Stopping Super-Earths from growing into Jupiters

2020 ◽  
Author(s):  
Mohamad Ali-Dib ◽  
Andrew Cumming ◽  
Doug Lin
Keyword(s):  
Planet Formation ◽  
Thermal State ◽  
Relative Size ◽  
Protoplanetary Disk ◽  
Outer Envelope ◽  
Dominant Type ◽  
Lower Entropy ◽  
Gas Accretion ◽  
The Hill

<p>Super-Earths are by far the most dominant type of exoplanet, yet their formation is<br />still not well understood. In particular, planet formation models predict that many<br />of them should have accreted enough gas to become gas giants. Here we examine the<br />role of the protoplanetary disk in the cooling and contraction of the protoplanetary<br />envelope. In particular, we investigate the effects of 1) the thermal state of the disk as<br />set by the relative size of heating by accretion or irradiation, and whether its energy is<br />transported by radiation or convection, and 2) advection of entropy into the outer envelope by disk flows that penetrate the Hill sphere, as found in 3D global simulations.<br />We find that, at 0.1 AU, the envelope quickly becomes fully radiative, nearly isothermal, and thus cannot cool down, stalling gas accretion. This<br />effect is significantly more pronounced in convective disks, leading to envelope mass or-<br />ders of magnitude lower. Entropy advection at 0.1 AU in either radiative or convective<br />disks could therefore explain why super-Earths failed to undergo runaway accretion.</p> <p>Ali-Dib, Cumming, & Lin (MNRAS 2020)</p>

scholarly journals The imprint of the protoplanetary disc in the accretion of super-Earth envelopes

2020 ◽  
Vol 494 (2) ◽  
pp. 2440-2448 ◽  
Author(s):  
Mohamad Ali-Dib ◽  
Andrew Cumming ◽  
Douglas N C Lin
Keyword(s):  
Energy Transport ◽  
Thermal State ◽  
Relative Size ◽  
Outer Envelope ◽  
Dominant Type ◽  
The Core ◽  
Lower Entropy ◽  
Gas Accretion ◽  
The Hill

ABSTRACT Super-Earths are by far the most dominant type of exoplanet, yet their formation is still not well understood. In particular, planet formation models predict that many of them should have accreted enough gas to become gas giants. Here, we examine the role of the protoplanetary disc in the cooling and contraction of the protoplanetary envelope. In particular, we investigate the effects of (1) the thermal state of the disc as set by the relative size of heating by accretion or irradiation, and whether its energy is transported by radiation or convection, and (2) advection of entropy into the outer envelope by disc flows that penetrate the Hill sphere, as found in 3D global simulations. We find that, at 5 and 1 au, this flow at the level reported in the non-isothermal simulations where it penetrates only to ∼0.3 times the Hill radius has little effect on the cooling rate since most of the envelope mass is concentrated close to the core, and far from the flow. On the other hand, at 0.1 au, the envelope quickly becomes fully radiative, nearly isothermal, and thus cannot cool down, stalling gas accretion. This effect is significantly more pronounced in convective discs, leading to envelope mass orders of magnitude lower. Entropy advection at 0.1 au in either radiative or convective discs could therefore explain why super-Earths failed to undergo runaway accretion. These results highlight the importance of the conditions and energy transport in the protoplanetary disc for the accretion of planetary envelopes.

Rural Dalit Women Entrepreneurs and Development Scenario: A Study

2016 ◽  
Vol 5 (1) ◽  
Author(s):  
Amaldass M. ◽  
Neema Gnanadev
Keyword(s):  
Rural Women ◽  
Women Entrepreneurs ◽  
Cultural Aspects ◽  
Self Employment ◽  
Dalit Women ◽  
Integral Development ◽  
Entrepreneurial Activities ◽  
The Hill ◽  
The Village

