51 research outputs found
Institutional Membership and the Experience of the Philadelphia-Baltimore-Washington Stock Exchange
Explorations in Economic Research, Volume 2, number 3 (Regional Stock Exchanges in a Central Market System)
Earth and Terrestrial Planet Formation
The growth and composition of Earth is a direct consequence of planet
formation throughout the Solar System. We discuss the known history of the
Solar System, the proposed stages of growth and how the early stages of planet
formation may be dominated by pebble growth processes. Pebbles are small bodies
whose strong interactions with the nebula gas lead to remarkable new accretion
mechanisms for the formation of planetesimals and the growth of planetary
embryos.
Many of the popular models for the later stages of planet formation are
presented. The classical models with the giant planets on fixed orbits are not
consistent with the known history of the Solar System, fail to create a high
Earth/Mars mass ratio, and, in many cases, are also internally inconsistent.
The successful Grand Tack model creates a small Mars, a wet Earth, a realistic
asteroid belt and the mass-orbit structure of the terrestrial planets.
In the Grand Tack scenario, growth curves for Earth most closely match a
Weibull model. The feeding zones, which determine the compositions of Earth and
Venus follow a particular pattern determined by Jupiter, while the feeding
zones of Mars and Theia, the last giant impactor on Earth, appear to randomly
sample the terrestrial disk. The late accreted mass samples the disk nearly
evenly.Comment: Accepted for publication in Early Earth an AGU Monograph edited by
James Badro and Michael J. Walte
The early impact histories of meteorite parent bodies
We have developed a statistical framework that uses collisional evolution
models, shock physics modeling and scaling laws to determine the range of
plausible collisional histories for individual meteorite parent bodies. It is
likely that those parent bodies that were not catastrophically disrupted
sustained hundreds of impacts on their surfaces - compacting, heating, and
mixing the outer layers; it is highly unlikely that many parent bodies escaped
without any impacts processing the outer few kilometers. The first 10 - 20 Myr
were the most important time for impacts, both in terms of the number of
impacts and the increase of specific internal energy due to impacts. The model
has been applied to evaluate the proposed impact histories of several meteorite
parent bodies: up to 10 parent bodies that were not disrupted in the first 100
Myr experienced a vaporizing collision of the type necessary to produce the
metal inclusions and chondrules on the CB chondrite parent; around 1 - 5% of
bodies that were catastrophically disrupted after 12 Myr sustained impacts at
times that match the heating events recorded on the IAB/winonaite parent body;
more than 75% of 100 km radius parent bodies which survived past 100 Myr
without being disrupted sustained an impact that excavates to the depth
required for mixing in the outer layers of the H chondrite parent body; and to
protect the magnetic field on the CV chondrite parent body, the crust would
have had to have been thick (~ 20 km) in order to prevent it being punctured by
impacts.Comment: 30 pages, 11 figures, 3 tables. Accepted for publication in
Meteoritics & Planetary Scienc
Thermal Evolution and Magnetic Field Generation in Terrestrial Planets and Satellites
Timescale and morphology of Martian mantle overturn immediately following magma ocean solidification
The role of person-environment interactions in increased alcohol use in the transition to college
A Recount of the Early Joint Stock Companies and Securities Trading in the United States (1620s-1850s)
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