Astrochemistry FOPCU

7/28/2019 Astrochemistry FOPCU

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Astrochemistry

By

Mayada El Olamy 1001 Mirna Emad 1006

Mayar Raouf 1002 Mirna Hany 1007

Miar Mohie Al-Dien 1003 Mirna Wadia 1008

Mirna Samir 1004 Mirette Hanna 1009

Mirna Sabry 1005 Mina Onsy 1010
http://en.wikipedia.org/wiki/File:Starsinthesky.jpg


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Astrochemistry is the study of chemistry in space. More specifically, it is the study of the

chemical interactions between the gases and dust interspersed between the stars. It is the

study of the abundance and reactions of chemical elements and molecules in the universe,

and their interaction with radiation. The discipline is an overlap ofastronomy and

chemistry. The word "astrochemistry" may be applied to both the Solar System and theinterstellar medium. The study of the abundance of elements and isotope ratios in SolarSystem objects, such as meteorites, is also called cosmochemistry, while the study of

interstellar atoms and molecules and their interaction with radiation is sometimes also

called molecular astrophysics. The formation, atomic and chemical composition, evolution

and fate ofmolecular gas clouds is of special interest, because it is from these clouds that

solar systems form.

Molecular Chemistry in Space

Giant clouds of gas and dust called Giant Molecular Clouds or GMC's contain enormous

numbers of molecules. These clouds stretch across vast distances, up to a light year or moreacross. Throughout most of their volume, pressures, densities and temperatures are

exceedingly low, a tiny fraction of those found here on Earth. Comparing molecular

processes in GMC's with those on Earth can provide insights into how our planet'schemistry evolved given its unique environment.

Molecular evolution in space involves several chemical reactions, each tending to yield

more complex molecules than the previous. Forged in the cores of stars, then returned to the

interstellar medium during stardeath, elements such carbon, oxygen, hydrogen, and nitrogencombine to form hydrogen cyanide, water, and ammonia. Evidence is mounting that these
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molecules could, in turn, combine to produce simple amino acids, one of the main chemicalbuilding blocks of life.

Photochemistry of Titan's atmosphere. Image credit: NASA

The "astronomer's periodic table," in which the area of the element in the table is proportional toits abundance in space.

From Amino Acids to Life

For decades, astronomers have debated whether the molecules of life were formed in thedepths of space, or evolved amidst the violent volcanic eruptions and severe lighting storms
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that raged on the young Earth. If amino acids evolve in interstellar space, then how much

more likely are they, and perhaps even carbon-based life itself, to be found elsewhere in the

universe. Conversely, if the molecules required for biochemistry evolved exclusively onEarth, then life is surely a one-time deal, maybe never to be repeated in the cosmos.

While these questions remain hotly debated, evidence is mounting that at least some of life's

precursor molecules were formed between the stars. Embedded in meteorites and moon

rocks, some amino acids may have been first created in interstellar space, then frozen inmeteors which bombarded the Earth during its early history. In hopes of unmasking more

evidence, astronomers are searching for amino acids in the cold, molecular gas found in

some regions of our own Milky Way galaxy.

One such region is Sagittarius B2, commonly referred to as Sgr B2. A giant, star-forming

molecular cloud some 30 thousand light years away, SGr B2 lies near the center of our

galaxy. Containing an abundance of carbon- and nitrogen-rich molecules, Sgr B2 presents aperfect target for the search.

Employing the BIMA array, astronomers are probing this region for glycine, one of the

smallest, simplest amino acids. The BIMA array's flexible spectrometerand high spectralresolution allow astronomers to map the precise abundances and locations of the molecules

present in Sgr B2, as well as their velocities. Taken together, this information will help

researchers ascertain how simple molecules such as hydrogen cyanide (HCN), water (H2O),

ammonia (NH3), and formaldehyde (H2CO) might combine in space to yield glycine and

other amino acids.

For many years astronomers possessed little knowledge of the composition of interstellar

space. Optical astronomy revealed only stars, galaxies, and nebulae. Darkness appeared to
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reign between the stars, as if nothing was there. With the arrival of radio-astronomy in the50s and 60s, astounding discoveries began to emerge.

Observation of molecular hydrogen's 21 centimeterspectral line, revealed an abundance of

hydrogen between the stars. Up until that time, optical astronomy pointed to an absence ofmaterial; the presence of so much gas in interstellar space was inconceivable.

