Jet Propulsion Laboratory

About: Jet Propulsion Laboratory is a facility organization based out in La Cañada Flintridge, California, United States. It is known for research contribution in the topics: Mars Exploration Program & Telescope. The organization has 8801 authors who have published 14333 publications receiving 548163 citations. The organization is also known as: JPL & NASA JPL.

Cross-correlation weak lensing of sdss galaxy clusters. i. measurements

Abstract: This is the first in a series of papers on the weak lensing effect caused by clusters of galaxies in Sloan Digital Sky Survey. The photometrically selected cluster sample, known as MaxBCG, includes ~130,000 objects between redshift 0.1 and 0.3, ranging in size from small groups to massive clusters. We split the clusters into bins of richness and luminosity and stack the surface density contrast to produce mean radial profiles. The mean profiles are detected over a range of scales, from the inner halo (25 kpc h^(–1)) well into the surrounding large-scale structure (30 Mpc h^(–1)), with a significance of 15 to 20 in each bin. The signal over this large range of scales is best interpreted in terms of the cluster-mass cross-correlation function. We pay careful attention to sources of systematic error, correcting for them where possible. The resulting signals are calibrated to the ~10% level, with the dominant remaining uncertainty being the redshift distribution of the background sources. We find that the profiles scale strongly with richness and luminosity. We find that the signal within a given richness bin depends upon luminosity, suggesting that luminosity is more closely correlated with mass than galaxy counts. We split the samples by redshift but detect no significant evolution. The profiles are not well described by power laws. In a subsequent series of papers, we invert the profiles to three-dimensional mass profiles, show that they are well fit by a halo model description, measure mass-to-light ratios, and provide a cosmological interpretation.

High Spatial Resolution Imaging of NGC 1068 in the Mid-Infrared

Abstract: Mid-infrared observations of the central source of NGC 1068 have been obtained with a spatial resolution in the deconvolved image of 0.”1 (~7 pc). The central source is extended by ~1'' in the north-south direction but appears unresolved in the east-west direction over most of its length. About 2/3 of its flux can be ascribed to a core structure that is itself elongated north-south and does not show a distinct unresolved compact source. The source is strongly asymmetric, extending significantly farther to the north than to the south. The morphology of the mid-infrared emission appears similar to that of the radio jet and has features which correlate with the images in [O III]. Its 12.5–24.5 μm color temperature ranges from 215 to 260 K and does not decrease smoothly with distance from the core. Silicate absorption is strongest in the core and to the south and is small in the north. The core, apparently containing 2/3 of the bolometric luminosity of the inner 4'' diameter area, may be explained by a thick, dusty torus near the central active galactic nucleus (AGN) viewed at an angle of ~65° to its plane. There are, however, detailed difficulties with existing models, especially the narrow east-west width of the thin extended mid-infrared "tongue" to the north of the core. We interpret the tongue as reprocessed visual and ultraviolet radiation that is strongly beamed and that originates in the AGN.

Coseismic and postseismic slip associated with the 2010 Maule Earthquake, Chile: Characterizing the Arauco Peninsula barrier effect

Abstract: Observations of coseismic and postseismic deformation associated with the 2010 Mw = 8.8 Maule earthquake in south-central Chile provide constraints on the spatial heterogeneities of frictional properties on a major subduction megathrust and how they have influenced the seismic rupture and postseismic effects. We find that the bulk of coseismic slip occurs within a single elongated patch approximately 460 km long and 100 km wide between the depths of 15 and 40 km. We infer three major patches of afterslip: one extends northward along strike and downdip of the major coseismic patch between 40 and 60 km depth; the other two bound the northern and southern ends of the coseismic patch. The southern patch offshore of the Arauco Peninsula is the only place showing resolvable afterslip shallower than 20 km depth. Estimated slip potency associated with postseismic slip in the 1.3 years following the earthquake amounts to 20-30% of that generated coseismically. Our estimates of the megathrust frictional properties show that the Arauco Peninsula area has positive but relatively low (a−b)σn values (0.01 ~ 0.22 MPa), that would have allowed dynamic rupture propagation into this rate-strengthening area and afterslip. Given the only modestly rate-strengthening megathrust friction in this region, the barrier effect may be attributed to its relatively large size of the rate-strengthening patch. Coseismic and postseismic uplift of the Arauco Peninsula exceeds interseismic subsidence since the time of the last major earthquake in 1835, suggesting that coseismic and postseismic deformation has resulted in some permanent strain in the forearc.

