Global resurfacing of Mercury 4.0-4.1 billion years ago by heavy bombardment and volcanism.

The most heavily cratered terrains on Mercury have been estimated to be about 4 billion years (Gyr) old, but this was based on images of only about 45 per cent of the surface; even older regions could have existed in the unobserved portion. These terrains have a lower density of craters less than 100 km in diameter than does the Moon, an observation attributed to preferential resurfacing on Mercury. Here we report global crater statistics of Mercury's most heavily cratered terrains on the entire surface. Applying a recent model for early lunar crater chronology and an updated dynamical extrapolation to Mercury, we find that the oldest surfaces were emplaced just after the start of the Late Heavy Bombardment (LHB) about 4.0-4.1 Gyr ago. Mercury's global record of large impact basins, which has hitherto not been dated, yields a similar surface age. This agreement implies that resurfacing was global and was due to volcanism, as previously suggested. This activity ended during the tail of the LHB, within about 300-400 million years after the emplacement of the oldest terrains on Mercury. These findings suggest that persistent volcanism could have been aided by the surge of basin-scale impacts during this bombardment.

Flood volcanism in the northern high latitudes of Mercury revealed by MESSENGER.

MESSENGER observations from Mercury orbit reveal that a large contiguous expanse of smooth plains covers much of Mercury's high northern latitudes and occupies more than 6% of the planet's surface area. These plains are smooth, embay other landforms, are distinct in color, show several flow features, and partially or completely bury impact craters, the sizes of which indicate plains thicknesses of more than 1 kilometer and multiple phases of emplacement. These characteristics, as well as associated features, interpreted to have formed by thermal erosion, indicate emplacement in a flood-basalt style, consistent with x-ray spectrometric data indicating surface compositions intermediate between those of basalts and komatiites. The plains formed after the Caloris impact basin, confirming that volcanism was a globally extensive process in Mercury's post-heavy bombardment era.

Evidence for young volcanism on Mercury from the third MESSENGER flyby.

During its first two flybys of Mercury, the MESSENGER spacecraft acquired images confirming that pervasive volcanism occurred early in the planet's history. MESSENGER's third Mercury flyby revealed a 290-kilometer-diameter peak-ring impact basin, among the youngest basins yet seen, having an inner floor filled with spectrally distinct smooth plains. These plains are sparsely cratered, postdate the formation of the basin, apparently formed from material that once flowed across the surface, and are therefore interpreted to be volcanic in origin. An irregular depression surrounded by a halo of bright deposits northeast of the basin marks a candidate explosive volcanic vent larger than any previously identified on Mercury. Volcanism on the planet thus spanned a considerable duration, perhaps extending well into the second half of solar system history.

Evolution of the Rembrandt impact basin on Mercury.

MESSENGER's second Mercury flyby revealed a ~715-kilometer-diameter impact basin, the second-largest well-preserved basin-scale impact structure known on the planet. The Rembrandt basin is comparable in age to the Caloris basin, is partially flooded by volcanic plains, and displays a unique wheel-and-spoke-like pattern of basin-radial and basin-concentric wrinkle ridges and graben. Stratigraphic relations indicate a multistaged infilling and deformational history involving successive or overlapping phases of contractional and extensional deformation. The youngest deformation of the basin involved the formation of a approximately 1000-kilometer-long lobate scarp, a product of the global cooling and contraction of Mercury.

Trading places: adolescents as teachers.

The traditional criteria for granting status to adolescents are no longer appropriate and, unless replaced, could produce alienation and excessive reliance upon peers for communication and acceptance. The status that youth seek can be attained if their technology skills are valued and seen to qualify them as helpful sources of learning for adults. A new perspective for teaching and learning in the digital environment is described. Recommendations are given for shifting from a hierarchical relationship between adults and adolescents to more equitable forms of interaction that acknowledge the strengths and limitations of both generations.

Comparing Black, Hispanic, and White mothers with a national standard of parenting.

Black, Hispanic, and White mothers (N = 739) and adolescents (N = 806) completed a Parent Success Indicator to assess maternal behavior related to Communication, Use of Time, Teaching, Frustration, Satisfaction, and Information Needs. Comparisons between each ethnic group and a previously established national parenting standard revealed that both generations from each group judged the overall performance of mothers to be favorable. Teaching received the highest rating followed by Satisfaction. Mothers indicated that a need to have more Information about a particular adolescent was their greatest learning challenge, while adolescents reported that their mothers were prone to Frustration. While each group demonstrated favorable and unfavorable variations from a national standard, Hispanic generational differences indicated the least congruence by ethnicity.

Single mothers of early adolescents: perceptions of competence.

