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Date:
Icy Planet Formation
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Title: Coagulation Calculations of Icy Planet Formation at 15--150 AU: A Correlation Between the Maximum Radius and the Slope of the Size Distribution for Transneptunian Objects
Authors: Scott J. Kenyon, Benjamin C. Bromley

We investigate whether coagulation models of planet formation can explain the observed size distributions of transneptunian objects (TNOs). Analysing published and new calculations, we demonstrate robust relations between the size of the largest object and the slope of the size distribution for sizes 0.1 km and larger. These relations yield clear, testable predictions for TNOs and other icy objects throughout the solar system. Applying our results to existing observations, we show that a broad range of initial disk masses, planetesimal sizes, and fragmentation parameters can explain the data. Adding dynamical constraints on the initial semimajor axis of `hot' KBOs along with probable TNO formation times of 10-700 Myr restricts the viable models to those with a massive disk composed of relatively small (1-10 km) planetesimals.

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Posts: 131433
Date:
Formation of Gas Giant Planets
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Title: A New Hybrid N-Body-Coagulation Code for the Formation of Gas Giant Planets
Authors: Benjamin C. Bromley (University of Utah), Scott J. Kenyon (SAO)
(Version v2)

We describe an updated version of our hybrid N-body-coagulation code for planet formation. In addition to the features of our 2006-2008 code, our treatment now includes algorithms for the 1D evolution of the viscous disk, the accretion of small particles in planetary atmospheres, gas accretion onto massive cores, and the response of N-bodies to the gravitational potential of the gaseous disk and the swarm of planetesimals. To validate the N-body portion of the algorithm, we use a battery of tests in planetary dynamics. As a first application of the complete code, we consider the evolution of Pluto-mass planetesimals in a swarm of 0.1-1 cm pebbles. In a typical evolution time of 1-3 Myr, our calculations transform 0.01-0.1 solar mass disks of gas and dust into planetary systems containing super-Earths, Saturns, and Jupiters. Low mass planets form more often than massive planets; disks with smaller alpha form more massive planets than disks with larger alpha. For Jupiter-mass planets, masses of solid cores are 10-100 Earth masses.

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Posts: 131433
Date:
The Snow Border
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Title: The Snow Border
Authors: M.G. Marseille, S. Cazaux

Context. The study of the snow line is an important topic in several domains of astrophysics, and particularly for the evolution of proto-stellar environments and the formation of planets.
Aims. The formation of the first layer of ice on carbon grains requires low temperatures compared to the temperature of evaporation (T > 100 K). This asymmetry generates a zone in which bare and icy dust grains coexist. Methods. We use Monte-Carlo simulations to describe the formation time scales of ice mantles on bare grains in protostellar disks and massive protostars environments. Then we analytically describe these two systems in terms of grain populations subject to infall and turbulence, and assume steady-state.
Results. Our results show that there is an extended region beyond the snow line where icy and bare grains can coexist, in both proto-planetary disks and massive protostars. This zone is not negligible compared to the total size of the objects: on the order of 0.4 AU for proto-planetary disks and 5400 AU for high-mass protostars. Times to reach the steady-state are respectively estimated from 10^2 to 10^5 yr.
Conclusions. The presence of a zone, a so-called snow border, in which bare and icy grains co-exist can have a major impact on our knowledge of protostellar environments. From a theoretical point of view, the progression of icy grains to bare grains as the temperature increases, could be a realistic way to model hot cores and hot corinos. Also, in this zone, the formation of planetesimals will require the coagulation of bare and icy grains. Observationally, this zone allows high abundances of gas phase species at large scales, for massive protostars particularly, even at low temperatures (down to 50 K).

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Posts: 131433
Date:
RE: Planet Formation
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Title: A new view on planet formation
Authors: Sergei Nayakshin (Leicester)

The standard picture of planet formation posits that giant gas planets are over-grown rocky planets massive enough to attract enormous gas atmospheres. It has been shown recently that the opposite point of view is physically plausible: the rocky terrestrial planets are former giant planet embryos dried of their gas "to the bone" by the influences of the parent star. Here we provide a brief overview of this "Tidal Downsizing" hypothesis in the context of the Solar System structure.