Detection of local H2O exposed at the surface of Ceres.

Abstract: INTRODUCTION Dwarf planet Ceres’ low average-density (2162 ± 3 kg m −3 ) indicates that it must contain considerable water. Water is likely a key component in the chemical evolution and internal activity of Ceres, possibly resulting in a layer of ice-rich material and perhaps liquid in the mantle. Mineral hydroxides (OH-bearing) and hydrates (H 2 O-bearing), such as clays, carbonates, and various salts, would be created. These hypotheses were supported by the detection of hydroxyl (OH)–rich materials, OH-bearing molecule releases, H 2 O vapor molecules, and haze. However, the presence of H 2 O on the surface has not previously been confirmed. The detection and mapping of H 2 O on Ceres is one objective of the Dawn spacecraft, in orbit around Ceres since March 2015. RATIONALE The purpose of the Dawn space mission at Ceres is to study the geology, geophysics, and composition remotely by means of high-resolution imagery and spectrometry. Dawn’s Visible and InfraRed Mapping Spectrometer (VIR) measures the sunlight scattered by the surface of Ceres in a range of wavelengths between 0.25 and 5.1 μm. The position and shape of absorption features in VIR reflectance spectra are sensitive to the surface mineral and molecular composition. In spectroscopy, absorption bands at 2.0, 1.65, and 1.28 μm are characteristic of vibration overtones in the H 2 O molecule. RESULTS Dawn has detected water-rich surface materials in a 10-km-diameter crater named Oxo, which exhibit all absorption bands that are diagnostic of the H 2 O molecule (see the figure). These spectra are most similar to those of H 2 O ice, but they could also be attributable to hydrated minerals. Oxo crater appears to be geologically very young (~1 million to 10 million years); it has sharp rims and its floor is almost devoid of impacts, suggesting a recent exposure of surface H 2 O. The high latitude and morphology of the Oxo crater protects much of the surface area from direct solar illumination for most of the cerean day, presenting favorable conditions for the stability of water ice or heavily hydrated salts. CONCLUSION Four ways to create or transport H 2 O on Ceres are considered: (i) Exposure of near-surface H 2 O-rich materials by a recent impact or an active landslide seems most consistent with the presence of both mineral hydrates and water ice. (ii) Release of subsurface H 2 O may occur on Ceres, similar to release on comet nuclei, but may never recondense on the surface. (iii) Infall of ice-bearing objects is not likely to deposit water on Ceres, because the H 2 O molecule likely would dissociate upon impact. (iv) Implantation of protons from the solar wind on the surface is not a probable origin of OH on Ceres because of the low flux of solar wind charged particles. We therefore conclude that surface H 2 O or hydrated minerals are the most plausible explanation.

SAR interferometric signatures of forest

Abstract: The potential of SAR interferometry for forest mapping and monitoring is discussed. It is shown that forest can clearly be discriminated from other land categories. Furthermore it is possible to distinguish a number of forest types. The presented approach is based on the SAR interferometric correlation and the backscatter intensities using ERS-1 SAR repeat-pass data. Baseline, time interval, and seasonal dependences were analyzed, substantiating a wide applicability of the approach. Data over an Alaskan test site were used to extend the results found over temperate forest to boreal forest and to demonstrate the potential of the described technique over remote areas. In addition, repeat-pass SAR interferometry was found to be particularly sensitive to change. Examples for the recognition of freezing, mechanical cultivation of agricultural fields, and canopy growth are shown. >