Pre-mare cratering and early solar system history

An evaluation of the application of the high extralunar flux in pre-mare times to more general problems of early solar system history is attempted by combining the results of dynamic studies with lunar chronological data. There is a twofold to fourfold contrast in the integral impact flux between the Apollo 14 and 16 sites and the older mare surfaces. This is judged insufficient to account for the contrasting lithology between these two sites: basalts and soil breccias in the maria, annealed breccias and impact melts in the highlands. Therefore, these rocks and their ages (3.9-4.0 b.y.) are thought to predate the surfaces in which they are found. Estimation of the flux needed to produce these lithologies, and difficulties associated with extrapolating this further back in lunar history give support to the "cataclysm" hypothesis of Tera, Papanastassiou, and Wasserburg. Dynamical studies permit separate evaluation of the possible sources for both the "normal" flux during the first 600 million years of lunar history and the "peak" that apparently occurred 4.0 billion years ago. The most likely sources for the normal flux are comets from the vicinity of Uranus and Neptune. The most promising source for the peak is tidal disruption by Earth or Venus of a Ceres-size asteroid initially in a Mars-crossing orbit. Alternative possibilities are suggested

Dynamical evidence regarding the relationship between asteroids and meteorites

Meteorites are fragments of small solar system bodies transferring into the vicinity of earth from the inner edge of the asteroid belt. Photometric measurements support an association between Apollo objects and chondritic meteorites. Dynamical arguments indicate that most Apollo objects are devolatilized comet residues, however; petrographic and cosmogonical reasons argue against this conclusion

Accumulation of the planets

In modeling the accumulation of planetesimals into planets, it is appropriate to distinguish between two stages: an early stage, during which approximately 10 km diameter planetesimals accumulate locally to form bodies approximate 10 to the 25th g in mass; and a later stage in which the approximately 10 to the 25th g planetesimals accumulate into the final planets. In the terrestrial planet region, an initial planetesimal swarm corresponding to the critical mass of dust layer gravitational instabilities is considered. In order to better understand the accumulation history of Mercury-sized bodies, 19 Monte-Carlo simulations of terrestrial planet growth were calculated. A Monte Carlo technique was used to investigate the orbital evolution of asteroidal collision debris produced interior to 2.6 AU. It was found that there are two regions primarily responsible for production of Earth-crossing meteoritic material and Apollo objects. The same techniques were extended to include the origin of Earth-approaching asteroidal bodies. It is found that these same two resonant mechanisms predict a steady-state number of Apollo-Amor about 1/2 that estimated based on astronomical observations

Formation of the terrestrial planets from planetesimals

Formation of the terrestrial planets from planetesimals is discussed. The following subject areas are covered: (1) formation of the original planetesimals; (2) growth of planetesimals into planetary embryos; and (3) growth of runaway planetary embryos into terrestrial planets

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

Distinguishing Hidden Markov Chains

Hidden Markov Chains (HMCs) are commonly used mathematical models of probabilistic systems. They are employed in various fields such as speech recognition, signal processing, and biological sequence analysis. We consider the problem of distinguishing two given HMCs based on an observation sequence that one of the HMCs generates. More precisely, given two HMCs and an observation sequence, a distinguishing algorithm is expected to identify the HMC that generates the observation sequence. Two HMCs are called distinguishable if for every $\varepsilon > 0$ there is a distinguishing algorithm whose error probability is less than $\varepsilon$. We show that one can decide in polynomial time whether two HMCs are distinguishable. Further, we present and analyze two distinguishing algorithms for distinguishable HMCs. The first algorithm makes a decision after processing a fixed number of observations, and it exhibits two-sided error. The second algorithm processes an unbounded number of observations, but the algorithm has only one-sided error. The error probability, for both algorithms, decays exponentially with the number of processed observations. We also provide an algorithm for distinguishing multiple HMCs. Finally, we discuss an application in stochastic runtime verification.Comment: This is the full version of a LICS'16 pape

