Augé, B.

Bardin, N.

Boduch, P.

Dartois, E.

Duprat, J

Engrand, C

Godard, M.

Guerquin-Kern, J-L

Rothard, H.

Slodzian, G.

Vermesse, H.

Wu, T-D

Hal-Diderot

ON THE ORIGIN OF ORGANICS IN ULTRACARBONACEOUS ANTARCTIC MICROMETEORITES (UCAMMS), IRRADIATION OF N-RICH ICES IN THE OUTER SOLAR SYSTEM

HAL - Normandie Université

HAL-IN2P3

HAL-INSU

En-Grand, C

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ON THE ORIGIN OF ORGANICS IN
ULTRACARBONACEOUS ANTARCTIC
MICROMETEORITES (UCAMMS), IRRADIATION
OF N-RICH ICES IN THE OUTER SOLAR SYSTEM
J Duprat, B. Augé, E. Dartois, C En-Grand, N. Bardin, M. Godard, G.
Slodzian, P. Boduch, H. Rothard, H. Vermesse, et al.
To cite this version:
J Duprat, B. Augé, E. Dartois, C En-Grand, N. Bardin, et al.. ON THE ORIGIN OF ORGANICS IN
ULTRACARBONACEOUS ANTARCTIC MICROMETEORITES (UCAMMS), IRRADIATION OF
N-RICH ICES IN THE OUTER SOLAR SYSTEM. 50th Lunar and Planetary Science Conference
2019, Mar 2019, The Woodlands, Texas, United States. ￿hal-02354996￿
ON THE ORIGIN OF ORGANICS IN ULTRACARBONACEOUS ANTARCTIC MICROMETEORITES (UCAMMS), 
IRRADIATION OF N-RICH ICES IN THE OUTER SOLAR SYSTEM. J. Duprat1, B. Augé1, E. Dartois2, C. En-
grand1, N. Bardin1, M. Godard1, G. Slodzian1, P. Boduch3, H. Rothard3, H. Vermesse4, T-D Wu5 , J-L. Guerquin-
Kern5. 1CSNSM, CNRS -Univ. Paris Sud-Univ. Paris-Saclay, Fr. (Jean.Duprat@csnsm.in2p3.fr); 2ISMO CNRS -
Univ. Paris-Sud, Univ. Paris-Saclay, Fr. 3CIMAP, Normandie Univ, ENSICAEN, UNICAEN, CEA, CNRS, Fr. 
4IFPEN, Rueil-Malmaison, Fr.  5Institut Curie; INSERM; CNRS, Fr. 
 
Introduction: The origin of interplanetary organic 
matter (OM) is still debated, considering either a di-
rect heritage from the parent molecular cloud or pro-
cesses in the solar protoplanetary disk. Large hydro-
gen fractionation, i.e. deuterium (D) excesses, can 
result from ion-molecule reactions at low tempera-
ture. Such reactions can produce molecular reservoirs 
with extreme D/H ratios (e.g. H2D+), that may be 
transferred to other gas phase molecules then to ices 
and, eventually, to refractory organic phases [e.g. 1]. 
Most approaches consider that the high D/H compo-
nent result from ion-molecule reactions at early stages 
(i.e. prior planetary formation) in the low temperature 
and dense gas-phase of the protosolar cloud or in the 
outer regions of the protoplanetary disk [2,3]. Some 
recent studies showed that, more limited, D enrich-
ments may also result from intense irradiation of or-
ganics by electrons or X-rays [4-6].  
Samples & methods : It is possible to recover 
from Antarctic ice and snow Ultra-Carbonaceous 
Antarctic Micrometeorites (UCAMMs) that exhibit 
exceptional OM concentrations associated with ex-
treme D excesses [7,8]. Deciphering the D enrichment 
mechanism of the OM of UCAMMs can help placing 
constraints on the formation process of this specific 
interplanetary organic matter. 
Formation of organic matter can occur at later 
stages of solar system evolution, when small bodies 
such as asteroids or comets are already formed. The 
irradiation by Galactic Cosmic Rays (GCR) of the 
(sub-)surface of icy objects can explain the character-
istics of specific organic components observed in car-
bon rich interplanetary dust such as UCAMMs [9,10]. 
The D/H ratio imaging performed on UCAMMs 
fragments reveals the spatial heterogeneities of the D 
excesses and the presence of distinct OM components 
(e.g. Fig 1 and [8,11]). A major component of 
UCAMM OM also exhibit N/C ratio substantially 
higher than that observed in insoluble organic matter 
(IOM) or bulk analysis from chondrites [9, 12-15]. A 
recent IR and Raman survey of eight UCAMMs con-
firmed that the OM components observed in 
UCAMMs are different from that of IOM extracted 
from carbonaceous chondrites [15]. The fact that 
some UCAMM OM components exhibit high N/C 
ratio (similar or even above the inferred value for the 
interstellar medium) while containing less O than 
meteoritic IOM requires a specific process involving 
the incorporation of substantial amounts of N in their 
organic component in a specific O poorer environ-
ment. This formation reservoir of UCAMMs has to be 
highly depleted in minerals to explain the unusually 
high C/Si of these particles.  
 
 
Figure 1 : Mosaic of NanoSIMs maps of the D/H 
ratio in an UCAMM fragment (DC94). Each square is 
50 x50 µm2. 
 
