Comparison of Early Evolutions of Mimas and Enceladus

Thermal history of Mimas and Enceladus is investigated from the beginning of accretion to 400 Myr. The numerical model of convection combined with the parameterized theory is used. The following heat sources are included: short lived and long lived radioactive isotopes, accretion, serpentinization, and phase changes. The heat transfer processes are: conduction, solid state convection, and liquid state convection. We find that temperature of Mimas’ interior was significantly lower than that of Enceladus. If Mimas accreted 1.8 Myr after CAI then the internal melting and differentiation did not occur at all. Comparison of thermal models of Mimas and Enceladus indicates that conditions favorable for the start of tidal heating lasted for a short time (~10⁷ yr) in Mimas and for ~10⁸ yr in Enceladus. This could explain the Mimas—Enceladus paradox. In fact, in view of the chronology based on cometary impact rate, one cannot discard a possibility that also Mimas was for some time active and it has the interior differentiated on porous core and icy mantle.     

Thermal convection in the porous methane-soaked regolith in Titan: Finite amplitude convection

Titan is the only body, beside the Earth, where liquid is present on the surface. This paper is aimed to show the properties of possible convection in a porous regolith on Titan. In our previous work (Czechowski, L., Kossacki, K.J. [2009]. Icarus 202, 599–607) we showed, that the Rayleigh number Ra can exceed its critical value Ra_c. Hence, the convective motion of liquid filling pores in the regolith is likely for Titan relevant parameters. In the present work we investigate the properties of finite amplitude convection, i.e. for Ra > Ra_cr. We study the basic properties of the steady state solution, the Nusselt number, the density of the heat flow and the average temperatures. Evolution of the convection is also considered. We conclude that any reasonable thermal model of Titan’s regolith should take into account the possibility of the considered convection. We discuss also possibility of identification of this convection (or its consequences in the form of evaporates) by the Cassini and possible future spacecrafts.     

On geophysical explanation of some irregular variations of the mean latitudes of latitude stations

Mean latitude variations computed by Orlovs or other filters have some irregular variations in addition to secular ones. These are of the order of ±0.05 to ±0.1, they can last several years and sometimes show regional similarities. In looking for an explanation of such latitude variations several physical mechanisms have been investigated. The most probable one is the mechanism of stress propagation in the lithosphere and asthenosphere. The consequent gravitational and deformational effects could explain both the magnitude and the time dependance of the irregular latitude variations.     

Physicochemical structural characterization of ambers from deposits in Poland

The physical and chemical properties of 8 samples of amber from different localities in Poland (Baltic Coast, Bełchatów Tertiary brown coal, and Jaroszów clay mine) were investigated by N₂ sorption at 77 K, positron annihilation spectroscopy for chemical analysis (PASCA) and by organic geochemical methods (FT-IR,¹H and¹³C NMR, GC, and GC-MS). The porosity of the ambers as determined by PASCA consists of narrow micropores with diameters ranging from 0.8 to 0.9 nm and a volume 0.025 cm³ g⁻¹. In the external eroded part of the amber samples (rind) the concentration of pores where positronium atoms can form is lower and consists of approximately12 the concentration as in their interior. Values of pore parameters determined from sorption of N₂ are comparable with those found by the PASCA method. The average diameter of pores ranges from 2 to 12 nm, while their volume varies from 0.018 to 0.048 cm³ g⁻¹.. The chemical character of the ambers is similar based on FT-IR spectroscopy. However, noticeable differences in concentrations of ester and hydroxyl groups are observed in both exterior and interior regions, where the abundances of the ester groups are lower in the exterior rind. The proportion of organic material extractable with chloroform-methanol (1:1, v/v) ranges from 15 to 50% and correlates inversely to the average reflectances (R_r) of polished amber surfaces which range from 1.7 to 0.1 %. These variations are attributed to differing concentrations of oxygenated groups in the respective amber samples. The FT-IR spectra of the non-polar fractions (NP) from the extracts resemble the spectra of the source ambers. However, the intensities of the absorbance for the hdroxyl group are much lower, while absorbances for exomethylene groups are not present. The¹H and¹³C NMR data of NP fractions showed a complex diversity of components in mixtures with different relative concentrations but predominantly aliphatic in character for the respective samples.GC and GC-MS analyses of these fractions revealed that they are comprised of a mixture of compounds typical for Baltic amber but with variable relative concentrations. Two groups of compounds are found to be common to all NP fractions. The first is a minor concentration of homologousn-alkanes with a characteristic Gaussian distribution in the range from C₂₂ to C₃₂ and maximizing at C₂₆–C₂₇. In addition C₂₂ is characteristically slightly higher in concentration compared to C₂₃. The second group of compounds is comprised of succinates with methyl, fenchyl, bomyl and isobornyl alcohols. The composition of these diesters revealed the same equilibrium ratio between compounds with fenchyl, bornyl and isobornyl alcohols in all NP fractions. We suggest an early enzymatically controlled (bacterial) process in the formation of succinates during resin diagenesis from the biotic precursors, yielding the same characteristic ratio of the respective succinates in these ambers. These results show that all the ambers analyzed here fall into a common class of fossil resin, succinite (class Ia) independent of the sample location in Poland.     

Touchable topography: 3D printing elevation data and structural models to overcome the issue of scale

The fundamental problem of geology is scale. Geological length scales range from angstroms for atoms to thousands of kilometres for planets. Geological processes are often very slow (and geological events so very infrequent). Since the beginning of our discipline, it has been the business of geologists to integrate observations at a variety of length and time scales to answer questions about Earth's history and to make predictions about its future. While this may sound like one of the most academic of pursuits, multi‐billion dollar decisions are routinely made by governments and the largest multi‐national corporations on the basis of geological studies that, for example, model groundwater or petroleum occurrence.