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

Spitzer observations of the Hyades: Circumstellar debris disks at 625 Myr of age

We use the Spitzer Space Telescope to search for infrared excess at 24, 70, and 160 micron due to debris disks around a sample of 45 FGK-type members of the Hyades cluster. We supplement our observations with archival 24 and 70 micron Spitzer data of an additional 22 FGK-type and 11 A-type Hyades members in order to provide robust statistics on the incidence of debris disks at 625 Myr of age an era corresponding to the late heavy bombardment in the Solar System. We find that none of the 67 FGK-type stars in our sample show evidence for a debris disk, while 2 out of the 11 A-type stars do so. This difference in debris disk detection rate is likely to be due to a sensitivity bias in favor of early-type stars. The fractional disk luminosity, L_dust/L*, of the disks around the two A-type stars is ~4.0E-5, a level that is below the sensitivity of our observations toward the FGK-type stars. However, our sensitivity limits for FGK-type stars are able to exclude, at the 2-sigma level, frequencies higher than 12% and 5% of disks with L_dust/L* > 1.0E-4 and L_dust/L* > 5.0E-4, respectively. We also use our sensitivity limits and debris disk models to constrain the maximum mass of dust, as a function of distance from the stars, that could remain undetected around our targets.Comment: 33 pages, 11 figures, accepted by Ap

Semantic Satiation among Lexically Ambiguous Words

Semantic satiation research indicates that weakly-related semantic information is more satiated than highly-related information (Balota & Black, 1997). In the current studies, we used biased ambiguous words to investigate possible differences in satiation and the duration of satiation. Participants read ambiguous cues 3 or 30 times and either immediately or after a delay made a CUE----TARGET relatedness judgement. Targets were consistent with the dominant or subordinate meaning or unrelated to either. Experiments 1 and 2 satiated noun-noun homographs (e.g.,calf). Experiment 2 included a delayed relatedness judgement and indicated that satiation becomes extinct after no more that one minute (contrary to, e.g., Kuhl & Anderson, 2011). Experiment 3 also satiated noun-verb homographs (e.g., duck). Evidence of satiation was found among the immediate response tasks. Experiment 3 supported the theory that greater semantic distance exists between alternative meanings of noun-verb ambiguous words compared with noun-noun ambiguous words (Mirman et al., 2010)

Externalizing Disorders : Genetics or Prenatal Alcohol Exposure?

Indiana University-Purdue University Indianapolis (IUPUI)Introduction: Externalizing disorders such as attention deficit hyperactivity disorder (ADHD), conduct disorder (CD), and oppositional defiant disorder (ODD) have a high prevalence rate in both children of alcoholics and in those with prenatal alcohol exposure (PAE). These disorders are also predictors of alcohol dependence (alcdep), heritable, and share an underlying genetic liability with alcdep. Furthermore, a mother who drinks while pregnant is likely to be alcohol dependent (AD), and vice-versa. This study incorporated these factors into one model, including as well as a measure of broad genetic risk for ADHD and alcdep to test for the contributions of these effects simultaneously. An independent sample was used to confirm the results for PAE and broad genetic risk. The hypothesis is that PAE will increase the risk to ADHD but not to CD or ODD. Methods: Each of these factors was evaluated independently to test if that effect on its own, significantly contributed to each disorder. Another model included several demographic covariates, to determine which of these environmental effects also contributed to the disorder. The final model for each disorder included environmental effects along with the primary effects of interest. Results: PAE resulted in increased risk for the inattentive (INATT) sub-type of ADHD and conduct disorder (CD) in the discovery sample and for the hyperactive-impulsive (HYPIMP), INATT and CD in the replication sample. PAE and the PAE*maternal alcohol dependence interaction increased the risk for ADHD and INATT. A broad genetic risk for ADHD was associated with all disorders except HYPIMP in the replication sample. Conclusion: This study further supports the trending evidence of a unique etiology of ADHD in those with PAE, and more specifically, that INATT and HYPIMP are affected according to two different mechanisms of action, independent of a genetic contribution due to either ADHD or alcohol dependence, both of which also were associated with a risk for INATT. The contribution of PAE to INATT and CD were the only consistent results across all definitions of alcohol exposure and in both datasets, indicating that PAE is a veritable risk for INATT and CD