Pandit Nehru affirmed that women development/ empowerment is the basis for the substantial growth of a family, a village, or a nation. Development/upliftment of women is an essential ingredient of human development. Entrepreneurship development among the rural women folk would strengthen the village economy and promote regional development. The women entrepreneurs have proved that there is a source of immense untapped power in the womanhood of India (Margaret, 1992). Women undoubtedly are the backbone of the socio-economic-cultural aspects in the hill scenario. The subsistence agriculture which leads to low and unstable incomes, which in turn lead to a sizeable out-migration of male members that leads to only women headed families behind, and the role of women in the household economy becomes more important (Rawat, 2004). In the midst of limited opportunities, tough terrains and lack of resources, the contribution of women entrepreneurs to the society is enormous. An attempt was made to highlight the strategies and development aspects of rural women entrepreneurs in Almora district. Entrepreneurs who are engaged in self-employment and innovative entrepreneurial activities were selected for the study. A total of 50 samples were selected and the data were collected through interviews and focus groups. The study reveals various aspects related to rural women entrepreneurship and constraints that need attention so to empower women in their efforts toward integral development.

The Germans and Air Power at Dieppe: The Raid and its Lessons from the ‘Other Side of the Hill’

2021 ◽  
pp. 096834452199586
Author(s):  
James Shelley
Keyword(s):  
Armed Forces ◽  
The Other ◽  
Air Power ◽  
Coastal Defence ◽  
German Armed Forces ◽  
Popular Interest ◽  
The Hill

Despite the vast academic and popular interest in the Dieppe raid of 19 August 1942, there remains a curious oversight of the German side of the story. This contribution interrogates German sources in order to explore the Dieppe air battle and its consequences from the perspective of the German armed forces. The paper ultimately demonstrates that the Germans learnt much about the role of air power in coastal defence from their experiences at Dieppe, but that the implementation of those lessons was lacking.

Interaction of solid bodies with atmospheres of protoplanets

2018 ◽  
Vol 14 (S345) ◽  
pp. 351-352
Author(s):  
Ernst A. Dorfi ◽  
Florian Ragossnig
Keyword(s):  
Kinetic Energy ◽  
Physical Properties ◽  
Planet Formation ◽  
Frictional Heating ◽  
Protoplanetary Disk ◽  
Small Bodies ◽  
Early Stages ◽  
Break Up ◽  
Solid Bodies ◽  
Stellar Source

AbstractDuring the early stages of planet formation accretion of small bodies add mass to the planet and deposit their energy kinetic energy. Caused by frictional heating and/or large stagnation pressures within the dense and extended atmospheres most of the in-falling bodies get destroyed by melting or break-up before they impact on the planet’s surface. The energy is added to the atmospheric layers rather than heating the planet directly. These processes can significantly alter the physical properties of protoplanets before they are exposed with their primordial atmospheres to the early stellar source when the protoplanetary disk becomes evaporated.

scholarly journals Galaxy Dynamics: Secular Evolution and Accretion

2010 ◽  
Vol 6 (S271) ◽  
pp. 119-126 ◽  
Author(s):  
Francoise Combes
Keyword(s):  
Angular Momentum ◽  
Galaxy Evolution ◽  
Resonant Scattering ◽  
Relative Role ◽  
Radial Migration ◽  
Galaxy Dynamics ◽  
Secular Evolution ◽  
Minor Mergers ◽  
Gas Accretion

AbstractRecent results are reviewed on galaxy dynamics, bar evolution, destruction and re-formation, cold gas accretion, gas radial flows and AGN fueling, minor mergers. Some problems of galaxy evolution are discussed in particular, exchange of angular momentum, radial migration through resonant scattering, and consequences on abundance gradients, the frequency of bulgeless galaxies, and the relative role of secular evolution and hierarchical formation.

