Download Phys 1830: Lecture 33 - University of Manitoba Physics Department

Phys 1810:
Lecture 34 Life on Other Worlds continued.
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Recall column
No more Star Fleet
Academy
Monday is last office
hour.
Note: typo
λ should be
capital Λ in
ΛCDM
Example of Extremophiles:
Tube worms near Black Smoker
Those who have been floating between
morning and afternoon, please go to
P&A office Allen 301 and do an SEEQ
2. Chemical Evolution off planet
Panspermia: possible that complex organic molecules came from outside Earth, on
meteorites or comets.
Lab experiment: Droplets rich in amino
acids, formed when a freezing mix of
primordial matter was subjected to
harsh ultraviolet radiation.
2. Chemical Evolution Off Planet
Complex Molecules:
• Organic molecules usually found in star-forming regions consist of a single
“backbone” of carbon atoms arranged in a straight chain.
• ALMA found, in ISM, isopropyl cyanide which has branching structure.
• Branched carbon structure is common feature in amino acids
• May find way to planets.
2. Chemical Evolution Off Planet
This meteorite contains 12 different amino acids found in Earthly life, although some
of them are slightly different in form.
2. Chemical Evolution Off Planet
Would amino acids survive impact?
•two-stage light gas gun,
fired frozen pellets of algae
into H2O
• v = 6.93 km/s, expected
velocity of meteorite hitting
earth-like planet
•a small proportion survived.
2. Chemical Evolution Off Planet
Would amino acids survive? Simulations
 at ~1% level.
Comparable with Urey-Miller experiment
level.
2. Chemical Evolution Off Planet
Meteorite/Comet – produce instead of deliver
-oblique collision:
-CO2 icy comet impacts a planetary atmosphere with glancing blow 
thermodynamic conditions conducive to organic synthesis e.g. PAHs.
- also for rocky meteorite with icy surface.
-impact creates shock wave that generates molecules that make up
amino acids.
- impact of the shock wave also generates heat
 transforms these molecules into amino acids.
- fired projectiles through a large high speed gun at speeds of 7.15 km/s
into targets of ice mixtures (comet-like)  amino acids
Why not both 1 & 2? 
Role of the Moon
• Early Earth environment had fast lunar tidal oscillations since
moon closer.
highly saline low-tide environment needed for protonucleic
acid fragments to assemble into complementary molecular
strands.
• Rocks can provide scaffold-like structure to help chains grow.
 DNA
Cosmic Evolution
• Simple one-celled creatures, such as algae, appeared on Earth ~ 3.5
billion years ago.
• More complex one-celled creatures, such as amoeba, appeared ~ 2 billion
years ago.
• Multicellular organisms began to appear ~1 billion years ago.
• The entirety of human civilization has been created in the last 10,000
years.
Life in the Solar System
Even on Earth, organisms called extremophiles
survive in environments long thought impossible—
here, hydrothermal vents emitting boiling water rich
in sulfur.
Extremophiles:
•under 4km ice
•cut off from the outside
world for millions of
years
•unique microbial
communities
•3,500+ species in
conditions similar to
Jupiter’s Europa
Extremophiles:
summary
Recall column
Tube worms
near Black
Smoker
Dr Verena Tunnicliffe,
University of Victoria
(UVic)
• Example of energy source where the is no sunlight.
• Deep in the ocean, hydrothermal vent called a Black
Smoker.
• Rich ecosystem near the vent.
• Relevant to moons like Europa which has internal heat
caused by the tidal force of Jupiter and seems to have a
liquid ocean.
Extremophiles
Methanogenic microbes:
•H consuming.
•Produce methane.
 Europa, Titan?
Endoliths:
Rock eating microbes
 Mars?
Extremophiles:
summary
Recall column
Pointing to
microbes living
in rock in
Yellowstone
Park
University of Colorado,
Jeffrey Walker
• Other examples include
– microbes in salty ice (relevant to Mars, Europa
and other Jovian moons).
– microbes in layers of rock (relevant to Mars)
Life in the Solar System
Has Mars had liquid water on its surface in past? Martian landers have analyzed
soil, looking for signs of life—either fossilized or recent.
Spirit Rover/NASA
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Life on Mars
Recall column
•Toxic for humans
• evidence of carbon
compounds
Phoenix mission discovered a chemical -Perchlorates – that
a)is food for some microbes on Earth.
b) is toxic to some microbes on Earth.
c) collects water from an atmosphere.
d) is capable of creating on Mars wet habitats that
are about the size of sand grains.
