Isotopic-geochemical study of nitrogen and carbon in peat from the Tunguska Cosmic Body explosion site

Isotopic-geochemical investigations were carried out on peat samples from the 1908 Tunguska Cosmic Body (TCB) explosion area. We analyzed two peat columns from the Northern peat bog, sampled in 1998, and from the Raketka peat bog, sampled during the 1999 Italian expedition, both located near the epicenter of the TCB explosion area. At the depth of the “catastrophic” layer, formed in 1908, and deeper, one can observe shifts in the isotopic composition of nitrogen (up to Δ¹⁵N = +7.2‰) and carbon (up to Δ¹³C = +2‰) and also an increase in the nitrogen concentration compared to those in the normal, upper layers, unaffected by the Tunguska event. One possible explanation for these effects could be the presence of nitrogen and carbon from TCB material and from acid rains, following the TCB explosion, in the “catastrophic” and “precatastrophic” layers of peat. We found that the highest quantity of isotopically heavy nitrogen fell near the explosion epicenter and along the TCB trajectory. It is calculated that 200,000 tons of nitrogen fell over the area of devastated forest, i.e., only about 30% of the value calculated by Rasmussen et al. (1984). This discrepancy is probably caused by part of the nitrogen having dispersed in the Earth’s atmosphere. The isotopic effects observed in the peat agree with the results of previous investigations [Kolesnikov et al 1998a], [Kolesnikov et al 1998b], [Kolesnikov et al 1999] and [Rasmussen et al 1999] and also with the increased content of iridium and other platinoids found in the corresponding peat layers of other columns [Hou et al 1998] and [Hou et al 2000]. These data favor the hypothesis of a cosmochemical origin of the isotopic effects.     

Searching for the Parent of the Tunguska Cosmic Body

We present the results of an extensive study of the Tunguska Cosmic Body (TCB) origin on dynamical grounds. To identify the TCB parent, or a plausible candidate, we applied the well-known concept of dynamical similarity whereby we have compared the geocentric and heliocentric dynamical parameters of a selected set of the Near Earth Objects (NEOs) and TCB particles. First, we made use the idea of Kresak by comparing geocentric coordinates of the TCB radiant with those of the NEOs. Second, we studied the long-term dynamical evolution of all NEOs and TCB particles searching for similarities between their heliocentric orbits. As a general result, we observed many more similar cases and a different pattern of the high orbital similarity among the TCB particles and the asteroid orbits than we did for comets.     

Tidal disruptions: II. A continuum theory for solid bodies with strength, with applications to the Solar System

We present a comprehensive theory for the breakup conditions for ellipsoidal homogeneous secondary bodies subjected to the tidal forces from a nearby larger primary: for materials ranging from purely fluid ones, to granular rubble-pile gravel-like ones, and to those with either cohesive or granular strength including cohesive rocks and metals. The theory includes but greatly extends the classical analyses given by Roche in 1847, which dealt only with fluids, and also our previous analysis [Holsapple, K.A., Michel, P., 2006. Icarus 183, 331-348], which dealt only with solid but non-cohesive bodies. The results here give the distance inside of which breakup must occur, for both a steadily orbiting satellite and for a passing or impacting object. For the fluid bodies there is a single specific shape (a “Roche Ellipsoid”) that can be in equilibrium at any given distance from a primary, and especially only one shape that can exist at the overall minimum distance (d/R)(ρ/ρp)^1/3=2.455, the classical well-known “Roche limit.” In contrast, solid bodies can exist at a given distance from a primary with a range of shapes. Here we give multiple plots of the minimum distances for various important combinations of body shape, spin, mass density, and the strength parameters characterized by an angle of friction and cohesive strength. Such results can be used in different ways. They can be used to estimate limits on strengths and mass densities for orbiting bodies at a known distance and shape. They can be used to determine breakup distances for passing bodies with an assumed strength and shape. They can be used to constraint physical properties such as bulk density of bodies with a known shape that were known to breakup at a given distance. A collection of approximately 40 satellites of the Solar System is used for comparison to the theory. About half of those bodies are closer than the Roche fluid limit and must have some cohesion and/or friction angle to exist at their present orbital distance. The required solid strength for those states is determined. Finally, we apply the theory to the break up of the SL9 comet at close approach with Jupiter. Our results make clear that the literature estimates of its bulk density depend markedly on unknown parameters such as shape, orientation and spin, and most importantly, material strength characterization.     

