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.

On the Nature of the Dust in the Debris Disk around HD 69830

Abstract: We have used the infrared mineralogical model derived from the Spitzer IRS observations of the Deep Impact experiment to study the nature of the dust in the debris found around the K0 V star HD 69830. Using a robust approach to determine the bulk average mineralogical composition of the dust, we show it to be substantially different from that found for comets 9P/Tempel 1 and C/Hale-Bopp 1995 O1 or for the comet-dominated YSO HD 100546. Lacking in carbonaceous and ferrous materials but including small icy grains, the composition of the HD 69830 dust most closely resembles that of a disrupted P- or D-type asteroid. The amount of mass responsible for the observed emission is the equivalent of a 30 km radius, 2500 kg m-3 sphere, while the radiative temperature of the dust implies that the bulk of the observed material is at ~1.0 AU from the central source, coincident with the 2 : 1 and 5 : 2 mean motion resonances of the outermost of three Neptune-sized planets detected by Lovis and coworkers. In our solar system, P- and D-type asteroids are both large and numerous in the outer main belt and near Jupiter (e.g., the Hildas and Trojans) and have undergone major disruptive events to produce debris disk-like structures (cf. the Karin and Veritas families 5-8 Myr ago). The short-lived nature of the small and icy dust implies that the disruption occurred within the last year, or that replenishment due to ongoing collisional fragmentation is occurring.

Lengths of Hawaiian lava flows

Abstract: Comparison of length, volume, and effusion rate for 87 historic Hawaiian basaltic lava flows shows little support for a direct relationship between flow length and effusion rate. A statistically more significant relationship exists between flow length and total volume of material extruded. Cross-sectional area, effusion rate, and volume all play important roles in governing the emplacement of lava flows in Hawaii; no single factor appears most important. One reason for the observed relationships in Hawaii may be that tube-fed flows, with approximately constant cross-sectional area, advance farther than other types of flows for similar effusion rates and volumes.

Multi-scale meteorological conceptual analysis of observed active fire hotspot activity and smoke optical depth in the Maritime Continent

Abstract: . Much research and speculation exists about the meteorological and climatological impacts of biomass burning in the Maritime Continent (MC) of Indonesia and Malaysia, particularly during El Nino events. However, the MC hosts some of the world's most complicated meteorology, and we wish to understand how tropical phenomena at a range of scales influence observed burning activity. Using Moderate Resolution Imaging Spectroradiometer (MODIS) derived active fire hotspot patterns coupled with aerosol data assimilation products, satellite based precipitation, and meteorological indices, the meteorological context of observed fire prevalence and smoke optical depth in the MC are examined. Relationships of burning and smoke transport to such meteorological and climatic factors as the interannual El Nino-Southern Oscillation (ENSO), El Nino Modoki, Indian Ocean Dipole (IOD), the seasonal migration of the Intertropical Convergence Zone, the 30–90 day Madden Julian Oscillation (MJO), tropical waves, tropical cyclone activity, and diurnal convection were investigated. A conceptual model of how all of the differing meteorological scales affect fire activity is presented. Each island and its internal geography have different sensitivities to these factors which are likely relatable to precipitation patterns and land use practices. At the broadest scales as previously reported, we corroborate ENSO is indeed the largest factor. However, burning is also enhanced by periods of El Nino Modoki. Conversely, IOD influences are unclear. While interannual phenomena correlate to total seasonal burning, the MJO largely controls when visible burning occurs. High frequency phenomena which are poorly constrained in models such as diurnal convection and tropical cyclone activity also have an impact which cannot be ignored. Finally, we emphasize that these phenomena not only influence burning, but also the observability of burning, further complicating our ability to assign reasonable emissions.

Submillimetre galaxies reside in dark matter haloes with masses greater than 3 × 10 11 solar masses

Abstract: The extragalactic background light at far-infrared wavelengths comes from optically faint, dusty, star-forming galaxies in the Universe with star formation rates of a few hundred solar masses per year. These faint, submillimetre galaxies are challenging to study individually because of the relatively poor spatial resolution of far-infrared telescopes. Instead, their average properties can be studied using statistics such as the angular power spectrum of the background intensity variations. A previous attempt at measuring this power spectrum resulted in the suggestion that the clustering amplitude is below the level computed with a simple ansatz based on a halo model. Here we report excess clustering over the linear prediction at arcminute angular scales in the power spectrum of brightness fluctuations at 250, 350 and 500 μm. From this excess, we find that submillimetre galaxies are located in dark matter haloes with a minimum mass, Mmin, such that log10[Mmin/M⊙] = at 350 μm, where M⊙ is the solar mass. This minimum dark matter halo mass corresponds to the most efficient mass scale for star formation in the Universe, and is lower than that predicted by semi-analytical models for galaxy formation

The Sun as a Variable Star: Solar and Stellar Irradiance Variations; Colloquium of the International Astronomical Union, 143rd, Boulder, CO, Jun. 20-25, 1993

Abstract: Variations in solar and stellar irradiances have long been of interest. An International Astronomical Union (IAU) colloquium reviewed such relevant subjects as observations, theoretical interpretations, and empirical and physical models, with a special emphasis on climatic impact of solar irradiance variability. Specific topics discussed included: (1) General Reviews on Observations of Solar and Stellar Irradiance Variability; (2) Observational Programs for Solar and Stellar Irradiance Variability; (3) Variability of Solar and Stellar Irradiance Related to the Network, Active Regions (Sunspots and Plages), and Large-Scale Magnetic Structures; (4) Empirical Models of Solar Total and Spectral Irradiance Variability; (5) Solar and Stellar Oscillations, Irradiance Variations and their Interpretations; and (6) The Response of the Earth's Atmosphere to Solar Irradiance Variations and Sun-Climate Connections.