Molecular composition of comet 46P/Wirtanen from millimetre-wave spectroscopy
N. Biver, D. Bockelée-Morvan, J. Boissier, R. Moreno, J. Crovisier, D.C. Lis, P. Colom, M. Cordiner, S. Milam, N.X. Roth, B.P. Bonev, N. Dello Russo, R. Vervack, M. A. DiSanti
aa r X i v : . [ a s t r o - ph . E P ] F e b Astronomy & Astrophysicsmanuscript no. 40125final © ESO 2021February 26, 2021
Molecular composition of comet 46P/Wirtanen frommillimetre-wave spectroscopy ⋆ ⋆⋆
N. Biver , D. Bockelée-Morvan , J. Boissier , R. Moreno , J. Crovisier , D.C. Lis , P. Colom , M. Cordiner , , S.Milam , N.X. Roth , B.P. Bonev , N. Dello Russo , R. Vervack , and M. A. DiSanti LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen,F-92195 Meudon, France IRAM, 300, rue de la Piscine, F-38406 Saint Martin d’Hères, France Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA Solar System Exploration Division, Astrochemistry Laboratory Code 691, NASA-GSFC, Greenbelt, MD 20771, USA Department of Physics, Catholic University of America, Washington, DC 20064, USA Department of Physics, American University, Washington, DC, USA Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA Solar System Exploration Division, Planetary System Laboratory Code 693, NASA-GSFC, Greenbelt, MD 20771, USAFebruary 26, 2021
ABSTRACT
We present the results of a molecular survey of comet 46P / Wirtanen undertaken with the IRAM 30-m and NOEMA radio telescopesin December 2018. Observations at IRAM 30-m during the 12–18 Dec. period comprise a 2 mm spectral survey covering 25 GHzand a 1 mm survey covering 62 GHz. The gas outflow velocity and kinetic temperature have been accurately constrained by theobservations. We derive abundances of 11 molecules, some being identified remotely for the first time in a Jupiter-family comet,including complex organic molecules such as formamide, ethylene glycol, acetaldehyde, or ethanol. Sensitive upper limits on theabundances of 24 other molecules are obtained. The comet is found to be relatively rich in methanol (3.4% relative to water), butrelatively depleted in CO, CS, HNC, HNCO, and HCOOH.
Key words.
Comets: general – Comets: individual: 46P / Wirtanen – Radio lines: planetary system – Submillimeter: planetary system
1. Introduction
Comets are the most pristine remnants of the formation of theSolar System 4.6 billion years ago. They sample some of theoldest and most primitive material in the Solar System, includ-ing ices, and are thus our best window to the volatile com-position of the solar proto-planetary disk. Comets may alsohave played a role in the delivery of water and organic mate-rial to the early Earth (see Hartogh et al. 2011, and referencestherein). The latest simulations of the early Solar System’s evo-lution (Brasser & Morbidelli 2013; O’Brien et al. 2014) sug-gest a more complex scenario. On the one hand, ice-rich bodiesformed beyond Jupiter may have been implanted in the outer as-teroid belt and participated in the supply of water to the Earth, or,on the other hand, current comets coming from either the OortCloud or the scattered disk of the Kuiper belt may have formedin the same trans-Neptunian region, sampling the same diversityof formation conditions. Understanding the diversity in com-position and isotopic ratios of comet material is thus essentialin order to assess such scenarios (Altwegg & Bockelée-Morvan2003; Bockelée-Morvan et al. 2015). ⋆ Based on observations carried out with the IRAM-30m andNOEMA telescopes. IRAM is supported by INSU / CNRS (France),MPG (Germany), and IGN (Spain). ⋆⋆ The radio spectra are available at the CDS via anony-mous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp: // cdsweb.u-strasbg.fr / cgi-bin / qcat?J / A + A / . Comet 46P / Wirtanen is a Jupiter-family comet (JFC) orbit-ing the Sun in 5.4 years on a low inclination (11.7 ◦ ) orbit. Itreached perihelion on 12.9 Dec. 2018 UT at 1.055 au from theSun. It made its closest ever approach to the Earth on 16 Decem-ber at only 0.078 au. It remained within 0.1 au from the Earthfor three weeks, and this provided one of the best opportunitiesfor ground-based investigation of a Jupiter-family comet. Suchan orbit makes it well suited for spacecraft exploration, and 46Pwas the initial target of the ESA Rosetta mission, until it wasreplaced by comet 67P / Churyumov-Gerasimenko.We observed comet 46P with the Institut de RadioAs-tronomie Millimétrique (IRAM) 30-m telescope between 11.8and 18.1 Dec. 2018 UT, on 21.0, 25.2 and 25.8 Dec. UT with theNOrthern Extended Millimeter Array (NOEMA) and with theNançay radio telescope. In this paper, we report the detectionof a dozen of molecules and significant upper limits for nearlytwo dozen additional ones, obtained in single-dish mode. Sect. 2presents the observations and Sect. 3 presents the spectra of thedetected molecules. The information extracted from the obser-vations to analyse the data and compute production rates is pro-vided in Sect. 4. In Sect. 5, we discuss the uncertainties relatedto the molecular lifetimes and present the retrieved productionrates and abundances or upper limits, which are discussed andcompared to other comets in Sect. 6.
Article number, page 1 of 36 & Aproofs: manuscript no. 40125final
2. Observations of comet 46P/Wirtanen
Comet 46P / Wirtanen was observed around the time of its clos-est approach to the Sun and the Earth with several radio facil-ities (Nançay, IRAM, NOEMA, the Atacama Large Millime-ter / submillimeter Array (ALMA) and the Stratospheric Observa-tory for Infrared Astronomy (SOFIA)). We focus here on single-dish measurements obtained with the IRAM and NOEMA mil-limetre radio telescopes. The OH radical was observed with theNançay radio telescope between 1 Sept. 2018 and 28 Feb. 2019,and observations covering the period of interest are presentedin Sect. 4.3. ALMA data will be presented in a future paper(Biver et al. 2021), and SOFIA results are reported in Lis et al.(2019). Comet 46P / Wirtanen was the target of the observing proposal112-18 scheduled at the IRAM 30-m telescope between 11 and18 December 2018. Weather conditions were very good to av-erage, with precipitable water vapour (pwv) in the 0.4 to 8 mmrange (Table 1). The worst (cloudy) conditions were at the endof the 12 Dec. run (pwv up to 8 mm on 13.1 Dec. UT) followedby a day without observations. Around 17.0 Dec. UT, very lowopacity ( ∼ ′′ every 2 seconds.Comet 46P was tracked using the latest JPL / orbitalelements, and following orbit solutions, to compute a positionin real time with IRAM New Control System (NCS) software.Unfortunately, the proximity of the comet to the Earth (0.08 au)challenged the accuracy of the NCS software and resulted in anephemeris error of the order of 24 ′′ in R.A. and 10 ′′ in declina-tion, changing by a few arc-seconds from day to day. These ini-tial o ff sets were estimated from a map of HCN(3-2) on the firstday and used for the following days. The exact ephemeris errorwas computed afterwards from the comparison of the output ofthe NCS ephemeris and the JPL /
16 ephemeris solution. Thepointing was regularly checked on bright pointing sources (rms < ′′ ). Uranus pointing data were also used to check the beame ffi ciency of the antenna, and the beam size, which follows theformula θ ∼ /ν [GHz] in ′′ . Coarse maps obtained on HCN(e.g. Fig. 1), CH OH, and H S show an average residual o ff setbetween the maximum brightness and the target position of (-1 ′′ ,-1 ′′ ) that was used to compute the final average radial o ff setsgiven in Table A.1.We used the EMIR (Carter et al. 2012) 2 mm and 1 mm bandreceivers in 2SB mode connected to the FTS and VESPA high-resolution spectrometers (see Table 1). Comet 46P / Wirtanen was also observed with the NOEMA inter-ferometer on 21.0, 25.2, and 25.8 Dec. UT, as part of the pro-posal W18AB, at 3 mm, 1 mm, and 2 mm wavelengths. Here,we only report the ON-OFF position switching data obtainedduring part of these observations for the zero-spacing informa-tion needed to analyse interferometric data. The versatile Polyfixcorrelator was used to target some dedicated molecular lines inaddition to the continuum, and here we analyse the spectra of thelines detected in this autocorrelation mode. The frequency cov- https: // ssd.jpl.nasa.gov / horizons.cgi Fig. 1.
Map of HCN(3-2) line-integrated intensity in comet46P / Wirtanen on 17.82 Dec. 2018. O ff sets are relative to JPL / − . erage and total integration time (adding up the 8 to 10 antennas)is provided in Table 1.
3. Spectra and line intensities
A sample of IRAM spectra at 1 mm and 2 mm is shown inFigs. 2–3. These are averages over the six nights of observations,sampling most of the detected species in the two wavelength-domains. For some species, the spectra are the weighted aver-ages of several lines to increase the signal-to-noise ratio (S / N),with a weight inferred from to the noise of individual spectra.Spectra are aligned on the velocity scale to provide informationon the line shape. However, the computation of production rateis not based on the average line intensity but on the weighted av-erage of the production rates derived from each individual line(the weight is larger for the lines expected to be the strongest).Full spectra are shown in the appendix (Figure B-C.1). Exam-ples of CH OH lines used to derive the gas temperature are alsoshown in Figs. 4 and 5. Only spectra obtained at pointing o ff set < ′′ are shown.Line intensities are given in Tables 2 and A.1, including val-ues obtained at the o ff set position (radial averages). Table 2 fo-cuses on species for which several individual lines, eventuallygrouped by series probing levels of similar energy, were aver-aged. We also provide, for other molecules, the average intensityor upper limits for non-detections. Where individual lines are notdetected, we selected the strongest transitions that are expectedto have a similar intensity for the averages (within a factor of 2to 3).