The purpose of this study was to examine similarities and differences in single mothers' and adolescents' perceptions of parenting competencies from a developmental assets approach. A multi-source (mothers [n = 29] and 10-14-year-old adolescent children [n = 29]), single-method (both generations completed the Parent Success Indicator) investigation was employed. Generational assessments were compared and effects of independent variables were examined. Generational views significantly differed on 9 of 10 items implicating a mother's need for additional information. The presence of an adult at home when the child returned from school and the amount of time the dyad spent together each week significantly differentiated both groups of respondents on areas of parenting. Implications for group-specific parenting curriculum were also discussed.

Volcanism on Mercury: evidence from the first MESSENGER flyby.

The origin of plains on Mercury, whether by volcanic flooding or impact ejecta ponding, has been controversial since the Mariner 10 flybys (1974-75). High-resolution images (down to 150 meters per pixel) obtained during the first MESSENGER flyby show evidence for volcanic vents around the Caloris basin inner margin and demonstrate that plains were emplaced sequentially inside and adjacent to numerous large impact craters, to thicknesses in excess of several kilometers. Radial graben and a floor-fractured crater may indicate intrusive activity. These observations, coupled with additional evidence from color images and impact crater size-frequency distributions, support a volcanic origin for several regions of plains and substantiate the important role of volcanism in the geological history of Mercury.

Geology of the Caloris basin, Mercury: a view from MESSENGER.

The Caloris basin, the youngest known large impact basin on Mercury, is revealed in MESSENGER images to be modified by volcanism and deformation in a manner distinct from that of lunar impact basins. The morphology and spatial distribution of basin materials themselves closely match lunar counterparts. Evidence for a volcanic origin of the basin's interior plains includes embayed craters on the basin floor and diffuse deposits surrounding rimless depressions interpreted to be of pyroclastic origin. Unlike lunar maria, the volcanic plains in Caloris are higher in albedo than surrounding basin materials and lack spectral evidence for ferrous iron-bearing silicates. Tectonic landforms, contractional wrinkle ridges and extensional troughs, have distributions and age relations different from their counterparts in and around lunar basins, indicating a different stress history.

Mercury cratering record viewed from MESSENGER's first flyby.

Morphologies and size-frequency distributions of impact craters on Mercury imaged during MESSENGER's first flyby elucidate the planet's geological history. Plains interior to the Caloris basin displaying color and albedo contrasts have comparable crater densities and therefore similar ages. Smooth plains exterior to Caloris exhibit a crater density approximately 40% less than on interior plains and are thus volcanic and not Caloris impact ejecta. The size distribution of smooth-plains craters matches that of lunar craters postdating the Late Heavy Bombardment, implying that the plains formed no earlier than 3.8 billion years ago (Ga). At diameters less than or equal to 8 to 10 kilometers, secondary impact craters on Mercury are more abundant than primaries; this transition diameter is much larger than that on the Moon or Mars. A low density of craters on the peak-ring basin Raditladi implies that it may be younger than 1 Ga.

Adolescent perception of mothers' parenting strengths and needs: a cross-cultural approach to curriculum development for parent education.

Black, Hispanic, and White American early adolescents (N = 573) were administered the Parent Success Indicator. The performance of their mothers was rated for 60 items, included within six subscales, that consider Communication, Use of Time, Teaching, Frustration, Satisfaction, and Information Needs. Each racial group described favorable attributes of mothers and noted realms of learning where further growth seemed warranted. Statistically significant main effects for race, time spent together, and presence of an adult at home when the adolescent returned from school were reported. No significant main effects for child gender were reported. Based on perceptions of the participants, topics were identified for a common parent curriculum that can serve mothers of each racial group. Additional topics, based on the ratings within each race, were recommended to meet the distinctive learning needs of Black, Hispanic, and White mothers of early adolescents.

The success of Taiwanese fathers in guiding adolescents.

The purpose of this study was to examine similarities and differences in Taiwanese fathers' and adolescents' perceptions of paternal competencies. A multi-source (fathers (n = 176) and 10- 14-year-old adolescent children (n = 176), single-method (both generations completed the Parent Success Indicator) investigation was employed. Generational assessments were compared, and effects of independent variables were examined. Impressions from both generations were significantly different by child school grades and the amount of time fathers spent talking to and doing things with their adolescents.

Venus, Mars, and the ices on Mercury and the moon: astrobiological implications and proposed mission designs.

