scholarly journals Water transport throughout the TRAPPIST-1 system: the role of planetesimals

2020 ◽  
Vol 499 (4) ◽  
pp. 4626-4637
Author(s):  
Vladimir Đošović ◽  
Bojan Novakovć ◽  
Branislav Vukotć ◽  
Milan M Ćirković
Keyword(s):  
Water Transport ◽  
Early Phase ◽  
Planetary System ◽  
Source Region ◽  
Dynamical Evolution ◽  
Water Delivery ◽  
Dynamical Mechanism ◽  
Nominal Model ◽  
Water Amount

ABSTRACT Observational data suggest that a belt of planetesimals is expected close to the snow line in protoplanetary discs. Assuming there is such a belt in the TRAPPIST-1 system, we examine possibilities of water delivery to the planets via planetesimals from the belt. The study is accomplished by numerical simulations of dynamical evolution of a hypothetical planetesimal belt. Our results show that the inner part of the belt is dynamically unstable and planetesimals located in this region are quickly scattered away, with many of them entering the region around the planets. The main dynamical mechanism responsible for the instability are close encounters with the outermost planet Trappist-1h. A low-order mean-motion resonance 2:3 with Trappist-1h, located in the same region, also contributes to the objects transport. In our nominal model, the planets have received a non-negligible amount of water, with the smallest amount of 15 per cent of the current Earth’s water amount (EWA) being delivered to the planet 1b, while the planets Trappist-1e and Trappist-1g have received more than 60 per cent of the EWA. We have found that while the estimated efficiency of water transport to the planets is robust, the amount of water delivered to each planet may vary significantly, depending on the initial masses and orbits of the planets. The estimated dynamical ‘half-lives’ have shown that the impactors’ source region should be emptied in less then 1 Myr. Therefore, the obtained results suggest that the transport of planetesimals through the system preferably occurs during an early phase of the planetary system evolution.

scholarly journals Realistic collisional water transport during terrestrial planet formation

2020 ◽  
Vol 634 ◽  
pp. A76 ◽  
Author(s):  
C. Burger ◽  
Á. Bazsó ◽  
C. M. Schäfer
Keyword(s):  
Water Content ◽  
Water Transport ◽  
Planet Formation ◽  
Hybrid Approach ◽  
Dynamical Evolution ◽  
Terrestrial Planet ◽  
Giant Planets ◽  
Asteroid Belt ◽  
Water Delivery ◽  
Hit And Run

Context. According to the latest theoretical and isotopic evidence, Earth’s water content originates mainly from today’s asteroid belt region, or at least from the same precursor material. This suggests that water was transported inwards to Earth, and to similar planets in their habitable zone, via (giant) collisions of planetary embryos and planetesimals during the chaotic final phase of planet formation. Aims. In current dynamical simulations water delivery to terrestrial planets is still studied almost exclusively by assuming oversimplified perfect merging, even though water and other volatiles are particularly prone to collisional transfer and loss. To close this gap we have developed a computational framework to model collisional water transport by direct combination of long-term N-body computations with dedicated 3D smooth particle hydrodynamics (SPH) collision simulations of differentiated, self-gravitating bodies for each event. Methods. Post-collision water inventories are traced self-consistently in the further dynamical evolution, in accretionary or erosive as well as hit-and-run encounters with two large surviving bodies, where besides collisional losses, water transfer between the encountering bodies has to be considered. This hybrid approach enables us for the first time to trace the full dynamical and collisional evolution of a system of approximately 200 bodies throughout the whole late-stage accretion phase (several hundred Myr). As a first application we choose a Solar System-like architecture with already formed giant planets on either circular or eccentric orbits and a debris disk spanning the whole terrestrial planet region (0.5–4 au). Results. Including realistic collision treatment leads to considerably different results than simple perfect merging, with lower mass planets and water inventories reduced regularly by a factor of two or more. Due to a combination of collisional losses and a considerably lengthened accretion phase, final water content, especially with giant planets on circular orbits, is strongly reduced to more Earth-like values, and closer to results with eccentric giant planets. Water delivery to potentially habitable planets is dominated by very few decisive collisions, mostly with embryo-sized or larger objects and only rarely with smaller bodies, at least if embryos have formed throughout the whole disk initially. The high frequency of hit-and-run collisions and the differences to predominantly accretionary encounters, such as generally low water (and mass) transfer efficiencies, are a crucial part of water delivery, and of system-wide evolution in general.