4. Data analysis
We used the line profiles with the highest S / N and those ofCH OH obtained with the high spectral resolution (40 kHz)VESPA spectrometer (e.g. Figs 2,3). As lines are often double-peaked or asymmetric, we fitted two Gaussians, one to each ofthe blueshifted ( v <
0) and redshifted ( v >
0) peaks. The veloc-ity of the channel at half the maximum intensity (
VHM ) of thesefits provides a good estimate of the expansion velocity, towards
Article number, page 2 of 36iver et al.: Composition of comet 46P / Wirtanen
Table 1.
Log of millimetre observations.
UT date < r h > < ∆ > Tel. Integ. time pwv a Freq. range(yyyy / mm / dd.d–dd.d) (au) (au) (min) b (mm) (GHz)2018 / / / / / / / / / / / / / / + / / + + + + + + + / / + + + + Notes. ( a ) Mean precipitable water vapour in the atmosphere above the telescope. ( b ) Total (o ff set positions included) integration time (ON + OFF) on the source (adding 10, 8, and 9 antennas, respectively, for NOEMA).
Fig. 2.
Molecular lines observed in comet 46P / Wirtanen between 11.9and 18.1 Dec. 2018. For some complex organics, we averaged severallines between 210 and 272 GHz (1 mm wavelength band). The verticalscale is the main beam brightness temperature and the horizontal scaleis the Doppler velocity in the comet rest frame. the observer for the negative-velocity (blueshifted) side and forthe gas moving in the opposite direction for the positive-velocity(redshifted) side. We found the following for the velocities athalf the maximum intensity (
VHM ): – VHM (HCN(3-2)) = − . ± .
01 and + . ± .
01 km s − ; Fig. 3.
Molecular lines observed in comet 46P / Wirtanen between 11.9and 18.1 Dec. 2018 in the 2 mm band, except for HC N and OCS, forwhich we show the weighted average of five lines expected in the 1 mmband. For some complex organics, we averaged several lines between147 and 170 GHz (2 mm wavelength). The vertical scale is the mainbeam brightness temperature and the horizontal scale is the Dopplervelocity in the comet rest frame. – VHM (H S(1 − )) = − . ± .
02 and + . ± . − ; Article number, page 3 of 36 & Aproofs: manuscript no. 40125final
Table 2.
Line intensities from IRAM observations: multi-line averages.
Molecule Transitions Frequency Pointing o ff set IntensityN a J Ka , Kcb range [GHz] [ ′′ ] Average [mK km s − ]NH CHO 2 8 , + , . ± . CHO 3 10 , + , + , . ± . CHO 5 10 , Kc + , Kc + , Kc . ± . CHO 5 11 , + , Kc + , Kc . ± . CHO 5 11 , Kc + , Kc + , Kc . ± . CHO 5 12 , + , Kc + , Kc . ± . CHO 5 12 , Kc + , Kc + , Kc . ± . CHO 2 13 , + , . ± . CHO 30 J Ka , Kc , J = = . ± . < . CHO 6 8 , + , + , . ± . CHO 6 11 , + , + , . ± . CHO 10 12 , + , Kc + , Kc . ± . CHO 8 12 , Kc + , Kc . ± . CHO 10 13 , + , Kc + , Kc . ± . CHO 8 13 , Kc + , Kc . ± . CHO 6 13 , Kc + , Kc . ± . CHO 6 14 , + , + , . ± . CHO 4 14 , + , . ± . CHO 32 J Ka , Kc , J = = . ± . . ± . . ± . H OH 11 J Ka , Kc , J = = . ± . H OH 26 J Ka , Kc , J = . ± . H OH 65 J Ka , Kc , J = . ± . OH) J Ka , Kc ,J = = . ± . OH) J Ka , Kc ,J = = . ± . . ± . CS 3 7 + + ± N 2 17-16 + ± N 6 24-23 to 29-28 218–264 1.7 6 ± ± , + , + , ± J , Kc and J , Kc , J = . ± . J Ka , Kc :J = <
3; J = < . ± . H CN 14 J Ka , Kc ,J = = . ± . H CN 61 J Ka , Kc ,J = = . ± . H CN 13 J Ka , Kc ,J = < . H CN 40 J Ka , Kc ,J = < . COCH J Ka , Kc < . COOH 52 J Ka , Kc < . NH J Ka , Kc ,J = = . ± . / / ± Notes. ( a ) Number of lines averaged ( b ) J Ka , Kc quantum numbers of the upper level of the transitions, with range of values, or J up − J low for OCS, HC N, or PO. – VHM (CH OH(6 lines 165-266GHz)) = − . ± .
01 and + . ± .
02 km s − .On average, this suggests an expansion velocity of0.85 km s − on the observer or day side and 0.45 km s − onthe anti-observer or night side. For HCN, for example, if wemodel an hemispheric day side outgassing at 0.85 km s − andoutgassing at 0.45 km s − separately in the other hemisphere,to retrieve the observed Doppler shift ( − .
17 km s − ) we need aproduction rate ratio Q day / Q night = .
3. The corresponding totalproduction rate ( Q day + Q night ) is only 2 ±
2% higher than thevalue found when assuming isotropic outgassing at a velocity of0.65 km s − . Since modelling an asymmetric outgassing patterndoes not significantly change the retrieved total outgassingrates, to compute the production rates we assumed isotropicoutgassing at the mean velocity, that is, 0.65 km s − . Many series of lines (especially of methanol but also CH CN)were detected at several times during the observations. Exam-ples of these data as well as rotational diagrams are shown inFigs. 2-5 and Figs. 6-8, respectively. Inferred rotational temper-atures T rot are given in Table 3. For each of these measurements,we retrieve constraints on the gas temperature, T gas , needed toobtain such rotational temperatures. For some series of transi-tions, such as the CH OH lines at 165 or 252 GHz, T gas is closeand proportional to T rot . For CH CN, our code (e.g. Biver et al.1999, 2006) predicts T = T rot , but for species like H S thereis a large di ff erence due to rapid radiative decay of the levels’population in the inner coma. The evolution of T rot with nu-cleocentric distance (400–1500 km) does not show any trend(Fig. 9). A decrease of T rot (CH OH 242GHz) and a smaller onefor T rot (CH OH 252GHz) is expected and compatible with ob-
Article number, page 4 of 36iver et al.: Composition of comet 46P / Wirtanen
Fig. 4.
Series of methanol lines around 242 GHz observed in comet46P / Wirtanen between 12.0 and 17.9 Dec. 2018. The vertical scale isthe main beam brightness temperature, and the horizontal scale is theDoppler velocity in the comet rest frame and frequency in the cometframe on the upper scale.
Fig. 5.
Series of methanol lines around 252 GHz observed in comet46P / Wirtanen between 11.8 and 17.8 Dec. 2018. The vertical scale isthe main beam brightness temperature, and the horizontal scale is theDoppler velocity in the comet rest frame and frequency in the cometframe on the upper scale. servations. In Fig. 10, we also plotted the retrieved T gas temper-atures for the daily measurements from Table 3. The decrease ofthe gas temperature with radial distance from the nucleus wouldlikely explain the systematically higher T gas deduced from the252 GHz lines. There might also be a longer week-long trend,but the adopted T gas =
60 K value is within ∼ − σ of all valuesin Table 3. A ±
10 K variation of the gas temperature will not im-pact the production rates by more than ± −
10% (using severallines to retrieve the production rate of a molecule decreases theimpact).We also performed the rotation diagram analysis indepen-dently for the blue-shifted and red-shifted components of thelines. We derive the corresponding Earth ( ∼ day) side and op-posite ( ∼ night) rotational temperature for the average of theCH OH lines at 165 or 252 GHz. There is no day / night asymme-try based on the 165 GHz lines (beam ≈
900 km), but the 252 GHzlines that probe the gas closer ( <
600 km) to the nucleus do showa higher night-gas temperature (Table 3), an e ff ect observed in Fig. 6.
Rotational diagram of the 13–17 Dec. average of the methanollines around 166 GHz in comet 46P / Wirtanen. The neperian logarithmof a quantity proportional to the line intensity is plotted against the en-ergy of the upper level of each transition. Fit is shown by solid red lineand errors are displayed by red dashed lines. The black dots are themeasurements and green circles the predicted values for a model with agas temperature of 60 K.
Fig. 7.
Same as for Fig. 6, but for the 252 GHz lines of methanol ob-served between 11.8 and 17.8 Dec. UT. situ in the coma of comet 67P (Biver & Bockelée-Morvan 2019)that can be explained as a less e ffi cient adiabatic cooling on thenight side where the outgassing rate is lower.Infrared observations (Bonev et al. 2020; Khan et al. 2020)that probed the coma closer to the nucleus (within 50 km) foundhigher gas temperatures (80–90 K) decreasing slightly with pro-jected distance to the nucleus (100–200 km, Bonev et al. 2020)down to values closer to ours (Figs. 9 and 10). This is often thecase when comparing ground-based radio and infrared measure-ments, indicative of some degree of adiabatic cooling betweenthe distances probed by the two techniques. We used the water production rates derived from the observa-tion of the H
O line with the SOFIA airborne observatory –assuming O / O =
500 (Lis et al. 2019). These observationswere obtained with a somewhat larger beam (50 ′′ ; althoughsmaller than the Nançay or SWAN fields of view) but cover Article number, page 5 of 36 & Aproofs: manuscript no. 40125final
Fig. 8.
Same as for Fig. 6, but for the 257 GHz lines of CH CN observedbetween 12.0 and 17.9 Dec. UT.
Fig. 9.
