Abstract
We report and analyze updated molecular abundances in 20 comets obtained by employing modern data reduction procedures and molecular models. Using box and scatter plots, we examine how the ...different molecular species are distributed among the comet population, while by means of pie charts, we investigate the relative proportions of these molecular species in each comet. We compare these results with the orbital parameters of the selected comets to identify trends related to their dynamical history. With these analyses, we tentatively identify at least three chemical classes based mainly on relative abundances of CO, CH
3
OH, CH
4
, C
2
H
6
, HCN, and NH
3
. The combination of relative abundances and orbital parameters is then compared with recent chemical models of planetary system formation. This approach may help in investigating the origins and evolution of the material in cometary nuclei. Among other aspects, we underline the need to increase our sample size, especially for hypervolatiles (i.e., CH
4
and CO) in Jupiter family comets.
This paper presents results from our molecular characterization of comet 21P/Giacobini-Zinner during its 2018 apparition. We followed the comet during four observing runs, for a total of eight ...nights. The high-resolution spectra of 21P were acquired using iSHELL-the near-infrared high-resolution immersion echelle spectrograph on NASA/IRTF (Maunakea, Hawaii). We detected many cometary emission lines across four customized iSHELL settings in the (2.9-5.2) m range. CO abundances relative to water displayed a relatively constant behavior during the observing campaign, suggesting a possible correlation between the outgassing of water and CO. While CO mixing ratios in 21P are consistent with the reference median value for Jupiter family comets (JFCs), ethane was depleted relative to the reference median value for JFCs, except for one observing run (August 8 and 9) in which ethane appeared overabundant. We consider several possible causes: an ethane outburst, decreasing outgassing of water, or a seasonal effect owing to nucleus rotation. In the pre-perihelion runs, methanol was overabundant compared with the reference median value for JFCs, however it decreased steadily to a depleted value during 21P's post-perihelion phase, suggesting a possible seasonal effect. We report 3 upper limits for acetylene, formaldehyde, ammonia, and methane. The ratios of our measured 3 upper limits for acetylene and detections of hydrogen cyanide are consistent with the depletion of C2 relative to CN in 21P observed at optical wavelengths. This result confirms that 21P is depleted in the carbon-chain primary volatile responsible for C2 production.
We observed short-period comet 252P/LINEAR post-perihelion during its 2016 passage, which presented a favorable opportunity to survey its chemical composition at a close Earth approach (∼0.14 au). We ...characterized the comet's chemical composition on four dates (UT 2016 April 12, 19, 26, and 29) using spectroscopic measurements with the Near-infrared Spectrograph (NIRSPEC) at the Keck Observatory on Maunakea, HI. Our high-resolution infrared spectra yielded production rates for four species (H2O, CH3OH, C2H6, and HCN) and upper limits for five species (NH3, H2CO, C2H2, CO, and CH4). We measured water at an average production rate of 4.9 0.1 × 1027 molec s−1. The chemical properties of 252P suggest a rather typical composition, yet somewhat enriched in methanol and ethane but low in formaldehyde (upper limit) compared to other short-period comets surveyed at infrared wavelengths. Analysis of the ortho/para ratio in water indicates a nuclear spin temperature larger than ∼38 K, consistent with statistical equilibrium (2 ). Spatial distributions of gases, which are representative of possible heterogeneity in the nucleus and/or gas dynamics upon sublimation, showed rather symmetric profiles, with subtle enhancements of the more volatile species C2H6 and HCN toward the sunward hemisphere, while water showed spatial distributions that were extended toward the anti-sunward hemisphere. The continuum was characterized by a narrow distribution. We place our infrared results in the context of observations with the Discovery Channel Telescope, the James Clerk Maxwell submillimeter Telescope, and the Hubble Space Telescope.
