Cosmochemistry

The Cosmochemistry - also called astrochemistry - deals with the development and distribution of chemical elements and compounds in the universe. The chemical elements are produced in the interior of the fixed stars ( nucleosynthesis ), chemical compounds, however, in cosmic gas and dust clouds, on Planemos, moons, comets, asteroids and the like, colder objects.

The cosmochemistry is a modern, major branch of physics, chemistry and strongly linked with astrophysics, especially the physics of stars and supernovae. It also plays a major role in the Planetary Sciences and in an attempt to understand the origin and chemical evolution of our solar system and on other Planemos ( up to the origin of life - see under chemical evolution ).

However, since stars as well as virtually all other celestial bodies lie in for us unattainable distance, it is limited in terms of chemical analysis of specific methods, primarily instrumental methods of spectroscopy and ( spectral ) analysis, in which the incoming of the objects in our radiation (ultraviolet, visible light, infrared) is evaluated.

Specifically, the cosmochemistry not involved in the nucleosynthesis, but with the elemental and isotopic distribution in our solar system: A major contribution to this comes from the meteorite research because meteorites still have the original chemical composition of the beginnings of the formation of our solar system. But also from the ( unmanned ) space are a few samples of extraterrestrial material from the moon, comet dust, solar wind, and - one hopes - in a few years and decades, samples from other planets, moons and asteroids accessible.

The cosmochemistry was founded in the 50s of the 20th century by Friedrich Adolf Paneth.

• 3.3.1 biomolecules

Example: A " kosmochemisches " Project

The operation of the Cosmochemistry ( astrophysics, astrochemistry, planetary sciences ) can be illustrated by a recent example from the unmanned space exploration. Normally work Kosmochemiker on the evaluation of a spectral analysis or spectroscopy: Here you can choose from radiation spectra from the " light " also celestial bodies (usually stars) close to their chemical composition.

Since the first moon landings, samples of extraterrestrial material can now be captured by space probes directly from space and brought to Earth in order to analyze directly. The NASA mission "Stardust" has allowed not only the asteroid Anne Frank and the comet Wild 2 to take pictures, but also capture comet dust. On January 2, 2004 Stardust flew at a distance of 240 km and at a relative speed of 6.1 km / s at comet Wild 2 over. The probe fired several shots of the comet and its coma gathered material. Upon their return to Earth, the Stardust capsule was brought to Houston to the NASA control center and open there. In Houston, we considered the state of the airgel, an extremely lightweight solid body in which the dust particles of comet Wild 2 were slowed down and transported. A small amount of comet dust was then different groups of scientists available - for example, the Institute for Planetary Sciences in Münster. There you could investigate the chemical composition of the dust particles directly. This is expected to new insights into the origin of our solar system 4.6 billion years ago, because the comet Wild 2 had moved only in the outer regions since the early days of the solar system ( only in 1974 that he was old by the gravity of the giant planet Jupiter from his thrown train). On the comet researchers Cosmochemistry had found in previous missions by spectral complex carbon compounds. Although they are not yet equate with life, but maybe they have provided the impetus for the emergence of life on Earth.

The origin of the chemical elements

The formation of atomic nuclei ( nuclides ) and the chemical elements are described in detail in the article nucleosynthesis. Consequently, the chemical elements hydrogen and helium was directly after the Big Bang, primordial nucleosynthesis by. All heavier atomic species formed subsequently in the interior of the stars ( stellar nucleosynthesis ) and in supernova explosions. Towards the end of its focal length very massive stars explode and hurl large amounts of heavy elements in the universe. For example, the supernova SN 2006gy in the galaxy NGC 1260 had 150 solar masses and an estimated 20 solar masses of nickel blown in their explosion in the universe - but in about 240 million light years away. But if, for example, show the present in a similar pre- nova stage, only 7,500 light years distant star Eta Carinae a similar supernova outburst, then should it be also in the daytime clearly visible, for the earth possibly catastrophic event.

