Our modern day Solar System has 4.6 × 10⁹ yr of evolution behind it with just a few relics of its birth conditions remaining. Comets are thought to be some of the most pristine tracers of the initial ingredients that were combined to produce the Earth and the other planets. Other low-mass protostars may be analogous to our proto-Sun and hence, could be used to study the building blocks necessary to form Solar-like systems. This study tests this idea on the basis of new high sensitivity, high spatial resolution ALMA data on the protoplanetary disc-scales (∼70au) of IRAS16293-2422 and the bulk composition of comet 67P/Churyumov-Gerasimenko, as determined for the ﬁrst time with the unique in situ monitoring carried out by Rosetta. The comparative analysis of the observations from the Protostellar Interferometric LineSurvey (PILS) and the measurements made with Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) shows that the relative abundances of CHO-, N-, and S-bearing molecules correlate, with some scatter, between protostellar and cometary data. A tentative correlation is seen for the ﬁrst time for P- and Cl-bearing compounds. The results imply that the volatile composition of cometesimals and planetesimals is partially inherited from the pre- and protostellar phases of evolution.

/pdf/ingredients-for-solar-like-systems-protostar-iras-16293-2422-4xfhuhvd65.pdf

Ingredients for solar-like systems: protostar IRAS 16293-2422 B versus comet 67P/Churyumov–Gerasimenko

Context. Temperature is a crucial parameter in circumstellar disk evolution and planet formation because it governs the resistance of the gas to gravitational instability and sets the chemical composition of the planet-forming material.Aims. We set out to determine the gas temperature of the young disk-like structure around the Class 0 protostar IRAS 16293–2422A.Methods. We used Atacama Large Millimeter/submillimeter Array (ALMA) observations of multiple H2 CS J = 7 − 6 and J = 10 − 9 lines from the Protostellar Interferometric Line Survey (PILS) to create a temperature map for the inner ~200 AU of the disk-like structure. This molecule is a particularly useful temperature probe because transitions between energy levels with different K a quantum numbers operate only through collisions.Results. Based on the H2 CS line ratios, the temperature is between ~100–175 K in the inner ~150 AU, and drops to ~75 K at ~200 AU. At the current resolution (0.5′′~70 AU), no jump is seen in the temperature at the disk–envelope interface.Conclusions. The temperature structure derived from H2 CS is consistent with envelope temperature profiles that constrain the temperature from 1000 AU scales down to ~100 AU, but does not follow the temperature rise seen in these profiles at smaller radii. Higher angular resolution observations of optically thin temperature tracers are needed to establish whether cooling by gas-phase water, the presence of a putative disk, or the dust optical depth influences the gas temperature at ≲100 AU scales. The temperature at 100 AU is higher in IRAS 16293A than in the embedded Class 0/I disk L1527, consistent with the higher luminosity of the former.

/pdf/temperature-profiles-of-young-disk-like-structures-the-case-4wgqmrgqlc.pdf

Temperature profiles of young disk-like structures - The case of IRAS 16293A

Context. Complex organic molecules with three carbon atoms are found in the earliest stages of star formation. In particular, propenal (C2H3CHO) is a species of interest due to its implication in the formation of more complex species and even biotic molecules. Aims. This study aims to search for the presence of C2H3CHO and other three-carbon species such as propylene (C3H6) in the hot corino region of the low-mass protostellar binary IRAS 16293-2422 to understand their formation pathways. Methods. We use ALMA observations in Band 6 and 7 from various surveys to search for the presence of C3H6 and C2H3CHO towards the protostar IRAS 16293-2422 B (IRAS 16293B). The identification of the species and the estimates of the column densities and excitation temperatures are carried out by modeling the observed spectrum under the assumption of local thermodynamical equilibrium. Results. We report the detection of both C3H6 and C2H3CHO towards IRAS 16293B, however, no unblended lines were found towards the other component of the binary system, IRAS 16293A. We derive column density upper limits for C3H8, HCCCHO, n-C3H7OH, i-C3H7OH, C3O, and cis-HC(O)CHO towards IRAS 16293B. We then use a three-phase chemical model to simulate the formation of these species in a typical prestellar environment followed by its hydrodynamical collapse until the birth of the central protostar. Different formation paths, such as successive hydrogenation and radical-radical additions on grain surfaces, are tested and compared to the observational results in a number of different simulations, to assess which are the dominant formation mechanisms in the most embedded region of the protostar. Conclusions. The simulations reproduce the abundances within one order of magnitude from those observed towards IRAS 16293B, with the best agreement found for a rate of 10-12 cm3 s-1 for the gas-phase reaction C3 + O → C2 + CO. Successive hydrogenations of C3, HC(O)CHO, and CH3OCHO on grain surfaces are a major and crucial formation route of complex organics molecules, whereas both successive hydrogenation pathways and radical-radical addition reactions contribute to the formation of C2H5CHO.