In past, warm humid conditions BENEATH surface suitable.
Curiosity:
Found “habitable region” – just add
liquid H2O
Results: inconclusive.
Life in the Solar System
Life as we know it: carbon-based,
originated in liquid water
Is such life likely to be found elsewhere
in our Solar System?
Best bet: Mars
Long shots: Europa, Titan,
Ganymede, Enceladus
Other places are all but ruled out?
The Virus
Are viruses alive?
• contain some protein & genetic material
• cannot be considered alive until they become part of a host cell.
• They transfer their genetic material into cell, take over chemical activity,
& reproduce.
Viruses are in a “gray area” between living & nonliving, -- serve as a
reminder of how complex the definition of life can be.
Life in the Solar System
What about alternative biochemistries?
Some have suggested that life could be based on silicon rather than carbon, as it
has similar chemistry.
Or the liquid could be ammonia or methane rather than water.
However, silicon is much less likely to form complex molecules, & liquid
ammonia or methane would be very cold, making chemical reactions proceed
very slowly.
Alternatives – Life as we don’t know it:
summary
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• Astrobiologists ARE looking for
alternatives not found on Earth.
• e.g. silicon instead of carbon and sulfuric
acid instead of water.
• e.g. The University of Vienna’s
Alternative Solvents as a Basis for Life
Supporting Zones in (Exo-)Planetary
Systems.
summary
Life on Other Worlds
• Difficult to define life (e.g. viruses)
Recall column
• Expect these requirements:
1. solvent for metabolism
•
e.g. water or sulfuric acid
2. raw materials
•
e.g. carbon or silicon
3. clement conditions
•
e.g. distance from star for
temperature or magnetic field to
protect from cosmic rays or depth
within soil to protect from UV.
4. energy source
•
e.g. star or internal heat from tidal
forces (e.g. Europa).
Can we constrain this or is it hopeless?
Critical Thinking.
• Example: Jack is looking at Anne but Anne is
looking at George. Jack is married but George
is not. Is a married person looking at an
unmarried person?
a)Yes
b)No
c) Not enough information to decide
YES!
28.3 Intelligent Life in the Galaxy
The Drake equation, illustrated
here, is a series of estimates of
factors that must be present for a
long-lasting technological
civilization to arise.
Estimates the number of
civilizations we could attempt to
communicate with in the Milky
Way Galaxy at any
representative time (such as the
present).
Make your own estimate!
28.3 Intelligent Life in the Galaxy
Look at 1st term in
more detail than
textbook.
Divide by time at
the end.
Life as we know it – searching for Mr. Spock.
Recall column
More
accurately
determined.
Difficult to
estimate.
summary
• N = the number of civilizations now
= # of stars in the Milky Way
* fraction of appropriate stars
* fraction of those stars with planetary
systems
* # of planets suitable for life in each exoplanet
system
* fraction of suitable planets upon which
intelligent life appears
* fraction of planets that produce a civilization
with interstellar communication
* lifetime of that civilization
/ time that appropriate stars have existed.
Life as we know it – searching for Mr. Spock.
Recall column
Term 1 
Term 2 
Term 3 
Term 4 
Term 5 
Term 6 
Term 7 
Term 8 
summary
• N = the number of civilizations now
= # of stars in the Milky Way
* fraction of appropriate stars
* fraction of those stars with planetary
systems
* # of planets suitable for life in each exoplanet
system
* fraction of suitable planets upon which
intelligent life appears
* fraction of planets that produce a civilization
with interstellar communication
* lifetime of that civilization
/ time that appropriate stars have existed.
Drake’s Equation: Term 1
Recall column
summary
• The number of stars in the Milky Way:
• F_orbit = F_gravity
M = (r * v**2) /G
 M = a few * 10 **11 solar masses.
• Adopt 300 billion stars as the estimate
– e.g. there are only a few % high
mass stars on the main sequence.
summary
Drake’s Equation: Term 2
Recall column
• The number appropriate stars:
a) Need high enough metallicity to have
carbon (or silicon) on their planets.
Galactic Habitable Zones:
PAH’s exist in these regions.
summary
Recall column
Which of the following stars are metalpoor?
a) Very young stars.
b)
Population II stars.
c)
Population I stars.
d) Stars forming in spiral arms of
galaxies.
