Extrasolar low-orbit planets: Dissipation of their atmospheres and probable magnetic field

Analysis of the data obtained during transits of low-orbit extrasolar planets across the stellar disk yields different estimates of their atmospheric loss rates. Experimental data point to the probable existence of several distinct subtypes of extrasolar giant planets, including “hot Jupiters” of low density (HD 209458b), with massive cores composed of heavy elements (HD 149026b), and others. We show that the expected hot-Jupiter mass losses due to atmospheric escape on a cosmogonic time scale do not exceed a few percent, while the losses through Jeans dissipation are negligible. We also argue that low-orbit giant planets should have a strong magnetic field that interacts with circumstellar plasma with the planet’s supersonic orbital velocity. The magnetic field properties can be used to search for extrasolar planets.     

http://www.sciencedirect.com/science/article/pii/S1674987110000307

The Polar Urals region of northern Russia is well known for large chromium (Cr)-bearing massifs with major chromite orebodies, including the Centralnoye I deposit in the Ray-Iz ultramafic massif of the Ural ophiolite belt. New data on platinum (Pt)-group elements (PGE), geochemistry and mineralogy of the host dunite shows that the deposit has anomalous iridium (Ir) values. These values indicate the predominance of ruthenium–osmium–iridium (Ru–Os–Ir)-bearing phases among the platinum-group mineral (PGM) assemblage that is typical of mantle-hosted chromite ores. Low Pt values in chromites and increased Pt values in host dunites might reflect the presence of cumulus PGM grains. The most abundant PGM found in the chromite is erlichmanite (up to 15 μm). Less common are cuproiridsite (up to 5 μm), irarsite (up to 4–5 μm), and laurite (up to 4 μm). The predominant sulfide is heazlewoodite, in intergrowth with Ni–Fe alloys, sporadically with pentlandite, and rarely with pure nickel. Based on the average PGE values and estimated Cr-ore resources, the Centralnoye I deposit can be considered as an important resource of PGE.     

A Long-Term Dissipation of the EUV He <Emphasis Type="SmallCaps">ii</Emphasis> (30.4 nm) Segmentation in Full-Disk Solar Images

Some quiet-Sun days observed by the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO) during the time interval in 2010?–?2017 were used to continue our previous analyses reported by Didkovsky and Gurman (Solar Phys.289, 153, 2014a) and Didkovsky, Wieman, and Korogodina (Solar Phys.292, 32, 2017). The analysis consists of determining and comparing spatial spectral ratios (spectral densities over some time interval) from spatial (segmentation-cell length) power spectra. The ratios were compared using modeled compatible spatial frequencies for spectra from the Extreme ultraviolet Imaging Telescope (EIT) on-board the Solar and Heliospheric Observatory (SOHO) and from AIA images. With the new AIA data added to the EIT data we analyzed previously, the whole time interval from 1996 to 2017 reported here is approximately the length of two “standard” solar cycles (SC). The spectral ratios of segmentation-cell dimension structures show a significant and steady increase with no detected indication of SC-related returns to the values that characterize the SC minima. This increase in spatial power at high spatial frequencies is interpreted as a dissipation of medium-size EUV network structures to smaller-size structures in the transition region. Each of the latest ratio changes for 2010 through 2017 spectra calculated for a number of consecutive short-term intervals has been converted into monthly mean ratio (MMR) changes. The MMR values demonstrate variable sign and magnitudes, thus confirming the solar nature of the changes. These changes do not follow a “typical” trend of instrumental degradation or a long-term activity profile from the He?ii (30.4 nm) irradiance measured by the Extreme ultraviolet Spectrophotometer (ESP) either. The ESP is a channel of the Extreme ultraviolet Variability Experiment (EVE) on-board SDO.     

A Model of an Active Region on the Surface of a Cometary Nucleus

An active region on the surface of a cometarynucleus is considered as a conic hole in the surface dust mantle with icy bottom and dusty side-walls. This conic structureshould concentrate solar energy onto the bottom andtherefore enhance sublimation. Preliminary results of thecalculation of this effect are given. The temperature distributionat the bottom of the crater is calculated for different sets ofits geometrical parameters. Effects of intensified sublimation depending on the geometrical parameters areconsidered for the specific case when a single active region islocated exactly at the pole of the nucleus and the pole is directed tothe Sun.     

A Huge Basin in the Unknown Portion of Mercury in the 250°–290° W Longitude Range

A basin with an interior about 1000 km across and an outer rim about 2000 km in diameter has been found on the side of Mercury that remained unknown after theMariner 10imaging in 1973–1975. In its size, which is as much as 1/2 of the Mercury's diameter, this formation is one of the largest basins on the terrestrial planets. The presence of other large features of global dimension on this side of the planet suggests their possible asymmetric allocation on Mercury, similar to that on the Moon. New methods of ground-based astronomical observations including data processing with a special software package have been used.     

