Formation conditions of Titan

<p>Satellites are generally believed to form in circumplanetary disks (CPDs): a gas disk containing icy and rocky particles that accumulate to form massive moons over time. The discoveries by the Cassini-Huygens mission have led to a revision of the birth environment of the Saturnian system.</p> <p>We aim to constrain the formation circumstances of Titan's building blocks by considering the moon's observed characteristics. We use radiation thermo-chemical CPD models and evaluate them on their capacity to reproduce a Titan-like satellite.</p> <p>To form a moon with Titan's ice-to-rock ratio, we find that the dust-to-gas ratio in the CPD must be in the order of solar nebula values, O(10<sup>-2</sup>). The ice availability upon accretion is otherwise incompatible with Titan's moment of inertia. Our models predict a large NH<sub>3</sub> inventory was available upon Titan's formation, ∼10-20wt.% of the total ice. This is consistent with the hypothesis that the observed N<sub>2</sub> in Titan is captured as NH<sub>3</sub> and converted by photolysis and shock heating, and is compatible with the possible presence of a conductive layer at 45±15 km as revealed by the Huygens probe.</p>

Distributions of LRS in varying environments

The lifetime reproductive success (LRS) of individuals is affected by random events such as death, realized growth, or realized reproduction, and the outcomes of these events can differ even when individuals have identical probabilities. Another source of randomness arises when these probabilities also change over time in variable environments. For structured populations in stochastic environments, we extend our recent method to determine how birth environment and birth stage determine the random distribution of the LRS. Our results provide a null model that quantifies effects on LRS of just the birth size or stage. Using Roe deer Capreolus capreolus as a case study, we show that the effect of an individual’s birth environment on LRS varies with the frequency of environments and their temporal autocorrelation, and that lifetime performance is affected by changes in the pattern of environmental states expected as a result of climate change.

Modelling the effect of birth and feeding modes on the development of human gut microbiota

The human gut microbiota is transmitted from mother to infant through vaginal birth and breastfeeding. Bifidobacterium , a genus that dominates the infants’ gut, is adapted to breast milk in its ability to metabolize human milk oligosaccharides; it is regarded as a mutualist owing to its involvement in the development of the immune system. The composition of microbiota, including the abundance of Bifidobacteria, is highly variable between individuals and some microbial profiles are associated with diseases. However, whether and how birth and feeding practices contribute to such variation remains unclear. To understand how early events affect the establishment of microbiota, we develop a mathematical model of two types of Bifidobacteria and a generic compartment of commensal competitors. We show how early events affect competition between mutualists and commensals and microbe-host-immune interactions to cause long-term alterations in gut microbial profiles. Bifidobacteria associated with breast milk can trigger immune responses with lasting effects on the microbial community structure. Our model shows that, in response to a change in birth environment, competition alone can produce two distinct microbial profiles post-weaning. Adding immune regulation to our competition model allows for variations in microbial profiles in response to different feeding practices. This analysis highlights the importance of microbe–microbe and microbe–host interactions in shaping the gut populations following different birth and feeding modes.

The birth environment of planetary systems

Star and planet formation are inextricably linked. In the earliest phases of the collapse of a protostar, a disc forms around the young star and such discs are observed for the first several million years of a star’s life. It is within these circumstellar, or protoplanetary, discs that the first stages of planet formation occur. Recent observations from the Atacama large millimetre array (ALMA) suggest that planet formation may already be underway after only 1 Myr of a star’s life. However, stars do not form in isolation; they form from the collapse and fragmentation of giant molecular clouds several parsecs in size. This results in young stars forming in groups—often referred to as ‘clusters’. In these star-forming regions, the stellar density is much higher than the location of the Sun and other stars in the Galactic disc that host exoplanets. As such, the environment where stars form has the potential to influence the planet formation process. In star-forming regions, protoplanetary discs can be truncated or destroyed by interactions with passing stars, as well as photoevaporation from the radiation fields of very massive stars. Once formed, the planets themselves can have their orbits altered by dynamical encounters—either directly from passing stars or through secondary effects such as the Kozai–Lidov mechanism. In this contribution, I review the different processes that can affect planet formation and stability in star-forming regions. I discuss each process in light of the typical range of stellar densities observed for star-forming regions. I finish by discussing these effects in the context of theories for the birth environment of the Solar System.

