Evolution of planetesimal velocities

A self-consistent set of equations for the velocity evolution of a general planetesimal population is presented. The equations are given in a form convenient for calculations of the early stages of planetary accumulation when it is necessary to model the planetesimal swarm by methods of gas dynamics, rather than follow the orbital evolution of individual bodies. Steady state velocities of a simple planetesimal population consisting of two different sizes of bodies are calculated. Dynamical friction is found to be an important mechanism for transferring kinetic energy from the larger planetesimals to the smaller ones. When the small planetesimals are relatively abundant, gas drag and inelastic collisions among the smaller bodies are of comparable importance for dissipating energy from the population

Regional tectonic analysis of Venus equatorial highlands and comparison with Earth-based Magellan radar images

Research on regional tectonic analysis of Venus equatorial highlands and comparison with earth-based and Magellan radar images is presented. Over the past two years, the tectonic analysis of Venus performed centered on global properties of the planet, in order to understand fundamental aspects of the dynamics of the mantle and lithosphere of Venus. These include studies pertaining to the original constitutive and thermal character of the planet, as well as the evolution of Venus through time, and the present day tectonics. Parameterized convection models of the Earth and Venus were developed. The parameterized convection code was reformulated to model Venus with an initially hydrous mantle to determine how the cold-trap could affect the evolution of the planet

Collisions between equal sized ice grain agglomerates

Following the recent insight in the material structure of comets, protoplanetesimals are assumed to have low densities and to be highly porous agglomerates. It is still unclear if planetesimals can be formed from these objects by collisional growth. Therefore, it is important to study numerically the collisional outcome from low velocity impacts of equal sized porous agglomerates which are too large to be examined in a laboratory experiment. We use the Lagrangian particle method Smooth Particle Hydrodynamics to solve the equations that describe the dynamics of elastic and plastic bodies. Additionally, to account for the influence of porosity, we follow a previous developed equation of state and certain relations between the material strength and the relative density. Collisional growth seems possible for rather low collision velocities and particular material strengths. The remnants of collisions with impact parameters that are larger than 50% of the radius of the colliding objects tend to rotate. For small impact parameters, the colliding objects are effectively slowed down without a prominent compaction of the porous structure, which probably increases the possibility for growth. The protoplanetesimals, however, do not stick together for the most part of the employed material strengths. An important issue in subsequent studies has to be the influence of rotation to collisional growth. Moreover, for realistic simulations of protoplanetesimals it is crucial to know the correct material parameters in more detail.Comment: 7 pages, 11 figures, accepted by A&

POSTNATAL BRAIN DYSMORPHOLOGY INDUCED BY PRENATAL ALCOHOL EXPOSURE: A PRECLINICAL MRI STUDY

poster abstractBrain dysmorphology is one of the most critical features of Fetal Alcohol Spectrum Disorders (FASD). This study was designed to use high resolution preclinical MRI system to compare the brain structures between alcohol exposed C57BL/6 mice with control. The objective is to examine how alcohol affects a dose- and timing-dependent brain dysmorphology during development comparable to that of human FASD. Three treated groups, ALC (pre- and pregnancy alcohol with 4.2 % (v/v) alcohol liquid), PF (pre alcohol and a calorically matched liquid pregnancy diet), and CHOW (ad lib chow/water), were examined. Mouse heads were imaged using 9.4T preclinical MRI system with 3D gradient echo (GRE) sequence to acquire volumetric images with voxel size as low as 40 microns. Whole brain, olfactory bulbs, cortex, hypothalamus, and cerebellum were segmented and the volumes were calculated. Data was examined by ANOVA followed with paired comparison between treatment groups to test the effect of prenatal alcohol exposure. ALC group had shown consistently smaller mean volumes of difference brain regions than the other two groups. Volume of total brain, olfactory bulbs and cerebellum were observed to be significantly different for ALC compared to PF pups. This indicated that prenatal alcohol exposure caused retarded fetal brain development. Comparing PF with CHOW pups, only cerebellum volume was observed to be significantly different. For cortex volume, no significant difference was shown for any pairwise comparison. These results suggest that alcohol effect contribute to brain dysmorphology, and match with our previous craniofacial dysmorphology study. This could be important to assist in the understanding of clinical variants of human FASD patients in brain dysmorphology

Collisional Velocities and Rates in Resonant Planetesimal Belts

We consider a belt of small bodies around a star, captured in one of the external or 1:1 mean-motion resonances with a massive perturber. The objects in the belt collide with each other. Combining methods of celestial mechanics and statistical physics, we calculate mean collisional velocities and collisional rates, averaged over the belt. The results are compared to collisional velocities and rates in a similar, but non-resonant belt, as predicted by the particle-in-a-box method. It is found that the effect of the resonant lock on the velocities is rather small, while on the rates more substantial. The collisional rates between objects in an external resonance are by about a factor of two higher than those in a similar belt of objects not locked in a resonance. For Trojans under the same conditions, the collisional rates may be enhanced by up to an order of magnitude. Our results imply, in particular, shorter collisional lifetimes of resonant Kuiper belt objects in the solar system and higher efficiency of dust production by resonant planetesimals in debris disks around other stars.Comment: 31 pages, 11 figures (some of them heavily compressed to fit into arxiv-maximum filesize), accepted for publication at "Celestial Mechanics and Dynamical Astronomy

Shape models and physical properties of asteroids

Despite the large amount of high quality data generated in recent space encounters with asteroids, the majority of our knowledge about these objects comes from ground based observations. Asteroids travelling in orbits that are potentially hazardous for the Earth form an especially interesting group to be studied. In order to predict their orbital evolution, it is necessary to investigate their physical properties. This paper briefly describes the data requirements and different techniques used to solve the lightcurve inversion problem. Although photometry is the most abundant type of observational data, models of asteroids can be obtained using various data types and techniques. We describe the potential of radar imaging and stellar occultation timings to be combined with disk-integrated photometry in order to reveal information about physical properties of asteroids.Comment: From Assessment and Mitigation of Asteroid Impact Hazards boo

Genome-wide association studies of the self-rating of effects of ethanol (SRE).