Large reservoirs of N2 and CH4 ices occur at the 
(sub-)surface of remote icy objects, as recently im-
aged by the New-Horizon space probe [16]. These 
ices endure irradiation by GCR. Recent experiments 
performed at the heavy ion accelerator in GANIL 
(Caen, France) demonstrated that irradiation of N2-
CH4 ices by such high-energy ions produces a N-rich 
refractory organic residue that could be the precursor 
of the OM observed in UCAMMs [10]. We pursued 
these experiments to: i) evaluate the D-enrichment 
levels induced by the irradiation of ices starting with a 
normal isotopic composition, and ii) study the charac-
teristic D/H spatial heterogeneities in an organic resi-
due produced by irradiation of an ice mixture includ-
ing an initial D-rich layer. These results are part of an 
article by Augé et al. in preparation [17].  
Irradiation experiments were performed at GANIL 
using the new experimental set-up IGLIAS [18] con-
sisting of an ultra-high vacuum chamber coupled to a 
cryogenic sample holder. Ice samples were deposited 
from CH4 and N2 gas condensation on IR-transparent 
windows. The first organic residue was obtained from 
irradiation of N2-CH4 (90:10) ices at 10K and exposed 
to 92 MeV Xe ion beam. The D/H ratio of the CH4 
2339.pdf50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132)
molecule of this first sample was measured and had a 
value of (126±1)x10-6 (i.e dDCH4=-189±2‰) slightly 
below the V-SMOW value. The second ice sample 
consisted of a very thin layer of CD4 ice deposited 
between two thicker layers of N2-CH4 (90:10) ices. It 
was exposed to 88 MeV Xe ion beam. The initial bulk 
D/H ratio of the D-rich ice sample (D/HIce2 = 
0.08 ± 0.02) was inferred using the integrated absorb-
ance of methane and heavy methane IR bands.  
Both mixtures were irradiated with a similar total 
dose of 19 eV.molecule-1, corresponding to about 100 
million years of exposure to GCR in the outer solar 
system. After irradiation of the ices, a slow warming-
up was performed to room temperature, and the resi-
dues were transferred under vacuum for NanoSIMS 
analyses at Institut Curie in Orsay. The samples were 
covered with 20 nm of gold for charge evacuation. 
The D/H was measured from CD-/CH- ratio imaging 
using a primary Cs+ ion beam at 16 keV using the 
high mass resolution protocol detailed in [19]. Multi-
stack scanning images were acquired over a field of 
view of 60x60 µm2 area, with a definition of 256 x 
256 pixels. The probe dwell time was 0.5 ms per pixel 
and the typical counting rate for CH- was 50 000 cs-1. 
The instrumental mass fractionation calibration was 
obtained using the procedure and the standards de-
scribed in [20].  
Results & Discussion : The D/H ratio of the resi-
due obtained after irradiation of the first ice sample 
(consisting in non-isotopically labelled N2-CH4 ices) 
revealed moderate D enrichment relative to V-SMOW  
value (dDRes1=150±100 ‰, i.e D/HRes1 = (180 ± 20) 
x10-6). As the initial ice was slightly depleted in D, 
this result indicate that the upper limit on the isotopic 
fractionation induced by irradiation is probably at 
most a few hundred ‰ (about 400‰). Although 
heavy ion irradiation may have induced a moderate 
increase of the D/H ratio in the organic refractory 
molecules, the resulting D/H ratio remains much 
smaller than that usually observed in D-rich compo-
nents of interplanetary OM and is not compatible with 
the large D-excesses observed in interplanetary dust 
particles or UCAMMs organics, implying that their 
hydrogen fractionation must be related to another 
process.  
The second sample (i.e the residue resulting from 
the D-rich ice mixture) does exhibit large D-
enrichments and pronounced D/H spatial heterogenei-
ties (Fig. 2). The average D/H ratio of the residue is 
D/HRes2 = 0.11 ± 0.01 that is, as expected, compatible 
with that of the original ice mixture (D/HIce2). How-
ever, large D/H heterogeneities are observed at the 
micron scale in this residue (Fig 2) demonstrating that 
that large spatial isotopic heterogeneities can result 
from irradiation of layers of ices with different D/H 
ratios. The fact that the residue exhibits such micron-
sized D-rich areas make irradiation of heterogeneous 
ices a promising process to reproduce the D/H ratio 
distribution observed in the OM of UCAMMs. This 
indicates that organics with highly heterogeneous D/H 
ratios can be obtained by irradiation of ices resulting 
from condensation of different gaseous reservoirs 
with distinct hydrogen isotopic composition at the 
surface of remote parent bodies from the outer solar 
system.  
 
 
 
Figure 2 : D/H ratio NanoSIMS image of the or-
ganic residue obtained by irradiation of an ice mixture 
including a D-rich layer [17]. The size of the image is 
60x60 µm2. 
 
Acknowledgements: This study was funded by 
several ANR projects (OGRESSE, IGLIAS and 
COMETOR), DIM-ACAV, CNES, CNRS (Défi 
Origines, PNP and PCMI). The field work at 
CONCORDIA station was supported by IPEV and 
PNRA.  
References: [1] Aikawa, Y., et al. A&A. 2002. 622-
632.; [2] Remusat, L., et al., EPSL 2006. 243: 15-25.; 
[3] Alexander, C.M.O.D., et al. Chemie der Erde / 
Geo., 2017. 77: 227-256.; [4] De Gregorio, B.T., et 
al., GCA 2010. 74: 4454-4470.; [5] Laurent, B., et al., 
Nature Com. 2015. 6.; [6] Gavilan, L., et al., ApJ 
2017. 840.; [7] Nakamura, T. et al., Meteoritics, 2005. 
40 Suppl #5046.; [8] Duprat, J., et al., Science 2010. 
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Bardin, N., et al., LPSC 2014. 45: 2647; [12] Yabuta, 
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2339.pdf50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132)


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ON THE ORIGIN OF ORGANICS IN ULTRACARBONACEOUS ANTARCTIC MICROMETEORITES (UCAMMS), IRRADIATION OF N-RICH ICES IN THE OUTER SOLAR SYSTEM

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