Elemental and molecular abundances in comet 67P/Churyumov-Gerasimenko

Rubin, Martin; Altwegg, Kathrin; Balsiger, H.; Berthelier, Jean‐Jacques; Combi, M. R.; Keyser, Johan De; Drozdovskaya, M. N.; Fiethe, Björn; Fuselier, S. A.; Gasc, Sébastien; Gombosi, T. I.; Hänni, Nora; Hansen, K. C.; Mall, U.; Rème, H.; Schroeder, Isaac; Schuhmann, Markus; Sémon, Thierry; Waite, J. H.; Wampfler, S. F.; Würz, Peter

doi:10.1093/mnras/stz2086

Cited by 149 publications

(218 citation statements)

References 98 publications

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“…A detailed comparison with thermochemical disk models is necessary to distinguish between the two competing scenarios. Finally, the [CH 3 OH]/[H 2 CO] abundance ratio in all disks except HD 163296 is comparable with the wide range found for comets 67P/C-G, Hale-Bopp, and Lovejoy (∼0.65−8, Biver et al 2015;Rubin et al 2019), even though IRAS 04302 sits at the lower limit of that range. The comparison in Fig.…”

Section: Discussionsupporting

confidence: 77%

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

Podio

Garufi

Codella

et al. 2020

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The chemical composition of planets is inherited from that of the natal protoplanetary disk at the time of planet formation. Increasing observational evidence suggests that planet formation occurs in less than 1−2 Myr. This motivates the need for spatially resolved spectral observations of young Class I disks, as carried out by the ALMA chemical survey of Disk-Outflow sources in Taurus (ALMA-DOT). In the context of ALMA-DOT, we observe the edge-on disk around the Class I source IRAS 04302+2247 (the butterfly star) in the 1.3 mm continuum and five molecular lines. We report the first tentative detection of methanol (CH3OH) in a Class I disk and resolve, for the first time, the vertical structure of a disk with multiple molecular tracers. The bulk of the emission in the CO 2−1, CS 5−4, and o–H2CO 31, 2 − 21, 1 lines originates from the warm molecular layer, with the line intensity peaking at increasing disk heights, z, for increasing radial distances, r. Molecular emission is vertically stratified, with CO observed at larger disk heights (aperture z/r ∼ 0.41−0.45) compared to both CS and H2CO, which are nearly cospatial (z/r ∼ 0.21−0.28). In the outer midplane, the line emission decreases due to molecular freeze-out onto dust grains (freeze-out layer) by a factor of > 100 (CO) and 15 (CS). The H2CO emission decreases by a factor of only about 2, which is possibly due to H2CO formation on icy grains, followed by a nonthermal release into the gas phase. The inferred [CH3OH]/[H2CO] abundance ratio is 0.5−0.6, which is 1−2 orders of magnitude lower than for Class 0 hot corinos, and a factor ∼2.5 lower than the only other value inferred for a protoplanetary disk (in TW Hya, 1.3−1.7). Additionally, it is at the lower edge but still consistent with the values in comets. This may indicate that some chemical reprocessing occurs in disks before the formation of planets and comets.

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Section: Discussionsupporting

confidence: 77%

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

Podio

Garufi

Codella

et al. 2020

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“…For this period, the comet was at heliocentric distances smaller than 2 AU, the Sun in the southern hemisphere and before the close perihelion period with a lot of short lived outbursts. Measurements during this period yielded relative abundances of NH3/H2O = (0.66 ±0.20) % and HCN/H2O = (0.14 ± 0.04) %, respectively (18), in line with the average comet (1). From figure 1a it is evident that during perihelion the NH3/H2O ratio is higher than further from the Sun and that there is quite some scattering in the ratio, reaching values of almost 3 %, uncorrelated with latitude/season ( fig.…”

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confidence: 53%

“…We consider them "uncorrelated" to ammonium salt. (b) elemental abundances in comets Halley (red) and 67P (purple) for a refractory to ice ratio of 1:1, compared to the Sun, meteorites (C1, C2, and C3, refer to type 1, type 2, and type 3 carbonaceous chondrites) and the Earth (after Rubin et al (18)). N* denotes the nitrogen abundance if we assume that most of the nitrogen is in ammonium salt and the dust/ice ratio is 1:1 (see text for an explanation).…”

