Organics in comet 67P – a first comparative analysis of mass spectra from ROSINA–DFMS, COSAC and Ptolemy

Abstract

The ESA Rosetta spacecraft followed comet 67P at a close distance for more than 2 yr. In addition, it deployed the lander Philae on to the surface of the comet. The (surface) composition of the comet is of great interest to understand the origin and evolution of comets. By combining measurements made on the comet itself and in the coma, we probe the nature of this surface material and compare it to remote sensing observations. We compare data from the double focusing mass spectrometer (DFMS) of the ROSINA experiment on ESA's Rosetta mission and previously published data from the two mass spectrometers COSAC (COmetary Sampling And Composition) and Ptolemy on the lander. The mass spectra of all three instruments show very similar patterns of mainly CHO-bearing molecules that sublimate at temperatures of 275 K. The DFMS data also show a great variety of CH-, CHN-, CHS-, CHO 2-and CHNO-bearing saturated and unsaturated species. Methyl isocyanate, propanal and glycol aldehyde suggested by the earlier analysis of the measured COSAC spectrum could not be confirmed. The presence of polyoxymethylene in the Ptolemy spectrum was found to be unlikely. However, the signature of the aromatic compound toluene was identified in DFMS and Ptolemy data. Comparison with remote sensing instruments confirms the complex nature of the organics on the surface of 67P, which is much more diverse than anticipated.

Formation of complex molecules in translucent clouds: acetaldehyde, vinyl alcohol, ketene, and ethanol via “nonenergetic” processing of C2H2ice

“…COM gas phase signatures have been unambiguously detected in various astronomical environments from massive sources in the Galactic Center to comets in our solar system (Herbst & van Dishoeck 2009;Biver et al 2014;Altwegg et al 2017;Herbst 2017 and references therein). Among ∼70 different COMs, which have been identified in the ISM, O-bearing COMs can conveniently be divided into two categories according to their chemical formulas; (1) C 2 H n O 2 , such as methyl formate (HCOOCH 3 ), glycol-aldehyde (HCOCH 2 OH), and ethylene glycol (HOCH 2 CH 2 OH), and (2) C 2 H n O, such as ketene (CH 2 CO), acetaldehyde (CH 3 CHO), ethanol (CH 3 CH 2 OH), and dimethyl ether (CH 3 OCH 3 ).…”

On the Synthesis of Chocolate Flavonoids (Propanols, Butanals) in the Interstellar Medium

“…Although future experiments have to be carried out to constrain the formation mechanisms of these COMs on the molecular level (Supporting Information), the present study embodies a significant first step toward elucidating possible abiotic pathways toward COMs carrying propyl (C 3 H 7 ) and butyl (C 4 H 9 ) groups with alcohol and aldehydes representing important redox systems in contemporary biochemistry on Earth. The identification of at least two C 3 H 8 O isomers (propanol, methyl ethyl ether) is fascinating as propanol has been detected on comet 67P/Churyumov‐Gerasimenko and tentatively identified toward Orion KL; methyl ethyl ether has also been detected, tentatively toward Orion KL with our experiments demonstrating that these isomers should be synthesized via a GCR mediated chemistry in the ISM as well. It is important to note that no simulation experiment worldwide can mimic the chemical complexity and diverse radiation environment of the ISM simultaneously; real interstellar grains are not only exposed to a range of energetic GCRs but also to UV photons.…”

“…Also, ion signals corresponding to 13 C 4 D 10 O + ( m / z= 88) and 13 C 5 D 10 O + ( m / z= 101) were detected; both of these molecular formulae contain isomers that are correlated with the taste and smell of chocolate along with possible molecules detected on comet 67P/Churyumov‐Gerasimenko, that is, i ‐butanol (C 4 H 10 O; (CH 3 ) 2 CHCH 2 OH) and 3‐pentanone (C 5 H 10 O; (C 2 H 5 ) 2 CO) (Figures S6 to S7) However, overlapping IEs of these isomers do not allow specific identifications. The 13 C 4 D 10 O + ion signal was narrowed to possibly contain i ‐butanol (IE=10.02±0.02 eV) and one or more of the following isomers: diethyl ether (IE=9.51±0.03 eV), n ‐propyl methyl ether (IE=9.41±0.07 eV), iso‐ propyl methyl ether (IE=9.45±0.04 eV) (Figure S6).…”

“…The i ‐butanol isomer could not be uniquely identified as another isomer, n ‐butanol ( 13 C 4 D 9 OD; IE=9.99±0.05 eV), has an overlapping IE. The ion signal corresponding to 13 C 5 D 10 O + remained even at a PI energy of 9.63 eV and therefore could be due to the isomer proposed to be part of the COMs on 67P/Churyumov‐Gerasimenko: 3‐pentanone (IE=9.31±0.02 eV) and/or the chocolate‐related molecule 2‐methyl butanal ( 13 CD 3 13 CD 2 ( 13 CD 3 ) 13 CD 13 CDO; IE=9.59±0.01 eV) (Figure S7) . However, multiple isomers with overlapping IEs exist making it impossible to uniquely identify either of those isomers (Supporting Information)…”

Rosetta Mission: Electron Scattering Cross Sections—Data Needs and Coverage in BEAMDB Database

“…The m/z 44 peak measured by COSAC was likely dominated by organic species, e.g., from acetaldehyde (C 2 H 4 O), formamide (HCONH 2 ) and acetamide (CH 3 CONH 2 ), whereas the peak measured by Ptolemy was interpreted to be mostly due to CO 2 . Recently, a comparison and comparative analysis of the Rosetta mass spectrometers (COSAC/Ptolemy/ROSINA) that puts some question mark on the presence of some of the nitrogen-bearing species was presented [9]. Ptolemy measurements confirmed many of the species observed by COSAC and through observation of regular peaks in the observed mass distributions indicated the presence of a sequence of compounds with additional -CH 2 -and -O-groups (mass/charge ratios 14 and 16, respectively) which confirms COSAC's observations of acetaldehyde and may be explained by the presence of a radiation-induced polymer at the surface.…”