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.

Powering prolonged hydrothermal activity inside Enceladus

Abstract: Geophysical data from the Cassini spacecraft imply the presence of a global ocean underneath the ice shell of Enceladus 1 , only a few kilometres below the surface in the South Polar Terrain 2–4 . Chemical analyses indicate that the ocean is salty 5 and is fed by ongoing hydrothermal activity 6–8 . In order to explain these observations, an abnormally high heat power (>20 billion watts) is required, as well as a mechanism to focus endogenic activity at the south pole 9,10 . Here, we show that more than 10 GW of heat can be generated by tidal friction inside the unconsolidated rocky core. Water transport in the tidally heated permeable core results in hot narrow upwellings with temperatures exceeding 363 K, characterized by powerful (1–5 GW) hotspots at the seafloor, particularly at the south pole. The release of heat in narrow regions favours intense interaction between water and rock, and the transport of hydrothermal products from the core to the plume sources. We are thus able to explain the main global characteristics of Enceladus: global ocean, strong dissipation, reduced ice-shell thickness at the south pole and seafloor activity. We predict that this endogenic activity can be sustained for tens of millions to billions of years. Tidal forcing within a very porous (unconsolidated) core can generate enough energy to drive all the observed global features of Enceladus. This activity can be sustained up to several billion years.

Development of a Pulsar-Based Time-Scale

Abstract: Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA) project we develop the first pulsar-based time-scale that has a precision comparable to the uncertainties in International Atomic Time-scales (TAI). Our ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the free atomic time-scale Echelle Atomique Libre. The EPS can be used to detect fluctuations in atomic time-scales and therefore can lead to a new realization of Terrestrial Time, TT(PPTA11). We successfully follow features known to affect the frequency of the TAI, and we find marginally significant differences between TT(PPTA11) and TT(BIPM11). We discuss the various phenomena that lead to a correlated signal in the pulsar timing residuals and therefore limit the stability of the pulsar time-scale.

Mercury's Surface: Preliminary Description and Interpretation from Mariner 10 Pictures.

Abstract: The surface morphology and optical properties of Mercury resemble those of the moon in remarkable detail and record a very similar sequence of events. Chemical and mineralogical similarity of the outer layers of Mercury and the moon is implied; Mercury is probably a differentiated planet with a large iron-rich core. Differentiation is inferred to have occurred very early. No evidence of atmospheric modification of landforms has been found. Large-scale scarps and ridges unlike lunar or martian features may reflect a unique period of planetary compression near the end of heavy bombardment by small planetesimals.

New 3 Micron Spectra of Young Stellar Objects with H2O Ice Bands

Abstract: We present new ground-based 3 μm spectra of 14 young stellar objects with H2O ice absorption bands. The broad absorption feature at 3.47 μm was detected toward all objects, and its optical depth is correlated with the optical depth of H2O ice, strengthening an earlier finding. The broad absorption feature at 3.25 μm was detected toward two more sources, and an upper limit is given for a third source. The optical depths of the 3.25 μm feature obtained to date are better correlated with the optical depth of the refractory silicate dust than with that of H2O ice. If this trend is confirmed, this would support our proposed identification of the feature as the C-H stretch of aromatic hydrocarbons at low temperature. An absorption feature at 3.53 μm due to solid methanol was detected for the first time toward Mon R2/IRS 2, as well as toward W33A and GL 2136. The wavelengths of the CH3OH features toward W33A, GL 2136, and NGC 7538/IRS 9 can be fitted by CH3OH-rich ices, whereas the wavelength of the feature toward Mon R2/IRS 2 suggests an H2O-rich ice environment. Solid methanol abundances toward GL 2136, NGC 7538/IRS 9, and Mon R2/IRS 2 are 3%-5% relative to H2O ice. There is an additional narrow absorption feature near 3.47 μm toward W33A. For the object W51/IRS 2, spatially resolved spectra from 2 to 4 μm indicate that the H2O ice is located predominantly in front of the eastern component and that the H2O ice extinction is much deeper than previously estimated. For the object RNO 91, spectra from 2 to 4 μm reveal stellar (or circumstellar) CO gas absorption and deeper H2O ice extinction than previously estimated.

Initial results for the north pole of the Moon from Mini‐SAR, Chandrayaan‐1 mission

Abstract: [1] We present new polarimetric radar data for the surface of the north pole of the Moon acquired with the Mini-SAR experiment onboard India's Chandrayaan-1 spacecraft. Between mid-February and mid-April, 2009, Mini-SAR mapped more than 95% of the areas polewards of 80° latitude at a resolution of 150 meters. The north polar region displays backscatter properties typical for the Moon, with circular polarization ratio (CPR) values in the range of 0.1–0.3, increasing to over 1.0 for young primary impact craters. These higher CPR values likely reflect surface roughness associated with these fresh features. In contrast, some craters in this region show elevated CPR in their interiors, but not exterior to their rims. Almost all of these features are in permanent sun shadow and correlate with proposed locations of polar ice modeled on the basis of Lunar Prospector neutron data. These relations are consistent with deposits of water ice in these craters.