The level of response (LR) to alcohol as measured with the Self-Report of the Effects of Alcohol Retrospective Questionnaire (SRE) evaluates the number of standard drinks usually required for up to four effects. The need for a higher number of drinks for effects is genetically influenced and predicts higher risks for heavy drinking and alcohol problems. We conducted genome-wide association study (GWAS) in the African-American (COGA-AA, N = 1527 from 309 families) and European-American (COGA-EA, N = 4723 from 956 families) subsamples of the Collaborative Studies on the Genetics of Alcoholism (COGA) for two SRE scores: SRE-T (average of first five times of drinking, the period of heaviest drinking, and the most recent 3 months of consumption) and SRE-5 (the first five times of drinking). We then meta-analyzed the two COGA subsamples (COGA-AA + EA). Both SRE-T and SRE-5 were modestly heritable (h2 : 21%-31%) and genetically correlated with alcohol dependence (AD) and DSM-IV AD criterion count (rg : 0.35-0.76). Genome-wide significant associations were observed (SRE-T: chromosomes 6, rs140154945, COGA-EA P = 3.30E-08 and 11, rs10647170, COGA-AA+EA P = 3.53E-09; SRE-5: chromosome13, rs4770359, COGA-AA P = 2.92E-08). Chromosome 11 was replicated in an EA dataset from the National Institute on Alcohol Abuse and Alcoholism intramural program. In silico functional analyses and RNA expression analyses suggest that the chromosome 6 locus is an eQTL for KIF25. Polygenic risk scores derived using the COGA SRE-T and SRE-5 GWAS predicted 0.47% to 2.48% of variances in AD and DSM-IV AD criterion count in independent datasets. This study highlights the genetic contribution of alcohol response phenotypes to the etiology of alcohol use disorders

Dust discs around intermediate mass and Sun-like stars in the 16 Myr old NGC 1960 open cluster

We present an analysis of Spitzer IRAC (3.6--8um) and MIPS (24um) imaging of members of the 16(+10/-5)Myr old open cluster NGC 1960 (M36). Models of terrestrial planet formation indicate that rocky planets are likely to achieve their final masses at around 10-30Myr, and thus this cluster is at an interesting epoch for planet formation. We find 21 B-F5 type stars and 14 F6-K9 type stars which have 24um excess emission, and thus determine that >30% of B-F5 type stars and >23% of F6-K9 type stars in this cluster have 24um excess emission. These excess frequencies are similar to those observed in other clusters of similar age. Three early type stars have excesses at near-infrared wavelengths. Analysis of their SEDs confirms that these are true debris discs and not remnant primordial or transitional discs. None of the 61 sun-like stars have confirmed near-infrared excess, and we can place a limit on the frequency of 8um excess emission around sun-like stars of <7%. All of the detected excesses are consistent with emission from debris discs and are not primordial.Comment: 16 pages, 10 figures, accepted for publication in MNRAS (tables 1-4 will be available in full online in the electronic version of the paper

On the dynamics and collisional growth of planetesimals in misaligned binary systems

Context. Abridged. Many stars are members of binary systems. During early phases when the stars are surrounded by discs, the binary orbit and disc midplane may be mutually inclined. The discs around T Tauri stars will become mildly warped and undergo solid body precession around the angular momentum vector of the binary system. It is unclear how planetesimals in such a disc will evolve and affect planet formation. Aims. We investigate the dynamics of planetesimals embedded in discs that are perturbed by a binary companion on a circular, inclined orbit. We examine collisional velocities of the planetesimals to determine when they can grow through accretion. We vary the binary inclination, binary separation, D, disc mass, and planetesimal radius. Our standard model has D=60 AU, inclination=45 deg, and a disc mass equivalent to the MMSN. Methods. We use a 3D hydrodynamics code to model the disc. Planetesimals are test particles which experience gas drag, the gravitational force of the disc, the companion star gravity. Planetesimal orbit crossing events are detected and used to estimate collisional velocities. Results. For binary systems with modest inclination (25 deg), disc gravity prevents planetesimal orbits from undergoing strong differential nodal precession (which occurs in absence of the disc), and forces planetesimals to precess with the disc on average. For bodies of different size the orbit planes become modestly mutually inclined, leading to collisional velocities that inhibit growth. For larger inclinations (45 degrees), the Kozai effect operates, leading to destructively large relative velocities. Conclusions. Planet formation via planetesimal accretion is difficult in an inclined binary system with parameters similar to those considered in this paper. For systems in which the Kozai mechanism operates, the prospects for forming planets are very remote.Comment: 24 pages, 16 figures, recently published in Astronomy and Astrophysic

Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets

Nature, 435, pp. 466-469, http://dx.doi.org./10.1038/nature03676International audienc