70 research outputs found
Physical Properties of Trans-Neptunian Object (20000) Varuna
We present new time-resolved photometric observations of the bright
trans-Neptunian object (20000) Varuna and use them to study the rotation
period, shape, and color. In observations from 2001 February and April, we find
a best-fit two-peaked lightcurve with period 6.3442 +-0.0002 hr. The
peak-to-peak photometric range in the R-band is 0.42 +-0.02 mag. We find no
rotational variation in colors over the 0.45 < lambda < 0.85 micron wavelength
range. From the short double-peaked period and large amplitude we suggest that
Varuna is an elongated, prolate body perhaps close in shape to one of the
Jacobi ellipsoids. If so, the ratio of the axes projected into the plane of the
sky is 1.5:1 and the density is near 1000 kg m^(-3). (20000) Varuna may be a
rotationally distorted rubble pile, with a weak internal constitution due to
fracturing by past impacts. The high specific angular momentum implied by our
observations and recent detections of binary Trans-Neptunian Objects both point
to an early, intense collisional epoch in which large Trans-Neptunian Objects
were about 100 times more abundant than now. In order to maintain a
cosmochemically plausible rock:ice mass ratio of about 0.5, Varuna must be
internally porous.Comment: 26 pages, 6 figures, 5 tables, accepted to A
Formation of sharp edges and planar areas of asteroids by polyhedral abrasion
While the number of asteroids with known shapes has drastically increased
over the past few years, little is known on the the time-evolution of shapes
and the underlying physical processes. Here we propose an averaged abrasion
model based on micro-collisons, accounting for asteroids not necessarily
evolving toward regular spheroids, rather (depending on the fall-back rate of
ejecta) following an alternative path, thus confirming photometry-derived
features, e.g. existence of large, relatively flat areas separated by edges. We
show that our model is realistic, since the bulk of the collisions falls into
this category.Comment: 17 pages, 3 figures, accepted by Astrophysical Journa
Conserving biodiversity in production landscapes
Alternative land uses make different contributions to the conservation of biodiversity and have different implementation and management costs. Conservation planning analyses to date have generally assumed that land is either protected or unprotected and that the unprotected portion does not contribute to conservation goals. We develop and apply a new planning approach that explicitly accounts for the contribution of a diverse range of land uses to achieving conservation goals. Using East Kalimantan (Indonesian Borneo) as a case study, we prioritize investments in alternative conservation strategies and account for the relative contribution of land uses ranging from production forest to well-managed protected areas. We employ data on the distribution of mammals and assign species-specific conservation targets to achieve equitable protection by accounting for life history characteristics and home range sizes. The relative sensitivity of each species to forest degradation determines the contribution of each land use to achieving targets. We compare the cost effectiveness of our approach to a plan that considers only the contribution of protected areas to biodiversity conservation, and to a plan that assumes that the cost of conservation is represented by only the opportunity costs of conservation to the timber industry. Our preliminary results will require further development and substantial stakeholder engagement prior to implementation; nonetheless we reveal that, by accounting for the contribution of unprotected land, we can obtain more refined estimates of the costs of conservation. Using traditional planning approaches would overestimate the cost of achieving the conservation targets by an order of magnitude. Our approach reveals not only where to invest, but which strategies to invest in, in order to effectively and efficiently conserve biodiversity. Copyright ESA. All rights reserved
The Kuiper Belt and Other Debris Disks
We discuss the current knowledge of the Solar system, focusing on bodies in
the outer regions, on the information they provide concerning Solar system
formation, and on the possible relationships that may exist between our system
and the debris disks of other stars. Beyond the domains of the Terrestrial and
giant planets, the comets in the Kuiper belt and the Oort cloud preserve some
of our most pristine materials. The Kuiper belt, in particular, is a
collisional dust source and a scientific bridge to the dusty "debris disks"
observed around many nearby main-sequence stars. Study of the Solar system
provides a level of detail that we cannot discern in the distant disks while
observations of the disks may help to set the Solar system in proper context.Comment: 50 pages, 25 Figures. To appear in conference proceedings book
