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.

Characterizing and navigating small bodies with imaging data

Abstract: Recent advances in the characterization of small body surfaces with stereophotoclinometry are discussed. The principal data output is an ensemble of landmark maps (L-maps), high-resolution topography/albedo maps of varying resolution that tile the surface of the body. Because they can have a resolution comparable to the best images, and can be located on a global reference frame to high accuracy, L-maps provide a significant improvement in discriminatory power for studies of small bodies, ranging from regolith processes to interior structure. These techniques are now being used to map larger bodies such as the Moon and Mercury. L-maps are combined to produce a standard global topography model (GTM) with about 1.57 million vectors and having a wide variety of applications. They can also be combined to produce high-resolution topography maps that describe local areas with much greater detail than the GTM. When combined with nominal predictions from other data sources and available data from other instruments such as LIDAR or RADAR, solutions for the spacecraft position and camera pointing are the most accurate available. Examples are drawn from studies of Phobos, Eros, and Itokawa, including surface characterization, gravity analysis, spacecraft navigation, and incorporation of LIDAR or RADAR data. This work has important implications for potential future missions such as Deep Interior and the level of navigation and science that can be achieved.

Bacterial and archaeal populations associated with freshwater ferromanganous micronodules and sediments.

Abstract: Biology is believed to play a large role in the cycling of iron and manganese in many freshwater environments, but specific microbial groups indigenous to these systems have not been well characterized. To investigate the populations of Bacteria and Archaea associated with metal-rich sediments from Green Bay, WI, we extracted nucleic acids and analysed the phylogenetic relationships of cloned 16S rRNA genes. Because nucleic acids have not been routinely extracted from metal-rich samples, we investigated the bias inherent in DNA extraction and gene amplification from pure MnO2 using defined populations of whole cells or naked DNA. From the sediments, we screened for manganese-oxidizing bacteria using indicator media and found three isolates that were capable of manganese oxidation. In the phylogenetic analysis of bacterial 16S rRNA gene clones, we found two groups related to known metal-oxidizing genera, Leptothrix of the beta-Proteobacteria and Hyphomicrobium of the alpha-Proteobacteria, and a Fe(III)-reducing group related to the Magnetospirillum genus of the alpha-Proteobacteria. Groups related to the metal-reducing delta-Proteobacteria constituted 22% of the gene clones. In addition, gene sequences from one group of methanogens and a group of Crenarchaeota, identified in the archaeal gene clone library, were related to those found previously in Lake Michigan sediments.

The far-infrared/radio correlation as probed by Herschel

Abstract: We set out to determine the ratio, q(IR), of rest-frame 8-1000um flux, S(IR), to monochromatic radio flux, S(1.4GHz), for galaxies selected at far-IR and radio wavelengths, to search for signs that the ratio evolves with redshift, luminosity or dust temperature, and to identify any far-IR-bright outliers - useful laboratories for exploring why the far-IR/radio correlation is generally so tight when the prevailing theory suggests variations are almost inevitable. We use flux-limited 250-um and 1.4-GHz samples, obtained in GOODS-N using Herschel (HerMES; PEP) and the VLA. We determine bolometric IR output using ten bands spanning 24-1250um, exploiting data from PACS and SPIRE, as well as Spitzer, SCUBA, AzTEC and MAMBO. We also explore the properties of an L(IR)-matched sample, designed to reveal evolution of q(IR) with z, spanning log L(IR) = 11-12 L(sun) and z=0-2, by stacking into the radio and far-IR images. For 1.4-GHz-selected galaxies, we see tentative evidence of a break in the flux ratio, q(IR), at L(1.4GHz) ~ 10^22.7 W/Hz, where AGN are starting to dominate the radio power density, and of weaker correlations with z and T(d). From our 250-um-selected sample we identify a small number of far-IR-bright outliers, and see trends of q(IR) with L(1.4GHz), L(IR), T(d) and z, noting that some of these are inter-related. For our L(IR)-matched sample, there is no evidence that q(IR) changes significantly as we move back into the epoch of galaxy formation: we find q(IR) goes as (1+z)^gamma, where gamma = -0.04 +/- 0.03 at z=0-2; however, discounting the least reliable data at z 1.

Alamouti-type space-time coding for free-space optical communication with direct detection

Abstract: A modification of the Alamouti code originally proposed for RF wireless applications is described that allows it to be applied in scenarios such as free-space optical communication with direct detection where unipolar modulations like pulse-position modulation and on-off keying are traditionally used to convey the information. The modification of the code and associated decision metric is such as to maintain all of the desirable properties of the original scheme.

Comet showers as a cause of mass extinctions

Abstract: Three independent pieces of evidence supporting a connection between comet showers and clustering in terrestrial cratering and mass extinctions are presented The temporal profile of a comet shower triggered by a star passing through the Oort cloud is calculated Four weak peaks are found in the age of distribution of impact craters over the past 100 Myr, as well as two compact clusters of ages of impact glass broadly coincident with crater-age peaks Recent paleontological observations are reviewed that indicate a stepwise character for some well-documented mass extinctions in the past 100 Myr which roughly coincide with three of the four peaks in crater ages and which have a duration compatible with comet shower predictions