The Discovery of the Chemistry among the Stars Arturo Arnau lnstituto d e Bachiilerato Fuente de San Luis, Seminario de Fisica y Quimica. Arabista Ambrosio Huici, 14.46013, Valencia, Spain ltiaki Tution and Estanislao Silla Departamento d e Quimica Fisica, Universidad d e Valencia, Dr. Moliner, 50. 46100 Burjassot, Valencia, Spain Laws of high flight govern... up there, in the celestial ether, whose only father is Olympus, and which were not created by man, of mortal nature... Saphoclesin Oedipus Rex, 5th century B.C.
nomena and realities i n nature itself, leaving out any intervention by inexplicable forces. According to these philosophers such explanations had to be logical and rational, not mysterious and imaginative as were the previously existing myths.
After the universe was formed some 15,000 million years ago, the material started coalescing to form enormous conglomerations in various forms called galaxies. It has been calculated that in our Universe some 10" galaxies exist, and each one of them contains a n average of 10" stars that light u p the surroundings, making these visible as a n immense and persistent shine on the dark background ofthe firmament. Throughout most of these thousands of mil. lions of "ears. the soace between the stars has been occu-
Anaxagoras and the Corpora'ify
Of
the Stars
In 467 B.C. a n enormous meteorite fell on Egos-Potamas, near Troy, The philosopher Anaxagoras (500-428 B.C., approx.), perhaps due to the flaming aspect that a meteorite presents as i t passes through the atmosphere, declared that it had Come from the Sun. So the Sun was
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the stars and ;each dimensions measured i n hundreds of lightyears. During the last few decades, a surprising discovery h a s been made: the presence of almost 100 complicated molecules in the interstellar clouds (the table). The existence of these interstellar molecules and t h e fact t h a t a n important part of them turn out to he well-known i n terrestrial c h e m i s t r y (e.g., HzO, NH3, CHsCHzOH) confirm the fulfillment of our physical and chemical laws i n different parts of the known universe. So the universe seems increasingly homogeneous and comprehensible. The delay in discovering the interstellar chemistry is explained by t h e m a n y conceptual a n d technical obstacles to be overcome t h r o u g h o u t o u r history. Over time mankind gradually came to question t h e material nature of the firmament and developed t h e techniques necessary for testing it. The long hist o r y of t h e discovery of t h e material universe is outlined in this paper.
Molecules Discovered in the Interstellar Gas (41) Observe the existence of molecules familiar on the Eatth and also species that can only exist in the extreme physical conditions of the intersteilar medium. The majority of the interstellar species possess carbon. Manv of these species are unsaturated. Hydrogen Molecules Containing Carbon and Hydrogen CH CHI CH4 'HzC=CHz
CaC ClCH
CSCH HzC=C=C H3CCSH H3C(C=C)zH
HC&H
'C=C=C
(C=C)zH HzC=CC=C (CS)zCH
Molecules Containing Oxygen, Carbon, and Hydrogen OH Hz0
(CICIICO CH30H HCO' HCOzH
H30+ HCO+ CO HOC+? C=CO HzCO CSCO HOCOt
CHzCO CHGHO CH3CHzOH
CH3COzH CH30CH3 CH3COCH3 HC-CCHO
*(C=C)z=C (CsC)3H
cC3H
Molecules Containing Nitrogen, Carbon, and Hydrogen HCNHt CHCN CHzNH CH3NC NH3 CH3NHz CSCN CN N H G N HC-CCN HCN 'HCCN HCSNC HNC CHzCN CH3CHzCN HzC=CNCN NH
N2H+
HKClCCN H(CS)zCN H3C(C=C)zCN H(CS)zCN H(CaC)nCN H(C=C)&N
Molecules Containing Oxygen and Nitrogen NO
HNO
HNCO
NHzCHO
Molecules Containing Sulfur, Silicon, and Other Elements Reason Interprets t h e Heavens SO+ SN CS H2S SO2 OCS HCS' HzCS CH3SH HNCS C2S Towards the end of the 7th cen- SO SiS SiO 'c-CzSi 'Sic 'SiN 'SiH4 'Sic4 tury B.C., i n a Greek polis of Asia 'CP 'NaCI 'AICI 'KC1 'AIF HCI PN Minor, we find the first ideas recardinc t h e material nature of ;he heavens. ~h~ pre-~ocratic The question mark indicates tentative detections. The asterisk indicates discovered in circumstellar shells. philosophers there looked for an The c indicates a cyclical molecule. explanation for the natural phe-