Plot of all rotational temperatures as a function of the projectedpointing o ff set and beam size (indicating which region of the coma isprobed). Most values are compatible with a constant gas temperature of ≈
60 K throughout the coma. This includes some low rotational temper-ature values such as that derived for H S lines, of which the rotationallevels are not expected to be thermalised. the same period (14–20 Dec. 2018) and were analysed with thesame numerical codes. The average value of Q H O = . × molec. s − was used for the computation of excitation con-ditions (collisions) and relative abundances. Water productionrates measured from infrared observations at the same time(Bonev et al. 2020) yield about the same value. The measure-ments of Combi et al. (2020) of Lyman- α emission with theSOHO / SWAN experiment do not cover the period of closest ap-proach to the Earth, but derived Q H O = . × molec. s − on10.9 Dec. 2018.We also tried to detect directly the H O(3 − ) line at183.3 GHz (Fig. B.1) during a period of very good weatherat IRAM, but we could not integrate long enough and theweather proved too marginal for this observation. In additionthe calibration uncertainty is likely large at this frequency( ±
50% probably): on the one hand the HCN(2-1) line in thesame band and a methanol line yield a correct productionrate, but on the other hand the water maser line observedin Orion spectra acquired for calibration purposes is some-what stronger than expected. We obtain a 3 − σ upper limit Table 3.
Rotational temperatures and inferred gas kinetic temperatures.
UT Molecule Freq. range lines o ff . a T rotb T gas (dd.d) (GHz) c ( ′′ ) (K) (K)11.9 CH OH 250-254 22 1.7 61 . ± . ± OH 241.8 14 1.7 44 . ± . ± OH 250-254 22 1.6 55 . ± . ± OH 213-230 4 1.0 63 ±
13 56 ± OH 165-169 10 1.4 54 . ± . ± OH 250-254 22 3.1 56 . ± . ± OH 241.8 14 1.8 43 . ± . ± OH 250-254 18 2.0 62 . ± . ± OH 165-169 10 1.4 49 . ± . ± OH 250-254 21 1.1 72 . ± . ± OH 165-169 10 2.2 55 . ± . ± OH 213-230 4 0.7 57 . ± . ± OH 165-169 9 1.4 52 . ± . ± OH 241.8 14 2.0 48 . ± . ± OH 250-254 22 1.3 74 . ± . ± OH 241.8 14 1.2 50 . ± . ± OH 165 3 3 43 . ± . ± ≈ OH 166 10 1.7 53 . ± . ±
210 3.8 62 . ± . ±
810 9.5 45 . ± . ±
510 11.4 70 ±
15 73 ± OH 213-234 5 0.9 62 . ± . ± OH 218-239 5 1.7 39 . ± . ± OH 242 14 1.7 47 . ± . ±
214 9.7 37 . ± . ± . ± . < OH 252 28 2.1 61 . ± . ±
222 8.9 63 . ± . ±
920 11.7 62 . ± . ±
920 15.9 44 . ± . ± ±
17 90 ± OH 250-267 5 2.1 58 . ± . ±
25 8.9 52 . ± . ± CN 165.4 5 1.7 79 + − − CN 257.3 5 1.7 62 ±
15 47 − S 169,216 2 2 19 . ± . ∼ CHO 149-270 68 1–2 67 + − − ≈ v < OH 252 28 2.1 57 . ± . ± OH 165 10 1.7 53 . ± . ± ≈ v > OH 252 27 2.1 71 . ± . ± OH 165 10 1.7 52 . ± . ± Notes. ( a ) Mean pointing o ff set. ( b ) Result of non-linear fit with χ minimisation. ( c ) Number of lines used for the determination of T rot . Q H O < × molec. s − , which is a factor ∼ Article number, page 6 of 36iver et al.: Composition of comet 46P / Wirtanen
Fig. 10.
Plot of daily gas temperatures T gas derived from the methanolrotational lines around 167, 213-230, 242, and 252 GHz as presented inthe first part of Table 3. Variations cannot be related to the rotation ofthe nucleus (when folded on a single 9 h period). Most of the dispersionis due to the di ff erent series of methanol lines used: the 252 GHz onessample a smaller region than the others and keep memory of T gas atlarger cometocentric distances than those at 242 GHz. The OH 18-cm lines were observed in 46P with the Nançay ra-dio telescope from 12 to 20 December, thanks to a small positiveinversion of the OH maser. The OH inversion peaked on 16 De-cember when the heliocentric radial velocity was 1.0 km s − , at0.040 according to Despois et al. (1981) or at 0.099 based onSchleicher & A’Hearn (1988).The time-averaged spectrum is shown in Fig. 11. An emis-sion line is definitely detected. The corresponding OH produc-tion rate is 1 . ± . × molec. s − using our nominal modelwith quenching (see Crovisier et al. 2002) and the inversion ofDespois et al. For the inversion of Schleicher & A’Hearn, theproduction rate is lowered to 0 . ± . × molec. s − . Thesevalues, although imprecise due to the uncertainty on the OH ex-citation, are in line with the other measurements of the waterproduction rate.The OH line is observed to be unusually narrow with aFWHM of 1 . ± . − . This is comparable to the line widthsobserved for parent molecules (Sect. 4.1) and may be due to thethermalisation of the OH radical in the near-nucleus region. Thismay also be due to the Greenstein e ff ect, which is the di ff erentialSwings e ff ect within the coma (Greenstein 1958). For the geom-etry of the observation and the OH inversion as a function of theheliocentric radial velocity, the expected OH inversion signifi-cantly drops for OH radicals at, for example, ± − radialvelocity.
5. Production rates and abundances
We determine the production rate or an upper limit for 35molecules. We assumed that all species follow a parent or daugh-ter Haser density distribution with a destruction scale length, asdiscussed in the next section and listed in Table 4. CS and SOare assumed to come from the photo-dissociation of CS andSO , respectively. H CO, as specified in Table 6, is assumed tocome from a distributed source with a scale length of 5000 km(Biver et al. 1999), which fits observations obtained at variouso ff sets and with di ff erent beam sizes (lines observed at 2 mm Fig. 11.
Eighteen-centimetre OH line of comet 46P / Wirtanen observedwith the Nançay radio telescope from 12 to 20 Dec. 2018. The 1665and 1667 MHz lines, both circular polarisations scaled to the 1667 MHzline, have been averaged. and 1 mm wavelengths). All production rates are provided in Ta-bles 5 and 6.
One major source of uncertainty for the abundance of several(complex) molecules is their photo-destruction rate (dissocia-tion and ionisation). For a molecule with a short lifetime, theuncertainty in the retrieved production rate can be as large as theuncertainty in the photo-destruction rate, but thanks to the prox-imity of comet 46P / Wirtanen to the Earth (0.08 au), the smallbeam size of IRAM mostly probed ‘young’ molecules: 90% ofthe signal comes from molecules younger than ≈ . × s,which should reduce the impact of the uncertainty in their pho-tolytic lifetime. In addition, the solar activity was close to a deepminimum, which caused the photo-dissociation rates to be closeto their minimum values and reduced other e ff ects such as, forexample, dissociative impact from ions.Table 4 summarises the latest information available on thelifetime of these molecules and the values that we adopted.For some well-observed molecules, we applied a solar-activity-dependent correction based on the 10.7-cm solar flux unit (70 sfuon average for the period, mostly representative of the ‘quiet’Sun) as in Crovisier (1989). For several molecules, there is alarge range of published values for their photo-destruction rate,or no values at all. For detected molecules, we can also ob-tain some constraints from their line shape. Since the expan-sion velocity generally increases with distance from the nu-cleus (e.g. acceleration due to photolytic heating), moleculeswith longer lifetimes will likely exhibit broader lines. This wasclearly evidenced for comets at small heliocentric distances(Biver et al. 2011). Table 4 and details hereafter provide someloose constraints we can derive for some molecules. Observa-tional data used for this purpose are presented in Appendix D.The H S, HCN, and CH OH molecules have well establishedphoto-dissociation rates, which can be used as references. Wenote that radiative excitation can also a ff ect the line width, forexample if the upper rotational state of the observed transitionis depopulated at a faster rate than it is modelled. However,in that case a bias in the lifetime compensates for the weak-ness of the excitation model. For secondary species such as CS,SO, and H CO, on the other hand, any excess energy converted
Article number, page 7 of 36 & Aproofs: manuscript no. 40125final into velocity might a ff ect the line shape, especially outside thecollision-dominated region. HC N : in Biver et al. (2011), cyanoacetylene clearlyshowed a narrower line than HCN, CH OH, and CS becauseof its shorter lifetime. It was detected with a high resolu-tion and high S / N in the comet Hale-Bopp in April-May 1997(Bockelée-Morvan et al. 2000), but its line shape did not suggesta much shorter lifetime than HCN or CH OH, while the meanwidth of HC N line is closer to that of H S in comet C / CH CN : methyl cyanide has a relatively long lifetime ac-cording to Crovisier (1994) and Heays et al. (2017), but mostobservations, including those of 46P (Figure 3,2, Table D.1),show lines with widths similar to or slightly smaller than those ofHCN or methanol. This suggests that its photo-destruction ratemight be a few times larger than assumed, although this does nota ff ect the retrieved production rate in comet 46P. In addition therotational and derived kinetic temperature of CH CN is most of-ten comparable to or higher than the one derived from CH OH(Fig. 9), again suggesting that the CH CN lines might probe theinner coma more, which is compatible with a shorter lifetime.Assuming β = × − s − for the observations of comet 46Pwill not increase the production rate by more than 2%, which isnegligible. NH CHO: the lifetime of formamide is poorly known, butconstraints from observations already discussed in Biver et al.(2014) and from line widths do suggest that its photo-destructionrate from Heays et al. (2017), similarly to the value we adopted,is a good estimate.