/pdf/the-alma-pils-survey-first-detection-of-the-unsaturated-3-41522jek8l.pdf

The ALMA-PILS survey: first detection of the unsaturated 3-carbon molecules Propenal (C2H3CHO) and Propylene (C3H6) towards IRAS 16293–2422 B

29P/Schwassmann Wachmann is an unusual solar system object. Originally classified as a short-period comet, it is now known as a Centaur that recently transferred to its current orbit, and may become a Jupiter Family comet. It has exhibited a dust coma for over 90 years, and regularly undergoes significant dust outbursts. Carbon monoxide is routinely detected in high amounts and is typically assumed to play a large role in generating the quiescent dust coma and outbursts. To test this hypothesis, we completed two 3-month long observing campaigns of the CO J=2-1 rotational line using the Arizona Radio Observatory 10m Sub-millimeter Telescope during 2016 and 2018-2019, and compared the results to visible magnitudes obtained at the same time. As the Centaur approached its 2019 perihelion, the quiescent dust coma grew $\sim$45\% in brightness, while it is unclear whether the quiescent CO production rate also increased. A doubling of the CO production rate on 2016 Feb 28.6 UT did not trigger an outburst nor a rise in dust production for at least 10 days. Similarly, two dust outbursts occurred in 2018 while CO production continued at quiescent rates. Two other dust outbursts may show gas involvement. The data indicate that CO- and dust-outbursts are not always well-correlated. This may be explained if CO is not always substantially incorporated with the dust component in the nucleus, or if CO is primarily released through a porous material. Additionally, other minor volatiles or physical processes may help generate dust outbursts.

/pdf/co-gas-and-dust-outbursts-from-centaur-29p-schwassmann-3n2a38lqof.pdf

CO Gas and Dust Outbursts from Centaur 29P/Schwassmann–Wachmann

Context. Comets are planetesimals left over from the formation of planets in the solar system. With a growing number of observed molecular abundances in many comets, and an improved understanding of chemical evolution in protoplanetary disk midplanes, comparisons can be made between models and observations that could potentially constrain the formation histories of comets.Aims. Our aim is to carry out the first statistical comparison between cometary volatile ice abundances and modelled evolving abundances in a protoplanetary disk midplane.Methods. A χ 2 -method was used to determine maximum likelihood surfaces for 14 different comets that formed at a given time (up to 8 Myr) and place (out to beyond the CO iceline) in the pre-solar nebula midplane. This was done using observed volatile abundances for the 14 comets and the evolution of volatile abundances from chemical modelling of disk midplanes. Two assumptions for the chemical modelling starting conditions (cloud inheritance or chemical reset), as well as two different sets of cometary molecules (parent species, with or without sulphur species) were investigated.Results. Considering all parent species (ten molecules) in the reset scenario, χ 2 likelihood surfaces show a characteristic trail in the parameter space with high likelihood of formation around 30 AU at early times and 12 AU at later times for ten comets. This trail roughly traces the vicinity of the CO iceline in time.Conclusions. A statistical comparison between observed and modelled chemical abundances in comets and comet-forming regions could be a powerful tool for constraining cometary formation histories. The formation histories for all comets were constrained to the vicinity of the CO iceline, assuming that the chemistry was partially reset early in the pre-solar nebula. This is found, both when considering carbon-, oxygen-, and sulphur-bearing molecules (ten in total), and when only considering carbon- and oxygen-bearing molecules (seven in total). Since these 14 comets did not previously fall into the same taxonomical categories together, this chemical constraint may be proposed as an alternative taxonomy for comets. Based on the most likely time for each of these comets to have formed during the disk chemical evolution, a formation time classification for the 14 comets is suggested.