"Astrophysics in the Next Decade
Phylogenomic analyses of the genus Drosophila reveals genomic signals of climate adaptation
Many Drosophila species differ widely in their distributions and climate niches, making them excellent subjects for evolutionary genomic studies. Here, we have developed a database of high-quality assemblies for 46 Drosophila species and one closely related Zaprionus. Fifteen of the genomes were newly sequenced, and 20 were improved with additional sequencing. New or improved annotations were generated for all 47 species, assisted by new transcriptomes for 19. Phylogenomic analyses of these data resolved several previously ambiguous relationships, especially in the melanogaster species group. However, it also revealed significant phylogenetic incongruence among genes, mainly in the form of incomplete lineage sorting in the subgenus Sophophora but also including asymmetric introgression in the subgenus Drosophila. Using the phylogeny as a framework and taking into account these incongruences, we then screened the data for genome-wide signals of adaptation to different climatic niches. First, phylostratigraphy revealed relatively high rates of recent novel gene gain in three temperate pseudoobscura and five desert-adapted cactophilic mulleri subgroup species. Second, we found differing ratios of nonsynonymous to synonymous substitutions in several hundred orthologues between climate generalists and specialists, with trends for significantly higher ratios for those in tropical and lower ratios for those in temperate-continental specialists respectively than those in the climate generalists. Finally, resequencing natural populations of 13 species revealed tropics-restricted species generally had smaller population sizes, lower genome diversity and more deleterious mutations than the more widespread species. We conclude that adaptation to different climates in the genus Drosophila has been associated with large-scale and multifaceted genomic changes
Genome‑wide patterns of differentiation over spaceand time in the Queensland fruit fly
The Queensland fruit fly, Bactrocera tryoni, is a major pest of Australian horticulture which has expanded its range in association with the spread of horticulture over the last ~ 150 years. Its distribution in northern Australia overlaps that of another fruit fly pest to which some authors accord full species status, Bactrocera aquilonis. We have used reduced representation genome-wide sequencing to genotype 359 individuals taken from 35 populations from across the current range of the two taxa, plus a further 73 individuals from six of those populations collected 15-22 years earlier. We find significant population differentiation along an east-west transect across northern Australia which likely reflects limited but bidirectional gene flow between the two taxa. The southward expansion of B. tryoni has led to relatively little genetic differentiation, and most of it is associated with a move into previously marginal inland habitats. Two disjunct populations elsewhere in Australia and three on Melanesian islands are each clearly differentiated from all others, with data strongly supporting establishment from relatively few founders and significant isolation subsequently. Resequencing of historical samples from one of the disjunct Australian populations shows that its genetic profile has changed little over a 15-year period, while the Melanesian data suggest a succession of 'island hopping' events with progressive reductions in genetic diversity. We discuss our results in relation to the control of B. tryoni and as a model for understanding the genetics of invasion and hybridisation processes
The status of the world's land and marine mammals: diversity, threat, and knowledge
Knowledge of mammalian diversity is still surprisingly disparate, both regionally and taxonomically. Here, we present a comprehensive assessment of the conservation status and distribution of the world's mammals. Data, compiled by 1700+ experts, cover all 5487 species, including marine mammals. Global macroecological patterns are very different for land and marine species but suggest common mechanisms driving diversity and endemism across systems. Compared with land species, threat levels are higher among marine mammals, driven by different processes (accidental mortality and pollution, rather than habitat loss), and are spatially distinct (peaking in northern oceans, rather than in Southeast Asia). Marine mammals are also disproportionately poorly known. These data are made freely available to support further scientific developments and conservation action
A silicified Early Triassic marine assemblage from Svalbard
peerreview_statement: The publishing and review policy for this title is described in its Aims & Scope. aims_and_scope_url: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=tjsp2
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