CO: the lifetime of carbon monoxide is very long, but theCO line never shows a width larger than the species with a photo-dissociation rate around β = − s − . Rather than an underesti-mation of its photo-ionisation or dissociation rate, this might bethe result of, for example, a low translational collisional cross-section, which would make CO less sensitive to gas accelerationby photolytic heating, given the small size and dipole moment ofthe molecule. CH CHO: acetaldehyde has now been detected in sixcomets, and in all cases the width of the CH CHO lines issmaller than those of HCN and CH OH but slightly largerthan that of H S. Huebner & Mukherjee (2015) and Heays et al.(2017) suggested higher photo-destruction rates ( β = × − s − ) than the one we have used so far (Crovisier et al.2004a), but it is compatible with the observations. This might in-crease the retrieved abundance in comets observed further awayfrom the Earth, but for comet 46P it only increases it by ∼ / CHO is shorter than assumed, this might alsosignificantly increase its abundance as it gets closer to the Sun,and this would need to be explained.
HCOOH: there are few observations of formic acid witha good S / N (mostly in Hale-Bopp and C / S, so its photo-destruction rate might be closer to β = × − s − , but it is likely not as large as was suggested byHuebner & Mukherjee (2015). Using this value or the one ofCrovisier (1994) does not a ff ect the abundance determinationin 46P, but if we use β = × − s − instead, as suggested byHuebner & Mukherjee (2015), the limit on the abundance in 46Pis 40% higher, and likely to be much higher in other comets. (CH OH) : ethylene glycol has an unknown lifetime, butsince the first identification of this molecule in a comet (Crovisier et al. 2004a), we used β = × − s − . There are fewhigh spectral resolution detections with a good S / N. Biver et al.(2014, 2015) and Biver & Bockelée-Morvan (2019) show the av-erage of several lines in a few comets: the line shape is gen-erally narrower than it is for HCN and CH OH, but the uncer-tainty is too large for definite conclusions – except in C / / β = × − s − for comet 46P will not change the retrievedproduction rate. H CS: thioformaldehyde was first detected through a singleline in the comet Hale-Bopp (Woodney et al. 1999). Since thattime, it has only been observed with su ffi cient spectral resolutionand S / N in the comet C / ffi cient to accurately measure the line width. The linewidth seems barely larger than the H S one. Therefore, in theabsence of any photolysis information, a lifetime comparable toor a bit longer than H S looks like a reasonable assumption. CH NH : methylamine has not yet been detected re-motely in comets. We assumed β = × − s − inBiver & Bockelée-Morvan (2019), which is comparable to thevalue from Heays et al. (2017) but lower than the one referred toin Crovisier (1994). CH SH: methanethiol (or methyl mercaptan) has only beendetected in situ in comet 67P with an abundance relative to wa-ter of 0.04% (Rubin et al. 2019). In Crovisier et al. (2004a), weassumed a photo-dissociation rate β = − s − , whereas recentevaluations give values 25 × or 3 × higher (Huebner & Mukherjee2015; Heays et al. 2017), with some confidence. With such shortlifetimes, the assumed value of β (CH SH) will directly impactthe retrieved abundance. We will use β = × − s − . Withthe Huebner & Mukherjee (2015) value, which is 5 × higher, theretrieved production rate (upper limit) would be a factor of 2higher.For other molecules, either the available photo-destructionrates are compatible with observations, or no information at all isavailable and we must rely on a priori values β = − × − s − as used in some previous studies (e.g. Crovisier et al. 2004a,b)generally based on similar molecules. Figure E.1 can be used toinfer the change of column density and inversely the productionrate, due to a change in the photo-destruction rate. As we observed several molecules regularly (such as HCN,which was mapped daily to check the pointing, or CH OH,which shows lines in every observing setup), we also looked fordaily variations of the activity. Table 5 provides the derived pro-duction rates for each time interval, corresponding to 1–2 h in-tegration on a specific observing setup. The values are derivedfrom both the on-nucleus pointing and o ff set positions when theS / Ns are high enough (e.g. HCN). Production rates are givenfor the four molecules (HCN, CH OH, CH CN, and H S) thatare detected with su ffi cient S / Ns at di ff erent epochs. Productionrates as a function of time are shown in Fig. 12. Time variationsdo not exceed ± −
30% from the average value. An appar-ent rotation period of ≈ Article number, page 8 of 36iver et al.: Composition of comet 46P / Wirtanen
Table 4.
Photo-dissociation + photo-ionisation rates of the molecules at r h = Molecule Photo-dissociation + photo-ionisation rate [ × − s − ]C1994 a H2015 b H2017 c Adopted d Comets e H O 1.3 1.21–2.20 N 6.6 3.92–6.79 3.7 6.6 2–10CH CN 0.67 1.12–2.63 CHO 67 – ∼ NH
67 – H CN – 2C H CN – 2CH OH 1.3 1.14-2.07 CO 20 21–22 19.3 20.0 1–8 f CO 0.075 0.075–0.188 < . CHO 7.5 17.9–18.2 H OH 1.8 – OH) – 2–5 3–10HCOOCH OHCHO – 2CH CO 44 – 44CH COOH 5.1 – 5.1CH OCH COCH – 5.0c-C H O – 10H S 25 32.6–26.8 g H CS – 20 h ∼ f SO
21 25–28 SH 250–253 32.6 50NS – 5 i Glycine – 1000 j PH Notes. ( a ) From Crovisier (1994) and references therein. ( b ) For the quiet and active Sun from Huebner & Mukherjee (2015). ( c ) Solar value from Heays et al. (2017): values given in bold have anuncertainty below 30%, and values in italics have an uncertainty largerthan a factor of 2. d Assumed values with no constraint are in italics. e Constraints obtained from line width (see text, Appendix D, and e.g.Biver et al. (2011)). f For H CO and SO, the constraint from line width is on the combinedscale length of parent + daughter. For SO, it is compatible with theassumed SO and SO lifetimes (see also Boissier et al. (2007)). g Estimate from Biver et al. (2011). h Value proposed by Woodney et al. (1999). i Centre of the range proposed by Irvine et al. (2000), which isestimated from the analogy between NS and NO and the fact thatsulphur species have shorter lifetimes. j Value used in Hadraoui et al. (2019).
Fig. 12.
Evolution of production rates in comet 46P / Wirtanen between12 and 25 Dec. 2019 (perihelion was on 12.9 Dec.) for the nine mainmolecules. Downward-pointing empty triangles are 3- σ upper lim-its. Coloured symbols are in the vertical order of the correspondingmolecules’ names on the right. Water production rates have been com-puted from data in Lis et al. (2019). Table 6 lists a large number of upper limits on the production rateof various molecules of interest. Besides the detection of somecomplex organic molecules (Biver & Bockelée-Morvan 2019),these observations were also the most sensitive ones ever under-taken in a Jupiter-family comet. In most cases, we only took intoaccount collisions and radiative decay to compute the excitation.We did not take into account infrared pumping via the rotationalbands. The comet was not very active, so the collision regionwas not large, but due to its proximity to the Earth (0.08 au), theIRAM beam was still probing regions (within 1000 km) unlikelyto be a ff ected by infrared pumping. As discussed in Sect. 5.1, weprobed molecules younger than about 2500 s so that any radia-tive (IR-pumping, photo-destruction) process that takes longer(g-factor, β < × − s − ) would not significantly a ff ect theexpected signal and derived production rate. The correspondingupper limits in abundances relative to water are given in Table 7. Table 7 provides the mean abundances relative to water or up-per limits derived from this study. Table 7 also lists values
Article number, page 9 of 36 & Aproofs: manuscript no. 40125final
Table 5.
Daily production rates in comet 46P in December 2018.
UT day r h Production rate Q [ × molec. s − ][dd.dd] [au] HCN CH OH H S CH CN11.89 1.055 0 . ± .
01 21 . ± . . ± . . ± . . ± . . ± . . ± .
01 26 . ± . . ± . . ± . . ± . . ± . . ± . . ± .
01 26 . ± . . ± . . ± . . ± . . ± . . ± .
03 28 . ± . . ± . . ± . . ± . . ± . . ± . . ± .
02 25 . ± . . ± . . ± . . ± . . ± . . ± . . ± .
06 20 . ± . . ± . . ± . . ± . . ± . . ± .