Wide binaries are rare in open clusters

ABSTRACT The population statistics of binary stars are an important output of star formation models. However, populations of wide binaries evolve over time due to interactions within a system’s birth environment and the unfolding of wide, hierarchical triple systems. Hence, the wide binary populations observed in star-forming regions or OB associations may not accurately reflect the wide binary populations that will eventually reach the field. We use Gaia DR2 data to select members of three open clusters, Alpha Per, the Pleiades, and Praesepe and to flag cluster members that are likely unresolved binaries due to overluminosity or elevated astrometric noise. We then identify the resolved wide binary population in each cluster, separating it from coincident pairings of unrelated cluster members. We find that these clusters have an average wide binary fraction in the 300–3000 au projected separation range of 2.1$\pm ^{0.4}_{0.2}$ per cent increasing to 3.0$\pm ^{0.8}_{0.7}$ per cent for primaries with masses in the 0.5–1.5 M⊙ range. This is significantly below the observed field wide binary fraction, but shows some wide binaries survive in these dynamically highly processed environments. We compare our results with another open cluster (the Hyades) and two populations of young stars that likely originated in looser associations (young moving groups and the Pisces-Eridanus stream). We find that the Hyades also has a deficit of wide binaries while the products of looser associations have wide binary fractions at or above field level.

Hunting for hot corinos and WCCC sources in the OMC-2/3 filament

Context. Solar-like protostars are known to be chemically rich, but it is not yet clear how much their chemical composition can vary and why. So far, two chemically distinct types of Solar-like protostars have been identified: hot corinos, which are enriched in interstellar Complex Organic Molecules, such as methanol (CH3OH) or dimethyl ether (CH3OCH3), and warm carbon chain chemistry (WCCC) objects, which are enriched in carbon chain molecules, such as butadiynyl (C4H) or ethynyl radical (CCH). However, none of these have been studied so far in environments similar to that in which our Sun was born, that is, one that is close to massive stars. Aims. In this work, we search for hot corinos and WCCC objects in the closest analogue to the Sun’s birth environment, the Orion Molecular Cloud 2/3 (OMC-2/3) filament located in the Orion A molecular cloud. Methods. We obtained single-dish observations of CCH and CH3OH line emission towards nine Solar-like protostars in this region. As in other similar studies of late, we used the [CCH]/[CH3OH] abundance ratio in order to determine the chemical nature of our protostar sample. Results. Unexpectedly, we found that the observed methanol and ethynyl radical emission (over a few thousands au scale) does not seem to originate from the protostars but rather from the parental cloud and its photo-dissociation region, illuminated by the OB stars of the region. Conclusions. Our results strongly suggest that caution should be taken before using [CCH]/[CH3OH] from single-dish observations as an indicator of the protostellar chemical nature and that there is a need for other tracers or high angular resolution observations for probing the inner protostellar layers.

Watery mouth disease in neonatal lambs: a systematic literature review

Watery mouth disease is considered to be a significant cause of neonatal mortality in lambs. The clinical signs are strongly associated with an endotoxaemia produced as a result of the lysis of Gram-negative bacteria. It has been associated with mass antibiosis to neonatal lambs at birth, a practice which is now untenable. It can be prevented in many cases through the timely administration of good quality colostrum and a hygienic birth environment. However, despite this, much remains unknown about the specific aetiopathogenesis. Alternative strategies for prevention, treatment and control are required, particularly when colostrum quality is poor, or delivery is absent, and where unhygienic conditions predominate.