The distribution of the elements in the cosmos

According to the described under " nucleosynthesis " genesis of the elements cosmochemical the frequency distribution of the atomic species is explainable. Although the element frequency differs depending on the region to be considered: However, in the entire universe by far the most common element is hydrogen - on earth he is rather rare, but again often to be found in man.

In space, hydrogen and helium dominate, since both already emerged during the Big Bang. From 1000 atoms in the universe are 900 hydrogen atoms, a further 99 atoms are helium atoms. Only one atom of 1000 is therefore not hydrogen or helium. All other types of atoms (except for lithium, beryllium and boron) originated in stars (see above and below nucleosynthesis ). While more atoms with a straight proton number were formed, for example, oxygen, neon, iron, or sulfur, which are thus more frequently compared to other elements having an odd number of protons.

For every 1 trillion hydrogen atoms (H ) with respect - so each 1012 H atoms - come 1010.8 helium atoms, oxygen atoms, 108.8, 108.6 and 108.0 carbon atoms nitrogen atoms, but in addition each approximately 107.9 iron and neon atoms and 107.4 silicon atoms up even lead 101.7, 100.7 and 100.3 gold - silver atoms. Unlike the metallicity of the stars of the 1st generation ( Population II ) with a high age over 10 billion years: They have a total of 1/1000 on to heavier elements, as it corresponds to the specified "Normal Distribution" in space.

Interstellar Matter - kosmochemisch seen

Interstellar matter contains the chemical elements in similar distributions such as our Sun and other stars of population I. Here the atoms, however, have their outer electrons, so that chemical compounds may arise due to lower temperatures, gases and dust between the star systems.

Between the stars there is hydrogen gas ( neutral) with a density of 0.8 and 1.3 x 10-24 g/cm3 H-Atomen/cm3. Some areas are poorer in hydrogen ( galakt. center ), in other places there are condensations (fog, clouds) - and occasionally there even glowing regions stimulated to emit light through partly intense UV radiation of nearby stars ( emission nebula ) or reflection ( reflection nebula ).

At equilibrium between production rate and decay rate are now emerging in some nebulae complex organic molecules that are often decomposed by ionizing cosmic radiation again. Nevertheless, they exist, and shielded by dust clouds, molecules such as water, ammonia, methane and formaldehyde ( methanal ) have lifetimes of decades, nitrogen and carbon monoxide even 1000 years. Also by freezing on the surface of dust grains can survive long periods of time ( up to 100,000 years). Even at densities of 50 atoms/cm3 can atomic collisions molecules such as hydrogen and carbon monoxide or the hydroxyl radical Monocyan (CN ) are formed.

Meteorites Kosmochemiker even found alkanes such as 2,6,10,14 -tetramethyl- pentadecane, aromatics such as benzene, toluene, xylenes and naphthalene, fatty acids with 14-28 carbon atoms, thiophenes, p-dichlorobenzene, amino acids such as proline, aspartic acid, glycine, alanine and glutamic acid ( meteorite Murchison, 1969) and even adenine and guanine. The discovery of amino acids of extraterrestrial origin in 1970 was considered a foregone sensation, as they are the basic building blocks of life on earth.

The formation of these organic molecules is explained via several mechanisms. Miller and Urey irradiated gas mixtures of methane, ammonia and water. Resulting ions and radicals by radiolysis ions form with up to seven carbon atoms. Can then grow even polymers via radical such as NH 2 * and H 2 O * even carboxyl and amino groups are incorporated and further reacted after several mechanisms to amino acids via the ethene:

Even better conditions for building rule of course protected by atmospheres planetary surfaces. Seen Astro Chemically, it is therefore classified as highly probable that exist in the depths of space a number of places to the emergence of biochemical molecules so the origin of life itself, and probably also exists for a long time have ( The problem of establishing contacts with extraterrestrial civilizations, however, is not in the absence, incontrovertible evidence of their existence - but in the seemingly unbridgeable, great distance between them).