02 24 . ± . . ± . . ± . . ± . . ± . . ± . . ± . . ± . . ± . . ± . . ± . / Wirtanensince the technique was often very di ff erent. In comet 67P,for some of the main species (e.g. CO, HCN, CH OH, H S)Läuter et al. (2020) or Biver et al. (2019) derived relative bulkabundances from the integration of molecular loss over twoyears. They also use di ff erent techniques: numerous local sam-plings by mass spectroscopy (with the Rosetta Orbiter Spec-trometer for Ion and Neutral Analysis – ROSINA) vs. sub-millimetre mapping of the whole coma of some transitions (withthe Microwave Instrument for the Rosetta Orbiter – MIRO), andthey show some discrepancies. For species of lower abundances,mass spectroscopy with ROSINA is mostly based on specificobserving campaigns at specific times (e.g. before perihelion,Rubin et al. 2019) and may not be representative of the bulkabundance of the species. Most complex organic molecules seemto be depleted in comet 67P, which could be due to this observa-tional bias, or it could be more specific to 67P. Comet 46P hasa composition quite comparable to most comets, although somespecies such as HC N, HNCO, HNC, CS, and SO seem to berelatively under-abundant. The proximity to the Earth of comet 46P / Wirtanen o ff ered arare opportunity to attempt measurements of isotopic ratios ina Jupiter-family comet. However, limited information was ob-tained due to the relatively low activity level of the comet. Thederived upper limit for the deuterium-to-hydrogen ratio (D / H)in water (Table 8) is five times higher than the D / H value of1 . ± . × − measured with SOFIA from the detection of the 509 GHz HDO line (Lis et al. 2019). Only H S could beclearly detected (Fig. 13). The S / S in H S and the limits ob-tained in comet 46P for other isotopologues, with comparison toother references, are provided in Table 8. The S / S in H S iscompatible with the terrestrial value. HC N shows a marginal3 − σ signal both in the FTS and VESPA backends leading to N / N = ±
26. This is significantly lower than the mean value( ≈
6. Discussion and conclusion
Comet 46P / Wirtanen was the target of a worldwide observ-ing campaign in December 2018. It was observed withother millimetre-to-sub-millimetre facilities such as JCMT(Coulson et al. 2020), ALMA (Roth et al. 2020; Biver et al.2021), and the Purple Mountain Observatory (Wang et al. 2020),which yield similar abundances. The short-term variation of themethanol line shifts and intensity, likely related to nucleus rota-tion, are observed in ALMA data (Roth et al. 2020, 2021).Other observations (Moulane et al. 2019; Handzlik et al.2019) suggest an excited rotation state of the nucleus with a pri-mary period around 9 h at the time of the observations. The tem-poral sampling of our data set does not allow us to investigatetime variations related to nucleus rotation. Infrared observationsof comet 46P / Wirtanen (Dello Russo et al. 2019; Bonev et al.2020; Khan et al. 2020) with the IRTF and Keck Telescope wereobtained at similar times: they find similar methanol productionrates, and that, compared to mean abundances measured among https: // wirtanen.astro.umd.edu / Article number, page 10 of 36iver et al.: Composition of comet 46P / Wirtanen
Fig. 13. H S(1 − ) line at 167910.516 MHz together with themain isotopologue H S line divided by 10 and observed in the sameFTS spectrum between 13.0 and 17.0 Dec. 2018. The vertical scale isthe main beam brightness temperature, and the horizontal scale is theDoppler velocity in the comet rest frame. The feature at -11km s − doesnot correspond to any known molecular line and could be spurious. comets, 46P is relatively methanol rich, while it presents typicalabundances of C H , C H , and NH . Table 7 gives the abundances relative to water, or upper lim-its we derived in comet 46P / Wirtanen and a comparison withvalues measured in all other comets from millimetre-to-sub-millimetre ground-based observations and values measured insitu in comet 67P. Besides the di ff erences in abundances rela-tive to water between 46P and 67P due to di ff erent techniques(Sect. 5.4), the abundances found in comet 46P match most ofthose measured in other comets. However, some species seemrather depleted: CO (as is often observed in short period comets),HNCO, HCOOH, HNC, CS, and SO . This is not surprising forHNC, which is produced by a distributed source and thereforerarefied within small fields of view (Cordiner et al. 2014). As-suming that it comes from a distributed source with a parentscale length of 1000 km (Cordiner et al. 2014, 2017), we finda HNC / HCN of 3.3%, 2 . × higher, but still relatively low incomparison to other comets observed at r h = , its abundance is still lower than inother comets, as suggested in Coulson et al. (2020). The pres-ence of another distributed source of CS, which was proposed toexplain the variation of its abundance with heliocentric distance(Biver et al. 2011) could explain this low abundance. Likewise,a possible interpretation for the HCOOH depletion in the innercoma of 46P is its production in the coma from the degradationof the ammonium salt NH + HCOO − , which was observed in 67P(Altwegg et al. 2020). We undertook a sensitive survey at millimetre wavelengthsof the Jupiter-family comet 46P / Wirtanen in December 2018at its most favourable apparition. This allowed us to detect 11 molecules and obtain sensitive upper limits on 24 othermolecules. This is the most sensitive millimetre survey of aJupiter-family comet regarding the number of measured molec-ular abundances.Because the observations probed the inner coma ( < ff ected byuncertainties in molecular radiative and photolysis lifetimes.The abundances of complex molecules in 46P (e.g. CH CHO,(CH OH) , NH CHO, C H OH) are similar to values measuredin long period comets. However, CH OH is more abundant.C H OH / CH OH is lower (3%) than in C / / ∼ . ∼ < + + HCOO − , NH + + OCN − , and NH + + CN − have been identified in 67P’s dust grains, impacting the ROSINAsensor (Altwegg et al. 2020). Our measurements in 46P are con-sistent with HCOOH, HNCO, and HNC being produced by thesublimation of ammonium salts. The low CS abundance in 46P(0.03% vs 0.05-0.20% measured in other comets 1 au from theSun) suggests a distributed source of CS, other than CS , incometary atmospheres. The investigation of isotopic ratios onlyyielded the measurements of the S / S in H S, which is con-sistent with the terrestrial value.
Acknowledgements.
This work is based on observations carried out underprojects number 112-18 with the IRAM 30-m telescope and project numberW18AB with the NOEMA Interferometer. IRAM is supported by the InstitutNationnal des Sciences de l’Univers (INSU) of the French Centre national de larecherche scientifique (CNRS), the Max-Planck-Gesellschaft (MPG, Germany)and the Spanish IGN (Instituto Geográfico Nacional). We gratefully acknowl-edge the support from the IRAM sta ff for its support during the observations.The data were reduced and analysed thanks to the use of the GILDAS, class soft-ware (http: // / IRAMFR / GILDAS). This research has been supportedby the Programme national de planétologie de l’Institut des sciences de l’univers(INSU). The Nançay Radio Observatory is operated by the Paris Observatory,associated with the CNRS and with the University of Orléans. Part of this re-search was carried out at the Jet Propulsion Laboratory, California Institute ofTechnology, under a contract with the National Aeronautics and Space Adminis-tration. B. P. Bonev and N. Dello Russo acknowledge support of NSF grant AST-2009398 and NASA grant 80NSSC17K0705, respectively. N.X. Roth was sup-ported by the NASA Postdoctoral Program at the NASA Goddard Space FlightCenter, administered by Universities Space Research Association under con-tract with NASA. M.A. Cordiner was supported in part by the National ScienceFoundation (under Grant No. AST-1614471). S.N. Milam and M.A. Cordineracknowledge the Planetary Science Division Internal Scientist Funding Programthrough the Fundamental Laboratory Research (FLaRe) work package, as well asthe NASA Astrobiology Institute through the Goddard Center for Astrobiology(proposal 13-13NAI7-0032). M. DiSanti acknowledges support through NASAGrant 18-SSO18_2-0040.
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Table 6.
Average production rates in 46P in December 2018.
UT date Molecule r h Production rate Q Lines a [dd.d-dd.d] [au] [ × molec. s − ]11.8–17.8 HCN 1.056 0 . ± .
01 211.8–17.8 HNC 1.056 0 . ± .
003 1HNCext b . ± .
009 112.0–18.1 CH CN 1.056 0 . ± .
007 2011.8–18.1 CH OH 1.056 26 . ± . S 1.056 7 . ± .
07 213.1–17.1 H
S 1.056 0 . ± .
05 112.0–17.9 CS 1.056 0 . ± .
02 225.83 CS 1.070 0 . ± .
05 112.1–18.1 H CO 1.056 0 . ± .
08 4H COext c . ± . CO 1.068 0 . ± .
05 2H COext c . ± . CHO 1.056 0 . ± .
01 (32)11.9–18.1 CH CHO 1.056 0 . ± .
05 (72)11.9–18.1 C H OH 1.056 0 . ± .
28 (97)11.9–18.1 (CH OH) . ± . < . S 1.056 < .
36 (1)12.0–18.1 HDS 1.056 < .
43 (2)11.8–18.1 OCS 1.056 < .
56 (6)11.8–18.1 H CS 1.056 ∼ .
13 (7)12.0–18.1 SO 1.056 < .
72 (5)11.8–18.1 SO < .
24 (5)12.0–17.9 NS 1.056 < .
09 (2)11.9–18.1 CH SH 1.056 < .
49 (30)12.0–18.1 H CN 1.056 < .
014 (1)12.0–18.1 HC N 1.056 < .
011 (1)12.1–18.1 DCN 1.056 < .
018 (1)11.9–18.1 HC N 1.056 < .
025 (8)11.9–18.1 C H CN 1.056 < . H CN 1.056 < . NH < . < .
07 (3)11.9–18.1 HCOOH 1.056 < .
28 (16)11.9–18.1 CH OCHO 1.056 < . CO 1.056 < .
27 (9)11.9–18.1 CH OHCHO 1.056 < .
33 (11)11.9–18.1 CH OCH < . CH O 1.056 < .
23 (6)11.9–18.1 CH COCH < .
32 (95)11.9–18.1 CH COOH 1.056 < .
70 (58)11.9–18.1 Glycine I 1.056 < .
55 (33)11.8–17.8 PH < . < .
02 (1)11.8–17.8 PO 1.056 < .
11 (4)17.1 H O 1.057 < < . Notes. ( a ) Number of lines used for the determination of Q , in parenthe-ses when individual lines are not clearly detected. ( b ) Where we assume that HNC is produced in the coma with a Haserparent scale length of 1000 km (Cordiner et al. 2017). ( c ) Where we assume that H CO is produced in the coma with a Haserparent scale length of 5000 km.Article number, page 12 of 36iver et al.: Composition of comet 46P / Wirtanen
Table 7.
Molecular abundances.
Molecule Name Abundance relative to water in %in 46P in comets in 67P a HCN hydrogen cyanide 0 . ± .
01 0.08–0.25 0.20HNC hydrogen isocyanide 0 . ± . b . ± . CN methyl cyanide 0 . ± .
001 0.008-0.054 0.0059HC N cyanoacetylene < .
003 0.002-0.068 0.0004HNCO isocyanic acid < .
009 0.009-0.080 0.027NH CHO formamide 0 . ± .
002 0.016-0.022 0.004CO carbon monoxide < .
23 0.4- 35 0.3-3H CO ext c formaldehyde 0 . ± .
02 0.13- 1.4 0.5CH OH methanol 3 . ± .
03 0.7 - 6.1 0.5-1.5HCOOH formic acid < .
035 0.03–0.18 0.013CH CHO acetaldehyde 0 . ± .
01 0.05–0.08 0.047 d (CH OH) ethylene glycol 0 . ± .