scholarly journals The Grand Tack model: a critical review

2014 ◽  
Vol 9 (S310) ◽  
pp. 194-203 ◽  
Author(s):  
Sean N. Raymond ◽  
Alessandro Morbidelli
Keyword(s):  
Solar System ◽  
Building Blocks ◽  
Protoplanetary Disk ◽  
Giant Planets ◽  
Asteroid Belt ◽  
Terrestrial Planets ◽  
Saturn’S Satellites ◽  
Internal Inconsistency ◽  
Solar System Bodies ◽  
Gas Accretion

AbstractThe “Grand Tack” model proposes that the inner Solar System was sculpted by the giant planets' orbital migration in the gaseous protoplanetary disk. Jupiter first migrated inward then Jupiter and Saturn migrated back outward together. If Jupiter's turnaround or “tack” point was at ~ 1.5 AU the inner disk of terrestrial building blocks would have been truncated at ~ 1 AU, naturally producing the terrestrial planets' masses and spacing. During the gas giants' migration the asteroid belt is severely depleted but repopulated by distinct planetesimal reservoirs that can be associated with the present-day S and C types. The giant planets' orbits are consistent with the later evolution of the outer Solar System.Here we confront common criticisms of the Grand Tack model. We show that some uncertainties remain regarding the Tack mechanism itself; the most critical unknown is the timing and rate of gas accretion onto Saturn and Jupiter. Current isotopic and compositional measurements of Solar System bodies – including the D/H ratios of Saturn's satellites – do not refute the model. We discuss how alternate models for the formation of the terrestrial planets each suffer from an internal inconsistency and/or place a strong and very specific requirement on the properties of the protoplanetary disk.We conclude that the Grand Tack model remains viable and consistent with our current understanding of planet formation. Nonetheless, we encourage additional tests of the Grand Tack as well as the construction of alternate models.

scholarly journals Magnetically induced termination of giant planet formation

2018 ◽  
Vol 619 ◽  
pp. A165 ◽  
Author(s):  
A. J. Cridland
Keyword(s):  
Magnetic Field ◽  
Cross Section ◽  
Planet Formation ◽  
Giant Planet ◽  
Effective Cross Section ◽  
Cold Start ◽  
Population Synthesis ◽  
Hot Start ◽  
Gas Accretion ◽  
Planetary Magnetic Field

Here a physical model for terminating giant planet formation is outlined and compared to other methods of late-stage giant planet formation. As has been pointed out before, gas accreting into a gap and onto the planet will encounter the planetary dynamo-generated magnetic field. The planetary magnetic field produces an effective cross section through which gas is accreted. Gas outside this cross section is recycled into the protoplanetary disk, hence only a fraction of mass that is accreted into the gap remains bound to the planet. This cross section inversely scales with the planetary mass, which naturally leads to stalled planetary growth late in the formation process. We show that this method naturally leads to Jupiter-mass planets and does not invoke any artificial truncation of gas accretion, as has been done in some previous population synthesis models. The mass accretion rate depends on the radius of the growing planet after the gap has opened, and we show that so-called hot-start planets tend to become more massive than cold-start planets. When this result is combined with population synthesis models, it might show observable signatures of cold-start versus hot-start planets in the exoplanet population.

scholarly journals Size-mediated, density-dependent cannibalism in the signal crayfish Pacifastacus leniusculus (Dana, 1852) (Decapoda, Astacidea), an invasive crayfish in Britain

Crustaceana ◽  
2017 ◽  
Vol 90 (4) ◽  
pp. 417-435 ◽  
Author(s):  
R. J. Houghton ◽  
C. Wood ◽  
X. Lambin
Keyword(s):  
Relative Size ◽  
Pacifastacus Leniusculus ◽  
Gut Contents ◽  
Size Distributions ◽  
Signal Crayfish ◽  
Density Dependent ◽  
Invasive Crayfish ◽  
The Relationship ◽  
Best Fit