Earthly matter - kosmochemisch considered

The frequency distribution of the elements in the cosmos as a whole can change very locally. One such, this average distribution changing process is gravity. It is the power by which the solar system formed from a rotating cloud of gas and dust ( nebular hypothesis, originally formulated by Immanuel Kant in 1755 in his book Universal Natural History and Theory of the Heavens ).

Formation of Earth, planetary and solar systems

After views of today moved around 4.6 billion years ago in place of our solar system a sprawling cloud of material around the center of the galaxy. The cloud was more than 99% of the gases hydrogen and helium, as well as a small proportion of only micrometer-sized dust particles were composed of heavier elements and compounds such as water, carbon monoxide, carbon dioxide, other carbon compounds, ammonia, and silicon compounds. The hydrogen and the vast majority of helium was already created during the Big Bang. The heavier elements and compounds were produced in the interior of stars and released in the explosion. Parts of matter cloud drew together as a result of its own gravity and coalesced. The impetus for this purpose could the explosion have provided a relatively nearby supernova, the pressure waves wandered through the cloud. These consolidations have led to the formation of probably several hundred or even thousands of stars in a star cluster, which probably broke up in free single or double star after a few hundred million years.

Since the contraction of the angular momentum must be maintained, an already existing minimal rotation of the collapsing cloud as a figure skater has increased similarly achieved by applying rapid rotation of the arms. The resulting, acting outward centrifugal forces meant that the cloud in the outer regions trained on a rotating disk.

However, almost all the matter in the cloud crashed into the center and formed a protostar, the collapse continues until nuclear fusion process was ignited: Our Sun was born. In the remaining protoplanetary disk caused the clumping of dust particles ( coagulation) to the formation of planetesimals. Planetesimals are the precursors and building blocks of planets. They are formed by accretion, a process in which coalesce microscopic dust particles of a pre-solar nebula ( the precursor of a solar system ) to form larger particles. Put those particles with low speed together, they stick together through chemical bonds or surface adhesion with each other.

This soon kilometer-long structure possessed enough mass to unite by their gravity with other planetesimals into larger objects. The heaviest objects exerted the greatest gravitational forces, pulled matter from a wide area and were able to grow even faster. The " proto- Jupiter" finally bothered with its gravitational field other planetesimals and influenced their growth. Obviously, he also prevented the formation of a larger body between Mars and Jupiter's orbit, which led to the creation of the asteroid belt. In just 100,000 years, the planetesimals in the early solar system could evolve into planetary bodies of the size of Earth's moon or the planet Mars.

Similar processes of planetary system formation must also be expired elsewhere in space. And many exoplanets Planemos been discovered in recent years. Again, the condensed volatile and less volatile elements in space to chemical compounds, and many astronomers and astro chemists assume that Planemos exist that move in temperate zones around their respective fixed stars. Thus, it is conceivable that an extraterrestrial chemistry has brought forth life in the unreachable depths of the cosmos.

The chemistry of the solar system

Solar systems caused by gravitational contraction of the discus-shaped, rotating discs matter. Thermodynamic calculations in respect of this away faster and faster cooling from the center and increasingly lighter wheel that condensation occurs when the partial pressure p (i) and vapor pressure of a substance i are equal. The partial pressure of an element in a cosmic gas is calculated equal to the product of its frequency of A (i ) relative to that of the water material A (H 2), multiplied by the overall pressure Pg of the gas, A (i) / p (i) = A ( H2) x Pg

Now, if the vapor pressure P of an element according to the Clausius- Clapeyron appears as a function of temperature, for identification of partial and vapor pressure of the member its condensation temperature is calculated (thus: log Po = A / T B, wherein the factor A, the by 2.3 x R divided enthalpy of vaporization, and B represents the entropy of vaporization divided by 2.3 x R where R is the universal gas constant ).

