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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

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

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.

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.

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

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

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

• 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

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

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/

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