Since the discovery of molecular hydrogen, many more types of molecules have been

detected. Some do not exist on Earth, while others abound, particularly hydrogen, carbon

monoxide, ammonia, and water. Scientists are now expanding their search to more complex

molecules, carbon-rich compounds that may hold the key to how life began on our planet.

More Windows on Astrochemistry

To obtain a full understanding of molecular evolution in space, one that may settle the

question of whether the precursor molecules of life, or even life itself, could have evolved

in the hostile environment of the young Earth, or if these same molecules could have beentransported here by comets and meteorites, radioastronomers cannot rely upon results

obtained solely from millimeter observations. Comparison with observations in other

wavebands, especially the centimeter and infrared regions of the electromagnetic spectrum,provide important details about the physical conditions favoring chemical evolution in

space. All of these studies involve detecting a variety oftracer molecules.

Cloaked deep within GMC's, newborn stars emit radiowaves in the centimeter waveband.

This radiation reveals the presence of hot, ionized gases close to the surfaces of stars and

also surrounding them. From centimeter emissions, astrochemists know where the star is

located and how much energy it gives off to the surrounding molecular gases within theGMC.

Infrared observations of tracer gases provide a measure of how hot the enveloping gas hasbecome. Its temperature indicates how much energy is available to drive chemical reactionsthought to yield complex molecules, including perhaps amino acids.

Cool Ractions :
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As a general rule, atoms and moleculesvery much like humanstend to slow down as they

get colder, which means less movement and interactions with their peers. Astrochemist Ian

Sims and colleagues at the Rennes-based PALMS laboratory,1 together with colleagues

from the United Kingdom and the United States, recently showed how some particles shake

off this tendency to hibernate, and become more chemically active when getting near thefrigid temperatures found in outer space.

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In chemistry, the Arrhenius equation, which was first formulated in the 19th century, states

that chemical reactions become faster as temperatures increase. Atoms and molecules need

to overcome an energy barrier to react with each other, and as Sims explains, an increase

in temperature can give them the impulse to get over that hill. But the Arrhenius equation

does not apply to all reactions. In the frigid vastness of space, interstellar clouds have to bechemically active to become stars. Figuring out which chemicals will react and at what

temperatures is difficult: Theory can't answer everything, and low-temperature experiments

are both time-consuming and expensive.

To investigate this matter, Sims and his team used the CRESU3 technique in which a low-

density gas moves at supersonic speeds through a tube, creating temperatures as low as -

263C. Measuring the reaction of oxygen atoms and different gas phase hydrocarbons

called alkenes, they found that the speed of the reactions was connected to the ionization

potential of the alkene. If the ionization potential was above a certain threshold, the alkene

and oxygen were unable to overcome the energy barrier to react with each other in cold

environments. On the other hand, if the ionization potential was just below the threshold,

the chemicals could overcome this barrier and react with one another.

These [atoms and molecules] need a certain amount of time to adjust their configuration to

get over the barrier, and they have that time at lower temperatures, explains Sims. In otherwords, low temperatures actually aid the reaction process.

With Sims' experiments, and theoretical calculations from his American colleagues, it

should now be possible to predict extreme-cold reactions from room-temperature

experiments.

Spectroscopy

One particularly important experimental tool in astrochemistry is spectroscopy, the use of

telescopes to measure the absorption and emission oflight from molecules and atoms invarious environments. By comparing astronomical observations with laboratorymeasurements, astrochemists can infer the elemental abundances, chemical composition,

and temperatures ofstars and interstellar clouds. This is possible because ions, atoms, and

molecules have characteristic spectra: that is, the absorption and emission of certain

wavelengths (colors) of light, often not visible to the human eye. However, these

measurements have limitations, with various types of radiation (radio, infrared, visible,

ultraviolet etc.) able to detect only certain types of species, depending on the chemical

properties of the molecules. Interstellar formaldehyde was the first polyatomic organic

molecule detected in the interstellar medium.
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Perhaps the most powerful technique for detection of individual molecules is radio

astronomy, which has resulted in the detection of over a hundred interstellar species,

including radicals and ions, and organic (i.e. carbon-based) compounds, such as alcohols,

acids, aldehydes, and ketones. One of the most abundant interstellar molecules, and among

the easiest to detect with radio waves (due to its strong electric dipole moment), is CO(carbon monoxide). In fact, CO is such a common interstellar molecule that it is used tomap out molecular regions.[1]The radio observation of perhaps greatest human interest is

the claim of interstellarglycine,[2]the simplest amino acid, but with considerable

accompanying controversy.[3]

One of the reasons why this detection was controversial is

that although radio (and some other methods like rotational spectroscopy) are good for the

identification of simple species with large dipole moments, they are less sensitive to morecomplex molecules, even something relatively small like amino acids.

