Dust ejection from planetary bodies by temperature gradients: Laboratory experiments

Laboratory experiments show that dusty bodies in a gaseous environment eject dust particles if they are illuminated. We find that even more intense dust eruptions occur when the light source is turned off. We attribute this to a compression of gas by thermal creep in response to the changing temperature gradients in the top dust layers. The effect is studied at a light flux of 13 kW/m² and 1 mbar ambient pressure. The effect is applicable to protoplanetary disks and Mars. In the inner part of protoplanetary disks, planetesimals can be eroded especially at the terminator of a rotating body. This leads to the production of dust which can then be transported towards the disk edge or the outer disk regions. The generated dust might constitute a significant fraction of the warm dust observed in extrasolar protoplanetary disks. We estimate erosion rates of about 1 kg s^?1 for 100 m parent bodies. The dust might also contribute to subsequent planetary growth in different locations or on existing protoplanets which are large enough not to be susceptible to particle loss by light induced ejection. Due to the ejections, planetesimals and smaller bodies will be accelerated or decelerated and drift outward or inward, respectively. The effect might also explain the entrainment of dust in dust devils on Mars, especially at high altitudes where gas drag alone might not be sufficient.     

Variations of Magnetic Bright Point Properties with Longitude and Latitude as Observed by Hinode/SOT G-band Data

Small-scale magnetic fields can be observed on the Sun in high-resolution G-band filtergrams as magnetic bright points (MBPs). We study Hinode/Solar Optical Telescope (SOT) longitude and latitude scans of the quiet solar surface taken in the G-band in order to characterise the centre-to-limb dependence of MBP properties (size and intensity). We find that the MBP’s sizes increase and their intensities decrease from the solar centre towards the limb. The size distribution can be fitted using a log–normal function. The natural logarithm of the mean (μ parameter) of this function follows a second-order polynomial and the generalised standard deviation (σ parameter) follows a fourth-order polynomial or equally well (within statistical errors) a sine function. The brightness decrease of the features is smaller than one would expect from the normal solar centre-to-limb variation; that is to say, the ratio of a MBP’s brightness to the mean intensity of the image increases towards the limb. The centre-to-limb variations of the intensities of the MBPs and the quiet-Sun field can be fitted by a second-order polynomial. The detailed physical process that results in an increase of a MBP’s brightness and size from Sun centre to the limb is not yet understood and has to be studied in more detail in the future.     

The ionization balance of the Fe in the solar corona for a non-Maxwellian electron distribution function

The ionization equilibrium of the Fe in the solar corona for a non-Maxwellian electron distribution with an enhanced number of particles in the high-energy tail is presented. A parametric form of the distribution function is used to demonstrate the changes in the ionization equilibrium with changes in the shape of the distribution. The results over the range of temperature 10⁵ K T 10⁸ K for different deviations of the distribution from a Maxwellian are given in tabular form. The results can be used for specific applications in the solar corona, especially in the active corona, where deviations from the Maxwellian distribution can be significant.     

High-pressure phase transitions — examples of classical predictability

We present 19 examples of materials whose high pressure phase transition points can be determined within a particular classical theory of dense matter. Theoretical predictions are compared with experimental results, and some possible causes of discrepancies are discussed.     

Assessment of Raman spectroscopy as a tool for the non-destructive identification of organic minerals and biomolecules for Mars studies

Several characteristic geological features found on the surface of Mars by planetary rovers suggest that a possible extinct biosphere could exist based on similar sources of energy as occurred on Earth. For this reason, analytical instrumental protocols for the detection of biomarkers in suitable geological matrices unequivocally have to be elaborated for future unmanned explorations including the forthcoming ESA ExoMars mission. As part of the Pasteur suite of analytical instrumentation on ExoMars, the Raman/LIBS instrument will seek elemental and molecular information about geological, biological and biogeological markers in the Martian record. A key series of experiments on terrestrial Mars analogues, of which this paper addresses a particularly important series of compounds, is required to obtain the Raman spectra of key molecules and crystals, which are characteristic for each biomarker. Here, we present Raman spectra of several examples of organic compounds which have been recorded non-destructively—higher n-alkanes, polycyclic aromatic hydrocarbons, carotenoids, salts of organic acids, pure crystalline terpenes as well as oxygen-containing organic compounds. In addition, the lower limit of β-carotene detection in sulphate matrices using Raman microspectroscopy was estimated.     

Observational Evidence for Rising Penumbral Flux Tubes?