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Journal of Chemical Education
C3S
(The Peloponnesian peninsula has a n extension of some 21,000 km2, similar to that of the State of Massachusetts.) This may be why the dramatist Euripides, friend of the philosopher, in his tragedy Phaeton, called the Sun a mass of f i r e . - ~ u tAnaxagoras b e n t even further. For him the stars and the planets were also solid physical bodies, incandescent rocks (constituted by the element fire) t h a t made themselves visible during the night. H e thought that all the heavenly objects of the firmament had been generated by means of the same kinds of processes that rule on the Earth, starting from a chaotic Universe. Anaxagoras was accused of lack of godliness and was hrought to trial for his ideas when he was teaching in Athens ( 3 ) .The Athenians of those times were not ready to acceDt the cor~oralitvof the stars: their relieions beliefs led them to consider t h e celestial &dies as d&e entities exempt of any materiality. The intervention of Pericles himself was necessary for Anaxagoras to survive the trial. Afterwards Athens was no longer a comfortable place for the philosopher, and he went into exile. Anaxagoras is the first case in history in which a scientist-naturalistic hilosopher is seated on the accused bench to defend his theories. Later many more were brought to court. Pre-Socratic /mmateria/Interpretation
In the 5th find 4th centuries B C., Aihuns w.is an important c ~ l t u r accnterwhtw, l ~ h ~ l o w ~ hcontinued ers the task of the rational interpretatihn of the world, initiated by the pre-Socratics. They gave to their philosophy a more moralizing and idealistic tone that led to animmaterial interpretation of the heavens. Thus, even though the philosophy of Aristotle (384-322 B.C.), who figured a t the top in this stage of thinking, was fundamentally naturalistic, his conception of the Universe is influenced by the idealism of Plato (427-347 B.C., approx.). Aristotle believes in the existence of two radically different worlds: a material terrestrial world with four sublunar spheres corresponding to each of the elements. and a sublime celestial world where the heavenly bodies move in different spheres with a "perfect" movement, circular and uniform (4). Aristotle's Ether To avoid the concept of a vacuum, Aristotle believed in a heaven constituted of a n immaterial, light, and cunning suhstance, which would fill the celestial spheres, a fifth element or fifth essence, a s i t was literally defined in the Middle Ages. He called i t ether. It is equally reasonable to assume that this body will he ungenerated and indestructibleand exempt from increase and alteration.... (5) And to implying i n 3 1 t h primary hrdy 8s pomrrhing rlir l,cyond eanh, fire, m r and w.itcr, the" g.%acthe htghrst plnrc t l w name of ;wrhrr, drriwd t i u m the fact th.21 it "runs alwnvs"
31. Kroto, H. W. In,. Rev. Phys Cham. 1981,1,30%376. 32. Smith. 0. Chem. Re". 1992,92.1473-1485. 1213-1235 33. Kmto. H.W.:Allaf A. W.: Ba1m.S.P. Chem Rev. 1891.91 . 34. Bohm% D. K. ~ h e hRe". . 1992.'42,1187-1508. 35. Dalgamo, A. lnler J. Maas Speclrom. Ion Prom. 1987.81, 1-13. 36. Arnau,A.:Tufi6n, I.: Sills,E.:Andr6% J.M. J Chrm. E d u c 19XD67.905-906. I QuonlumChem. 1893.46.213-238. 37. Amau,A.;Tufi6n. I.; Sil1a.E. I n l . . 38. Arnau,A.:TuMn. I.: Sills, EArrmp. J. Supp. S. 1993.8R.595-608. 39. Miller, S. L.;Orgel, L. E. The Origmro/Lifeon iheEnrrh; Prenti-Hall: Englewwd CliWw NewYork 197&~ 40. Eschenmoser, A: Loewenthal E. Chrm Soc. Re". 1892,1-16. 41. Smith.D. Chem.Reu. 1992,92.1473-1485.
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