Here is the result of this calculation, starting with the highest condensation temperature under steady progressive cooling: the element osmium condensed at temperatures around 1860 K, 1780 condense zirconium IV oxide and rhenium, 1700 alumina to 1560-1500 calcium titanate ( perovskite ) and gehlenite ( a silicate ) and rare earth elements ( U, Th, Ta, Nb), about 1390, the ferromagnetic metals ( Fe, Ni, Co), at 1370-1250 magnesium silicates, and the metals copper, germanium, and gallium ( alloyed with Fe) as well as alkali metal silicates ( with CaAl2Si2O8 ), wherein K 1100-700 silver (Ag) and at 750 K it is condensed to oxidize iron ( to minerals such as FeO FeS ).

In cooler, more distant from the initial sun condensed regions at 600-400 K lead, bismuth, indium and thallium, from 350 K crystallized hydrated silicates, and - in the sun- distant region of the gas giants - at temperatures below 180 K and water ice ( then NH4SH, at <140 Kelvin, at < 100 K solid ammonium hydroxide, at < 60 Kelvin methane hydrate and only at very low temperatures of <20 Kelvin also solid methane and argon).

During the condensation now enters fractionation, ie the " freezing " to sort the materials according to their density, both within small lumps ( chondrules, meteorites ) and large scale ( planetesimals outdoor subsequent gas giants like Jupiter and Saturn, or " snowball " as the comet, inside more compact planets like Mercury and Venus). Also, the separate substances in the red-hot molten proto-planets (reduction of metals in the core, then cooling the outer silicate crust ).

Thus, the present-day chemical composition of our solar system from the inner rocky planets to the outer, cool gas giant to distant objects in the Kuiper Belt and the Oort cloud from the Cosmochemistry explains ago.

According to Oort (1950 ) comets come from a reservoir of 0.1-0.01 solar masses in about 50,000 AU aphelion. In 1 AE perihelion passes, they develop with expansion velocities of 500 m / sec halos and - in the immediate vicinity of the nucleus - coma, the gas density extends from 1014 molecules/cm.sup.3 near the core to the outside to 100 molecules / cm3. The gas and dust particles are driven away by the solar wind and form the ion and dust tail of the comet.

Emission spectra of the coma have been studied extensively, also could Giotto probe the coma of comet Halley already fly through unscathed. At a distance of <2 AE comets coma shows bands of cyan, OH radicals, neutral oxygen, sodium, and - closer than 1 AU to the core - lines of the elements Cr, Mn, Fe, Co, Ni, Cu, K, and Ca, the radicals NH and CH as well as the gases Methylcyan, HCN and water. The CN radicals could be caused by photodissociation of Methylcyans, the NH * radicals by photolysis of hydrazine or of amines such as methylamine, isocyanic acid ( HNCO ), methyleneimine H2C = NH or formamide. Radicals such as C2 and C3 were also discovered. They probably originate from the acetylene and the Diazomethylacetylen. Also ionized molecules of carbon monoxide, carbon dioxide, water and nitrogen were detected.

In terms of silicate- like materials can be calculated that the comet dust particles are lost by the radiation pressure of the sun and its diameter, therefore, must be less than 10-6 cm. First one held comet for " dirty ice balls ." However, as very little methane was found in Comet Kohoutek, you came to the conclusion that it could not have come from in cooling, solar gas, but have major components such as water, carbon monoxide, nitrogen, hydrogen cyanide, methyl cyanide and dust - materials including from unattainable depths of space, the interstellar gas.

Terrestrial matter

On Earth, some other elements - distribution is commonly referred to as in comets, on distant gas planet or even in the cosmos. Considering the earth's crust, so dominates bound oxygen ( O) with a mass fraction of 49.2 %, it followed silicon (Si, 25.7 % ), aluminum ( Al 7.5% ), iron ( Fe 4.7%), calcium (Ca 3.4% ), sodium (Na 2.6% ), potassium (K 2.4%), magnesium (Mg 1.9% ), hydrogen ( H 0.9%) and titanium (Ti 0, 6%). all other elements have only one mass fraction of less than 0.2 %.

Looking at the whole earth along with its core, the result is a somewhat different picture. The most frequent elements in the overall earth, iron ( Fe, 35%) from oxygen (30% ), silicon (15%) and magnesium ( 13% ) followed by nickel, sulfur, calcium, aluminum and others ( less than three percent ).