Two-integral distribution functions for axisymmetric systems

Some formulae are presented for finding two-integral distribution functions (DFs) which depend only on the two classical integrals of the energy and the magnitude of the angular momentum with respect to the axis of symmetry for stellar systems with known axisymmetric densities. They come from a combination of the ideas of Eddington and Fricke and they are also an extension of those shown by Jiang and Ossipkov for finding anisotropic DFs for spherical galaxies. The density of the system is required to be expressed as a sum of products of functions of the potential and of the radial coordinate. The solution corresponding to this type of density is in turn a sum of products of functions of the energy and of the magnitude of the angular momentum about the axis of symmetry. The product of the density and its radial velocity dispersion can be also expressed as a sum of products of functions of the potential and of the radial coordinate. It can be further known that the density multiplied by its rotational velocity dispersion is equal to a sum of products of functions of the potential and of the radial coordinate minus the product of the density and the square of its mean rotational velocity. These formulae can be applied to the Binney and the Lynden-Bell models. An infinity of the odd DFs for the Binney model can be also found under the assumption of the laws of the rotational velocity.     

The surface of Mercury in the 210–350° W longitude range

New ground based observations of Mercury in the morning elongation were carried out under good meteorological conditions. During 20–24 November 2006, at the SAO observatory of the Russian Academy of Science (Lower Arkhiz, Karachaevo-Circassia, Russia, 41°^26′ E, 43°^39′ N), the sector of longitudes 265–350° W of Mercury was observed using the short exposures method. The sector was not covered by imaging from the spacecraft Mariner-10 in 1974–1975 or by MESSENGER at its first flyby of the planet (January 2008). One of the main tasks of new observations was acquiring a full image of the object Basin S, which was investigated earlier only in a fragmentary way due to the illumination conditions. During 20–24 November 2006 Basin S was partly or full on the lit side of the planet. By the processing of the large number of the initial electronic photos a full high resolution image of Basin S was obtained, together with other elements of the surface of Mercury in this longitude sector.     

Glacier extent in a Novaya Zemlya fjord during the "Little Ice Age" inferred from glaciomarine sediment records

Glacier activity at Russkaya Gavan', north-west Novaya Zemlya (Arctic Russia), is reconstructed by particle size analysis of three fjord sediment cores in combination with ¹⁴C and ²¹⁰Pb dating. Down-core logging of particle size variation reveals at least two intervals with sediment coarsening during the past eight centuries. By comparing them with reconstructions of summer temperature and atmospheric circulation, these intervals are interpreted to represent two cycles of glacier advance and retreat sometime during ca. AD 1400–1700 and AD 1700–present. Sediment accumulation thus appears to be sensitive to century-scale fluctuations of the Barents Sea climate. The identification of two glacier cycles in the glaciomarine record from Russkaya Gavan' demonstrates that during the "Little Ice Age" major glacier fluctuations on Novaya Zemlya occurred in broad synchrony with those in other areas around the Barents Sea.     

Seafloor evidence for ice shelf flow across the Alaska–Beaufort margin of the Arctic Ocean

New imagery of ～14 100 km² of seafloor along a 640 km stretch of the Alaska and Beaufort margins (ABM) in water depths from 250 to 2800 m depicts a repetitive association of glaciogenic bedforms (lineations and iceberg scours), broad erosional bathymetric features and adjacent downslope turbidite gullies. These bedforms have styles, depths and orientations similar to features discovered earlier on the Chukchi Borderland, up to 800 km northwest of the ABM. Lineations occur across the surface of a flattened bathymetric bench interpreted to have formed by an ice shelf sliding along the continental slope and scraping the seafloor at temporary grounding locations. The glacial geology of surrounding areas suggests that an ice shelf probably flowed from the mouths of overdeepened glacial troughs in the Canadian Arctic Archipelago westward along the ABM and across the Chukchi Borderland. This curved pathway indicates an obstruction to ice flow in the central Canada Basin, possibly caused by either a basin‐wide ice shelf or by a pile‐up of mega‐bergs originating from the Eurasian side of the Arctic Ocean. The ice shelf that affected the ABM may have formed between Oxygen Isotopic Stage 4 to 5b, possibly correlating to an inferred intra‐Stage 5 widespread Beringian glaciation. Evidence for glaciogenic features on the ABM corroborates suggestions that large ice volumes and extents existed in the Arctic during Pleistocene glacial periods. These findings have far‐reaching implications for Arctic climate studies, ocean circulation, sediment stratigraphy and the stability of circum‐Arctic continental ice masses. Copyright © 2007 John Wiley & Sons, Ltd.