Drake’s Equation: Term 2
Recall column
summary
• The number appropriate stars:
a) Need high enough metallicity to have
carbon (or silicon) on their planets.
Population I stars.
– up to 1/5 are Pop II
leaves us with roughly
250 * 10**9 stars.
Drake’s Equation: Term 2
Recall column
summary
• The number appropriate stars:
b) Need long enough lifetime for life to
form and evolve. On Earth it formed at
roughly 3 billion years. So a star can’t
be too massive.
Spectral Types F through K.
1/17 * 250 * 10**9 stars
= 15 * 10**9 stars.
 ~ 15 billion stars
summary
Drake’s Equation: Term 3
Recall column
• The number appropriate stars with
planetary systems:
a) Should have Jupiter-size planets far from
planet hosting life. These will attract comets
away from planet with life. From studies of
exoplanet systems:
1/5 * 15 * 10**9 stars
= 3 * 10**9 stars
summary
Drake’s Equation: Term 3
Recall column
Start to
incorporate your
own values!
Optimists use “1”
i.e. all systems
have rocky
planets.
• The number appropriate stars with
planetary systems:
b) How many have rocky planets? 50-50
chance:
½ * 3 * 10**9 stars
= roughly 1.5 * 10**9 stars with at least 1
rocky planet.
Text notes that
planets in binary
systems unlikely to
have stable orbit.
Uses 1/10.
Drake’s Equation: Term 4
Recall column
summary
• The number of planets suitable for life
in each exoplanet system:
How many rocky planets reside in the Habitable
Zone (HZ)? This zone is around each star and
has a temperature such that water condenses
on the planet’s surface but does not
permanently freeze. That is, it is a spherical
shell bound on the interior by regions with T
> 100C and outside by T<0C.
For example, our sun
(G star)
0.85 AU < HZ < 2 AU
0.85 AU < HZ < 2 AU
Drake’s Equation: Term 4
Recall column
summary
• The number of planets suitable for life
in each exoplanet system:
How many rocky planets reside in the Habitable
Zone (HZ)?
Using our solar system as an example, almost 3
rocky planets are in the HZ.
– 1 planet is too hot
– 1 planet has too little mass to retain its
solvent as a liquid.
When you make your
own calculation, adjust this
up to “3 times” if you like.
adopt the value of 1 appropriate
planet in the HZ
1 * 1.5 * 10**9 stars
Drake’s Equation: Term 5
Recall column
summary
• What fraction of suitable planets
produce life?
– e.g. given the ingredients (C, N, H
and H20) and assuming life
spontaneously arises.
– 50-50 chance
½ * 1.5 * 10**9 stars
= roughly 1 * 10**9 stars
with a planet with life on it.
Textbook uses 1 – optimistically = 1.5 billion stars.
Dimitar Sasselov TED talk 2010: 100 million habitable planets.
Sara Seager TEDX talk 2013: ~2 dozen Earth-like planets discovered.
summary
Drake’s Equation: Term 6
Recall column
•
•
What fraction of planets with life
produce intelligent civilizations that
develop a technology that releases
detectable signs of their existence
into space?
e.g. of Issues - Mass extinctions:
– one needed to wipe out the dinosaurs.
– alternatively it could wipe out life either altogether or
to the microbial stage.
– perhaps less than 50% of the exoplanet systems are
lucky to have this happen and survive???
 1/3 * 10**9 stars
The least constrained term is term 7, life time of the
technological civilization. Let’s leave this for the moment.
summary
Recall column
• What is true about this image?
a) It is the famous Ring Nebula.
b) Our sun will look like this as it dies.
c) Carbon is an element in these objects.
d) It is a Planetary Nebula.
e) All of the above.
Drake’s Equation: Term 8
Recall column
summary
• How long have appropriate stars
existed?
• i.e. How long has carbon existed?
– study elements in Planetary
Nebulae and those that are younger
than ~6 * 10**9 years old have
enough carbon.
 the civilizations we seek have
occurred within the last 10 billion
years (c.f. Universe’s age 13.5 billion
years)
Life as we know it – searching for Mr. Spock.
Recall column
• N = the number of civilizations now
N = 1/3 * 10**9 stars * lifetime of that civilization / 10 * 10**9 yr
N = lifetime of that civilization / 30
What is your estimate for N?
N=
your_fraction * lifetime of that civilization
Other estimates in next lecture.
summary