03 0.07–0.35 0.011HCOOCH methyl formate < .
14 0.06–0.08 0.0034 e CH OHCHO glycolaldehyde < .
041 0.016–0.039 0.0034 e C H OH ethanol 0 . ± .
04 0.11–0.19 0.10 f H S hydrogen sulphide 0 . ± .
01 0.09- 1.5 2.0CS carbon monosulphide 0 . ± .
003 0.05–0.20 0.02 h OCS carbonyl sulphide < .
07 0.05–0.40 0.07SO sulphur monoxide < .
09 0.04–0.30 0.071SO sulphur dioxide < .
03 0.03–0.23 0.127H CS thioformaldehyde ≤ .
016 0.009–0.090 0.0027NS nitrogen sulphide < .
012 0.006-0.012CH SH methyl mercaptan < . < .
023 0.038CH CO ketene < . ≤ . COCH acetone < . ≤ .
011 0.0047 g CH OCH dimethyl ether < . < .
025 0.04 f c-C H O ethylene oxide < . < .
006 0.047 d CH COOH acetic acid < . < .
026 0.0034 e CH NH methylamine < . < . H CN acrylonitrile < . < . H CN ethyl cyanide < . < . phosphine < . < . < . < . < . < . < . < . CH COOH glycine I < . < .
18 0.000017
Notes. ( a ) Based on Biver & Bockelée-Morvan (2019); Rubin et al. (2019); Läuter et al. (2020). ( b ) Assuming a daughter distribution with Lp = ( c ) Assuming a daughter distribution. ( d,e,f,g ) Isomers not distinguished by ROSINA; abundance is for their sum. ( h ) From CS with ROSINA. Article number, page 13 of 36 & Aproofs: manuscript no. 40125final
Table 8.
Isotopic ratios.
Ratio Molecule Value in 46P other comets a in 67P b on Earth C / C HCN >
66 88–114 89.4 N / N HCN >
84 139–205 272 S / S H S 20 . ± . S / S H S >
21 – 151 126.9D / H HCN < .
02 0.0023H S < . < . − < .
017 0.0012H O < . × − c H O 1 . ± . × − d . − . × − . × − . × − Notes. ( a ) (Bockelée-Morvan et al. 2015; Biver et al. 2016; Cordiner et al. 2019) ( b ) (Altwegg 2018) ( c ) This paper, IRAM 30m upper limit. ( d ) From SOFIA observations (Lis et al. 2019).Article number, page 14 of 36iver et al.: Composition of comet 46P / Wirtanen
Appendix A: Supplementary line list table
Table A.1.
Line intensities from IRAM and NOEMA observations.
Date Molecule Transition Frequency Pointing o ff set a Intensity b Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]2018 / / . ± . − . ± . . ± . − . ± . . ± . − . ± . . ± . − . ± . . ± . − . ± . . ± . − . ± . . ± . − . ± . . ± . − . ± . . ± . − . ± . / / . ± . − . ± . . ± . − . ± . . ± . − . ± . / / . ± . − . ± . . ± . − . ± . . ± . − . ± . / / . ± . − . ± . . ± . − . ± . . ± . − . ± . . ± . − . ± . / / . ± . − . ± . . ± . − . ± . . ± . − . ± . / / . ± . − . ± . / / . ± . − . ± . . ± . − . ± . . ± . − . ± . . ± . − . ± . / / OH 1 − E 165050.229 1.4 0 . ± . − . ± . − E 165061.187 0 . ± . − . ± . − E 165099.300 0 . ± . − . ± . − E 165190.539 0 . ± . − . ± . − E 165369.410 0 . ± . − . ± . − E 165678.724 0 . ± . + . ± . − E 166169.179 0 . ± . − . ± . − E 166898.566 0 . ± . − . ± . − E 167931.056 0 . ± . − . ± . − E 169335.219 0 . ± . + . ± . OH 3 − E 170060.581 0 . ± . − . ± . / / OH 1 − E 165050.229 1.4 0 . ± . − . ± . − E 165061.187 0 . ± . − . ± . − E 165099.300 0 . ± . − . ± . − E 165190.539 0 . ± . − . ± . − E 165369.410 0 . ± . − . ± . − E 165678.724 0 . ± . − . ± . − E 166169.179 0 . ± . − . ± . − E 166898.566 0 . ± . − . ± . − E 167931.056 0 . ± . − . ± . − E 169335.219 0 . ± . − . ± . OH 3 − E 170060.581 0 . ± . − . ± . / / OH 1 − E 165050.229 2.2 0 . ± . − . ± . − E 165061.187 0 . ± . − . ± . − E 165099.300 0 . ± . − . ± . − E 165190.539 0 . ± . − . ± . − E 165369.410 0 . ± . − . ± . − E 165678.724 0 . ± . − . ± . − E 166169.179 0 . ± . − . ± . − E 166898.566 0 . ± . − . ± . Article number, page 15 of 36 & Aproofs: manuscript no. 40125final
Table A.1.
Continued.
Date Molecule Transition Frequency Pointing o ff set Intensity Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]9 − E 167931.056 0 . ± . − . ± . − E 169335.219 0 . ± . − . ± . OH 3 − E 170060.581 0 . ± . − . ± . / / OH 1 − E 165050.229 1.4 0 . ± . − . ± . − E 165061.187 0 . ± . − . ± . − E 165099.300 0 . ± . − . ± . − E 165190.539 0 . ± . − . ± . − E 165369.410 0 . ± . − . ± . − E 165678.724 0 . ± . − . ± . − E 166169.179 0 . ± . − . ± . − E 166898.566 0 . ± . − . ± . − E 167931.056 0 . ± . − . ± . OH 7 − − E 181295.971 0 . ± . − . ± . / / OH 1 − E 213427.118 2.0 0 . ± . − . ± . OH 5 − E 216945.559 0 . ± . − . ± . OH 8 − − E 229758.811 0 . ± . − . ± . OH 3 − − − E 230027.002 0 . ± . / / OH 1 − E 213427.118 1.0 0 . ± . − . ± . OH 5 − E 216945.559 0 . ± . − . ± . OH 8 − − E 229758.811 0 . ± . − . ± . OH 3 − − − E 230027.002 0 . ± . − . ± . / / OH 1 − E 213427.118 1.4 0 . ± . − . ± . OH 5 − E 216945.559 0 . ± . − . ± . OH 8 − − E 229758.811 0 . ± . − . ± . OH 3 − − − E 230027.002 0 . ± . − . ± . / / OH 1 − E 213427.118 0.7 0 . ± . − . ± . OH 5 − E 216945.559 0 . ± . − . ± . OH 8 − − E 229758.811 0 . ± . − . ± . OH 3 − − − E 230027.002 0 . ± . − . ± . / / OH 8 − − E 229758.811 0 . ± . − . ± . OH 3 − − − E 230027.002 0 . ± . − . ± . / / OH 4 − E 218440.050 2.2 0 . ± . − . ± . OH 8 − E 220078.490 0 . ± . + . ± . OH 5 − A + . ± . − . ± . / / OH 4 − E 218440.050 1.6 0 . ± . − . ± . OH 8 − E 220078.490 0 . ± . − . ± . OH 5 − A + . ± . − . ± . / / OH 5 − E 241700.168 1.7 0 . ± . − . ± . − − − E 241767.247 0 . ± . − . ± . − A + . ± . − . ± . − A 241806.521 0 . ± . − . ± . − − − E 241813.248 0 . ± . − E 241829.629 0 . ± . − . ± . − A 241832.910 0 . ± . − . ± . − A − . ± . − . ± . − E 241843.608 0 . ± . − . ± . − − − E 241852.299 0 . ± . − . ± . − E 241879.038 0 . ± . − . ± . − A + . ± . − . ± . ± − ± E 241904.401 0 . ± . − . ± . − A − . ± . − . ± . / / OH 5 − E 241700.168 1.8 0 . ± . − . ± . − − − E 241767.247 0 . ± . − . ± . − A + . ± . − . ± . − A 241806.521 0 . ± . + . ± . − − − E 241813.248 0 . ± . − E 241829.629 0 . ± . − A 241832.910 0 . ± . − . ± . − A − . ± . − . ± . − E 241843.608 0 . ± . + . ± . − − − E 241852.299 0 . ± . − . ± . Article number, page 16 of 36iver et al.: Composition of comet 46P / Wirtanen
Table A.1.
Continued.
Date Molecule Transition Frequency Pointing o ff set Intensity Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]5 − E 241879.038 0 . ± . − . ± . − A + . ± . − . ± . ± − ± E 241904.401 0 . ± . − . ± . − A − . ± . − . ± . / / OH 5 − E 241700.168 2.0 0 . ± . − . ± . − − − E 241767.247 0 . ± . − . ± . − A + . ± . − . ± . − A 241806.521 0 . ± . − . ± . − − − E 241813.248 0 . ± . − . ± . − E 241829.629 0 . ± . − A 241832.910 0 . ± . − . ± . − A − . ± . − . ± . − E 241843.608 0 . ± . + . ± . − − − E 241852.299 0 . ± . + . ± . − E 241879.038 0 . ± . − . ± . − A + . ± . − . ± . ± − ± E 241904.401 0 . ± . − . ± . − A − . ± . − . ± . / / OH 5 − E 241700.168 2.0 0 . ± . − . ± . − − − E 241767.247 0 . ± . − . ± . − A + . ± . − . ± . − A 241806.521 0 . ± . − . ± . − − − E 241813.248 0 . ± . − E 241829.629 0 . ± . − . ± . − A 241832.910 0 . ± . − . ± . − A − . ± . − . ± . − E 241843.608 0 . ± . + . ± . − − − E 241852.299 0 . ± . − . ± . − E 241879.038 0 . ± . − . ± . − A + . ± . − . ± . ± − ± E 241904.401 0 . ± . − . ± . − A − . ± . − . ± . / / OH 3 − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . + . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . − A − + . ± . / / OH 3 − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . Article number, page 17 of 36 & Aproofs: manuscript no. 40125final
Table A.1.