Moreover, such methods are completely blind to molecules that have no dipole. For

example, by far the most common molecule in the universe is H2(hydrogen gas), but it doesnot have a dipole moment, so it is invisible to radio telescopes. Moreover, such methods

cannot detect species that are not in the gas-phase. Since dense molecular clouds are very

cold (10-50 K = -263 to -223 C = -440 to -370 F), most molecules in them (other than

hydrogen) are frozen, i.e. solid. Instead, hydrogen and these other molecules are detected

using other wavelengths of light. Hydrogen is easily detected in the ultraviolet (UV) and

visible ranges from its absorption and emission of light (the hydrogen line). Moreover, most

organic compounds absorb and emit light in the infrared (IR) so, for example, the recent

detection ofmethane in the atmosphere of Mars[4]was achieved using an IR ground-based

telescope, NASA's 3-meterInfrared Telescope Facility atop Mauna Kea, Hawaii. NASAalso has an airborne IR telescope called SOFIA and an IR space telescope called Spitzer.

Infrared astronomy has also revealed that the interstellar medium contains a suite of

complex gas-phase carbon compounds called polyaromatic hydrocarbons, often abbreviated

PAHs or PACs. These molecules, composed primarily of fused rings of carbon (either

neutral or in an ionized state), are said to be the most common class of carbon compound in

the galaxy. They are also the most common class of carbon molecule in meteorites and in

cometary and asteroidal dust (cosmic dust). These compounds, as well as the amino acids,

nucleobases, and many other compounds in meteorites, carry deuterium and isotopes ofcarbon, nitrogen, and oxygen that are very rare on earth, attesting to their extraterrestrialorigin. The PAHs are thought to form in hot circumstellar environments (around dying,carbon-rich red giant stars).

Infrared astronomy has also been used to assess the composition of solid materials in the

interstellar medium, including silicates, kerogen-like carbon-rich solids, and ices. This is

because unlike visible light, which is scattered or absorbed by solid particles, the IR

radiation can pass through the microscopic interstellar particles, but in the process there are

absorptions at certain wavelengths that are characteristic of the composition of the grains.[5]
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As above with radio astronomy, there are certain limitations, e.g. N2 is difficult to detect byeither IR or radio astronomy.

Such IR observations have determined that in dense clouds (where there are enough

particles to attenuate the destructive UV radiation) thin ice layers coat the microscopicparticles, permitting some low-temperature chemistry to occur. Since hydrogen is by far the

most abundant molecule in the universe, the initial chemistry of these ices is determined by

the chemistry of the hydrogen. If the hydrogen is atomic, then the H atoms react with

available O, C and N atoms, producing "reduced" species like H2O, CH4, and NH3.However, if the hydrogen is molecular and thus not reactive, this permits the heavier atoms

to react or remain bonded together, producing CO, CO2, CN, etc. These mixed-molecular

ices are exposed to ultraviolet radiation and cosmic rays, which results in complex

radiation-driven chemistry.[6]

Lab experiments on the photochemistry of simple interstellar

ices have produced amino acids.[7]

The similarity between interstellar and cometary ices (as

well as comparisons of gas phase compounds) have been invoked as indicators of aconnection between interstellar and cometary chemistry. This is somewhat supported by the

results of the analysis of the organics from the comet samples returned by the Stardust

missionbut the minerals also indicated a surprising contribution from high-temperaturechemistry in the solar nebula.

Research

Research is progressing on the way in which interstellar and circumstellar molecules form

and interact, and this research could have a profound impact on our understanding of thesuite of molecules that were present in the molecular cloud when our solar system formed,

which contributed to the rich carbon chemistry of comets and asteroids and hence the

meteorites and interstellar dust particles which fall to the Earth by the ton every day.