The role of cannibalism in crayfish populations is not well understood, despite being a potentially key density-dependent process underpinning population dynamics. We studied the incidence of cannibalism in an introduced signal crayfish Pacifastacus leniusculus population in a Scottish lowland river in September 2014. Animals were sampled using six different sampling techniques simultaneously, revealing variable densities and size distributions across the site. Cannibalism prevalence was estimated by analysing the gut contents of crayfish >20 mm CL for the presence of crayfish fragments, which was found to be 20% of dissected individuals. When seeking evidence of relationships between the sizes of cannibals and ‘prey’, the density of conspecifics <56% the size of a dissected individual yielded the best fit. The relationship between cannibalism probability and crayfish size and density was equally well described by three different metrics of crayfish density. Cannibalism increased with crayfish size and density but did not vary according to sex. These results suggest that large P. leniusculus frequently cannibalize smaller (prey) conspecifics, and that the probability of cannibalism is dependent upon the relative size of cannibal-to-prey and the density of the smaller crayfish. We suggest that removing large individuals, as targeted by many traditional removal techniques, may lead to reduced cannibalism and therefore a compensatory increase in juvenile survival.

scholarly journals Differences in acid phosphomonoesterase activity in forest soils of the Smrk Massive in the Moravskoslezské Beskydy Mts. (Czech Republic)

Beskydy ◽  
2012 ◽  
Vol 5 (2) ◽  
pp. 135-152
Author(s):  
A. Bajer ◽  
P. Samec ◽  
M. Žárník
Keyword(s):  
Relative Size ◽  
Chemical Properties ◽  
Principal Component ◽  
European Beech ◽  
Soil Characteristics ◽  
Strong Correlations ◽  
Spruce Stands ◽  
The Individual ◽  
A Site

The purpose of this paper is to determine the individual relations between APEA and specific soils and environmental factors. To disclose these relations, analysis of component vectors and principal component analysis (PCA) were performed. Vectors of soil characteristics with participation of APEA (aAKFE) and vectors of pedochemical variables (aCHEM) were also calculated. Their ratio (ia) indicated the relative size of the APEA impact on the relations between pedochemical characteristics. Based on the statistical analyses, different role of APEA in Norway spruce and in European beech stands was detected. While APEA in spruce stands did not show significant correlations with the other examined soil chemical properties, soils under beech stands displayed strong correlations with some of the pedochemical variables. The idea of this research is to find out whether APEA could be used as an indicator of forest vegetation status and of the anthropogenic load on a site.

On apposition

1999 ◽  
Vol 3 (1) ◽  
pp. 59-81 ◽  
Author(s):  
Juan Carlos Acuña-Fariña
Keyword(s):  
Distinctive Feature ◽  
Local Domain ◽  
Syntactic Relation ◽  
The Hill

This paper seeks to redefine apposition, a term that is often used in the literature with a remarkable lack of precision. Starting from paradigmatic instances of apposition (Romulus, the legendary founder; Santiago, the capital of Galicia), the main resemblances to the paradigm are analysed in an attempt to measure the validity of a general syntactic relation that is often put on a par with co-ordination and dependency. Paradigmatic appositions and other related nominal patterns are shown to be structures of nonrestrictive modification (i.e. not really appositions) which are best understood in reference to the concept of a Local Domain. The second unit of these structures has its scope in the local domain of the first unit, of which it is an expansion, not in the larger domain of the sentence. By contrast, most instances of non-nominal apposition (e.g. He ran – absolutely raced – up the hill; Burton-Roberts, 1975) are seen as true appositions, as defined in this paper, namely as structures whose two units relate independently to a Sentence Domain without forming a superordinate node in it. Crucial to the distinction between the Local and the Sentence domains is the role of intonation boundaries. These are strongly obligatory only with those structures which have been considered paradigmatic appositions in the literature (Romulus, the legendary founder), and their role is to isolate the second unit within them from the remainder of the sentence, thus preventing it from having a function in it. The intonation boundaries are also responsible for the most distinctive feature of these structures, namely the predicative relationship binding the two units together (Dupont, 1985; Koktová, 1985; Longrée, 1987; Forsgren, 1988).

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