Continued.
Date Molecule Transition Frequency Pointing o ff set Intensity Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]6 − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . + . ± . − A + − . ± . − A − + . ± . − . ± . / / OH 3 − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . + . ± . / / OH 3 − A + − . ± . + . ± . − A − + . ± . + . ± . − A + − . ± . − . ± . − A − + . ± . + . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . + . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . + . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . / / OH 3 − A + − . ± . − . ± . − A − + . ± . + . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . Article number, page 18 of 36iver et al.: Composition of comet 46P / Wirtanen
Table A.1.
Continued.
Date Molecule Transition Frequency Pointing o ff set Intensity Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]6 − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . + . ± . − A + − . ± . + . ± . − A − + . ± . + . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − − . ± . − A − + . ± . / / OH 3 − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . + . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . + . ± . − A + − . ± . + . ± . − A − + . ± . / / OH 2 − − E 254015.377 1.7 0 . ± . − . ± . OH 5 − E 266838.123 1.7 0 . ± . − . ± . . ± . − . ± . / / OH 2 − − E 254015.377 1.6 0 . ± . − . ± . OH 5 − E 266838.123 0 . ± . − . ± . / / OH 2 − − E 254015.377 3.1 0 . ± . − . ± . OH 5 − E 266838.123 0 . ± . − . ± . / / OH 2 − − E 254015.377 2.0 0 . ± . − . ± . OH 5 − E 266838.123 0 . ± . − . ± . / / OH 2 − − E 254015.377 1.1 0 . ± . OH 5 − E 266838.123 0 . ± . − . ± . / / OH 2 − − E 254015.377 1.3 0 . ± . − . ± . OH 5 − E 266838.123 0 . ± . − . ± . / / OH 2 − E 261805.736 1.7 0 . ± . − . ± . / / . ± . − . ± . / / . ± . − . ± . / / . ± . − . ± . / / S 1 − . ± . − . ± . . ± . − . ± . . ± . + . ± . / / S 1 − . ± . − . ± . . ± . − . ± . . ± . − . ± . Article number, page 19 of 36 & Aproofs: manuscript no. 40125final
Table A.1.
Continued.
Date Molecule Transition Frequency Pointing o ff set Intensity Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]11.7 0 . ± . − . ± . / / S 1 − . ± . − . ± . . ± . − . ± . . ± . − . ± . . ± . − . ± . / / S 1 − . ± . − . ± . / / S 2 − . ± . + . ± . / / S 2 − . ± . − . ± . / / S 2 − . ± . + . ± . / / S 2 − . ± . − . ± . / / S 2 − . ± . − . ± . / / O 3 − < . / / . ± . − . ± . / / . ± . / / CN 3-2 259011.798 1.7 0 . ± . / / N 3-2 258156.996 1.7 0 . ± . − . ± . / / < . / / CN 8,0-7,0 147174.588 1.7 0 . ± . − . ± . . ± . . ± . . ± . CN 8-7 Sum of 4 lines 10.2 0 . ± . / / CN 9,0-8,0 165569.082 1.7 0 . ± . − . ± . . ± . . ± . . ± . / / CN 9,0-8,0 165569.082 10.2 0 . ± . − . ± . . ± . . ± . . ± . / / CN 12,0-11,0 220747.261 1.7 0 . ± . + . ± . . ± . . ± . . ± . CN 13,0-12,0 239137.916 1.7 0 . ± . − . ± . . ± . . ± . . ± . / / CN 14,0-13,0 257527.393 1.7 0 . ± . + . ± . . ± . . ± . . ± . / / OH 1 − E 165050.229 1.7 0 . ± . − . ± . − E 165061.187 0 . ± . − . ± . − E 165099.300 0 . ± . − . ± . − E 165190.539 0 . ± . − . ± . − E 165369.410 0 . ± . − . ± . − E 165678.724 0 . ± . − . ± . − E 166169.179 0 . ± . − . ± . − E 166898.566 0 . ± . − . ± . − E 167931.056 0 . ± . − . ± . − E 169335.219 0 . ± . − . ± . / / OH 3 − E 170060.581 1.7 0 . ± . − . ± . / / OH 1 − E 165050.229 3.7 0 . ± . − . ± . − E 165061.187 0 . ± . − . ± . − E 165099.300 0 . ± . − . ± . − E 165190.539 0 . ± . − . ± . − E 165369.410 0 . ± . − . ± . Article number, page 20 of 36iver et al.: Composition of comet 46P / Wirtanen
Table A.1.
Continued.
Date Molecule Transition Frequency Pointing o ff set Intensity Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]6 − E 165678.724 0 . ± . − . ± . − E 166169.179 0 . ± . − . ± . − E 166898.566 0 . ± . − . ± . − E 167931.056 0 . ± . + . ± . − E 169335.219 0 . ± . − . ± . / / OH 1 − E 165050.229 9.5 0 . ± . − . ± . − E 165061.187 0 . ± . − . ± . − E 165099.300 0 . ± . − . ± . − E 165190.539 0 . ± . − . ± . − E 165369.410 0 . ± . − . ± . − E 165678.724 0 . ± . − . ± . − E 166169.179 0 . ± . − . ± . − E 166898.566 0 . ± . + . ± . − E 167931.056 0 . ± . − . ± . − E 169335.219 0 . ± . − . ± . OH 3 − E 170060.581 0 . ± . − . ± . / / OH 1 − E 165050.229 11.4 0 . ± . − . ± . − E 165061.187 0 . ± . − . ± . − E 165099.300 0 . ± . − . ± . − E 165190.539 0 . ± . − . ± . − E 165369.410 0 . ± . − . ± . − E 165678.724 0 . ± . − . ± . − E 166169.179 0 . ± . − . ± . − E 166898.566 0 . ± . − . ± . − E 167931.056 0 . ± . + . ± . − E 169335.219 0 . ± . + . ± . OH 3 − E 170060.581 0 . ± . − . ± . / / OH 4 − E 168577.831 1.7 0 . ± . + . ± . / / OH 1 − E 213427.118 0.9 0 . ± . − . ± . OH 5 − E 216945.559 0 . ± . − . ± . OH 8 − − E 229758.811 0 . ± . − . ± . OH 3 − − − E 230027.002 0 . ± . − . ± . OH 10 − − − E 232945.835 0 . ± . OH 1 − E 213427.118 10.0 0 . ± . − . ± . OH 5 − E 216945.559 0 . ± . − . ± . OH 8 − − E 229758.811 0 . ± . − . ± . OH 3 − − − E 230027.002 0 . ± . − . ± . / / OH 4 − E 218440.050 1.7 0 . ± . − . ± . OH 8 − E 220078.490 0 . ± . − . ± . OH 4 − A − . ± . + . ± . OH 5 − A + . ± . − . ± . OH 5 − E 240241.502 0 . ± . − . ± . OH 4 − E 218440.050 10.1 0 . ± . − . ± . OH 8 − E 220078.490 0 . ± . − . ± . OH 5 − A + . ± . − . ± . / / OH 5 − E 241700.168 1.7 0 . ± . − . ± . − − − E 241767.247 0 . ± . − . ± . − A + . ± . − . ± . − A 241806.521 0 . ± . − . ± . − − − E 241813.248 0 . ± . − . ± . − E 241829.629 0 . ± . − . ± . − A 241832.910 0 . ± . − . ± . − A − . ± . − . ± . − E 241843.608 0 . ± . − . ± . − − − E 241852.299 0 . ± . − . ± . − E 241879.038 0 . ± . − . ± . − A + . ± . − . ± . ± − ± E 241904.401 0 . ± . − . ± . − A − . ± . − . ± . / / OH 5 − E 241700.168 9.7 0 . ± . − . ± . − − − E 241767.247 0 . ± . − . ± . Article number, page 21 of 36 & Aproofs: manuscript no. 40125final
Table A.1.
Continued.
Date Molecule Transition Frequency Pointing o ff set Intensity Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]5 − A + . ± . − . ± . − A 241806.521 0 . ± . − − − E 241813.248 0 . ± . − E 241829.629 0 . ± . − A 241832.910 0 . ± . − A − . ± . − . ± . − E 241843.608 0 . ± . − . ± . − − − E 241852.299 0 . ± . − E 241879.038 0 . ± . − . ± . − A + . ± . − . ± . ± − ± E 241904.401 0 . ± . − . ± . − A − . ± . − . ± . / / OH 5 − E 241700.168 11.5 0 . ± . − . ± . − − − E 241767.247 0 . ± . − . ± . − A + . ± . − . ± . − A 241806.521 0 . ± . − − − E 241813.248 0 . ± . − E 241829.629 < . − A 241832.910 0 . ± . − A − < . − E 241843.608 < . − − − E 241852.299 0 . ± . − E 241879.038 0 . ± . + . ± . − A + . ± . − . ± . ± − ± E 241904.401 0 . ± . − . ± . − A − . ± . + . ± . / / OH 4 − A + . ± . − . ± . / / OH 3 − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . + . ± . − A + − . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . + . ± . OH 11 − A + . ± . − . ± . / / OH 3 − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . Article number, page 22 of 36iver et al.: Composition of comet 46P / Wirtanen
Table A.1.
Continued.
