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Astrobiology
An introductory overview Felipe Leon
What is it all about?
• Emerging field of science
• Not independent „fundamental“ science but a mixture of well established disciplines * Interdisciplinary!
– Physics
– Chemistry
– Astronomy
– Biology
– Molecular biology
– Ecology
– Geology
– Phylosophy
To date no proof of extraterrestrial life has been found!
„Astrobiology is the study of the origin, evolution and distribution of
life in the universe“
Greek: ἄστρον (astron= star); βίος (bios=life)
λογία (logia=study)
Outline of Astrobiology
• Changes of finding life from a statistical point of view
• This could of course be intelligent or not (e.g.,
Drake‘s equation)
• Prebiotic chemistry and origins of life building blocks
• habitability in other celestial bodies
– with an open mind for other forms of life not
exclusively based on carbon (carbon chauvinism)
• Study the relationship between potential life and the
development of a Planet → Strong link with
Geomicrobiology, microbial ecology and
environmental microbiology
Famous astrobiologists
• One of the most influential figures in the search for extra terrestrial life
• Co-founder of SETI, a center dedicated to the Search of ExtraTerrestrial Inteligence
• An extremely effective science communicator – COSMOS a personal voyage could have been seen
for more than 100 million people around the world
Carl Sagan Carl Edward Sagan
Nov 9th, 1934 – Dec 20, 1996
COSMOS a personal voyage
„Like a mote of dust
in the morning sky“
Astrobiology
or
From life on Earth to life in the Universe
Epicurus
(to Herodotus in 300 b.c.):
There is an infinite number
of worlds and one cannot
demonstrate that they are
not lived in.
Jacques Monod
(in his 1970 book):
The probability of life’s
appearance was quasi
Zero.
Drake„s equation
N = R x fp x ne x fl x fi x fc x L
Optimistic : N = 107
Pesimistic : N = 1
Depends greatly on last terms of eq.
video
Light spectral properties for long distances
= What we know about composition of matter in universe
Technology limits
immensely astrobiology
+ Actual sampling on „nearby“ objects
(depends strongly on spaceship and robotics technl.)
Approachable bodies are scarce
Sampling in biology is very important
Huge amount of data relies on
Light spectral characteristics
Importance on „looking“ very far
away can not be underestimated • Light is our main tool to know: composition
and history of the universe.
• To look very far away is to look far away in
history!!
• If we put everything on speed of light /
space terms the we could say that:
Oldest stuff on earth
Fossils, rocks, etc
Formation
of earth Formation
of stars
Formation
of H Big Bang! ?
Can we „see“ this?
Space/Time
From the Big
Bang on...
Components of the Universe
1 2 3 4 5
73% dark energy
23% dark mass
4% H , He (gas+stars)
0.3% neutrinos
0.04% heavy elements
(C,N,O,...)
Modified from: Astrobiology Lecture Curse
Lecture 2.
Formation of H and He
• Hot, dense, and opaque at start
• Protons and neutrons form at
T >1012 K, or t = 0.1msec from the start
• Universe cools
• α-particles (He cores) start to form at
T = 108 K, or t = 100 s from the start
• Continues for 300 s; 2 n +14 p α + 12 p
• Tiny amounts of Li, B, and Be also form.
Modified from: Astrobiology Lecture Curse
Lecture 2.
Nuclei of heavier elements
• Universe expands and cools
• Cannot form heavier elements because
would need T >108 K, and by the
formation of the -particles the temp was
already too low!
• ¾ H, ¼ He, and « 1% Be, Li, and B
• Still no stars or galaxies
Modified from: Astrobiology Lecture Curse
Lecture 2.
Stars are factories of CHNOPS
• Stars come in different sizes
• Stars are big spheres of hot H and He plasma
• Population II stars have very small amounts of
heavier elements (C, N, O, etc.)
• Bigger star higher pressure in the center of
the star hotter central temp faster nuclear
reactions in center shorter life
The engine
• Stars not only fuse hidrogen
• In more massive stars (M > 1.5 M
), the central temperarture is above T = 18x106 K. Helium is now formed by the more effective carbon cycle. Here, carbon acts as a catalyst. N and O are formed as side products.
• In most stars (M > 0.26 M
) after H in the core is fused into He, the core collapses, becomes more dense, and temperature of the core rises.
• At about T = 100•106 K, the triple-alpha reactions begin. Three helium nuclei form a carbon nucleus.
The engine II
• Once He is consumed, the core collapses again and becomes even denser. If the temp is over T = 500•106 K
(M > 3 M
), oxygen starts to form very rapidly from 12C+12C16O+24He, with side products 23/24Mg, 23Na, and 20Ne.
• Heavier elements form in stars of even larger masses and in slightly higher temperatures (16O+16O 31/32S, 31P, 28Si, 24Mg, 28Si+ 28Si 56Ni ,56Fe).