The sparseness of interstellar and interplanetary space results in some unusual chemistry,

since symmetry-forbidden reactions cannot occur except on the longest of timescales. Forthis reason, molecules and molecular ions which are unstable on Earth can be highly

abundant in space, for example the H3+ion. Astrochemistry overlaps with astrophysics and

nuclear physics in characterizing the nuclear reactions which occur in stars, the

consequences forstellar evolution, as well as stellar 'generations'. Indeed, the nuclear

reactions in stars produce every naturally occurring chemical element. As the stellar'generations' advance, the mass of the newly formed elements increases. A first-generation

star uses elemental hydrogen (H) as a fuel source and produces helium (He). Hydrogen is

the most abundant element, and it is the basic building block for all other elements as its

nucleus has only one proton. Gravitational pull toward the center of a star creates massive

amounts of heat and pressure, which cause nuclear fusion. Through this process of merging

nuclear mass, heavier elements are formed. Carbon, oxygen and silicon are examples of

elements that form in stellar fusion. After many stellar generations, very heavy elements are

formed (e.g. iron and lead).
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In October 2011, scientists reported that cosmic dust contains complex organic matter

("amorphous organic solids with a mixed aromatic-aliphatic structure") that could becreated naturally, and rapidly, by stars.[8][9][10]

Meteorites are often studied as part of cosmochemistry.

Cosmochemistry orchemical cosmology is the study of the chemical composition of matter

in the universe and the processes that led to those compositions.[1]

This is done primarily

through the study of the chemical composition ofmeteorites and other physical samples.

Given that the asteroid parent bodies of meteorites were some of the first solid material to

condense from the early solar nebula, cosmochemists are generally, but not exclusively,concerned with the objects contained within the solar system.

History

In 1938, Swiss mineralogist Victor Goldschmidt and his colleagues compiled a list of what

they called "cosmic abundances" based on their analysis of several terrestrial and meteoritesamples.[2]Goldschmidt justified the inclusion of meteorite composition data into his table

by claiming that terrestrial rocks were subjected to a significant amount of chemical changedue to the inherent processes of the Earth and the atmosphere. This meant that studying

terrestrial rocks exclusively would not yield an accurate overall picture of the chemical

composition of the cosmos. Therefore, Goldschmidt concluded that extraterrestrial materialmust also be included to produce more accurate and robust data. This research is consideredto be the foundation of modern cosmochemistry.[1]

During the 1950's and 1960's, cosmochemistry became more accepted as a science. Harold

Urey, widely considered to be one of the fathers of cosmochemistry,[1]engaged in research

that eventually led to an understanding of the origin of the elements and the chemical

abundance of stars. In 1956, Urey and his colleague, German scientist Hans Suess,

published the first table of cosmic abundances to include isotopes based on meteoriteanalysis.

[3]

The continued refinement of analytical instrumentation throughout the 1960's, especially

that ofmass spectrometry, allowed cosmochemists to perform detailed analyses of the

isotopic abundances of elements within meteorites. in 1960, John Reynolds determined,through the analysis of short-lived nuclides within meteorites, that the elements of the solar

system were formed before the solar system itself[4]which began to establish a timeline of

the processes of the early solar system.
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In October 2011, scientists reported that cosmic dust contains complex organic matter

("amorphous organic solids with a mixed aromatic-aliphatic structure") that could becreated naturally, and rapidly, by stars.[5][6][7]

Meteorites

Meteorites are one of the most important tools that cosmochemists have for studying thechemical nature of the solar system. Many meteorites come from material that is as old as

the solar system itself, and thus provides scientists with a record from the early solar

nebula.[1]

Carbonaceous chondrites are especially primitive; that is they have retained many

of their chemical properties since their formation 4.56 billion years ago[8]

, and are thereforea major focus of cosmochemical investigations.

Recent findings by NASA, based on studies ofmeteorites found on Earth, suggests DNA

and RNA components (adenine, guanine and related organic molecules), building blocks forlife as we know it, may be formed extraterrestrially in outer space.