On 13 May 2000 parts of a penumbra were observed in an active region NOAA 8990 with the La Palma Stokes Polarimeter attached to the Swedish Vacuum Solar Telescope. The stratification over the solar atmosphere of different physical parameters is retrieved from these data by using the Stokes inversion based on response functions. The results confirm the previous findings of the penumbral structure. In general, the magnetic field becomes weaker and more horizontal with increasing distance from the umbra and the line-of-sight velocities are increasing towards the outer boundary of the penumbra. The results also suggest the existence of the unresolved fine structure of the penumbra. The stratifications of the temperature and of the magnetic field strength indicate the presence of rising flux tubes, which were predicted theoretically by Schlichenmaier, Jahn and Schmidt (1998, Astron. Astrophys. 337, 897).     

Diffuse Interstellar Band at 862 nm as a Reddening Tracer for GAIA

We investigate the plausibility of using diffuse interstellar band at862 nm for tracing interstellar extinction with the ESA's astrometric space mission GAIA. For this purpose we perform numerical tests to simulate the conditions of real observations, covering a wide range of stellar parameters and different amounts of interstellar extinction. Our simulations indicate that with the present Radial Velocity Spectrometer setup the uncertainty in color excess of σ_E(B-V)≤ 0.05 can be achieved only for the interstellar reddening tracers brighter than V ∼ 13. None of the plausible tracers can provide accurate color excesses (σ _E(B-V) ≤ 0.05) at the distances beyond 2 kpc. We therefore conclude that with the currently planned instrumentation onboard GAIA this method can not be used as a stand-alone approach for probing interstellar extinction on the Galactic distance scales within the framework of the GAIA mission. This revised version was published online in July 2006 with corrections to the Cover Date.     

A predator–prey model for moon-triggered clumping in Saturn’s rings

UVIS occultation data show clumping in Saturn’s F ring and at the B ring outer edge, indicating aggregation and disaggregation at these locations that are perturbed by Prometheus and by Mimas. The inferred timescales range from hours to months. Occultation profiles of the edge show wide variability, indicating perturbations by local mass aggregations. Structure near the B ring edge is seen in power spectral analysis at scales 200–2000 m. Similar structure is also seen at the strongest density waves, with significance increasing with resonance strength. For the B ring outer edge, the strongest structure is seen at longitudes 90° and 270° relative to Mimas. This indicates a direct relation between the moon and the ring clumping. We propose that the collective behavior of the ring particles resembles a predator–prey system: the mean aggregate size is the prey, which feeds the velocity dispersion; conversely, increasing dispersion breaks up the aggregates. Moons may trigger clumping by streamline crowding, which reduces the relative velocity, leading to more aggregation and more clumping. Disaggregation may follow from disruptive collisions or tidal shedding as the clumps stir the relative velocity. For realistic values of the parameters this yields a limit cycle behavior, as for the ecology of foxes and hares or the “boom-bust” economic cycle. Solving for the long-term behavior of this forced system gives a periodic response at the perturbing frequency, with a phase lag roughly consistent with the UVIS occultation measurements. We conclude that the agitation by the moons in the F ring and at the B ring outer edge drives aggregation and disaggregation in the forcing frame. This agitation of the ring material may also allow fortuitous formation of solid objects from the temporary clumps, via stochastic processes like compaction, adhesion, sintering or reorganization that drives the denser parts of the aggregate to the center or ejects the lighter elements. Any of these more persistent objects would then orbit at the Kepler rate. We would also expect the formation of clumps and some more permanent objects at the other perturbed regions in the rings… including satellite resonances, shepherded ring edges, and near embedded objects like Pan and Daphnis (where the aggregation/disaggregation cycles are forced similar to Prometheus forcing of the F ring).     

Possibilities of GPS kinematic measurements for geological survey in East Slovakia

This paper deals with transformation procedures for observed GPS data from the world geodetic system WGS-84 into the national geodetic grid datum S-UTCN (system of united trigonometric cadaster network) and Baa (the Baltic Sea after adjustment). Transformation from WGS-84 into SUTCN is performed most frequently by means of the 7-element Helmert transformation with three identical points. Geodetic network was adjusted by two ways.     

Approximate spectral analysis by least-squares fit

An approximate method of spectral analysis called successive spectral analysis based upon the mean-quadratic approximation of an empirical function by generalised trigonometric polynomial with both unknown frequencies and coefficients is developed. A few quotations describing some properties of the method as well as one of the possible methods for numerical solution are given.