scholarly journals Dynamical evolution of multiple-population globular clusters

2021 ◽  
Vol 502 (3) ◽  
pp. 4290-4304
Author(s):  
Enrico Vesperini ◽  
Jongsuk Hong ◽  
Mirek Giersz ◽  
Arkadiusz Hypki
Keyword(s):  
Structural Properties ◽  
Globular Clusters ◽  
First Generation ◽  
Radial Profile ◽  
Dynamical Evolution ◽  
Evolutionary Phase ◽  
Dynamical Parameters ◽  
Energy Equipartition

ABSTRACT We have carried out a set of Monte Carlo simulations to study a number of fundamental aspects of the dynamical evolution of multiple stellar populations in globular clusters with different initial masses, fractions of second generation (2G) stars, and structural properties. Our simulations explore and elucidate: (1) the role of early and long-term dynamical processes and stellar escape in the evolution of the fraction of 2G stars and the link between the evolution of the fraction of 2G stars and various dynamical parameters; (2) the link between the fraction of 2G stars inside the cluster and in the population of escaping stars during a cluster’s dynamical evolution; (3) the dynamics of the spatial mixing of the first-generation (1G) and 2G stars and the details of the structural properties of the two populations as they evolve toward mixing; (4) the implications of the initial differences between the spatial distribution of 1G and 2G stars for the evolution of the anisotropy in the velocity distribution and the expected radial profile of the 1G and 2G anisotropy for clusters at different stages of their dynamical history; and (5) the variation of the degree of energy equipartition of the 1G and the 2G populations as a function of the distance from the cluster’s centre and the cluster’s evolutionary phase.

Water transport across mammalian cell membranes

1996 ◽  
Vol 270 (1) ◽  
pp. C12-C30 ◽  
Author(s):  
A. S. Verkman ◽  
A. N. van Hoek ◽  
T. Ma ◽  
A. Frigeri ◽  
W. R. Skach ◽  
...  
Keyword(s):  
Water Transport ◽  
Cell Membranes ◽  
Water Channel ◽  
Water Channels ◽  
Channel Structure ◽  
Level Information ◽  
Selective Channel ◽  
Transcriptional Units ◽  
Measurement Strategies

This review summarizes recent progress in water-transporting mechanisms across cell membranes. Modern biophysical concepts of water transport and new measurement strategies are evaluated. A family of water-transporting proteins (water channels, aquaporins) has been identified, consisting of small hydrophobic proteins expressed widely in epithelial and nonepithelial tissues. The functional properties, genetics, and cellular distributions of these proteins are summarized. The majority of molecular-level information about water-transporting mechanisms comes from studies on CHIP28, a 28-kDa glycoprotein that forms tetramers in membranes; each monomer contains six putative helical domains surrounding a central aqueous pathway and functions independently as a water-selective channel. Only mutations in the vasopressin-sensitive water channel have been shown to cause human disease (non-X-linked congenital nephrogenic diabetes insipidus); the physiological significance of other water channels remains unproven. One mercurial-insensitive water channel has been identified, which has the unique feature of multiple overlapping transcriptional units. Systems for expression of water channel proteins are described, including Xenopus oocytes, mammalian and insect cells, and bacteria. Further work should be directed at elucidation of the role of water channels in normal physiology and disease, molecular analysis of regulatory mechanisms, and water channel structure determination at atomic resolution.

