Formation of planetesimals

Formation of planetesimals is discussed. The following subject areas are covered: (1) nebular structure; (2) aerodynamics of the solid bodies in the nebula; (3) problems with gravitational instability; (4) particle growth by coagulation; properties of fractal aggregates; and (5) coagulation and settling of fractal aggregates

Collisional and Dynamical Evolution of Planetary Systems

Senior Scientst S. J. Weidenschilling presents his final administrative report in the research program entitled "Collisional and Dynamical Evolution of Planetary Systems," on which he was the Principal Investigator. This research program produced the following publications: 1) "Jumping Jupiters" in binary star systems. F. Marzari, S. J. Weidenschilling, M. Barbieri and V. Granata. Astrophys. J., in press, 2005; 2) Formation of the cores of the outer planets. To appear in "The Outer Planets" (R. Kallenbach, ED), ISSI Conference Proceedings (Space Sci. Rev.), in press, 2005; 3) Accretion dynamics and timescales: Relation to chondrites. S. J. Weidenschilling and J. Cuzzi. In Meteorites and the Early Solar System LI (D. Lauretta et al., Eds.), Univ. of Arizona Press, 2005; 4) Asteroidal heating and thermal stratification of the asteroid belt. A. Ghosh, S. J.Weidenschilling, H. Y. McSween, Jr. and A. Rubin. In Meteorites and the Early Solar System I1 (D. Lauretta et al., Eds.), Univ. of Arizona Press, 2005

Aerodynamic and Gasdynamic Effects in Cosmogony

Senior Scientist Stuart J. Weidenschilling presents his final administrative report for the research program entitled "Aerodynamic and Gasdynamic Effects in Cosmogony" on which he was the Principal Investigator. The research program produced the following publications: 1) Particle-gas dynamics and primary accretion. J . N. Cuzzi and S. J. Weidenschilling. In Meteorites and the Early Solar System II (D. Lauretta and H. Y . McSween, Eds.). Univ. Arizona Press. in press, 2005; 2) Timescales of the solar protoplanetary disk. S. Russell, L. Hartmann. J. N. Cuzzi. A. Krot. M. Gounelle and S . J Weidenschilling. In Meteorites and the Early Solar System II (D. Lauretta and H. Y. McSween, Eds.). Univ. Arizona Press, in press, 2005; 3) From icy grains to comets. In Comets II (M. Festou et al., Eds.). Univ. Arizona Press, pp. 97-104. 2004; 4) Gravitational instability and clustering in a disk of planetesimals. P. Tanga, S. J. N'eidenschilling, P. Michel and D. C. Richardson. Astron. Astrophys. 327, 1 105- 1 1 15, 2004

Enhancement of the Accretion of Jupiters Core by a Voluminous Low-Mass Envelope

We present calculations of the early stages of the formation of Jupiter via core nucleated accretion and gas capture. The core begins as a seed body of about 350 kilometers in radius and orbits in a swarm of planetesimals whose initial radii range from 15 meters to 100 kilometers. We follow the evolution of the swarm by accounting for growth and fragmentation, viscous and gravitational stirring, and for drag-induced migration and velocity damping. Gas capture by the core substantially enhances the cross-section of the planet for accretion of small planetesimals. The dust opacity within the atmosphere surrounding the planetary core is computed self-consistently, accounting for coagulation and sedimentation of dust particles released in the envelope as passing planetesimals are ablated. The calculation is carried out at an orbital semi-major axis of 5.2 AU and an initial solids' surface density of 10/g/cm^2 at that distance. The results give a core mass of 7 Earth masses and an envelope mass of approximately 0.1 Earth mass after 500,000 years, at which point the envelope growth rate surpasses that of the core. The same calculation without the envelope gives a core mass of only 4 Earth masses

Formation and Evolution of Planetary Systems: Placing Our Solar System in Context with Spitzer

We summarize the progress to date of our Legacy Science Program entitled "The Formation and Evolution of Planetary Systems" (FEPS) based on observations obtained with the Spitzer Space Telescope during its first year of operation. In addition to results obtained from our ground-based preparatory program and our early validation program, we describe new results from a survey for near-infrared excess emission from the youngest stars in our sample as well as a search for cold debris disks around sun-like stars. We discuss the implications of our findings with respect to current understanding of the formation and evolution of our own solar system.Comment: 8 postscript pages including 3 figures. To appear in "Spitzer New Views of the Cosmos" ASP Conference Series, eds. L. Armus et al. FEPS website at http://feps.as.arizona.ed

A Possible Origin for Giant Planets Found at Small Stellar Distances

aps other ices) to provide enough mass to allow growth of the core before dissipation of the gas. High temperatures within a few astronomical units (AU) of the Sun would preclude such an origin. Jupiter, at 5.2 AU, is widely believed to have formed near the boundary of ice condensation in the solar nebula (7). In contrast, as of this writing six planets are known with masses comparable to Jupiter and orbits well inside 1 AU; these are companions of the stars 51 Peg, t Boo, Ups And, 55 Cnc, HD114762, and 70 Vir. The first three all have semimajor axes a 0.05 AU, the next has a 0.1 AU, and the last two are at 0.4 and 0.47 AU. In addition, a planet of 47 UMa is at a distance of 2.1 AU. Lin et al. (5) suggested that giant planets migrated inward while tidally linked to an evolving circumstellar disk that was accreting onto the star. This mechanism implies that planets must have formed simultaneously with the star itself, bu

Evaluating planetesimal bow shocks as sites for chondrule formation

We investigate the possible formation of chondrules by planetesimal bow shocks. The formation of such shocks is modeled using a piecewise parabolic method (PPM) code under a variety of conditions. The results of this modeling are used as a guide to study chondrule formation in a one-dimensional, finite shock wave. This model considers a mixture of chondrule-sized particles and micron-sized dust and models the kinetic vaporization of the solids. We found that only planetesimals with a radius of ~1000 km and moving at least ~8 km/s with respect to the nebular gas can generate shocks that would allow chondrule-sized particles to have peak temperatures and cooling rates that are generally consistent with what has been inferred for chondrules. Planetesimals with smaller radii tend to produce lower peak temperatures and cooling rates that are too high. However, the peak temperatures of chondrules are only matched for low values of chondrule wavelength-averaged emissivity. Very slow cooling (<~100s of K/hr) can only be achieved if the nebular opacity is low, which may result after a significant amount of material has been accreted into objects that are chondrule-sized or larger, or if chondrules formed in regions of the nebula with small dust concentrations. Large shock waves of approximately the same scale as those formed by gravitational instabilities or tidal interactions between the nebula and a young Jupiter do not require this to match the inferred thermal histories of chondrules.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202