Organic Dust in Space Sun Kwok University of British Columbia, Vancouver, Canada & Laboratory for Space Research, University of Hong Kong, Hong Kong Cosmic Dust and Magnetism, Daejeon, Korea October 31, 2018
Organic Matter • Before the 19 th century, organic matter was assumed to be associated only with living organisms ( amino acid asparagine from asparagus, 1806; leucine from cheese, 1819; glycine from gelatin, 1820 ) and was assumed to possess a “vital force” • Living yeast was needed for fermentation of sugar into alcohol
Laboratory synthesis of organics • Urea from ammonium cyanate (1823) • Amino acid alanine from acetaldehyde, ammonia, and hydrogen cyanide (1850) • Sugars from formaldehyde (1861) • Nucleobase adenine from HCN and NH 3 (1960) Vital force not necessary Organics: a group of molecules and compounds based on the element carbon, together with H, O, N, S, and P.
Carbon Reservoirs on Earth Pools Quantity (Giga tons) Atmosphere 720 Oceans 38,400 Organic matter Total inorganic 37,400 on Earth is the Surface layer 670 result of life Deep layer 36,730 Total organic 1,000 Lithosphere Sedimentary carbonates >60,000,000 Is there organic Kerogen 15,000,000 Terrestrial biosphere 2,000 matter in the (total) Universe? Living biomass 600-1,000 Dead biomass 1,200 Aquatic biosphere 1-2 Fossil fuels 4,130 Coal 3,510 Oil 230 Gas 140 Table adapted from Other (peat) 250 Falkowski et al. (2000)
Organic matter on Earth • Kerogen, coal, oil, natural gas • random arrays of aromatic carbon sites, aliphatic chains and linear chains with functional groups made up of H, O, N, and S attached • a solid sedimentary, insoluble, organic material found in the upper crust of the Earth • Under pressure and thermal processing, transform into more stable forms of carbon such as graphite and diamond • Biological in origin
Organics beyond the Earth • Earth was thought to be the sole domain of organics • Existence of complex organics in space was proposed but not believed (Hoyle & Wickramasinghe 1977) • Organic molecules and solids are now found throughout the Universe, from our solar system to distant galaxies (Kwok 2016, A&AR , 24 , 8)
Carbonaceous chondrites • Paraffins in Orgueil meteorite ( Nagy et al. 1961 ) • Aromatic and aliphatic compounds in Murchison meteorite ( Cronin et al. 1987 ) • From amino acids to 30-C-long nonpolar hydrocarbons
The soluble component of carbonaceous chondrites • Carboxylic acids, sulfonic and phosphonic acids, amino acids, aromatic hydrocarbons, heterocyclic compounds, aliphatic hydrocarbons, amines and amides, alcohols, aldehydes, ketones, and sugar related compounds • 14,000 compounds with millions of diverse structures • Almost all biologically relevant organic compounds are present in carbonaceous meteorites Schmidt-Kopplin et al. 2010, PNAS, 107, 2763 Decreasing abundance with increasing C number within the same class of compounds suggests abiotic origin.
Non-terrestrial origin • Amino acids: equal mixture of D and L chirality amino acids, non-protein amino acids not found in the biosphere, non- terrestrial values of deuterium • Nucleobases are achiral • Unusual nucleobases ( Callahan et al. 2011, PNAS, 108, 13995 ).
Insoluble Organic Matter (IOM) in carbonaceous chondrites • Insoluble macromolecular solids • 70% of organic matter in IOM • Destructive: thermal and chemical degradations followed by GC/MS • Nondestrutive: NMR, FTIR, XANES, EPR, HRTEM • Small (1-4) aromatic rings, short aliphatic chains, heteroelements (O, S, N) ( Derenne & Robert 2010 ) • Average abundance C 100 H 46 N 10 O 15 S 4.5 ( Pizzarello & Shock 2010 )
Comets: the volatile component • Mm and IR spectroscopy: CH 4 , C 2 H 2 , C 2 H 6 , CH 3 OH, H 2 CO, HOCH 2 CH 2 OH, HCOOH, HCOOCH 3 , CH 3 CHO, H 2 CHO,NH 3 ,HCN, HNCO, HNC, CH 3 CN, HC 3 N • ROSATA: methyl isocyanate (CH 3 NCO), acetone (CH 3 COCH 3 ), propanal (C 2 H 5 CHO), and acetamide (CH 3 CONH 2 ) • STARDUST: glycine of extraterrestrial origin (Elsila et al. 2009)
Comets: not dirty snow balls • ROSETTA: 27000 particles collected from Comet 67P • Large macromolecular compound similar Fray et al. 2016, Nature , to IOM 538, 72 3.3 and 3.4 features in Comet Wild2 (Keller et al. 2006)
Complex organics in comets • Comparison between cometary dust, IDP, meteorites, and kerogen • D and 15 N enrichment suggests presolar origin Raman spectra (Sandford et al. 2006)
Asteroids • Extreme red color and low (0.01-0.15) albedos of some asteroids are inconsistent with minerals or ice. • Optical properties of 5145 Pholus can be fitted with tholins ( Cruikshank et al. 1998 ) • Terrestrial coal, tar sands, asphaltite, anthraxolite, kerite, etc., show low albedo and red colors similar to those of asteroids ( Roush & Cruikshank 2004 ).