/pdf/cometary-compositions-compared-with-protoplanetary-disk-o4o9vjhpn1.pdf

Cometary compositions compared with protoplanetary disk midplane chemical evolution - An emerging chemical evolution taxonomy for comets

Recent measurements carried out at comet 67P/Churyumov–Gerasimenko (67P) with the Rosetta probe revealed that molecular oxygen, O₂, is the fourth most abundant molecule in comets. Models show that O₂ is likely of primordial nature, coming from the interstellar cloud from which our solar system was formed. However, gaseous O₂ is an elusive molecule in the interstellar medium with only one detection towards quiescent molecular clouds, in the ρ Oph A core. We perform a deep search for molecular oxygen, through the 2₁−0₁ rotational transition at 234 GHz of its ¹⁶O¹⁸O isotopologue, towards the warm compact gas surrounding the nearby Class 0 protostar IRAS 16293–2422 B with the ALMA interferometer. We also look for the chemical daughters of O₂, HO₂, and H₂O₂. Unfortunately, the H₂O₂ rotational transition is dominated by ethylene oxide c-C₂H₄O while HO₂ is not detected. The targeted ¹⁶O¹⁸O transition is surrounded by two brighter transitions at ± 1 km s−1 relative to the expected ¹⁶O¹⁸O transition frequency. After subtraction of these two transitions, residual emission at a 3σ level remains, but with a velocity offset of 0.3−0.5 km s⁻¹ relative to the source velocity, rendering the detection “tentative”. We derive the O₂ column density for two excitation temperatures Tex of 125 and 300 K, as indicated by other molecules, in order to compare the O₂ abundance between IRAS 16293 and comet 67P. Assuming that ¹⁶O¹⁸O is not detected and using methanol CH₃OH as a reference species, we obtain a [O₂]/[CH₃OH] abundance ratio lower than 2−5, depending on the assumed Tex, a three to four times lower abundance than the [O₂]/[CH₃OH] ratio of 5−15 found in comet 67P. Such a low O₂ abundance could be explained by the lower temperature of the dense cloud precursor of IRAS 16293 with respect to the one at the origin of our solar system that prevented efficient formation of O₂ in interstellar ices.

/pdf/linking-interstellar-and-cometary-o-a-deep-search-for-o-o-in-4jcbv1cg15.pdf

Linking interstellar and cometary O₂: a deep search for ¹⁶O¹⁸O in the solar-type protostar IRAS 16293–2422

Recent measurements carried out at comet 67P/Churyumov–Gerasimenko (67P) with the Rosetta probe revealed that molecular oxygen, O2 , is the fourth most abundant molecule in comets. Models show that O2 is likely of primordial nature, coming from the interstellar cloud from which our solar system was formed. However, gaseous O2 is an elusive molecule in the interstellar medium with only one detection towards quiescent molecular clouds, in the ρ Oph A core. We perform a deep search for molecular oxygen, through the 21 −01 rotational transition at 234 GHz of its 16 O18 O isotopologue, towards the warm compact gas surrounding the nearby Class 0 protostar IRAS 16293–2422 B with the ALMA interferometer. We also look for the chemical daughters of O2 , HO2 , and H2 O2 . Unfortunately, the H2 O2 rotational transition is dominated by ethylene oxide c-C2 H4 O while HO2 is not detected. The targeted 16 O18 O transition is surrounded by two brighter transitions at ± 1 km s−1 relative to the expected 16 O18 O transition frequency. After subtraction of these two transitions, residual emission at a 3σ level remains, but with a velocity offset of 0.3−0.5 km s−1 relative to the source velocity, rendering the detection “tentative”. We derive the O2 column density for two excitation temperatures T ex of 125 and 300 K, as indicated by other molecules, in order to compare the O2 abundance between IRAS 16293 and comet 67P. Assuming that 16 O18 O is not detected and using methanol CH3 OH as a reference species, we obtain a [O2 ]/[CH3 OH] abundance ratio lower than 2−5, depending on the assumed T ex , a three to four times lower abundance than the [O2 ]/[CH3 OH] ratio of 5−15 found in comet 67P. Such a low O2 abundance could be explained by the lower temperature of the dense cloud precursor of IRAS 16293 with respect to the one at the origin of our solar system that prevented efficient formation of O2 in interstellar ices.

/pdf/linking-interstellar-and-cometary-o2-a-deep-search-for-5433quy1am.pdf

Linking interstellar and cometary O2: a deep search for 16O18O in the solar-type protostar IRAS 16293-2422

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Linking interstellar and cometary O₂: a deep search for ¹⁶O¹⁸O in the solar-type protostar IRAS 16293–2422

Linking interstellar and cometary O2: a deep search for 16O18O in the solar-type protostar IRAS 16293-2422