Transcript Mystery of Enceladus - Washington University in St. Louis

Lecture 13. Panspermia
announcement: Exam on Friday - move to Monday?
availability for office hours: Thursday
reading: Chapter 5
Polymerization Problem
Somehow organic molecules came together, began reacting.
Key: understanding polymerization.
Called “The Polymerization Problem”
amino acid 1 + amino acid 2 <----> dipeptide (aa1-aa2) + H2O
Is called a problem because:
1. reaction produces water.
2. reactions must occur in the presence of water
3. life requires liquid water
4. water drives the chemical equilibrium in the wrong direction!
Any valid hypothesis of the origin of life has to explain The
Polymerization Problem.
Problem of Chirality
Chiral compounds have multiple stereoisomers.
Amino acids occur in D and L forms in the universe.
Any valid hypothesis of the origin of life has to explain The Chirality Problem:
- amino acids in proteins “chose” L-amino acids
- sugars/carbohydrates “chose” D-sugars
When Did Life Originate?
Don’t know when life originated.
Knowing when gives us some clues about the environment.
If we have cellular life at 3.8 Ga:
- during late heavy bombardment.
- origin of life some time before this (4.1-4.2 Ga)
- only took a couple hundred million years
- hot conditions
If cellular life arose later:
- after late heavy bombardment
- may have taken much longer to originate - billion years
Impact Frustration of Life
Likely several 150-190 km diameter impactors
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3.8 Ga.
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If life originated in the deep sea:
could have originated 4.2 - 4.0 Ga
If life originated at the surface:
could have originated 4.0 - 3.7 Ga
Life could have arisen multiple times, and then
gone extinct several times.
Panspermia - The Alternative Hypothesis
began with the Greeks!
500 BCE Anaxagoras
Stated the principal of Panspermia: the seeds of animal and plant
life are inherent to the cosmos, and they take root whenever
conditions are favorable.
1908 Svante Arrhenius
Put Panspermia in a scientific theoretical framework
Book “Worlds in the Making”
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“…life-giving seeds are drifting about in space. They encounter
the planets, and fill their surfaces with life as soon as the necessary
conditions for the existence of organic beings are established.
… We must regard it as possible that there are countless seed-bearing
meteoric stones moving through space.”
Panspermia Unravels
Panspermia treated with skepticism, almost as anti-science.
It moves the problem of the OOL elsewhere.
In the last decade, research in the field of Panspermia has
been revitalized. Now treated as a serious field of study.
Perhaps life originated elsewhere in the solar system.
Transported to Earth where it then diverged into the diversity of
organisms we are familiar with today.
Alternatively, life transferred from Earth to another
body of the solar system.
Observations Suggesting Panspermia is Possible
1. We find intact Mars rock on Earth
e.g., ALH84001
best place to find meteorites: Antarctica!
- cold (preserves them)
- easily visible
- ice is melting, so they are concentrated
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Observations Suggesting Panspermia is Possible, cont.
2. Bodies are moving through the solar system
3. Organic compounds
- are plentiful in the solar system (comets, asteroids, dust)
- can survive billions of years in space
- can survive atmospheric entry inside meteorites
(outer surface melts, inner part still cold as space)
The Process of Interplanetary Transfer
1. Origin of life has to occur SOMEWHERE
2. Have to get the organisms off the moon or planet
only real way: impacts
- impactor comes in and hits the parent body
- material is ejected out of the impact site = ejecta
- ejecta = dust and boulders
- whether ejecta makes it into space depends on
i. impact energy
ii. gravity of the parent body
iii. whether parent body has an atmosphere
iv. how thick the atmosphere of the parent body
wimpy impacts ---> little ejecta
huge impacts ---> lots of ejecta, but lots of melting
The Process of Interplanetary Transfer, cont.