scholarly journals Mass determination of the 1:3:5 near-resonant planets transiting GJ 9827 (K2-135)

2018 ◽  
Vol 618 ◽  
pp. A116 ◽  
Author(s):  
J. Prieto-Arranz ◽  
E. Palle ◽  
D. Gandolfi ◽  
O. Barragán ◽  
E. W. Guenther ◽  
...  
Keyword(s):  
Planetary System ◽  
Initial Conditions ◽  
Dynamical Evolution ◽  
Space Mission ◽  
Mass Determination ◽  
Velocity Measurements ◽  
Orbital Periods ◽  
The Masses ◽  
Better Than

Context. Multiplanet systems are excellent laboratories to test planet formation models as all planets are formed under the same initial conditions. In this context, systems transiting bright stars can play a key role, since planetary masses, radii, and bulk densities can be measured. Aims. GJ 9827 (K2-135) has recently been found to host a tightly packed system consisting of three transiting small planets whose orbital periods of 1.2, 3.6, and 6.2 days are near the 1:3:5 ratio. GJ 9827 hosts the nearest planetary system (~30 pc) detected by NASA’s Kepler or K2 space mission. Its brightness (V = 10.35 mag) makes the star an ideal target for detailed studies of the properties of its planets. Methods. Combining the K2 photometry with high-precision radial-velocity measurements gathered with the FIES, HARPS, and HARPS-N spectrographs we revised the system parameters and derive the masses of the three planets. Results. We find that GJ 9827 b has a mass of Mb = 3.69−0.46+0.48 M⊕ and a radius of Rb = 1.58−0.13+0.14 R⊕, yielding a mean density of ρb = 5.11−1.27+1.74 g cm−3. GJ 9827 c has a mass of Mc = 1.45−0.57+0.58 M⊕, radius of Rc = 1.24−0.11+0.11 R⊕, and a mean density of ρc = 4.13−1.77+2.31 g cm−3. For GJ 9827 d, we derive Md = 1.45−0.57+0.58 M⊕, Rd = 1.24−0.11+0.11 R⊕, and ρd = 1.51−0.53+0.71 g cm−3. Conclusions. GJ 9827 is one of the few known transiting planetary systems for which the masses of all planets have been determined with a precision better than 30%. This system is particularly interesting because all three planets are close to the limit between super-Earths and sub-Neptunes. The planetary bulk compositions are compatible with a scenario where all three planets formed with similar core and atmosphere compositions, and we speculate that while GJ 9827 b and GJ 9827 c lost their atmospheric envelopes, GJ 9827 d maintained its primordial atmosphere, owing to the much lower stellarirradiation. This makes GJ 9827 one of the very few systems where the dynamical evolution and the atmosphericescape can be studied in detail for all planets, helping us to understand how compact systems form and evolve.

scholarly journals The enigmatic ribosomal stalk

2018 ◽  
Vol 51 ◽  
Author(s):  
Anders Liljas ◽  
Suparna Sanyal
Keyword(s):  
Early Phase ◽  
Ribosomal Subunit ◽  
Structure And Function ◽  
Large Ribosomal Subunit ◽  
Translation Factors ◽  
Ribosomal Stalk ◽  
And Function ◽  
High Degree

Abstract The large ribosomal subunit has a distinct feature, the stalk, extending outside the ribosome. In bacteria it is called the L12 stalk. The base of the stalk is protein uL10 to which two or three dimers of proteins bL12 bind. In archea and eukarya P1 and P2 proteins constitute the stalk. All these extending proteins, that have a high degree of flexibility due to a hinge between their N- and C-terminal parts, are essential for proper functionalization of some of the translation factors. The role of the stalk proteins has remained enigmatic for decades but is gradually approaching an understanding. In this review we summarise the knowhow about the structure and function of the ribosomal stalk till date starting from the early phase of ribosome research.

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