Section: Fig 4: Abundance Ratios Normalized To Watermentioning

confidence: 99%

Evidence of ammonium salts in comet 67P as explanation for the nitrogen depletion in cometary comae

et al. 2020

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Cometary comae are generally depleted in nitrogen. The main carriers for volatile nitrogen in comets are NH3 and HCN. It is known that ammonia readily combines with many acids like e.g. HCN, HNCO, HCOOH, etc. encountered in the interstellar medium as well as in cometary ice to form ammonium salts (NH4 + X -) at low temperatures. Ammonium salts, which can play a significant role in prebiotic chemistry, are hard to detect in space as they are unstable in the gas phase and their infrared signature is often hidden by thermal radiation or by e.g. OH in minerals. Here we report the presence of all possible sublimation products of five different ammonium salts at comet 67P/Churyumov-Gerasimenko measured by the ROSINA instrument on Rosetta. The relatively high sublimation temperatures of the salts leads to an apparent lack of volatile nitrogen in the coma. This then also explains the observed trend of higher NH3/H2O ratios with decreasing perihelion distances in comets. MainNitrogen in the volatile part of a comet nucleus is predominantly in the form of NH3 and HCN, which are on average (0.80 ± 0.20) % and (0.21 ± 0.02) %, respectively relative to water, e.g. (1). The numbers for HCN are somewhat uncertain as IR observations generally differ from radio observations (2). Apart from these two molecules, nitrogen bearing species have rather low abundances in comets (2). Especially, neutral N2 escaped detection before the Rosetta mission. Already in 1988, after the Giotto flyby at comet 1P/Halley, Geiss (3) recognized that, while carbon and oxygen relative to silicon are close to solar abundance, comet Halley was clearly lacking nitrogen. One explanation for this depletion at that time was the high volatility of N2, which may not have been condensed in the cometary ice or may have been lost in the last 4.6 Gy. For comet 67P / Churyumov-Gerasimenko (67P hereafter), neutral N2 has now been found on the level of (8.9 ± 2.4) × 10 -4 relative to water (~3 % relative to CO) (4). Recently, a high N2/CO ratio of 6% has been reported for comet C/2016 R2 (Pan-STARRS) (5). This shows that N2 is condensed and stored in cometary ice, but the reported abundances are by far not enough to explain the deficiency in nitrogen. N/C atomic ratio in the solar photosphere is about 0.3 ± 0.1 (6). In the refractory phase, comets are also depleted in nitrogen with N/C = 0.05 ± 0.03 in comet 1P (7) and N/C= 0.035 ± 0.011 in comet 67P (8).While the spread in relative abundances of HCN is quite small among comets, the variation for NH3 seems to be much larger (1). What is quite remarkable is the fact that comets with small perihelion distances seem to have much higher NH3/H2O values (1). This suggests that ammonia has a higher sublimation temperature in comets than water, although for pure ice sublimation temperatures are 90 K and 140 K, respectively. In comet D/2012 S1 (ISON) between 1.2 and 0.34 AU, Di Santi et al. (9) found an increase in NH3/H2O from < 0.78 % up to (3.5 ± 0.3) % and in addition a distribution of NH3, inconsistent with release from ...

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“…Separately listed are relative abundances of 67P/C-G from Table 2 measured by VIRTIS (range given by green boxes; Bockelée-Morvan et al 2016), MIRO (black;, and ROSINA (red, different isomers may be present, e.g. HCN cannot be distinguished from HNC with ROSINA; Rubin et al 2019a) Figure 1 shows in blue boxes the abundance range of commonly observed volatile species with respect to water in comets. Shown is a selected set of species detected in at least 3 comets aside from 67P/C-G.…”

Section: Abundances Of Volatile Species In Comets and Classificationmentioning

confidence: 99%

“…This period, when Rosetta was passing rather closely over the then-active southern summer hemisphere and outbursts were still limited (Vincent et al 2016), was identified by Calmonte et al (2016) to be suitable to estimate bulk abundances. This approach assumes that the high erosion rate of the comet leads to relative abundances of the gases in Table 2 Measured coma abundances or abundance ranges by number (in % normalized to water) for a suite of volatile molecules from in situ ROSINA observations in May/June 2015 before perihelion (Rubin et al (2019a) and references therein) and via remote sensing by MIRO, integrated over the 2 years Rosetta followed the comet , VIRTIS-H at perihelion (Bockelée-Morvan et al 2016), and Alice from ∼2 au inbound to 2.5 au outbound (Keeney et al 2017). Species observed by mass spectrometry may (also) be present in the form of different isomers (cf.…”

Section: P/c-g Abundances Of Volatiles and Refractoriesmentioning

confidence: 99%

On the Origin and Evolution of the Material in 67P/Churyumov-Gerasimenko

et al. 2020

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Primitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth-and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semivolatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further

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Elemental and molecular abundances in comet 67P/Churyumov-Gerasimenko

Cited by 149 publications

References 98 publications

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

Evidence of ammonium salts in comet 67P as explanation for the nitrogen depletion in cometary comae

On the Origin and Evolution of the Material in 67P/Churyumov-Gerasimenko

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