Our biomass - kosmochemisch analyzed

Man is in turn composed differently from space and Earth: It consists primarily of hydrogen, oxygen, carbon and nitrogen, along with sodium, magnesium, potassium, calcium, phosphorus and sulfur make these elements 99.996 % of all the atoms of the human body ( The first systematic studies on the element frequency derived by Victor Moritz Goldschmidt, according to him means the graphical representation of the elemental abundances Goldschmidt diagram).

Kosmochemiker assume that initially in the formation of the solar system on Earth and all the other near the sun planet because of the relatively high temperatures and the effects of the solar wind with little or no light elements (including carbon, nitrogen and oxygen) are " left " remained. All of these elements that today make up the majority of the biosphere would have been only after a considerable time delivered according to this theory by comets from the outer regions of the solar system, after the proto-planet had cooled somewhat. Since constantly repeated large impact events of celestial bodies during the first few hundred million years after the solar system formed, were living systems that are already developed in these times, been repeatedly destroyed by global sterilizations, which were caused by large collisions. The development of life could start so only after liquid water could hold at least in the deepest areas of the oceans over time.

The slow cooling of the Earth, volcanism occurring ( outgassing from the earth ) and the global distribution of matter is proposed comet it came to the establishment of an atmosphere. Therein as compounds mainly steam ( up to 80% ), carbon dioxide (up to 20 %), hydrogen sulfide as main components to be expected (up to seven percent), ammonia, and methane.

The actual origin of the water is not entirely uncontroversial. Can, especially from water, methane and ammonia under the conditions of the early Earth first small organic molecules (acids, alcohols, amino acids), later also form organic polymers (polysaccharides, lipids, polypeptides), which are not stable in the oxidizing atmosphere.

The high UV - radiation -induced photochemical decomposition of water, methane and ammonia molecules, resulting in carbon dioxide and nitrogen accumulated. The light gases such as hydrogen or helium faded away for the most part into space, carbon dioxide dissolved in large quantities in the oceans, so their water was acidified and the pH is absenkte to about 4. The inert and sparingly soluble nitrogen N2 remained unchanged, collected at the time and formed about 3.4 billion years ago the main constituent of the atmosphere.

The precipitation of the carbon dioxide with metal ions as carbonates and the later development of living organisms, the carbon dioxide assimilated, led to a reduction in CO2 concentration and a re-increase of the pH values ​​of the waters. The O2 oxygen plays the major role only in the further development towards today's atmosphere. It was formed by the appearance of organisms with oxygener photosynthesis, namely since about 3.5 billion years ago; presumably there were cyanobacteria or cyanobacterial -like prokaryote.

Biomolecules

The chemical evolution was probably as that of the accumulated earth elements on the resulting complex organic molecules were formed - carbon compounds. The prebiotic formation of complex organic molecules can be divided roughly into three steps:

The elemental analysis of these molecules leads to the question of which inorganic compounds to their formation were necessary. These had to be present in the reducing primitive atmosphere of the earth - in the distribution and under the reaction conditions, the chemically made ​​possible the emergence of the first living things.

A particularly intense form of participation of minerals and rocks in the prebiotic synthesis of organic molecules must have occurred on the surface of iron sulfide minerals. The scenario for the early chemical evolution of life has been developed since the early 1980s by Günter Wächtershäuser.

After that, life on Earth would be at the surface of iron-sulfur minerals originated ( the iron-sulfur world ESW ), ie sulfides, which still formed through geological processes at deep-sea volcanoes, and the early Earth still significantly must have occurred more frequently ( " black smokers ").

Finally, ribonucleic acid ( RNA) is a molecule crucial for the emergence of life. The RNA world hypothesis has been proposed by Walter Gilbert in 1986. This assumption can be derived from the ability of the RNA to the storage, transmission, and reproduction of genetic information, as well as their ability to catalyze reactions as ribozymes. In an evolutionary environment those RNA molecules would frequently occur, the self-spawning preferred. RNA is due to various properties held for more than DNA.