000 ly distant.
SETI - Today
• Current SETI projects
Radio –vs.– Optical
• Radio is a logical choice since we developed
radio capability early (didn’t everyone?)
• Dust blocks light in the denser parts of the
Galactic plane.
– Limits our view to a few hundred parsecs.
– Not as big an issue today.
• But how?
– Laser pulses - doesn’t everyone know Morse code?
– Lick – 500 ly search distance
– Harvard also has a project going.
Artifacts
• 2001: A Space Odyssey
• The TMA is clearly not natural.
Artifacts
• Parking
spaces –
Lagrange
points
• Manufacturing
plants.
Types of Civilizations
Nikolai Kardashev – 20th century
Planetary (Type I) – use resources of home planet.
Stellar (Type II) – corral resources of home star.
Galactic (Type III) – employ resources of entire
galaxy.
 We’re in the first category.
 What would be the hallmark of the third?
“Any sufficiently advanced technology is
indistinguishable from magic.”
– Sir Arthur C. Clarke
Type II Civilizations
• Dyson Sphere
Freeman Dyson
• Could detect
the IR
radiation
Big Question
• What if we succeed in finding another
civilization?
– Declaration of Principles Concerning Activities
Following the Detection of Extraterrestrial
Sistilli NASA experience
Intelligence
Jill Tarter at Arecibo
UFOs
• Project Bluebook
• Day the Earth Stood Still
• War of the Worlds
• Mars Attacks
Evidence of Visitation
• Roswell, NM
• July 8, 1947
• 2009 Conference
Evidence of Visitation
• Crop Circles
• Abductions
“Extraordinary claims
require extraordinary
evidence.”
- Carl Sagan
Ancient Visitations?
• Nazca Line Drawings in
Peru, ~2000 years ago.
• Mayan pyramids
• Easter Island heads
Fermi Paradox
• If we're not special, then there should be older
civilizations in the galaxy. Where are they?
• Von Neumann machines – self replicating.
• Would other civilizations try to colonize the
galaxy?
– Coral model
– 10% c, 150 years to 5ly
– Entire galaxy in 10 Myr
– 100 Myr at 1% c
Motives to Colonize
• Humans want to explore. Are we unique?
• Extinction-proof civilization
• Population control? - Not likely.
Fermi Paradox - Solutions
1. We are alone, therefore we are it.
2. Civilizations are common – but no one
has colonized the galaxy.
A. Technological difficulties.
B. Sociological considerations.
C. Self-destruction.
3. There is a galactic civilization – they just
don't want to deal with us.
Zoo hypothesis
Sentinel hypothesis