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“Complex” organic molecules detected in space

April 22, 2009
Courtesy Max Planck Institute
for Radio Astronomy
and World Science staff

Sci­en­tists say they have de­tected two of the most com­plex mol­e­cules yet dis­cov­ered in space. Their com­put­er mod­els al­so in­di­cate still larg­er mol­e­cules may be out there, in­clud­ing the so-far elu­sive ami­no ac­ids, es­sen­tial for life as we know it.

Mod­els of or­gan­ic mole­cules new­ly iden­ti­fied in space. Above: eth­yl for­mate; be­low: n-Pro­p­yl cy­a­nide. Col­or code of the atom­ic con­sti­tu­ents of both mo­le­cules: hy­dro­gen: white, car­bon: grey, ox­y­gen: red and ni­tro­gen: blue. (Im­ages: Ol­i­ver Bau­m, U. of Co­logne)


The find­ings from the Max Planck In­sti­tute for Ra­dio As­tron­o­my in Bonn, Ger­ma­ny, Cor­nell Uni­ver­s­ity in New York, and the Uni­ver­s­ity of Co­logne, Ger­ma­ny, were pre­s­ented April 21 at the Eu­ro­pe­an Week of As­tron­o­my and Space Sci­ence at the Uni­ver­s­ity of Hert­ford­shire, U.K.

The re­search­ers used the IRAM 30-me­ter tel­e­scope in Spain to de­tect light emis­sions from mol­e­cules in the star-forming re­gion Sag­it­ta­ri­us B2, near the cen­ter of our gal­axy. The mol­e­cules were iden­ti­fied in a hot, dense gas cloud known as the Large Mol­e­cule Hei­mat, which con­tains a lu­mi­nous young star. 

Oth­er large, or­gan­ic mol­e­cules—car­bon-con­taining com­pounds typ­ic­ally found in life forms on Earth—have been found in this cloud, in­clud­ing types of al­co­hols, ac­ids and mem­bers of a group known as alde­hy­des. The new mol­e­cules, eth­yl for­mate and n-pro­pyl cy­a­nide, repre­s­ent dif­fer­ent clas­ses of mol­e­cule, called es­ters and al­kyl cy­a­nides.

Atoms and mol­e­cules are rec­og­niz­a­ble by light they emit at spe­cif­ic fre­quen­cies, or col­ors, on the light spec­trum. Rec­og­niz­ing the sig­na­ture of a mol­e­cule in the spec­trum is rath­er like iden­ti­fy­ing a fin­ger­print.

“The dif­fi­cul­ty in search­ing for com­plex mol­e­cules is that the best as­tro­nom­i­cal sources con­tain so many dif­fer­ent mol­e­cules that their ‘fin­ger­prints’ over­lap, and are dif­fi­cult to dis­en­tan­gle,” said Ar­naud Bel­loche of the Max Planck in­sti­tute, first au­thor of the re­search pa­per. 

“Larger mol­e­cules are even more dif­fi­cult to iden­ti­fy be­cause their ‘fin­ger­prints’ are barely vis­i­ble: their radia­t­ion is dis­trib­ut­ed over many more lines that are much weak­er,” added Hol­ger Mull­er of the Uni­ver­s­ity of Co­logne. Out of 3,700 spec­tral lines de­tected with the IRAM tel­e­scope, the team iden­ti­fied 36 from the two new mol­e­cules.

The re­search­ers then used a com­put­er mod­el to study the chem­i­cal pro­cesses that let these and oth­er mol­e­cules form in space. Chem­i­cal re­ac­tions re­sult from col­li­sions among gas­e­ous par­t­i­cles; but there are al­so small grains of dust in the gas float­ing be­tween stars. These grains can serve as land­ing sites for at­oms to meet and re­act, pro­duc­ing mol­e­cules. As a re­sult, the grains build up lay­ers of ice con­taining bas­ic or­gan­ic mol­e­cules like meth­a­nol, the sim­plest al­co­hol.

