Macromolecular Organic Compounds from the Depths of Enceladus

Transcription

1 Macromolecular Organic Compounds from the Depths of Enceladus Frank Postberg University of Heidelberg & Freie Universität Berlin N. Khawaja, B. Abel, G. Choblet, C. Glein, M. GudipaK, B. Henderson, H.-W. Hsu, S. Kempf, F. Klenner, G. Moragas-Klostermeyer, B. Magee, L. Nölle, M. Perry, R. Reviol, J. Schmidt, R. Srama, F. Stolz, G. Tobie, M. Trieloff, H. Waite OPAG MeeKng September 2018, Pasadena Image credits: NASA/JPL

2 Exploring a deep hydrothermal water world porous rocky core: Iess et al global subsurface ocean: Postberg et al. 2009, 2011 Thomas et al Tidal dissipa)on powerhouse Choblet et al south polar plume: Hansen et al Porco et al Spencer et al Spahn et al Hydrothermal ackvity: Hsu et al Hydrothermal ac)vity: Waite et al Hsu et al Waite et al water-rock interackon: Postberg et al Sekine et al. 2015

3 Cassini s Mass Spectrometers Ion Ion and & Neutral Mass Gass Spectrometer (INMS) Cosmic Dust Analyzer (CDA) Sampling Gas Sampling Ice Grains

4 Chemical characterisation of icy dust with Cassini s (CDA) Impact Ionization TOF-MS

5 Enceladus Postberg et al., 2009 Laboratory

6 Three ice grain populakons Three spectrum types Hillier et al. 2007; Postberg et al. 2008, 2009, 2011 Postberg et al. 2008, 2009, 2011 Type 1: pure water ( 65%) Type 3, salty water ( 10%) almost pure water ice salt-rich water ice Type 2: Organic bearing ice ( 25%)

7 Organics in Type 2 spectra C 2 H x NH 2 + C 3 H x + C 2 H X O + [H 3 O] +.(H 2 O) n=0,1,2 6 C 2 H 3 + C 2 H 4 + C 2 H 5 + CHO + CH 2 O + NH 2 CH 2 + CH 3 O + HCN u 39-45u This talk à complex organic material à subgroup ( 4%) of Type 2

8 Fragment b) ions from complex organic material ( 1% of E ring ice grains) /15:57:10 ( ) water species Na - species log Amplitude Time (µs) (c) CU/LASP SpectrumGui * T12:34:58 <Hi_mass_subset_Type_2_V7_FP3_newstretch_subset_76spectra.bin>

9 FormaKon and fragmentakon of aromakc cakons

10 Fragment b) ions from complex organic material ( 1% of E ring ice grains) /15:57:10 ( ) water species Na - species 19.2 C3 C C5 + log Amplitude Time (µs) (c) CU/LASP SpectrumGui * T12:34:58 <Hi_mass_subset_Type_2_V7_FP3_newstretch_subset_76spectra.bin>

11 Postberg et al., Nature (2018) AromaKc fingerprint reproduced with laboratory setup 19 (H 2 O)H + + [C 6 H 5,7 ] + Intensity [V] 0,1 37 (H 2 O) 2 H [C 7 H 7 ] , (H 2 O) 3 H Mass [u] 0.3 wt.% Benzoic acid and wt.% Benzyl alcohol

12 Fragment b) ions from complex organic material ( 1% of E ring ice grains) /15:57:10 ( ) log Amplitude water species Na - species C3 C C Time (µs) C8 C HMOC series C10 C12 C14 C11 C13 C (c) CU/LASP SpectrumGui * T12:34:58 <Hi_mass_subset_Type_2_V7_FP3_newstretch_subset_76spectra.bin>

13 water species Na - species saturated aliphakc species (C 1, C 2, C 3, C 4 ) heteroatoms required (O or N) Postberg et al., Nature (2018)

14 Impact ionizakon lab spectrum of Polystyrene (C / H = 1) Srama et al., 2009 similar to HMOC-Sequence

15 Postberg et al., Nature (2018) CDA extended low resolukon spectra

16 Summary I Chemical properkes of detected complex organic material u HMOC (High Mass Organic CaKons, C 8 C 16 ) are unsaturated fragments from parent molecules with a rako C/H 1-2. u IndicaKon of parent molecules with atomic masses >> 200u, some signals > 1000u. u Abundant sub-structures of isolated benzene rings. u Most rings are auached to non-carbon funckonal groups or to dehydrogenated C atoms. u Low mass saturated aliphakc species C 1 to C 4. u O-bearing species are indicated in both CDA & INMS spectra. u N-bearing species are in good agreement with some features but not a unique interpretakon.

17 Summary I Chemical properkes of detected complex organic material One plausible interpretakon Cross-linked macromolecular or polymeric material... à with oxygen- and nitrogen-bearing funckonal groups... à where mostly isolated aromakc rings... à are connected by short aliphakc chains.

18 Murchison IOM (Remusat, 2014)

19 Humic Acid (source: Wikipedia)

20 Bubble bursting & Formation of ice grains 272 K Lhuissier and Villermaux, Physics of Fluids(2009) Postberg et al., Nature (2009, 2011)

21 Hypothesis I Ø Diagnos)c observa)ons - HMOC are in salt poor grains à organics not dissolved in water - High molecular mass à not in the gas phase at 272 K. - High concentra)on of organics in ice grains (> 1%) à Organic material forms a thin layer at the oceanic water table. Ø Bubble burs)ng releases pure organic aerosols (in addi)on to salty ocean spray) Ø Vapour flow (driven by pressure gradient) carries grains upward through ice vents Ø Organic aerosols are then ice coated by freezing of salt poor vapours

22 Ocean water is parkally filling crustal cracks 300 m 3 km Postberg et al., Nature (2018)

23 Cloud nucleation after bubble bursting in Earth s ocean Sea-spray aerosol particles enriched in organic material are generated when bubbles burst at the air sea interface. Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approximately 0.2 µm in size. Simultaneous creakon of Ø Pure salt water grains Ø Pure organic (r < 200 nm) Ø Mixed phase grains T.W. Wilson et al. Nature 525, (2015)

24 Hypothesis II Ø The HMOC material probably emerges from the hydrothermal ac)ve Enceladus core Ø Transported upwards by a) large scale thermal convec)on b) ascending bubbles Ø HMOC material might only be the )p of an organic iceberg on Enceladus Postberg et al., (2018)