• Elements even heavier than iron can form in small amounts by slow neutron capture (s-process) and in supernovae by rapid neutron capture (r-process).
When stars die
• None of the smallest stars (brown and red dwarfs) have yet left the main sequence.
• Medium-size stars (M < 3 M) will develop an
onion-like structure with a C (or O) core and blow out the outer envelope as a stellar wind white dwarf star and a planetary nebula.
• Large stars (M >3 M) will also develop an onion
structure, with shells of H, He, C, O, Si, and even up to a Fe core, and stars larger than about 11 M
will undergo a supernova explosion
complete destruction of star. The core can collapse into a black hole or a neutron star.
Two generations of stars
• Although many heavy elements produced in first generation, no enough for formation of planets
• Further transformations and evolution of primordial components was done in the interstellar medium.
– Here (examples are nebulae and interstellar clouds), ices were formed and particles important for the formation of more complex elements (planet building material)
• Our sun is second generation and not much older (in cosmological terms) than earth
The solar system
• Formed from accretion disk in an enriched molecular cloud (with remnants of first generation stars)
• Due to molecular instabilities, material starts to fall in the center of the disk
• Denser part lights up, hydrogen engine starts and our sun is born
• Planets are formed from protoplanetary disks • A snow line is formed at about 5 AU (1 AU ~ 150
million km or 1.5x1011m)
– Important for the formation of comets and asteroids
Protoplanetary disk in Orion
Formation of Earth and other rocky
planets • Formation of rocky planets was possible around second-
generation stars because of the presence of heavy elements such as C, N, O, Si, Fe ...
• Formation happened at the same time as the rest of the solar system.
• Chondrites Earth was accreted from matter of about 700-1500 K No volatiles (CO2, CO, H2O) or gases. Volatiles arrived in comets.
• First, a magma ocean (liquid rock!) covered the earth.
• The first atmosphere was possibly 50-200 bar CO, CO2, H2O, and H2.
• When temp fell to 200°C, the rain began. Oceans formed.
Not all elements for life were
present at this stage
• Comets and asteroids brought (and continue
bringing) important molecules for life.
Ida Dactyl
NASA
Comets and asteroids
• Comets formed behind the snow line
• Comets contain significant amounts of H2O, C2O, and other ices with C, N, and O, the same molecules as in interstellar clouds.
• Comets appear to have brought enough water to form oceans and enough N2 for the atmosphere.
• Formed inside the snow line
• Brought silicates, iron, and nickel
• Also brought carbon (up to 4%) and water (up to 20%)
• Amino acids, complex molecules
• Destruction (biggest ones “ocean evaporating”)
• The largest asteroid, Ceres, appears to be differentiated and has a large amount of water “failed” planetesimal?
Micrometeorites
• They bring similar material to the earth as the comets and asteroids do.
• Not much is known about them.
• About ½ float onto Earth non-destructively could be good molecule carriers.
• Flux is still continuous, about 1 per m2 per day.
• ~ 10 000 Tons per year.
Micrometeorites collected at Cap–Prudhomme, Antarctica
Life elements and molecules
• Water: Cytoplasm in cells (H2O)
• Nucleic acids: DNA, RNA (CHNOP)
• Amino acids: Proteins (CHNOS)
• Lipids: Membranes (CH)
• Carbohydrates: Sugars/Starch (CHO)
From this ... To this?...
• Water (H2O)
• Formaldehyde (H2CO)
• Hydrocyanide (HCN)
• Sugars (at least 3 C and
= O)
• Hydrocarbons –(CH2)n–
Elements
• The 6 most important elements (C,H,N,O,P,S) make up 98% of living tissue
• 2% are made from trace elements: Na, Cl, K, F, Ca, Mg, B, Al, Si, Cr, Mg, Cu, Zn, Se, Sr, Mo, Ag, Sn, I, Pb, Ni, Br, Va
• A total of 25–30 elements are used by life – note that about 80 elements are not used.
A prebiotic soup of „chemical
robots“
A. Brack : Life is based
on little robots that make
copies of themselves and
are capable of evolution
(« mistakes » during
reproduction)
L.E. Orgel : Living
organisms are
CITROENS –
Complex Information,
Transforming
Reproducing Objects
that Evolve by
Natural Selection
Chemical ingredients for life
All known living systems are based on at least one
Structural and functional unit called a cell
Separation from the environment
Cell membrane:
Long organic
amphiphile chains.
With a polar head
that makes them
soluble in water
and an apolar tail
that makes them
insoluble.
Such structure may
self-organize into
vesicles.