Some results from the National Observatory of Turkey, Kazan State University, and Nikolaev Astronomical Observatory on small bodies of the solar system

A scientific collaboration between TÜB?TAK National Observatory (Turkey), Kazan State University (Russia) and Nikolaev Astronomical Observatory (Ukraine) involves observations of minor planets and near-Earth asteroids (NEAs) with the 1.5 m Russian-Turkish telescope (RTT150). Regular observations of selected asteroids in the range of 11-18 magnitudes began in 2004 with the view of determining masses of selected asteroids, improving the orbits of the NEAs, and studying physical characteristics of selected asteroids from photometric observations. More than 3000 positions of 53 selected asteroids and 11 NEAs have been obtained with an internal error in the range of 30-300 mas for a single determination. Photometric reductions of more than 4000 CCD frames are in progress. Masses of 21 asteroids were estimated through dynamical method using the ground-based optical observations, mainly from the RTT150 and Minor Planet Center. A comparison of the observational results from the RTT150 in 2004-2005 with observations of the same objects at other observatories allows us to conclude that RTT150 can be used for ground-based support in astrometry for the space mission GAIA.     

On the possible in situ elemental analysis of small bodies with laser ablation TOF-MS

An analysis is presented of the potential application of laser ablation time-of-flight mass spectrometry (LA-TOF-MS) to the study of small bodies on in situ and sample return missions. LA-TOF-MS provides the significant advantages of high-quality, low-ambiguity data, no requirement of sample contact or preparation, rapid analysis, and local probe capability. The ability to address particular scientific goals on a given mission depends strongly on obtaining reproducible instrument- and sample-dependent fractionation factors for heterogeneous samples in various operating conditions. LA-TOF-MS analyses of basalt and mineral separate standards, in both powdered and compressed forms, have been used to establish an understanding of elemental fractionation in the mass range from C to Zn and selected higher-mass elements. Results of a preliminary calibration applied to the bulk analysis of carbonaceous meteorites suggests that sufficient precision is obtained from replicate averaging of spectra to differentiate among some sub-classes. Complementary point-by-point LA analyses of such samples could also provide powerful diagnostic information for mineralogy.     

On the “strength” of the small bodies of the solar system: A review of strength theories and their implementation for analyses of impact disruptions

Composed of rocks, dirt, ices and metals, the small bodies of the Solar System generally show features of strength; and that property undoubtedly played a major role in their collisional evolution. But the quantification of strength is difficult because there are many different measures of strength, and those measures depend significantly on a body's composition, previous history and size. Although it is at the foundations of our scaling theories for the disruption of small bodies, and an essential part of code calculations, we have only recently begun to understand and come to grips with that strength property and in appropriate ways to model it in our theories and calculations.This is a general overview of strength theories for geological-type materials as needed for impact analyses. Dominant features of strength models are discussed, and comparisons of various models in the literature against that feature template is given. A summary of the use of strength theories in impact calculations is presented.     

Equations of motion of the restricted problem of (2 + 2) bodies when primaries are magnetic dipoles and minor bodies are taken as electric dipoles

In this problem of the restricted (2 + 2) bodies we have considered two magnetic dipoles of masses M ₁ and M ₂(M ₁ > M ₂) moving in circular Keplarian orbit about their centre of mass. Two minor bodies of masses m ₁, m ₂(m _j< M ₂) are taken as electric dipoles in the field of rotating magnetic dipoles. These minor bodies interact with each other but do not perturb the primaries.We have found equations of motions which differ from that of Goudas and Petsagouraki's (1985).     

Fluidization and multiphase transport of particulate cometary material as an explanation of the smooth terrains and repetitive outbursts on 9P/Tempel 1