[9][10][11]
http://en.wikipedia.org/wiki/Cosmic_dusthttp://en.wikipedia.org/wiki/Organic_compoundhttp://en.wikipedia.org/wiki/Aromatichttp://en.wikipedia.org/wiki/Aliphatichttp://en.wikipedia.org/wiki/Starshttp://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Space-20111026-4http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Space-20111026-4http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Nature-20111026-6http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Nature-20111026-6http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-McSween-0http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-McSween-0http://en.wikipedia.org/wiki/Carbonaceous_chondritehttp://en.wikipedia.org/wiki/Cosmochemistry#cite_note-McSween2-7http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-McSween2-7http://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/Meteoriteshttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Adeninehttp://en.wikipedia.org/wiki/Guaninehttp://en.wikipedia.org/wiki/Organic_moleculeshttp://en.wikipedia.org/wiki/Outer_spacehttp://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Callahan-8http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Callahan-8http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-DNA-10http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-DNA-10http://www.universetoday.com/wp-content/uploads/2006/11/2006-1107titan.jpghttp://en.wikipedia.org/wiki/Cosmochemistry#cite_note-DNA-10http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Callahan-8http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Callahan-8http://en.wikipedia.org/wiki/Outer_spacehttp://en.wikipedia.org/wiki/Organic_moleculeshttp://en.wikipedia.org/wiki/Guaninehttp://en.wikipedia.org/wiki/Adeninehttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Meteoriteshttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/Cosmochemistry#cite_note-McSween2-7http://en.wikipedia.org/wiki/Carbonaceous_chondritehttp://en.wikipedia.org/wiki/Cosmochemistry#cite_note-McSween-0http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Nature-20111026-6http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Space-20111026-4http://en.wikipedia.org/wiki/Cosmochemistry#cite_note-Space-20111026-4http://en.wikipedia.org/wiki/Starshttp://en.wikipedia.org/wiki/Aliphatichttp://en.wikipedia.org/wiki/Aromatichttp://en.wikipedia.org/wiki/Organic_compoundhttp://en.wikipedia.org/wiki/Cosmic_dust


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Astrochemistry is the area of study where astronomy and chemistry overlap. In essence it is

the study of the abundance and reactions of chemical elements and molecules in the

universe. The formation, atomic and chemical composition, evolution and fate of molecular

gas clouds is of special interest, because it is from these clouds that solar systems form. The

most important tool in this area of study is spectroscopy.

Spectroscopy is the use of telescopes to measure the absorption and emission of light from

molecules and atoms in various environments. The abundance of elements, chemical

composition, and temperatures can be inferred from astronomical observations whencompared to laboratory measurements. This is possible because ions, atoms, and molecules

have characteristic ways that they absorb and emit certain wavelengths (colors) of light,

often not visible to the human eye. On the other hand, these measurements have limitations,

with various types of radiation (radio, infrared, visible, ultraviolet etc.) able to detect onlycertain types of species, depending on the chemical properties of the molecules.

Radio astronomy is the most powerful technique for detection of individual molecules. It

has resulted in the detection of over a hundred interstellar species including:radicals, ions,

and carbon-based compounds(alcohols, acids, ketones). One of the most abundantinterstellar molecules is carbon monoxide(CO). It is such a common interstellar moleculethat it is used to map out molecular regions.

Infrared astronomy has also been used to assess the composition of solid materials in the

interstellar medium, including silicates, carbon-rich solids, and ices, because, unlike visiblelight, the IR radiation can pass through the microscopic interstellar particles, but there are

absorptions at certain wavelengths that are characteristic of the composition of the grains.

These observations have determined that in dense clouds thin ice layers coat the

microscopic particles, permitting some low-temperature chemistry to occur. Since hydrogenis by far the most abundant molecule in the universe, the initial chemistry of these ices is

determined by the chemistry of the hydrogen. If the hydrogen is atomic, then the H atoms

react with available O, C and N atoms; but, if the hydrogen is molecular and thus not

reactive, this permits the heavier atoms to react or remain bonded together. These mixed-

molecular ices are exposed to ultraviolet radiation and cosmic rays which results incomplex radiation-driven chemistry.
http://www.universetoday.com/24886/star-evolution/http://www.universetoday.com/24886/star-evolution/


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Image of the sun acquired by the Extreme ultraviolet Imaging Telescope (EIT) at the NASA

Goddard Space Flight Center July 15, 1999.

NASAYou may know the sun consists mainly of hydrogen and helium. Have you ever wondered

what about the other elements in the sun? I hunted up a table (source: NASA - Goddard

Space Flight Center) listing the sun's elemental composition, which we know from analysis

of its spectral signature. I'm sure you're not surprised that hydrogen is the most abundant

element. The sun is constantly fusing hydrogen into helium, but don't expect the ratio of

hydrogen to helium to change anytime soon. The sun is 4.5 billion years old and hasconverted about half of the hydrogen in its core into helium. It still has about 5 billion years

before the hydrogen runs out.

Elements in the Sun

Element % of total atoms % of total mass

Hydrogen 91.2 71.0

Helium 8.7 27.1

Oxygen 0.078 0.97

Carbon 0.043 0.40

Nitrogen 0.0088 0.096

Silicon 0.0045 0.099

Magnesium 0.0038 0.076

Neon 0.0035 0.058

Iron 0.030 0.014

Sulfur 0.015 0.040
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961112a.htmlhttp://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961112a.htmlhttp://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961112a.htmlhttp://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961112a.html

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