9 research outputs found
Dynamical orbital evolution of asteroids and planetesimals across distinct chemical reservoirs due to accretion growth of planets in the early solar system
N-body numerical simulations code for the orbital motion of
asteroids/planetesimals within the asteroid belt under the gravitational
influence of the sun and the accreting planets has been developed. The aim is
to make qualitative, and to an extent a semi-quantitative argument, regarding
the possible extent of radial mixing and homogenization of planetesimal
reservoirs of the two observed distinct spectral types , viz., the S-type and
C-type, across the heliocentric distances due to their dynamical orbital
evolution, thereby, eventually leading to the possible accretion of asteroids
having chemically diverse constituents. The spectral S-type and C-type
asteroids are broadly considered as the parent bodies of the two observed major
meteoritic dichotomy classes, namely, the non-carbonaceous (NC) and
carbonaceous (CC) meteorites, respectively. The present analysis is performed
to understand the evolution of the observed dichotomy and its implications due
to the nebula and early planetary processes during the initial 10 Myrs (Million
years). The homogenization across the two classes is studied in context to the
accretion timescales of the planetesimals with respect to the half-life of the
potent planetary heat source, 26Al. The accretion over a timescale of ~1.5 Myr.
possibly resulted in the planetary-scale differentiation of planetesimals to
produce CC and NC achondrites and iron meteorite parent bodies, whereas, the
prolonged accretion over a timescale of 2-5 Myrs. resulted in the formation of
CC and NC chondrites. Our simulation results indicate a significant role of the
initial eccentricities and the masses of the accreting giant planets,
specifically, Jupiter and Saturn, in triggering the eccentricity churning of
the planetesimals across the radial distances......Comment: Accepte
The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe
The preponderance of matter over antimatter in the early Universe, the
dynamics of the supernova bursts that produced the heavy elements necessary for
life and whether protons eventually decay --- these mysteries at the forefront
of particle physics and astrophysics are key to understanding the early
evolution of our Universe, its current state and its eventual fate. The
Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed
plan for a world-class experiment dedicated to addressing these questions. LBNE
is conceived around three central components: (1) a new, high-intensity
neutrino source generated from a megawatt-class proton accelerator at Fermi
National Accelerator Laboratory, (2) a near neutrino detector just downstream
of the source, and (3) a massive liquid argon time-projection chamber deployed
as a far detector deep underground at the Sanford Underground Research
Facility. This facility, located at the site of the former Homestake Mine in
Lead, South Dakota, is approximately 1,300 km from the neutrino source at
Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino
charge-parity symmetry violation and mass ordering effects. This ambitious yet
cost-effective design incorporates scalability and flexibility and can
accommodate a variety of upgrades and contributions. With its exceptional
combination of experimental configuration, technical capabilities, and
potential for transformative discoveries, LBNE promises to be a vital facility
for the field of particle physics worldwide, providing physicists from around
the globe with opportunities to collaborate in a twenty to thirty year program
of exciting science. In this document we provide a comprehensive overview of
LBNE's scientific objectives, its place in the landscape of neutrino physics
worldwide, the technologies it will incorporate and the capabilities it will
possess.Comment: Major update of previous version. This is the reference document for
LBNE science program and current status. Chapters 1, 3, and 9 provide a
comprehensive overview of LBNE's scientific objectives, its place in the
landscape of neutrino physics worldwide, the technologies it will incorporate
and the capabilities it will possess. 288 pages, 116 figure
Stellar sources of the short-lived radionuclides in the early solar system
We discuss the possible stellar sources of short-lived radionuclides (SLRs) known to have been present in the early solar system (26Al, 36Cl, 41Ca, 53Mn, 60Fe, 107Pd, 129I, 182Hf, 244Pu). SLRs produced primarily by irradiation (7Be, 10Be) are not discussed in this paper. We evaluate the role of the galactic background in explaining the inventory of SLRs in the early solar system. We review the nucleosynthetic processes that produce the different SLRs and place the processes in the context of stellar evolution of stars from 1 to 120 M. The ejection of newly synthesized SLRs from these stars is also discussed. We then examine the extent to which each stellar source can, by itself, explain the relative abundances of the different SLRs in the early solar system, and the probability that each source would have been in the right place at the right time to provide the SLRs. We conclude that intermediate-mass AGB stars and massive stars in the range from ~20 to ~60 M are the most plausible sources. Low-mass AGB stars fail to produce enough 60Fe. Core-collapse Type II supernovae from stars with initial masses of 20 M produce too much 60Fe and 53Mn. Sources such as novae, Type Ia supernovae, and core-collapse supernovae of O-Ne-Mg white dwarfs do not appear to provide the SLRs in the correct proportions. However, intermediate-mass AGB stars cannot provide 53Mn or the r-process elements, so if an AGB star provided the 41Ca, 36Cl, 26Al, 60Fe, and 107Pd, and if a late stellar source is required for 53Mn and the r-process elements, then two types of sources would be required. A separate discussion of the production of r-process elements highlights the difficulties in modeling their production. There appear to be two sources of r-process elements, one that produces the heavy r-process elements, including the actinides, and one that produces the elements from N to Ge and the elements ~110 A ~130. These can be assigned to SNII explosions of stars of ≤11 M and stars of 12-25 M, respectively. More-massive stars, which leave black holes as supernova remnants, apparently do not produce r-process elements
Isotopic records in CM hibonites: Implications for timescales of mixing of isotope reservoirs in the solar nebula
The magnesium isotopic compositions of 26 hibonite-bearing inclusions from the CM chondrite Murchison, as well as isotopic measurements on a subset of these samples for oxygen, titanium, and lithium-beryllium-boron are reported along with oxygen isotopi