1,228 research outputs found
Formation of terrestrial planets in disks evolving via disk winds and implications for the origin of the solar system's terrestrial planets
Recent three-dimensional magnetohydrodynamical simulations have identified a
disk wind by which gas materials are lost from the surface of a protoplanetary
disk, which can significantly alter the evolution of the inner disk and the
formation of terrestrial planets. A simultaneous description of the realistic
evolution of the gaseous and solid components in a disk may provide a clue for
solving the problem of the mass concentration of the terrestrial planets in the
solar system. We simulate the formation of terrestrial planets from planetary
embryos in a disk that evolves via magnetorotational instability and a disk
wind. The aim is to examine the effects of a disk wind on the orbital evolution
and final configuration of planetary systems. We perform N-body simulations of
sixty 0.1 Earth-mass embryos in an evolving disk. The evolution of the gas
surface density of the disk is tracked by solving a one-dimensional diffusion
equation with a sink term that accounts for the disk wind. We find that even in
the case of a weak disk wind, the radial slope of the gas surface density of
the inner disk becomes shallower, which slows or halts the type I migration of
embryos. If the effect of the disk wind is strong, the disk profile is
significantly altered (e.g., positive surface density gradient, inside-out
evacuation), leading to outward migration of embryos inside ~ 1 AU. Disk winds
play an essential role in terrestrial planet formation inside a few AU by
changing the disk profile. In addition, embryos can undergo convergent
migration to ~ 1 AU in certainly probable conditions. In such a case, the
characteristic features of the solar system's terrestrial planets (e.g., mass
concentration around 1 AU, late giant impact) may be reproduced.Comment: 8 pages, 4 figures, accepted for publication in A&
Evolution of Protoplanetary Discs with Magnetically Driven Disc Winds
Aims: We investigate the evolution of protoplanetary discs (PPDs hereafter)
with magnetically driven disc winds and viscous heating. Methods: We consider
an initially massive disc with ~0.1 Msun to track the evolution from the early
stage of PPDs. We solve the time evolution of surface density and temperature
by taking into account viscous heating and the loss of the mass and the angular
momentum by the disc winds within the framework of a standard alpha model for
accretion discs. Our model parameters, turbulent viscosity, disc wind mass
loss, and disc wind torque, which are adopted from local magnetohydrodynamical
simulations and constrained by the global energetics of the gravitational
accretion, largely depends on the physical condition of PPDs, particularly on
the evolution of the vertical magnetic flux in weakly ionized PPDs. Results:
Although there are still uncertainties concerning the evolution of the vertical
magnetic flux remaining, surface densities show a large variety, depending on
the combination of these three parameters, some of which are very different
from the surface density expected from the standard accretion. When a PPD is in
a "wind-driven accretion" state with the preserved vertical magnetic field, the
radial dependence of the surface density can be positive in the inner region
<1-10 au. The mass accretion rates are consistent with observations, even in
the very low level of magnetohydrodynamical turbulence. Such a positive radial
slope of the surface density gives a great impact on planet formation because
(i)it inhibits the inward drift or even results in the outward drift of
pebble/boulder-sized solid bodies, and (ii) it also makes the inward type-I
migration of proto-planets slower or even reversed. Conclusions: The variety of
our calculated PPDs should yield a wide variety of exoplanet systems.Comment: 16 pages, 11 figures embedded, accepted by A&A (comments are welcome
Microarray analysis of salt-responsive genes in common wheat
Dissertação apresentada à Faculdade de Direito da
Universidade de Coimbra no âmbito do 2º Ciclo de Estudos em
Direito, área de especialização
em Ciências Jurídico-Políticas, Direito Internacional
Público e Europeu
Formation of close-in super-Earths in evolving protoplanetary disks due to disk winds
Planets with masses larger than about 0.1 Earth-masses undergo rapid inward
migration (type I migration) in a standard protoplanetary disk. Recent
magnetohydrodynamical simulations revealed the presence of magnetically driven
disk winds, which would alter the disk profile and the type I migration in the
close-in region. We investigate orbital evolution of planetary embryos in disks
that viscously evolve under the effects of disk winds. The aim is to discuss
effects of altered disk profiles on type I migration. In addition, we aim to
examine whether observed distributions of close-in super-Earths can be
reproduced by simulations that include effects of disk winds. We perform N-body
simulations of super-Earth formation from planetary embryos, in which a recent
model for disk evolution is used. We explore a wide range of parameters and
draw general trends. We also carry out N-body simulations of close-in
super-Earth formation from embryos in such disks under various conditions. We
find that the type I migration is significantly suppressed in many cases. Even
in cases in which inward migration occurs, the migration timescale is
lengthened to 1 Myr, which mitigates the type I migration problem. This is
because the gas surface density is decreased and has a flatter profile in the
close-in region due to disk winds. We find that when the type I migration is
significantly suppressed, planets undergo late orbital instability during the
gas depletion, leading to a non-resonant configuration. We also find that
observed distributions of close-in super-Earths (e.g., period ratio, mass
ratio) can be reproduced. In addition, we show that in some results of
simulations, systems with a chain of resonant planets, like the TRAPPIST-1
system, form.Comment: 18 pages, 19 figures, accepted for publication in A&
Adaptive bill morphology for enhanced tool manipulation in New Caledonian crows
Early increased sophistication of human tools is thought to be underpinned by adaptive morphology for efficient tool manipulation. Such adaptive specialisation is unknown in nonhuman primates but may have evolved in the New Caledonian crow, which has sophisticated tool manufacture. The straightness of its bill, for example, may be adaptive for enhanced visually-directed use of tools. Here, we examine in detail the shape and internal structure of the New Caledonian crow’s bill using Principal Components Analysis and Computed Tomography within a comparative framework. We found that the bill has a combination of interrelated shape and structural features unique within Corvus, and possibly birds generally. The upper mandible is relatively deep and short with a straight cutting edge, and the lower mandible is strengthened and upturned. These novel combined attributes would be functional for (i) counteracting the unique loading patterns acting on the bill when manipulating tools, (ii) a strong precision grip to hold tools securely, and (iii) enhanced visually-guided tool use. Our findings indicate that the New Caledonian crow’s innovative bill has been adapted for tool manipulation to at least some degree. Early increased sophistication of tools may require the co-evolution of morphology that provides improved manipulatory skills
- …