Main Results

Comet Statistic

Implementation:

To compare molecular abundances of methanol (CH3OH), formaldehyde (H2CO) and ammonia (NH3) in 35 comets, we divided the sample in the following subgroups:

Comets observed at heliocentric distances larger or shorter than 1 au: to test observational differences due to possible chemical processes related to the solar radiation
Different dynamical types: to check for evolutionary trends from Dynamically New comets (expected to be less processed) to Jupiter Family comets (expected to be more processed due to their closeness to the Sun)
Pre and Post perihelion observations: to check for changes in activity due to thermal inertia
We further compared the results with the data collected by the Rosina mass spectrometer on board of the ESA Rosetta mission that studied in details comet 67P/Churyumov-Gerasimenko

Main Results:

Comet composition seems to be unaltered during their lifetime: In our sample, we do not observe statistically significant differences between comets from different dynamical classes (e.g., Jupiter family/short period vs. Oort Cloud/long period comets), implying that the comet material has not changed considerably after formation.
There are not well understood chemical processes in the coma: We identify instead the existence of temperature-activated processes in the coma that may affect the abundance of given species (e.g., formaldehyde), depending on the observing conditions.
The statistical approach is needed: When comparing the database results to those from the ESA-Rosetta mission, we find that 67P/Churyumov-Gerasimenko is not representative of the average comet population, highlighting the importance of not using this target as the sole reference point when comparing comets and planet-forming regions.In the figure below we show the main results. The significancy of the observed differences were tested using a Kolomogrov–Smirnov Statistical test.

Box plot statistic for methanol, formaldehyde, and ammonia abundances in comets. Starting from the left, we show the overall database, the heliocentric distance dependency (Rh < 1 vs. Rh > 1 au; see also Figure A1), different dynamical types (DN = dynamically new, LP = long-period, JF = Jupiter-family), pre- and post perihelion observations, and 67P measurements separated in pre- and post-perihelion. For each box plot the middle line corresponds to the median, the box limits correspond to the 25th and 75th percentiles, and the whiskers correspond to the 5th and 95th percentiles. Below every box, we report the median ± standard deviation

Comparisons with Star- and Planet Forming Regions

An inheritance scenario?

We compared the molecular abundance ratios of methanol/formaldehyde and ammonia/methanol in 35 comets and and 11 proto-stellar solar analogs and planet forming disks.

As shown in the figure below, when compared to planet-forming systems, the [CH3OH]/[H2CO] and [NH3]/[CH3OH] molecular abundance ratios in comets are consistent with those measured in Class 0 hot corinos and in the inner regions of Class II disks, hence suggesting an inheritance scenario.

Box plot statistic for [CH3OH]/[H2CO] and [NH3]/[CH3OH] ratios in comets and comparison with disks. Below each box, the [minimum, maximum] interval values are indicated. Starting from the left, we show the ratios measured in planet-forming systems as listed in Table 2, in comets divided in different dynamical families (DN = dynamically new, LP = long-period, JF = Jupiter-family), in comets at different heliocentric distances (Rh < 1 vs. Rh > 1 au, see also

Figure A2), and in 67P divided in pre- and post-perihelion. Below every box, we report the [min,max] interval.

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