اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدStatistics and Universality in Simplified Models of Planetary Formation
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In this paper, we modify Laskars simplified model of planetary evolution and accretion [J. Laskar, Phys. Rev. Lett, vol 84, p 3240 (2000)] to account for the full conservation of the total angular momentum of the system, and extend it to incorporate an accretion probability that depends on the mass and relative velocity of the colliding particles. We present statistical results for the mass and eccentricity of the planets formed, in terms of their semi-major axes, for a large number of realisations of differe
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This paper continues a series in which we predict the main observable characteristics of exoplanets based on their formation. In Paper I we described our global planet formation and evolution model. In Paper II we studied the planetary mass-radius re
lationship. Here we present an extensive study of the statistics of planetary luminosities during both formation and evolution. Our results can be compared with individual directly imaged (proto)planets as well as statistical results from surveys. We calculated three synthetic planet populations assuming different efficiencies of the accretional heating by gas and planetesimals. We describe the temporal evolution of the planetary mass-luminosity relation. We study the shock and internal luminosity during formation. We predict a statistical version of the post-formation mass versus entropy tuning fork diagram. We find high nominal post-formation luminosities for hot and cold gas accretion. Individual formation histories can still lead to a factor of a few spread in the post-formation luminosity at a given mass. However, if the gas and planetesimal accretional heating is unknown, the post-formation luminosity may exhibit a spread of as much as 2-3 orders of magnitude at a fixed mass covering cold, warm, and hot states. As a key result we predict a flat log-luminosity distribution for giant planets, and a steep increase towards lower luminosities due to the higher occurrence rate of low-mass planets. Future surveys may detect this upturn. During formation an estimate of the planet mass may be possible for cold gas accretion if the gas accretion rate can be estimated. Due to the core-mass effect planets that underwent cold gas accretion can still have high post-formation entropies. Once the number of directly imaged exoplanets with known ages and luminosities increases, the observed distributions may be compared with our predictions.
During the late stage of planet formation when Mars-size cores appear, interactions among planetary cores can excite their orbital eccentricities, speed their merges and thus sculpture the final architecture of planet systems. This series of work con
tributes to the final assembling of planet systems with N-body simulations, including the type I and II migration of planets, gas accretion of massive cores in a viscous disk. In this paper, the standard formulations of type I and II migrations are adopted to investigate the formation of planet systems around solar mass stars. Statistics on the final distributions of planetary masses, semi-major axes and eccentricities are derived, which are comparable to those of the observed systems. Our simulations predict some orbital signatures of planet systems around solar mass stars: 36% of the survival planets are giant planets (Mp>10Me). Most of the massive giant planets (Mp>30Me) locate at 1-10AU. Terrestrial planets distribute more or less evenly at <1-2 AU. Planets in inner orbits (<1 AU) may accumulate at the inner edges of either the protostellar disk (3-5 days) or its MRI dead zone (30-50 days). There is a planet desert in the mass-eccecntricity diagram, i.e., lack of planets with masses 0.005 - 0.08 MJ in highly eccentric orbits (e > 0.3 - 0.4). The average eccentricity (~ 0.15) of the giant planets (Mp>10Me) are bigger than that (~ 0.05) of the terrestrial planets (Mp< 10Me). A planet system with more planets tends to have smaller planet masses and orbital eccentricities on average.
As part of a national scientific network Pathways to Habitability the formation of planets and the delivery of water onto these planets is a key question as water is essential for the development of life. In the first part of the paper we summarize t
he state of the art of planet formation - which is still under debate in the astronomical community - before we show our results on this topic. The outcome of our numerical simulations depends a lot on the choice of the initial distribution of planetesimals and planetary embryos after gas disappeared in the protoplanetary disk. We also take into account that some of these planetesimals of sizes in the order of the mass of the Moon already contained water; the quantity depends on the distance from the Sun - close-by bodies are dry, but starting from a distance of about 2 AU they can contain substantial amounts of water. We assume that the gas giants and terrestrial planets are already formed when we check the collisions of the small bodies containing water (in the order of a few percent) with the terrestrial planets. We thus are able to give an estimate of the respective contribution to the actual water content (of some Earth-oceans) in the mantle, in the crust and on the surface of Earth. In the second part we discuss in more detail how the formation of larger bodies after a collision may happen as the outcome depends on parameters like collision velocity, impact angle, and the materials involved. We present results obtained by SPH (Smooth Particle Hydrodynamics) simulations. We briefly describe this method and show different scenarios with respect to the formed bodies, possible fragmentation and the water content before and after the collision. In an appendix we discuss detection methods for extrasolar planets (close to 2000 such objects have been discovered so far).
Stars and planets are the fundamental objects of the Universe. Their formation processes, though related, may differ in important ways. Stars almost certainly form from gravitational collapse and probably have formed this way since the first stars li
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In this era of spatially resolved observations of planet forming disks with ALMA and large ground-based telescopes such as the VLT, Keck and Subaru, we still lack statistically relevant information on the quantity and composition of the material that
is building the planets, such as the total disk gas mass, the ice content of dust, and the state of water in planetesimals. SPICA is an infrared space mission concept developed jointly by JAXA and ESA to address these questions. The key unique capabilities of SPICA that enable this research are (1) the wide spectral coverage 10-220 micron, (2) the high line detection sensitivity of (1-2) 10-19 W m-2 with R~2000-5000 in the far-IR (SAFARI) and 10-20 W m-2 with R~29000 in the mid-IR (SMI, spectrally resolving line profiles), (3) the high far-IR continuum sensitivity of 0.45 mJy (SAFARI), and (4) the observing efficiency for point source surveys. This paper details how mid- to far-IR infrared spectra will be unique in measuring the gas masses and water/ice content of disks and how these quantities evolve during the planet forming period. These observations will clarify the crucial transition when disks exhaust their primordial gas and further planet formation requires secondary gas produced from planetesimals. The high spectral resolution mid-IR is also unique for determining the location of the snowline dividing the rocky and icy mass reservoirs within the disk and how the divide evolves during the build-up of planetary systems. Infrared spectroscopy (mid- to far-IR) of key solid state bands is crucial for assessing whether extensive radial mixing, which is part of our Solar System history, is a general process occurring in most planetary systems and whether extrasolar planetesimals are similar to our Solar System comets/asteroids. ... (abbreviated)
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