Layering stratigraphy of eastern Coprates and northern Capri Chasmata, Mars

Distinct competent layers are observed in the slopes of eastern Coprates Chasma, part of the Valles Marineris system on Mars. Our observations indicate that the stratigraphy of Coprates Chasma consists of alternating thin strong layers and thicker sequences of relatively weak layers. The strong, competent layers maintain steeper slopes and play a major role in controlling the overall shape and geomorphology of the chasmata slopes. The topmost competent layer in this area is well preserved and easy to identify in outcrops on the northern rim of Coprates Chasma less than 100 m below the southern Ophir Planum surface. The volume of the topmost emplaced layer is at least 70 km³ and may be greater than 2100 km³ if the unit underlies most of Ophir Planum. The broad extent of this layer allows us to measure elevation offsets within the north rim of the chasma and in a freestanding massif within Coprates Chasma where the layer is also observed. Rim outcrop morphology and elevation differences between Ophir and Aurorae Plana may be indicative of the easternmost extent of the topmost competent layer. These observations allow an insight into the depositional processes that formed the stratigraphic stack into which this portion of the Valles Marineris is carved, and they present a picture of some of the last volcanic activity in this area. Furthermore, the elevation offsets within the layer are evidence of significant subsidence of the massif and surrounding material.     

Chemical studies of copper-organic complexes isolated from estuarine waters using C18 reverse-phase liquid chromatography

Dissolved organic matter (DOM) and dissolved copper-organic complexes were isolated from the estuarine waters of Narragansett Bay, RI, using reverse-phase liquid chromatography employing C₁₈ Sep-Pak cartridges (Waters Associates). The cartridges were found to have a constant retention efficiency for processing ? 1-l volumes of seawater. Fractionation of the isolated material, by sequential elution of the Sep-Pak with water: methanol mixtures of increasing organic solvent concentration, yielded a fraction of the organic matter with a specific copper activity six times greater than the overall activity for the isolated DOM. Analysis of this fraction by high performance liquid chromatography suggested that the organic components are of intermediate polarity and have appreciable aromatic character.An investigation of the protonation characteristics of the isolated complexes indicated that most of the copper is associated with a broad range of acidic sites on the DOM. Analysis by electron paramagnetic resonance spectroscopy confirmed the organic association of the isolated copper and also suggested the presence of several types of binding sites which probably involve oxygen donor ligands.Studies of the exchange of ⁶⁴Cu with these binding sites on the isolated DOM indicated that 70% of the sites undergo rapid exchange with copper in seawater while 20% of these sites did not exchange in a 24-h time period.     

The Nuclear Stellar Cluster in NGC 1068

We present new near-infrared integral field spectroscopy and adaptive optics imaging of the nucleus of NGC 1068. Using the stellar CO absorption features in the H and K bands, we have identified a moderately extincted stellar core centered on the nuclear position and of intrinsic size ~50 pc. We show that this nuclear stellar core is probably 5-16 × 108 years in age and contributes at least 7% of the total nuclear luminosity of ~1 × 1011 L⊙. This revised version was published online in July 2006 with corrections to the Cover Date.     

Three recent larger earthquakes offshore Norway

Three earthquakes of magnitude around 5 occurred offshore western Norway on 5th February, 1986, on 8th August, 1988, and on 23rd January, 1989. These earthquakes, representing the highest seismic activity level in this area for at least 30 years, were all felt by people over most of southern and central Norway. Focal-mechanism solutions for these earthquakes indicate thrust faulting along N-S to NNE-SSW striking fault planes, in response to NW-SE compressional stress, most probably of plate tectonic origin.
A number of high-quality digital recordings of the ground motions at various distances from these and other recent earthquakes in Norway have shown that source spectral as well as wave attenuation characteristics in this area are reasonably consistent with what has been derived from other intraplate areas.     

An improved lunar moment of inertia determination: a proposed strategy

The current error of 0.0025 on the lunar homogeneity parameterI/MR ² is dominated by the uncertainties in theC ₂₀ andC ₂₂ gravity harmonics. This error level is equivalent to a 4.20 gm cm^–3 density uncertainty for a lunar interior model having a core 300 km in radius. Covariance analyses are performed using Doppler data from the relay satellite of the proposed Lunar Polar Orbiter mission to determine an optimum reduction strategy which obtains an order of magnitude improvement in the gravity estimates. Error studies show the long-arc reduction method obtains results which are an order of magnitude more accurate than the short-arc technique. The nominal 4000 km circular orbit of the relay satellite is very sensitive to the unmodeled effects of gravity harmonics of degree 5 through 9. Results from this orbital geometry indicate that it may not be possible to achieve the desired order of magnitude accuracy improvement. A modified orbit having the identical orbital conditions as the nominal one, but with a larger semi-major axis of 7000 km is studied. Results show the desired order of magnitude improvement can be achieved when a complete fourth degree and order model and some fifth and sixth degree terms are estimated while considering the unmodeled effects of the remaining harmonics through degree and order eight. Studies also show a 50% additional improvement inC ₂₂ can be achieved if differential differenced Doppler is also processed with the direct Doppler. The improved uncertainty inI/MR ² reduces the core density error from 4.20 gm cm^–3 to 0.1 gm cm^–3 for the case of a lunar density model having a 300 km core radius.Contribution #2885 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.