Date Molecule Transition Frequency Pointing o ff set Intensity Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]5 − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − A − + . ± . − . ± . − A + − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . + . ± . − A + − . ± . − . ± . − A − + . ± . − A + − . ± . − . ± . − A − + . ± . + . ± . OH 11 − A + . ± . + . ± . / / OH 3 − A + − . ± . − . ± . − A − + . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . + . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − A − + . ± . − A + − . ± . − A − + . ± . OH 11 − A + . ± . + . ± . / / OH 3 − A + − . ± . − A − + . ± . − . ± . − A + − . ± . + . ± . − A − + . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − . ± . − . ± . − A − + . ± . − A + − . ± . − . ± . − A − + . ± . − . ± . − A + − − . ± . − A − + . ± . − A + − . ± . − A − + . ± . − A + − . ± . + . ± . − A − + − . ± . − A + − . ± . − A − + . ± . − . ± . − A + − . ± . − A − + . ± . / / OH 3 − A + − . ± . − A − + . ± . + . ± . Article number, page 23 of 36 & Aproofs: manuscript no. 40125final
Table A.1.
Continued.
Date Molecule Transition Frequency Pointing o ff set Intensity Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]4 − A + − . ± . − . ± . − A − + . ± . + . ± . − A + − . ± . + . ± . − A − + . ± . − . ± . − A + − − . ± . − A − + . ± . + . ± . − A + − . ± . + . ± . − A − + . ± . + . ± . − A + − . ± . − . ± . − A − + . ± . − A + − . ± . − . ± . − A − + . ± . + . ± . − A + − . ± . − A − + − . ± . − A + − . ± . − A − + . ± . / / OH 2 − − E 254015.377 2.1 0 . ± . − . ± . OH 6 − E 265289.616 0 . ± . − . ± . OH 5 − E 266838.123 0 . ± . − . ± . OH 9 − E 267403.394 0 . ± . + . ± . / / OH 2 − − E 254015.377 8.9 0 . ± . − . ± . OH 6 − E 265289.616 0 . ± . + . ± . OH 5 − E 266838.123 0 . ± . + . ± . OH 9 − E 267403.394 0 . ± . − . ± . / / OH 2 − − E 254015.377 11.6 0 . ± . OH 6 − E 265289.616 0 . ± . OH 5 − E 266838.123 0 . ± . − . ± . OH 9 − E 267403.394 0 . ± . / / OH 2 − − E 254015.377 15.9 0 . ± . OH 6 − E 265289.616 < . OH 5 − E 266838.123 0 . ± . − . ± . OH 9 − E 267403.394 < . / / OH 2 − E 261805.736 1.7 0 . ± . − . ± . / / . ± . − . ± . / / CO 2 − . ± . − . ± . / / . ± . − . ± . / / CO 3 − . ± . + . ± . / / CO 3 − . ± . − . ± . − . ± . − . ± . / / CO 3 − . ± . − . ± . − . ± . + . ± . / / . ± . / / S 1 − . ± . − . ± . / / . ± . − . ± . / / . ± . − . ± . / / . ± . − . ± . / / S 1 − . ± . − . ± . / / S 1 − < . / / − < . − < . / / S 2 − . ± . − . ± . . ± . − . ± . / / S 2 − . ± . / / . ± . + . ± . / / . ± . − . ± . / / . ± . − . ± . / / . ± . − . ± . / / . ± . − . ± . / / < . Article number, page 24 of 36iver et al.: Composition of comet 46P / Wirtanen
Table A.1.
Continued.
Date Molecule Transition Frequency Pointing o ff set Intensity Doppler shift[ yyyy / mm / dd . dd ] [GHz] [ ′′ ] [K km s − ] [km s − ]2018 / / CO 3 − . ± . − . ± . − . ± . + . ± . / / − . ± . − . ± . / / CN 8-7 Sum of 4 lines 3. 0 . ± . CN 9-8 Sum of 4 lines 3. 0 . ± . − . ± . / / OH 1 − E 165050.229 3. 0 . ± . − . ± . − E 165061.187 0 . ± . − . ± . − E 165678.724 0 . ± . − . ± . / / S 1 − . ± . − . ± . Notes.
Frequencies and line parameters are from Müller et al. (2005) and Pickett et al. (1998). ( a ) Mean pointing o ff set (for a series of lines). ( b ) Whole line, including correction for hyperfine components not measured (e.g. HCN, H CN, DCN, H
S). Article number, page 25 of 36 & Aproofs: manuscript no. 40125final
Appendix B: Full IRAM 30-m spectra of comet 46P/Wirtanen at 2 mm
The following pages present the 147–185 GHz ( λ = / Wirtanen obtained between 13.0 and 17.1Dec. 2018 with the IRAM 30-m telescope. The three wavelength domains covered are plotted by series of ≈ ′′ of the nucleus were taken into account, and the strongestlines are identified. We note the much higher noise level around the frequency of the atmospheric H O line at 183310 MHz.
Article number, page 26 of 36iver et al.: Composition of comet 46P / Wirtanen Article number, page 27 of 36 & Aproofs: manuscript no. 40125final
Fig. B.1.
Vertical scale in main beam brightness temperature adjusted to the lines or noise level. The frequency scale in the rest frame of the cometis indicated on the upper axis. A velocity scale with a reference at the centre of each band is indicated on the lower axis.Article number, page 28 of 36iver et al.: Composition of comet 46P / Wirtanen
Appendix C: Full IRAM 30-m spectra of comet 46P/Wirtanen at 1 mm
The following pages present the 210–272 GHz ( λ = . / Wirtanen obtained between 11.9 and 18.1Dec. 2018 with the IRAM 30-m telescope. The 62 GHz, ∼ × ≈ . × .
78 GHz.There are some overlaps and gaps in the final 62-GHz-wide frequency coverage. Only spectra obtained within 3 ′′ from the nucleuswere taken into account. The strongest lines (signal > . × < σ > ) are labelled. Some identifications might be misleading wherethe local noise is higher than < σ > and a noise peaks falls on a known molecular line resulting in a spurious detection. Article number, page 29 of 36 & Aproofs: manuscript no. 40125finalArticle number, page 30 of 36iver et al.: Composition of comet 46P / Wirtanen Article number, page 31 of 36 & Aproofs: manuscript no. 40125finalArticle number, page 32 of 36iver et al.: Composition of comet 46P / Wirtanen Article number, page 33 of 36 & Aproofs: manuscript no. 40125final
Fig. C.1.
Vertical scale in main beam brightness temperature adjusted to the lines or noise level. The frequency scale in the rest frame of the cometis indicated on the upper axis. A velocity scale with reference at centre of each band is indicated on the lower axis. The feature close to 230.5 GHzis due to contamination by galactic CO.Article number, page 34 of 36iver et al.: Composition of comet 46P / Wirtanen
Table D.1.
Molecular line width in comets in m s − FWHM
Hale-Bopp
VHM a C / VHM a Molecule b Dec. 2018 Feb.1997 c April 1997 May 1997 Jan. 2015H S 1050 ± − ± − ± − ± − ± – − ± − ± − ±
250 –H CS – – – – − ± CO 1260 ± − ± − ± − ± − ± − ±
37 – − ± − ± − ±
50 – − ± − ± CHO 1230 ± − ±
149 – − ± − ± CHO 1200 ±
198 – − ± − ± − ± − ±
45 – − ± − ± N – − ± − ± − ± − ± OH) ±
186 – − ±
200 – − ± − ±
62 – − ± − ± ± − ± − ± − ± − ± H OH 1293 ± − ±
437 – – − ± OHCHO – – – – − ± ± − ±
20 – − ± − ± ± − ±
15 – − ± − ± OH 1175 ± − ± − ± − ± − ± CN 1030 ±
118 – − ± − ± − ± − ± − ± − ± − ± Notes. ( a ) Negative
V HM values correspond to the blueshifted side of the line (due to a sun-ward jet). ( b ) Ordered by ∼ increasing lifetime. ( c ) Data obtained mostly with the 10.4 m Caltech Submillimeter Observatory or Plateau Bure 15 m antennas and a 24 ± ′′ beamsize. April-Maydata were obtained with the IRAM 30 m and a 12 ± ′′ beamsize. ( d ) CS, HNC, and more notably SO and H CO (which have a much shorter daughter / parent scale length ratio) are daughter molecules. Their scalelength can be much longer than expected for a parent molecule. Appendix D: Selected molecular line widths in comets
Table D.1 provides the full width at half maximum (
FWHM ) or velocity at half maximum (
VHM ) for asymmetric double peaklines, from Gaussian fitting for molecular lines in comets. We took the average of several lines when possible, and observations withsimilar beam sizes for a given comet, in order to avoid being biased by spatial sampling. When a (small) trend of line widths withbeam size is observed, the width has been interpolated to the mean beam size of the dataset. The objective is to correlate the linewidth with the molecule lifetime (when it is well known) or to constrain the lifetime of the molecule from its line width (when it ispoorly known), as described in Section 5.1.
Appendix E: Dependence of the production rate on the uncertainty in photo-destruction rate
Figure E.1 is provided here for the mean observing circumstances of the observations of comet 46P with IRAM 30-m telescope.In a first approximation, the line intensity is proportional to the column density N c , which is itself proportional to the molecularproduction rate Q . So, for a given observed line intensity, a change of N c due to a change of the photo-destruction rate β , has to becompensated by an inverse change of Q : ∆ QQ = − ∆ N c N c .From this plot, we can directly determine the change of the derived production rate Q when we change the value β . For example,if β is increased from 2 to 20 × − s − , we get ∆ QQ = + .
12, meaning the retrieved production rate will be increased by only 12%.More generally, if the photo-destruction rate is not known but can be assumed to be less than that of H S, an error of less than 16%on the retrieved production rate is anticipated from these observations of comet 46P.
Article number, page 35 of 36 & Aproofs: manuscript no. 40125final
Fig. E.1.
Plot showing evolution of the number of molecules in the IRAM 30-m beam as a function of molecule photo-destruction rate. We plot,more precisely, the average column density (number of molecules divided by the beam area) normalised to its value for infinite lifetime. We usedthe average beam size ( θ b = ′′ ) for an average pointing o ff set of 2 ′′′′