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NASA Scientists Theorise Final Growth Spurt for Planets

A team of NASA-funded researchers has unveiled a new theory that contends planets gained the final portions of their mass from a limited number of large comet or asteroid impacts more than 4.5 billion years ago. These impacts added less than one percent of the planets' mass.
Scientists hope the research not only will provide a better historical picture of the birth and evolution of Earth, the moon and Mars, but also allow researchers to better explore what happened in our solar system's beginning and middle stages of planet formation.

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Title: The Formation of Uranus and Neptune in Solid-Rich Feeding Zones: Connecting Chemistry and Dynamics
Authors: Sarah E. Dodson-Robinson (1), Peter Bodenheimer (2) ((1) University of Texas, (2) UCO/Lick Observatory)

The core accretion theory of planet formation has at least two fundamental problems explaining the origins of Uranus and Neptune: (1) dynamical times in the trans-Saturnian solar nebula are so long that core growth can take > 15 Myr, and (2) the onset of runaway gas accretion that begins when cores reach 10 Earth masses necessitates a sudden gas accretion cutoff just as the ice giant cores reach critical mass. Both problems may be resolved by allowing the ice giants to migrate outward after their formation in solid-rich feeding zones with planetesimal surface densities well above the minimum-mass solar nebula. We present new simulations of the formation of Uranus and Neptune in the solid-rich disk of Dodson-Robinson et al. (2009) using the initial semimajor axis distribution of the Nice model (Gomes et al. 2005; Morbidelli et al. 2005; Tsiganis et al. 2005), with one ice giant forming at 12 AU and the other at 15 AU. The innermost ice giant reaches its present mass after 3.8-4.0 Myr and the outermost after 5.3-6 Myr, a considerable time decrease from previous one-dimensional simulations (e.g. Pollack et al. 1996). The core masses stay subcritical, eliminating the need for a sudden gas accretion cutoff. Our calculated carbon mass fractions of 22% are in excellent agreement with the ice giant interior models of Podolak et al. (1995) and Marley et al. (1995). Based on the requirement that the ice giant-forming planetesimals contain >10% mass fractions of methane ice, we can reject any solar system formation model that initially places Uranus and Neptune inside the orbit of Saturn. We also demonstrate that a large population of planetesimals must be present in both ice giant feeding zones throughout the lifetime of the gaseous nebula.

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Title: The peculiar solar composition and its possible relation to planet formation
Authors: Jorge Melendez (CAUP), Martin Asplund (MPA), Bengt Gustafsson (Upssala), David Yong (Stromlo)

We have conducted a differential elemental abundance analysis of unprecedented accuracy (0.01 dex) of the Sun relative to 11 solar twins from the Hipparcos catalogue and 10 solar analogs from planet searches. We find that the Sun shows a characteristic signature with a ~20% depletion of refractory elements relative to the volatile elements in comparison with the solar twins. The abundance differences correlate strongly with the condensation temperatures of the elements. This peculiarity also holds in comparisons with solar analogs known to have close-in giant planets while the majority of solar analogs found not to have such giant planets in radial velocity monitoring show the solar abundance pattern. We discuss various explanations for this peculiarity, including the possibility that the differences in abundance patterns are related to the formation of planetary systems like our own, in particular to the existence of terrestrial planets.

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New computer simulations have suggested that dense swarms of asteroids collapsed under their own gravity to make the building blocks of the planets in our solar system.
The planets are thought to have formed from a disc of dust and gas around the infant sun.


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How our solar system was formed has fascinated scientists and laymen alike for -- well, for a really, really long time. New research may have answered a piece to the puzzle - how big were the first planetesimals? ?
For those of you scoring at home, "planetesimals" were the first solid objects in our newly minted solar system (also known as the protoplanetary disk). They began life as small grains of dust orbiting an infant sun. These grains would bump into each other, clump together and gradually form larger grains of dust, which eventually became small space rocks.
Now the theory goes that some of these small rock-sized planetesimals aspired for greater things, and continued to gradually grow in size to become asteroids, and that a few of those continued to grow beyond the asteroid stage and become planets.

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Did asteroids flock together to build planets?
Perhaps we should thank rapid-assembly asteroids for spawning the planets. New simulations suggest that dense swarms of boulders collapsed under their own gravity to make the building blocks of our solar system.

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