The Deep Impact mission discovered repetitive outbursts on Comet 9P/Tempel 1 and the presence of several smooth terrains on its surface. We present new measurements of the extent of the smooth terrains, the slopes along their centerlines, and the areas of their likely source regions. Our analysis of these features indicates that they are <700 orbits old and probably the result of an ongoing process. The implications of the recently found locations of the source regions of the repetitive outbursts are also analyzed. We propose that the origins of these phenomena are in the different regimes of fluidization and gas transport in a weakly bound particulate mixture of ice and dust above an assumed amorphous/crystalline H₂O phase change boundary where CO and/or CO₂ gas is released. The depth of this boundary is estimated to lie between 30 and 100 m below the surface. The smooth terrains are visualized as occurring about once every ∼70 orbits at random locations of the nucleus where a spurt in CO production occurs over a limited region of the phase change boundary. The weak (tensile strength ) crystalline and dust overburden is locally ruptured and fluidized by the CO gas pressure and is then extruded onto the surface at speeds of ∼0.003-0.03 m/s, well below the escape velocity of 1.3 m/s. Once on the surface a base pressure of only 2.5 Pa is required to ensure fluidization of the extruded material and it can remain fluidized for typically ∼20 h against diffusive loss of CO. As the material accelerates down the local topography it deflates due to diffusive gas loss. The flow becomes increasingly viscous until it is no longer fluidized at which point it quickly halts forming a terminal scarp. The mean speed of the laminar flow is estimated at 0.3 m/s for an emplacement time of ∼3 h. Topographic features on the flow >0.3 m in size should become fully relaxed during the emplacement time explaining the smooth texture seen in the images. In contrast, the repetitive outbursts require a gas-laden reservoir to have formed in the vicinity of the phase change boundary well below their preferred location. We visualize the outbursts to be the result of either spouting or bubble transport to the surface where the release of gas is diurnally modulated by either thermal stresses or H₂O sublimation back pressure. The source region for the i2 smooth terrain is found to coincide with an H₂O-ice rich area and we propose that the process of elutriation, i.e., the separation of different classes of particulates depending on their drag properties, occurs in the fluidized material as it flows up to and through the surface. In this way the material becomes enhanced in H₂O crystals relative to siliceous and carbonaceous particulates.     

On the reliability of C iv λ1549 as an abundance indicator for high-redshift star-forming galaxies

We reconsider the use of the equivalent width of C  iv  λ1549, EW(C  iv ), as an indicator of the oxygen abundance in star-forming galaxies, as proposed by Heckman et al. for nearby starbursts. We refine the local calibration of EW(C  iv ) versus log (O/H) by using a restricted wavelength window which minimizes blending with interstellar absorption lines. When applied to the stellar component only of the complex C  iv  λ1549 features in two high-redshift galaxies with good quality spectra,  MS 1512−cB58 ( z = 2.7268)  and  Q1307−BM1163 ( z = 1.4105)  , the local calibration gives values of the oxygen abundance which are in good agreement with other metallicity determinations based on nebular emission and interstellar absorption lines. Our main conclusion is that for this method to give reliable results at high redshifts, it should only be used on data of sufficiently high spectral resolution  ( R ≳ 1000)  for stellar and interstellar C  iv components to be clearly separated. Oxygen abundances will be systematically overestimated if the local calibration is applied to spectra of high-redshift galaxies obtained with the low resolving powers  ( R ≃ 200–300)  of many current wide-field surveys. It will also be necessary to understand better the causes of the scatter in the local relation, before we can be confident of inferences from it at high z .     

Equivalent width, shape and proper motion of the iron fluorescent line emission from molecular clouds as an indicator of the illuminating source X-ray flux history

Observations of the diffuse emission in the 8–22 keV energy range, elongated parallel to the Galactic plane, and detection of the strong 6.4-keV fluorescent line with ∼ 1 keV equivalent width from some giant molecular clouds (e.g. Sgr B2) in the Galactic Centre region suggest that the neutral matter of these clouds is (or was) illuminated by powerful X-ray radiation, which gave rise to the reprocessed radiation. The source of this radiation remains unknown. A transient source close to the Sgr B2 cloud, or a short outburst of the X-ray emission from a supermassive black hole at the Galactic Centre are the two prime candidates under consideration. We argue that a new generation of X-ray telescopes combining very high sensitivity and excellent energy and angular resolutions would be able to discriminate between these two possibilities when studying time-dependent changes of the morphology of the surface brightness distribution, the equivalent width and the shape of the fluorescent line in Sgr B2 and other molecular clouds in the region. We note also that detection of broad and complex structures near the 6.4-keV line in the spectra of distant AGNs, which are X-ray weak now, may prove the presence of violent activity in the central engines of these objects in the past. Accurate measurements of the line shape may provide information on the time elapsed since the outburst. Proper motion (super- or subluminal) of the fluorescent radiation wave front can give additional information on the location of the source. Observations of the described effects can provide unique information on the matter distribution inside Sgr B2 and other giant molecular clouds.