Interplanetary dust particles • Because of their small sizes (5-50 μ m, mass~nanogram), cannot be analyzed by traditional techniques • Scanning transmission X-ray microscope & X-ray absorption near-edge structure spectroscopy • Carbonaceous materials ( Messenger 2000, Keller et al. 2002 ) • 3.4 µm aliphatic feature and sometimes C=O group ( Flynn et al. 2003 )
Interplanetary Dust Particles • Few microns to tens of microns in size ( Brownlee 1978 ) • Silicates (olivine & pyroxene) • 10-12% carbon content • 3.4 µm aliphatic feature and sometimes C=O group ( Flynn et al. 2003 ) O-XANES spectrum of IDP
Titan • Organic haze in the atmosphere of Titan ( Waite 2007 ) • These nanoparticles are blown into dunes by wind • Lakes of liquid methane and ethane • Total amount of hydrocarbons on Titan is larger than the oil and gas reserves on Earth
Tholins • Tholins: refractory organic materials formed by UV photolysis of reduced gas mixtures (N 2 , NH 3 , CH 4 ) ( Sagan & Khare 1979 ) • Tholins=amorphous hydrogenated carbon nitrides • Colors from yellow to dark brown • Optical properties depend on sp 2 /sp 3 ratio
Planets and satellites Thiophenic, aromatic, and aliphatic Complex macromolecular compounds—in drill samples from organics in ocean on Mars’ Gale crater (Eigenbrode et al. 2018, Saturn’s moon Enceladus Science, 360, 1096) (sample analysis at Mars on (Postberg et al. 2018, Nature, 558, Curiosity rover) 564) (cosmic dust analyser and ion and neutral mass spectrometer on Cassini) Kerogen as precursor, abiological in origin
Elemental synthesis in the late stages of stellar evolution • Triple- α reaction (He → C) Mass loss • Slow neutron capture (s- process) (Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, etc) • Thermal pulse and dredge up • Synthesis of C 2 , C 3 , CN in the stellar atmosphere 3 M ⊙ track Bloecker
Molecular synthesis in the stellar winds of AGB stars • Rotational transitions of over 70 molecules have been detected in the circumstellar envelopes of AGB stars • Inorganics: CO, SiO, SiS, NH 3 , AlCl, .. • Organics: C 2 H 2 , CH 4 , H 2 CO, CH 3 CN, .. • Radicals: CN, C 2 H, C 3 , HCO + • Rings (C 3 H 2 ), chains (HC 9 N) AGB stars are prolific molecular factories
Unidentified infrared emission (UIE) bands (Russell et al. 1977) Aromatic nature 1500 [NeIII] [SiIV] first proposed [NeV] NGC 7027 by: Knacke 1977, 11.3 12.7 Duley & Williams λ F λ (10 -10 erg cm -2 s -1 ) 1979, 1981; Puetter 1000 13.5 12.0 et al. 1979 7.7 8.6 [MgV] 500 6.2 3.3: sp 2 C-H stretch 6.2: sp 2 C=C stretch 7.7: sp 2 C-C stretch 8.6: sp 2 =C-H in-plane bend 3.3 11.3: sp 2 =C-H out-of-plane bend 0 0 2 4 6 8 10 12 14 16 18 20 Wavelength ( µ m) Stretching and bending modes of aromatic compounds
UIE also seen in galaxies
UIE observed to z~2 The same aromatics are also widely seen in galaxies From a few to 20% of total luminosity AIB=aromatic infrared bands Smith et al. 2007
UIE are detected in many planetary nebulae. Since the carrier is synthesized in situ, PN are the best objects to study their origins 200 11.3 IRAS 21282+5050 180 12.4 160 λ F λ (10 -10 erg cm -2 s -1 ) 140 7.7 120 8.6 100 6.2 80 60 40 6.2: sp 2 C=C stretch 3.3 8.6: sp 2 C-H in-plane bend 20 7.7: sp 2 C-C stretch 11.3: sp 2 C-H out-of-plane bend 12.4: sp 2 C-H out-of-plane bend A young PN 0 -20 2 4 6 8 10 12 14 16 18 20 Wavelength ( µ m)
3.4 μ m aliphatic C-H stretch • 3.38 μ m: asymmetric CH 3 • 3.42 μ m: asymmetric CH 2 • 3.46 μ m: lone C-H group • 3.49 μ m: symmetric CH 3 • 3.51 μ m: asymmetric CH 2 Infrared spectroscopy reveals aliphatic features
Aliphatic in-plane and out-of- plane bending modes 1.4 IRAS 22272+5435 11.4 1.2 6.9 12.1 normalized spectrum 6.2 1.0 7.3 0.8 7.7 13.4 0.6 14.2 0.4 0.2 0.0 2 4 6 8 10 12 14 16 18 Wavelength ( µ m) Kwok et al. 2001 8 µ m plateau: -CH 3 (7.25 µ m), -C(CH 3 ) 3 (8.16 µ m, “e”), =(CH 3 ) 2 (8.6 µ m, “f”) • 12 µ m plateau: C-H out-of-plane bending modes of alkene (“a”, “b”), cyclic • alkanes (9.5-11.5 µ m, “c”), long chains of -CH 2 - groups (13.9 µ m, “d”).
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