Gravity of the parent body ---> escape velocity
Moon: 2.4 km/sec
Mars: 5.0 km/sec
Earth: 11.2 km/sec
Venus: 10.4 km/sec
ejecta must have velocity > espace velocity
Atmosphere:
a thick atmosphere slows down objects due to drag
Moon: none
Mars: 6 mbars
Earth: 1 bar (200x)
Venus: 60 bars (60x)
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The Process of Interplanetary Transfer, cont.
The Process of Interplanetary Transfer, cont.
3. The organisms have to survive the trip through space
Space Conditions:
- extreme cold
- T can vary with distance from Sun, whether in sunlight or in the shade
- extreme vacuum - desiccating, water boils away
- uv light from the Sun - constant exposure
- solar storms
energetically charged particles
- galactic cosmic rays
}
Transfer Time Varies:
- martian meteorites average a few million years
- lunar meteorites average a few thousand years
- thousands to several millions of years
Ejected Material Not Equally Distributed:
- material from the inner solar system rarely reaches Jupiter
Spore Formers
Made by a couple species of bacteria.
All evolutionarily related.
Found primarily in soils.
Some are human pathogens.
Bacillus
B. subtilis
B. anthracis
Clostridium
C. tetani (tetanus)
C. botulinum (botulism)
C. perfringens (gas gangrene)
Heliobacillus
are also photosynthetic!
don’t produce oxygen like cyanobacteria
Spores
Starved cells undergo a developmental process.
Spores have a large number of protective
coatings and layers.
Spores have very low water content.
Spores highly resistant to:
- heat
- strong acids and bases
- radiation
- heat
- desiccation
- nutrient depletion
- strong oxidants (hydrogen peroxide)
No metabolic activity until nutrients and water are available.
Spores Are Persistent:
- 1947 spores of Clostridium grew well when revived in 1981
- 2000 year old spores in archaeological materials
- 7000 year old spores from Minnesota lake sediments
- 30 Ma (controversial) spores in bee guts preserved in amber
Spores in Space!
3 missions sponsored by ESA, on a
Russian satellite, ‘94, ‘97, ‘99.
Lid opens once in orbit, exposes
material in space 10-15 days,
lid closes, re-enters atmosphere
lands.
Treatment:
# of Survivors:
Exposed to Space
and Sunlight
1/106 (in sunlight)
Below a quartz
window
1/10 (in dark)
1/107 (in sunlight)
Under a layer of
clay
1/10 (in dark)
1/103 (in sunlight)
Under a layer of
meteorite
1/10 (in dark)
1/103 (in sunlight)
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Becoming Radiation Resistant
Deinococcus radiodurans
“The world’s toughest bacterium”
extremely resistant to:
- uv
- ionizing radiation
- desiccation
lives in:
- cores of nuclear power plants
- deserts
- Antarctica
- soils
Can survive 3,000,000 rads
Human lethal dose: 500 rads
Survives well because it repairs DNA damage rapidly.
Prevents damaging free radicals OH• from accumulating in the cell.
The Process of Interplanetary Transfer, cont.
4. Organisms in space have to survive impact onto new body
Several Aspects:
- heating
- acceleration
- size of meteorite
small: burst in atmosphere and burn up
larger: outer surface melts, forms a fusion crust
very large: impactor melts or vaporizes upon impact
- impactor has to break up to release the organisms
5. Organisms have to survive, grow, and reproduce. Have
to find an optimal environment.
Is Panspermia common or rare now?
Has life been transferred once or twice?
Have their been many origins of life on other parent bodies?
Lecture 14. Source of Organic compounds,
Miller-Urey Experiment
reading: Chapter 5
Mystery of Enceladus
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Cassini Spacecraft found older terrains
and major fractures on moon Enceladus
Course crystalline ice which will degrade over
time.
Must be < 1000 years old!
Organic compounds found in the fractures.
Must be heated - required T > 100K (-173˚C)
Erupting jets of water observed.
Cause of eruptions not known….
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