Inside the cell
DNA is a complex
molecule that
carries
information,
makes copies of
itself, and is
capable of
evolution
(mutation)
Ribosomes are
made of proteins
and RNA
Basic
components to
have a cell
working:
Proteins
+
DNA & RNA
(similar in
structure)
Amino acids and
proteins
An example of a protein chain:
Structure of an amino acid :
If R ≠ H, then assymetric carbon (C*)
All the biological A.A. are L in configuration
(except glycine: no C*)
DNA and RNA
DNA and RNA are
linked chains of
nucleotides, each of
which consists of a
sugar, a phosphate,
and one of five kinds of
nucleobases (puric and
pyrimidic bases).
Structure
of DNA
Miller/Urey Experiment
Laboratory test of
Oparin‟s ideas
Production of a
large range of
organic compounds
including amino
acids (racemic
mixture)
electrodes
gas mixture
CH4, NH3,
H2O, H2
cooling
system
heat source
liquid
H2O
direction of
circulation
to vacuum
condensation
sampling
Building up life molecules
• Through years chemists have been
demonstrating the formation of constitutive
elements of proteins and nucleic acids
• They haven„t been able however of
reproducing the formation of a complex
molecule like DNA in the laboratory
Some examples Amino acid synthesis
Strecker synthesis: aldehyde (RCHO) + ammonia (NH3) + hydrogen
cyanide (HCN)
1) The addition of ammonia to aldehyde
produces an imine
2) The addition of HCN the imine
produces an α-aminonitrile
3) Hydrolysis of –CN → -CO2H → production of an amino acid
Some examples Synthesis of purine and pyrimidine bases
Synthesis of
adenine with
HCN and light
in aqueous
solution
(Ferris and
Orgel, 1966)
-Puric bases
Adenine (A) ADN/ARN
Guanine (G) ADN/ARN
-Pyrimidic bases
Cytosine (C) ADN/ARN
Uracil (U) ARN
Thymine (T) ADN
Some examples Synthesis of sugars
Formose reaction:
Formaldehyde solution
Suitable catalyst such as calcium hydroxyde Ca(OH)2, calcium
carbonate CaCO3 , or clay minerals
Products of formose reaction
Gas chromatogram in
which each peak
reflects the presence of
a sugar synthesized
through the formose
reaction. The arrow
points to the D-ribose,
form present in RNA
A nonspecific
synthesis
Some examples polynucleotides
Base + ribose in the solid state (100°C): association into a nucleoside with a
yield of about 3%.
But not specifically at the “natural” place.
Phosphate1 + nucleoside = nucleotide: association by heating (> 100°C).
Again, not specifically at the natural place.
1Phosphorus present in igneous rocks as fluoroapatite (Ca5(PO4)3F);
chloroapatite present in meteorites
Conclusions and open questions
• Astrobiology **can** be taken seriously – It has elements for experimentation and testing of hypothesis,
which is the base of any scientific endevour
• It requires many people with expertise in many areas to make it work.
• As it advances and new discoveries are made it might challenge already established principles in more fundamental sciences such as chemistry and biology
• It should not be centered on searching for life having as a model life on Earth (carbon chauvinism). Although is the obvious start, it should not close our minds to other possibilities for „life“.
• Are we „star stuff“ making questions about itself? – In phylosophical terms, perhaps yes
– Judging the difficulty for building something like us molecularly, probably the answer is out of our grasp.
Acknowledgements
• This presentation is greatly based in a
series of lectures from the European
Space Agency, ESA
– All the authors and material are therefore
acknowledged
• If you are interested these can be found in
Quicktime format here:
– http://streamiss.spaceflight.esa.int/
Interesting links, sources and
further reading
• http://www.seti.org/Page.aspx?pid=237
• http://www.astrobiology.com/
• http://astrobiology.nasa.gov/
• http://www.sciencemag.org/cgi/content/full/289/5483/1307
• http://journals.royalsociety.org/content/887701846v502u58/fulltext.pdf
• http://journals.royalsociety.org/content/817326x72r100146/fulltext.pdf
• http://journals.royalsociety.org/content/0r22726p7p97w854/fulltext.pdf
• http://en.wikipedia.org/wiki/Astrobiology • http://de.wikipedia.org/wiki/Chemische_Evolution
• Horneck, G. and Rettberg, P. (Eds.) Complete course in astrobiology, Wiley-VCH, 2007
Next talk points (abiogenesis)
• Most important molecules for life and their origin
• Highlight how hard is to „manufacture“ them from precursors – A bit about the synthesis of these with formulas, etc.
• Amino acids in comets great hope for exogenous origin.
• Describe millers experiment and the hoopla of the time but leave clear the limitations
• Where is easier in oxidizing environments? Or in reducing environments? – How people have change mind over which were the conditions
on early Earth.
Next talk points (abiogenesis II)
• RNA world
• Clay world
• Peptide world
• LUCA
• Taxonomic trees
– How similar are we with archea but not with
bacteria...