Evidence of plant food processing is a significant indicator of the human ability to exploit environmental resources. The recovery of starch grains associated with use-wear on Palaeolithic grinding ...tools offers proof of a specific technology for making flour among Pleistocene hunter-gatherers. Here we present the analysis of five grindstones from two Italian sites, Riparo Bombrini and Grotta di Castelcivita, both inhabited during a crucial phase spanning the decline of the Neanderthals and the establishment of Sapiens. The recovery of starch grains on a Mousterian grindstone at Bombrini suggests that the last Neanderthals not only consumed and processed plants but also made flour 43–41,000 years ago. Starch grains attributable to Triticeae on Protoaurignacian grindstones at both sites testify that Sapiens were processing wild cereals at least 41,500–36,500 years ago when they expanded into Eurasia, long before the dawn of agriculture. These new data suggest a profound knowledge of available plant resources in both human groups.
•Starch grains in association with use-wear traces on grinding tools indicate flour production.•The discovery of new grinding tools extends the chronological range of this knowhow to before 40ka.•The processing of Triticeae is demonstrated since the Protoaurignatian in two Italian sites.•The existence of similar techno-economic practices among Neanderthals and Sapiens is proposed.
An abundance of plant remains (pollen, seeds/fruits and wood) and wood artefacts was found during the excavation of an Etruscan-Roman well located at Cetamura del Chianti in Tuscany, Italy, which ...contained rich cultural and ecofact assemblages in a stratified context. The findings provide evidence for the presence of a mixed oak forest during the time span of the usage of the well. The main decline of deciduous
Quercus
, possibly due to forest clearance, is recorded during the late Etruscan period (ca. 300–100/50 B.C.). A diffusion of
Quercus ilex
occurred during the Roman period (from ca. 50 B.C. to 68 A.D.). Food plants are well represented in the well, particularly cereals and grapevine. The morphometric analysis of the grape pips suggests that fully domesticated forms were cultivated, and that wild fruits may have been gathered in the woods or harvested from weakly domesticated individuals. Some botanical finds could possibly be linked to ritual practices, although the state of preservation of the seed/fruit record, the majority waterlogged, does not meet criteria for carbonized remains used for attributing the plant remains to ritual offerings.
•Light microscopy, SEM and TEM morphological description of short cell phytoliths of Festuca exaltata.•Light-interaction modelling shows that silica-cell phytoliths do not appreciably affect light ...intensity in the cork-cells.•Decreasing protein content in developing silica-cells.
Short cells of Poaceae often contain a cell lumen (CL) phytolith. The aim of this investigation was to analyse the features, development and possible function of CL phytoliths in Festuca exaltata leaves. This study employed light microscopy (LM), scanning and transmission electron microscopy (SEM and TEM respectively). The interaction of light with these phytoliths was modeled using the Finite-Difference Frequency Domain (FDFD) method. The results showed that silica deposition begins within a medium electron density matrix. Proteins were detected in the center of the cytoplasm in a higher amount during the young stage. This occurrence suggests that proteins may be a possible component of the matrix or at least play a role in the silica deposition. At maturity, the short cell phytoliths have peculiar morphology and positioning. These were tested numerically to verify their possible role in either conveying or deflecting light rays, showing only a negligible influence of the phytoliths on the distribution of light within the leaf. A channel apparently connects the silica and the cork cell, suggesting that the cork cells have a metabolic activity related to the metabolism of the silica cells, but possibly not exclusively related to the development.
Reynoutria × bohemica is an invasive species causing significant damage to native ecosystems in North America and Europe.
In this work, we performed an in‐depth micromorphological characterisation of ...the extrafloral nectaries (EFN), during their secretory and post‐secretory phases, in combination with field monitoring of nectary activity over time and the qualitative pool of insect visitors.
EFN consist of secretory trichomes and vascularised parenchyma. Polysaccharides, lipids and proteins were histochemically detected in all trichome cells; phenolic substances were detected in parenchyma cells. Our data indicate that all nectary regions are involved in nectar production and release, constituting a functional unit. Moreover, the main compound classes of nectar and their transfer change over time: first, granulocrine secretion for sugars prevails, then eccrine secretion of the lipophilic fraction takes place. Active nectaries are mainly located in the apical portion of the stem during the growth phase (April–May), when we detected the highest number of individuals visited by ants; from mid‐August onwards, during flowering, the number of active nectaries declined then ceased production (September), with a concomitant decrease in visits by the ants. The spectrum of nectar‐foraging ants mainly included representatives of the genera Formica, Lasius and Camponotus.