“But,” said Rob­in Gar­rod, an as­tro­chem­istry re­searcher at Cor­nell, “the really large mol­e­cules don’t seem to build up this way, at­om by at­om.” Rath­er, the com­put­er mod­els sug­gest these mol­e­cules form sec­tion by sec­tion, us­ing mol­e­cules al­ready on the dust as pre-made build­ing blocks. The new­found mol­e­cules seem to be pro­duced this way, he added. “There is no ap­par­ent lim­it to the size of mol­e­cules that can be formed by this pro­cess—so there’s good rea­son to ex­pect even more com­plex or­gan­ic mol­e­cules to be there, if we can de­tect them,” he went on. 

Sen­ior team mem­ber Karl Menten at the Planck In­sti­tute argues this will hap­pen soon, as the req­ui­site in­stru­ments are rap­idly im­prov­ing. Fu­ture disco­veries may even in­clude ami­no ac­ids, which are re­quired for the pro­duc­tion of pro­teins, and are there­fore es­sen­tial to life on Earth. The sim­plest ami­no ac­id, gly­cine, is no more com­plex than the two new­found mol­e­cules, ac­cord­ing to re­search team mem­bers, whose work is to ap­pear in the jour­nal As­tron­o­my & As­t­ro­phys­ics.


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Scientists say they have detected two of the most complex molecules yet discovered in space. Their computer models also indicate still larger molecules may be present, including the so-far elusive amino acids, essential for life as we know it. The findings from the Max Planck Institute for Radio Astronomy in Bonn, Germany, Cornell University in New York, and the University of Cologne, Germany, were presented April 21 at the European Week of Astronomy and Space Science at the University of Hertfordshire, U.K. The researchers used the IRAM 30 m telescope in Spain to detect light emissions from molecules in the star-forming region Sagittarius B2, near the center of our galaxy. The molecules were identified in a hot, dense gas cloud known as the Large Molecule Heimat, which contains a luminous young star. Other large, organic molecules—carbon-containing compounds typically found in life forms on Earth—have been found in this cloud, including types of alcohols, acids and members of a group known as aldehydes. The new molecules, ethyl formate and n-propyl cyanide, represent different classes of molecule, called esters and alkyl cyanides. Atoms and molecules are recognizable by light that they emit at specific frequencies, or colors, on the light spectrum. Recognizing the signature of a molecule in the spectrum is rather like identifying a human fingerprint. “The difficulty in searching for complex molecules is that the best astronomical sources contain so many different molecules that their “fingerprints” overlap, and are difficult to disentangle,” said Arnaud Belloche of the Max Planck institute, first author of the research paper. “Larger molecules are even more difficult to identify because their ‘fingerprints’ are barely visible: their radiation is distributed over many more lines that are much weaker,” added Holger Muller of the University of Cologne. Out of 3700 spectral lines detected with the IRAM telescope, the team identified 36 lines belonging to the two new molecules. The researchers then used a computer model to study the chemical processes that let these and other molecules form in space. Chemical reactions can take place as the result of collisions between gaseous particles; but there are also small grains of dust in the gas floating between stars. These grains can serve as landing sites for atoms to meet and react, producing molecules. As a result, the grains build up layers of ice containing basic organic molecules like methanol, the simplest alcohol. “But,” said Robin Garrod, a researcher in astrochemistry at Cornell University, “the really large molecules don’t seem to build up this way, atom by atom.” Rather, the computer models suggest these molecules form section by section, using molecules already on the dust as pre-made building blocks. The newfound molecules seem to be produced this way, he added. “There is no apparent limit to the size of molecules that can be formed by this process—so there’s good reason to expect even more complex organic molecules to be there, if we can detect them,” he went on. Senior team member Karl Menten at the institute thinks that this will happen soon, as the requisite instruments are rapidly improving. Future discoveries may even include amino acids, which are required for the production of proteins, and are therefore essential to life on Earth. The simplest amino acid, glycine, is no more complex than the two newfound molecules, according to research team members, whose work is to appear in the journal Astronomy & Astrophysics.