Venus and Mars likely had liquid water bodies on their surface early in the Solar System history. The surfaces of Venus and Mars are presently not a suitable habitat for life, but reservoirs of liquid water remain in the atmosphere of Venus and the subsurface of Mars, and with it also the possibility of microbial life. Microbial organisms may have adapted to live in these ecological niches by the evolutionary force of directional selection. Missions to our neighboring planets should therefore be planned to explore these potentially life-containing refuges and return samples for analysis. Sample return missions should also include ice samples from Mercury and the Moon, which may contain information about the biogenic material that catalyzed the early evolution of life on Earth (or elsewhere). To obtain such information, science-driven exploration is necessary through varying degrees of mission operation autonomy. A hierarchical mission design is envisioned that includes spaceborne (orbital), atmosphere (airborne), surface (mobile such as rover and stationary such as lander or sensor), and subsurface (e.g., ground-penetrating radar, drilling, etc.) agents working in concert to allow for sufficient mission safety and redundancy, to perform extensive and challenging reconnaissance, and to lead to a thorough search for evidence of life and habitability.

Success of Taiwanese mothers in guiding adolescents.

Education for parents was recently mandated in Taiwan and presents a challenge to the schools. The purpose of this study was to determine how two generations perceive parenting strengths and learning needs. Taiwanese mothers of 10- to 14-year-olds (n=209) and their adolescent children (n=201) completed the Parent Success Indicator. Generational reports were compared, and effects of independent variables were examined. The amount of time mothers spent talking to and doing things with their adolescents had the greatest influence on how both groups rated mother success. Unfavorable ratings expressed by mothers and adolescents identified topics that would be appropriate for parent education. The findings will be used by educators and researchers to support parent development in Taiwan.

The origin of planetary impactors in the inner solar system.

Insights into the history of the inner solar system can be derived from the impact cratering record of the Moon, Mars, Venus, and Mercury and from the size distributions of asteroid populations. Old craters from a unique period of heavy bombardment that ended approximately 3.8 billion years ago were made by asteroids that were dynamically ejected from the main asteroid belt, possibly due to the orbital migration of the giant planets. The impactors of the past approximately 3.8 billion years have a size distribution quite different from that of the main belt asteroids but very similar to that of near-Earth asteroids.

Black, Hispanic, and White American mothers of adolescents: construction of a national standard.

Black, Hispanic, and White American mothers (n = 739) and adolescents (n = 806) completed the Parent Success Indicator to rate maternal performance on subscales of Communication, Use of Time, Teaching, Frustration, Satisfaction, and Information Needs. A weighted method corresponding to ethnic proportions in the American population was applied to construct a national standard for comparative reference. In general, both generations perceived mother performance as favorable. Teaching received the highest rating followed by Satisfaction levels. Mothers felt that Information Needs were their greatest limitation while adolescents reported that their mothers were prone to frustration. The amount of time mothers and adolescents spent together was the most significant independent variable influencing parent performance. Other variables such as income and marital status had limited impact.

Chinese immigrant mothers of adolescents: self-perceptions of acculturation effects on parenting.

Immigrant families in the United States experience many adjustments, including the challenge of parenting in a new context. The relationship between self-perceptions of parenting behavior and mothers' perceived acculturation levels for themselves and their children was examined in 95 Chinese immigrant mothers. Data showed that mothers perceived their children as more acculturated than themselves, mothers reported a great need to learn more about how their children are growing up today, a larger perceived acculturation gap was associated with more parenting difficulties, and several factors contributed to perceptions of a more favorable parenting experience. Culturally responsive methodologies used in the translation and administration of measures, and specific modifications made to develop the Chinese version of the Parent Success Indicator, are discussed.

The success of Caucasian mothers in guiding adolescents.

The purpose of this study was to determine how 391 Caucasian American mothers of 10- to 14-year-olds viewed their assets and limitations as parents and to find out how 352 adolescents perceived the parenting performance of their mothers. Both generations completed the Parent Success Indicator. It was found that the amount of time mothers spent talking to, and doing things with, their adolescent children had the greatest impact on how both generations rated mother success.

Evaluating the success of Caucasian fathers in guiding adolescents.

The purpose of this study was to identify guidance strengths and learning needs of fathers of adolescents. Perceptions of two generations were used to determine how well fathers perform as parents and realms of knowledge they have yet to acquire. The Parent Success Indicator, a 60-item Likert-type instrument, was administered to 126 Caucasian fathers and 185 adolescents. Significant differences obtained between generations for the total inventory, some scales, and many items. The amount of time spent together had the greatest influence on how both generations evaluated father success. Findings are discussed in terms of developing a curriculum to enhance the success of fathers.

Child-rearing expectations of families with atypical children.

The child-rearing expectations of 101 Australian parents of intellectually handicapped children were assessed, using the Parent As A Teacher Inventory. The overall PAAT index for subjects scoring at either the upper or lower extremes proved to be valuable in identifying those parents who would be the most and least successful teachers in a home-based language training program.