Reynoutria × bohemica produces an attractive secretion able to recruit local ants that may potentially act as ‘bodyguards’ for protecting young shoots, reducing secretions during the blooming stage. This defence mechanism against herbivores is the same as that displayed by the parental species in its native areas.
Sedum L. (Crassulaceae) is a large and taxonomically difficult genus whose delimitation and classification are under debate. Due to the controversial results of previous cytological, morphological, ...and molecular studies, further investigations are needed in order to gain a shared taxonomy of the current recognized species clades. In the present paper, morphological and micromorphological features of 23 selected Mediterranean species of Sedum s.l. - collected from exsiccata or fresh specimens throughout Italy - were investigated, in order to provide additional data toward their classification above species level. In particular, the study focused on flower structure and morphology, floral epidermal surfaces and pollen morphology. The distribution pattern of the examined microcharacters across the species revealed a wide range of variation and different combinations of the single characters. NMDS analysis allowed individuating discrete groups that showed a general consistency with the current systematic delimitation of species groups. Our study also evidenced for the first time the wide morphological variability of nectaries and of the glandular indumentum, not previously investigated in detail. In addition, we proposed the combined use of floral diagrams and floral formulae as valuable tools in studying the variability of flower structure at genus level.
We report measurements of eight primary volatiles (H2O, HCN, CH4, C2H6, CH3OH, C2H2, H2CO, and NH3) and two product species (OH and NH2) in comet 103P/Hartley 2 using high-dispersion infrared ...spectroscopy. We quantified the long- and short-term behavior of volatile release over a three-month interval that encompassed the comet's close approach to Earth, its perihelion passage, and flyby of the comet by the Deep Impact spacecraft during the EPOXI mission. We present production rates for individual species, their mixing ratios relative to water, and their spatial distributions in the coma on multiple dates. The production rates for water, ethane, HCN, and methanol vary in a manner consistent with independent measures of nucleus rotation, but mixing ratios for HCN, C2H6, and CH3OH are independent of rotational phase. Our results demonstrate that the ensemble average composition of gas released from the nucleus is well defined and relatively constant over the three-month interval (September 18 through December 17). If individual vents vary in composition, enough diverse vents must be active simultaneously to approximate (in sum) the bulk composition of the nucleus. The released primary volatiles exhibit diverse spatial properties which favor the presence of separate polar and apolar ice phases in the nucleus, establish dust and gas release from icy clumps (and from the nucleus), and provide insights into the driver for the cyanogen (CN) polar jet. The spatial distributions of C2H6 and HCN along the near-polar jet (UT October 19.5) and nearly orthogonal to it (UT October 22.5) are discussed relative to the origin of CN. The ortho-para ratio (OPR) of water was 2.85 ? 0.20; the lower bound (2.65) defines T spin > 32 K. These values are consistent with results returned from the Infrared Space Observatory in 1997.
Three examples of plant landscape shaping, carried out by Iron Age populations living in different geographical areas, are presented. The examples differ in population type (Garamantes, Etruscans, ...and Romans), archaeological context (settlement, necropolis, furnace, port), and area of plant exploitation (respectively, Fezzan - Libyan Sahara and Tuscany, Latium - central Italy). The leitmotiv of the three parallel investigations highlighted that humans induced clear changes in plant cover modifying the quantitative ratio among native elements and spreading the plants of economic interest even outside of their natural habitats. Micro- and macroremain analyses once more enhanced that landscape reconstruction depends on both wild and cultivated plants, and that the cultural plant landscape is composed of a complex mixture of indigenous and exotic elements. Archaeobotany results in great help in reviewing ancient prejudices, rewriting history in a modern ecological view, also discovering a different role in the landscape evolution of past civilizations. In this light, the Garamantes deeply transformed the oases in agrarian producer sites, and the Etruscans, in the area of the Gulf of Follonica, modified the previous forest vegetation, probably enhancing the xeric features. The Romans, believed as the main creators of the environmental changes in the Mediterranean basin, surprisingly did not produce consistent plant changes in the area of the Tiber delta, in the surroundings of the imperial port of Rome, during the first century AD.
PDF
